Ex vivo gene therapy
The genetic modification of cells outside the body. Also referred to as cell-based therapy.
In vivo gene therapy
Direct injection of viral vector harboring the therapeutic gene into the patient. Also referred to as direct delivery.
Ex vivo gene therapy
The genetic modification of cells outside the body. Also referred to as cell-based therapy.
In vivo gene therapy
Direct injection of viral vector harboring the therapeutic gene into the patient. Also referred to as direct delivery.
Accountability log
A log to trace steps in the handling of gene therapy products.
Activation-induced cell death (AICD)
AICD in T lymphocytes occurs when activation through the T-cell receptor results in apoptosis. AICD can occur in a cell-autonomous manner and is influenced by the nature of the initial T-cell activation events.
Acute lymphoblastic leukemia (ALL)
A type of cancer that occurs when the bone marrow produces a large number of immature lymphoblasts.
Acute myeloid leukemia (AML)
An aggressive and rapidly progressive type of cancer of the blood and bone marrow that originates when abnormal myeloblasts are produced in large numbers.
Adaptive immune response
A specific immune response to the infecting pathogen that is triggered when the innate immune response mechanisms are insufficient, and a threshold antigen dose is reached. It requires days or weeks to develop and will leave an immunological memory for a faster response to exposure of the same pathogen in the future.
Adenine 
It is one of four chemical bases that, together with phosphate and a deoxyribose sugar, form the fundamental building blocks of DNA; it is a purine base that pairs with thymine.
Adeno-associated virus (AAV)
A small (25 nm), non-enveloped virus that packages a linear single-stranded DNA genome. AAV has not been identified as an etiologic agent of human disease and is a naturally “defective” virus that requires a helper virus for productive replication of its genome. It has the ability to infect both dividing and non-dividing cells.
Adenosine 
A ribonucleoside comprising adenine bound to ribose. Phosphorylated forms of adenosine are important in the synthesis of RNA.
Adenovirus (Ad)
A member of a group of DNA viruses, originally discovered in adenoid tissue, most of which cause respiratory diseases. They can infect dividing and non-dividing cells.
Adrenoleukodystrophy (ALD)
An X-linked recessive genetic disorder caused by an abnormality in the ABCD1 gene on the X chromosome. This condition affects the white matter of the nervous system and the adrenal cortex.
Aerosol
A suspension of fine solid or liquid particles in gas.
Alpha‐1 antitrypsin deficiency
A genetic disorder that may cause lung disease and liver disease. It is inherited in an autosomal codominant manner and caused by mutations in the SERPINA1 gene.
Aminoacidopathies
A group of rare and diverse disorders caused by the deficiency of an enzyme or transporter involved in amino acid metabolism.
Amyloid-β
A shorter peptide that is formed from the cutting of the larger amyloid precursor protein. The aggregation of amyloid-β leads to the formation of plaques, which are one of the key features of Alzheimer’s disease pathology.
Amyotrophic lateral sclerosis (ALS)
Also known as Lou Gehrig’s disease. It is characterized by progressive degeneration and eventual death of motor neurons in the brain, brainstem, and spinal cord. Mutations in several genes (e.g. C9orf72, SOD1, TARDBP, and FUS) can cause familial ALS and contribute to the development of sporadic ALS. Most cases of ALS are sporadic, but a small percentage can be inherited.
Antibody
A protein produced by the immune system in response to an antigen. Antibodies bind specifically to their target antigen to help the immune system destroy the foreign entity.
Antibody titer (test)
A laboratory test that measures the level of antibodies in a blood sample.
Antigen
Any substance capable of inducing an immune response. Antigens include toxins, chemicals, bacteria, viruses, or other substances that come from outside the body.
Antigen-presenting cell (APC)
A heterogeneous group of immune cells that mediate the cellular immune response by processing and presenting antigens for recognition by certain lymphocytes such as T cells. Classical antigen-presenting cells include dendritic cells, macrophages, Langerhans cells, and B cells.
Antisense oligonucleotide (ASO)
Synthetic, short, single-stranded DNA or RNA molecules that interact with messenger RNA (mRNA) through base pairing to prevent translation of a targeted gene. Also known as “molecular patches”.
Apheresis
A procedure that involves removing the blood from a donor to separate its individual components (such as platelets or white blood cells), following which the remaining blood is transfused back into the donor. It is also referred to as pheresis. National Cancer Institute. NCI Dictionaries. Apheresis. Available at: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/apheresis. Accessed December 7, 2020.
Apoptosis
A type of cell death that involves a series of molecular steps in a cell, eventually leading to its death. Apoptosis is a mechanism by which the body disposes of abnormal cells.
Aromatic L‐amino acid decarboxylase (AADC) deficiency
A genetic disorder that affects the way signals are passed between certain cells in the nervous system. It is inherited in an autosomal recessive manner and caused by mutations in the DDC gene.
Aseptic technique
Refers to the manner of handling, preparing, and storing of medications and injection equipment/supplies (e.g. syringes, needles, and intravenous tubing) to prevent microbial contamination.
Attenuation
A modification that makes the replication of a vector defective.
Autoclave
A sterilizer in which items are exposed to steam at a specific pressure and temperature for an allotted amount of time.
Autoimmune diseases
Diseases that occur when the immune system attacks healthy cells in the body, resulting in inflammation. Autoimmune diseases tend to run in families and can affect many parts of the body.
Autoimmune encephalomyelitis
A condition in which the body’s immune system attacks healthy cells in the brain, leading to inflammation of the brain. It is a rare disease that can cause rapid changes in both physical and mental health.
Autologous stem cell transplantation (autoSCT)
A procedure in which a patient’s healthy stem cells (blood-forming cells) are collected from the blood or bone marrow before treatment, stored, and then given back to the patient after treatment. An autologous stem cell transplantation replaces a patient’s stem cells that were destroyed by treatment with radiation or high doses of chemotherapy. It is most often used to treat blood cancers, such as leukemia and lymphoma.
Autosomal dominant (inheritance pattern)
It occurs when one mutated copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder.
Autosomal recessive (inheritance pattern)
It occurs when mutations in both copies of the gene in each cell are needed to cause an autosomal recessive disease.
B lymphocytes (or B cells)
One of the two types of lymphocytes that makes antibodies. B cells are involved in humoral immunity; on encountering a foreign substance (antigen), the B lymphocyte differentiates into a plasma cell, which secretes immunoglobulin.
B-cell lymphoma (BCL)
A type of cancer that forms in B cells. Most B-cell lymphomas are non-Hodgkin lymphomas.
B-cell precursor acute lymphoblastic leukemia
An aggressive type of leukemia in which too many B-cell lymphoblasts (immature white blood cells) are found in the bone marrow and blood. It is the most common type of acute lymphoblastic leukemia (ALL). Also called B-cell acute lymphoblastic leukemia and B-cell acute lymphocytic leukemia.
Base editing 
A strategy that involves single base-pair conversions at a targeted genomic site independent of DNA double-strand breaks.
Batten disease
A broad class of rare, fatal, inherited disorders of the nervous system, also known as neuronal ceroid lipofuscinoses, or NCLs, which interfere with a cell’s ability to recycle certain molecules. Each form is caused by a mutation in a different gene.
Becker muscular dystrophy
A genetic disorder that causes progressive weakness and wasting of the skeletal and cardiac (heart) muscles. It is an X-linked recessive disease caused by mutations in the gene encoding for the dystrophin protein.
Biallelic RPE65 mutation-associated retinal dystrophy
An inherited mutation in both alleles of the RPE65 gene resulting in degeneration of photoreceptors in the retina. The RPE65 gene is responsible for encoding retinal pigment epithelium-specific 65 kDa proteins.
Biallelic RPE65 mutation-associated retinal dystrophy
An inherited mutation in both alleles of the RPE65 gene resulting in degeneration of photoreceptors in the retina. The RPE65 gene is responsible for encoding retinal pigment epithelium-specific 65 kDa proteins.
Binding antibody (non-neutralizing antibody)
An antibody that binds specifically to virus particles, but do not neutralize infectivity.
Biodistribution
The distribution (static and dynamic) of compounds within a biological system or within an organism.
Biohazard
A biological agent or condition that is a hazard to humans or the environment.
Biosafety cabinet (biological safety cabinet)
Specialized type of laboratory equipment designed to provide both a clean work environment and protection for employees who create aerosols when working with infectious agents or toxins. There are three classes of biosafety cabinets designated in the United States: Class I, Class II, and Class III. Most biosafety cabinets (e.g. Class II and Class III) use high-efficiency particulate air (HEPA) filters in both the exhaust and supply system to prevent exposure to biohazards.
Biosafety level
Each of the four levels that can be assigned to laboratory facilities based on a composite of the design features, construction, containment facilities, equipment, practices, and operational procedures required for working with infective organisms.
Biotinidase deficiency
An inherited disorder in which the body is unable to recycle the vitamin biotin. It is inherited in an autosomal recessive manner and caused by mutations in the BTD gene.
Birth defects
Structural changes present at birth that can affect any part of the body that may impact their function.
Bladder cancer
A type of cancer that begins in the bladder lining and can spread into the bladder muscle.
Blood–brain barrier (BBB)
A network of blood vessels and tissue that is made up of closely spaced cells and helps to keep harmful substances from reaching the brain.
Bone marrow transplantation
A procedure to replace damaged or destroyed bone marrow with healthy bone marrow stem cells.
Breast cancer
A type of cancer in which cells in the breast grow out of control. Most breast cancers are associated with somatic mutations in breast cells that are acquired during a person's lifetime, and they do not cluster in families. In hereditary breast cancer, the way that cancer risk is inherited depends on the gene involved. For example, mutations in the BRCA1 and BRCA2 genes are inherited in an autosomal dominant pattern.
C-C chemokine receptor 4 (CCR4)
A G protein-coupled receptor for C-C chemokines that is expressed on the surface of endothelial cells and certain types of T cells and neurons. It can be overexpressed in some types of T-cell lymphoma.
C-reactive protein (CRP)
An acute phase reactant protein made by the liver that is released into the blood within a few hours after tissue injury, the start of an infection, or other inflammation. It is often the first evidence of inflammation or an infection in the body, with rising concentrations frequently preceding pain, fever, or other clinical indicators.
Canavan disease
A rare genetic disorder that damages the ability of nerve cells (neurons) in the brain to send and receive messages. This disease is one of a group of genetic disorders called leukodystrophies. It is caused by mutations in the ASPA gene and inherited in an autosomal recessive manner.
Cancer
A disease that begins when cells continue to grow and divide more rapidly than their progenitors and become less dependent on cellular signals, particularly those for cell proliferation and cell death.
Capsid
The protein coat of a virus.
Carcinogen
Substances and exposures that can lead to cancer.
Carcinoma
A type of cancer that initiates in the skin or tissues that cover/line the internal organs.
Cardiovascular disease
A condition affecting the heart or blood vessels. It is usually associated with a build-up of fatty deposits inside the arteries (atherosclerosis) and an increased risk of blood clots. It can also be associated with damage to arteries in organs such as the brain, heart, kidneys, and eyes.
Carrier (molecule)
A molecule that is lipid soluble and can bind to lipid-insoluble molecules to transport them across membranes.
Caspase
An intracellular protease enzyme that has a cysteine residue at the active site, can cleave substrate proteins at specific aspartic acid residues, and is involved in the initiation and mediation of apoptosis.
CD34
A transmembrane glycoprotein expressed on the surface of hematopoietic progenitor cells and small blood vessel endothelial cells. While the specific function of CD34 remains to be elucidated, it is regarded as a marker of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells.
CD4
A glycoprotein that is found on the surface of helper T cells. It acts as coreceptor of the T-cell receptor that binds to the major histocompatibility complex class II molecule on the surface of antigen-presenting cells. It facilitates antigen recognition and activation of helper T cells.
CD4+ T cells
Also called helper T cells. They recognize peptides presented on major histocompatibility complex (MHC) Class II molecules, which are found on antigen-presenting cells. CD4+ T cells play a major role in instigating and shaping adaptive immune responses.
CD8
A glycoprotein that is found on the surface of cytotoxic T cells. It acts as coreceptor of the T-cell receptor that binds to the major histocompatibility complex class I molecule on the surface of antigen-presenting cells. It facilitates antigen recognition and activation of cytotoxic T cells.
CD8+ T cells
Also called cytotoxic T lymphocytes, or CTLs. They are generated in the thymus and express the T-cell receptor. CD8+ T cells recognize peptides presented by major histocompatibility complex (MHC) Class I molecules and are important for immune defense against intracellular pathogens, including viruses and bacteria, and for tumor surveillance.
Cell cycle
A series of events that occurs in a cell that results in the division of the cell.
Cell therapy
A technology that relies on replacing diseased or dysfunctional cells with healthy, functioning ones.
Cell-based therapy
The genetic modification of cells outside the body. Also referred to as ex vivo gene therapy.
Cellular immunity
A type of adaptive immune response that occurs inside infected cells and is mediated by T lymphocytes. The pathogen's antigens are expressed on the cell surface or on an antigen-presenting cell. Helper T cells release cytokines that help activated T cells bind to the infected cells’ major histocompatibility complex (MHC)–antigen complex and differentiate the T cell into a cytotoxic T cell. The infected cell then undergoes lysis.
Cellular immunotherapy
A type of immunotherapy involving the administration of T cells to the patient to help fight a disease.
Cellular immunotherapy
A type of immunotherapy involving the administration of T cells to the patient to help fight a disease.
Cellular senescence
A process in which irreversible cell cycle arrest often is coupled with widespread cellular alterations (e.g. in transcription, metabolism, secretion, morphology, and chromatin organization).
Chaperone therapy
The use of small molecule ligands (chaperones) that selectively bind to and stabilize misfolded, mutant proteins. Chaperones can assist misfolded enzymes in becoming functional by helping them to fold properly and remain stable.
Checkpoint inhibitor
A type of drug that works by blocking checkpoint proteins produced by immune cells, such as T cells, and some cancer cells. Checkpoint proteins regulate immune responses so that they are not too strong and can prevent T cells from destroying cancer cells. The inhibition of checkpoint proteins results in the more efficient killing of cancer cells. Examples of checkpoint proteins are programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) and cytotoxic T-lymphocyte-associated protein 4/B7-1 and B7-2 proteins (CTLA-4/B7-1/B7-2).
Chemokine
A type of cytokine that plays important roles in the body’s immune response, including attracting white blood cells to areas of inflammation to help the body fight infections, inflammatory conditions, and other diseases.
Chemotherapy
A treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing.
Chimeric
Containing two or more parts of different origins.
Chimeric antigen receptor (CAR)
A recombinant receptor with both tumor antigen-binding and T-cell–activating functions.
Chimeric antigen receptor T-cell (immuno)therapy (CAR-T)
A gene therapy approach by which patient’s T cells are engineered to express chimeric antigen receptors or CARs.
Choroideremia
A condition characterized by progressive vision loss that mainly affects males. It is inherited in an X-linked recessive pattern and caused by mutations in the CHM gene.
Chromatin
The material of chromosomes. It is a complex of DNA, histones, and non-histone proteins found within the nucleus of a cell.
Chronic granulomatous disease (CGD)
An inherited primary immunodeficiency disease that increases the body’s susceptibility to infections caused by certain bacteria and fungi. It can be caused by mutations in CYBB gene (X-linked recessive patterns) or in the CYBA, NCF1, NCF2, or NCF4 genes (inherited in an autosomal recessive pattern).
Chronic lymphocytic leukemia (CLL)
A type of cancer that affects white blood cells and starts in the bone barrow. A family history of the disease, aging, exposure to pesticides or herbicides, allergic conditions, and the presence of a hepatitis C infection have been associated with increased risk of developing CLL.
Clinical biosafety committee
A cross-departmental institutional committee that evaluates approved gene therapy products and develops and standardizes protocols for their safe handling.
CLN2 disease
A genetic disorder that primarily affects the nervous system. CLN2 disease is one of a group of disorders known as neuronal ceroid lipofuscinoses (NCLs), which may also be collectively referred to as Batten disease. It is inherited in an autosomal recessive manner and caused by mutations in the TPP1 gene.
Cluster of differentiation (CD)19
A type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. CD19 is a biomarker for normal and neoplastic B cells as well as follicular dendritic cells.
Clustered regularly interspaced short palindromic repeat (CRISPR)
A family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea that consists of short repeated sequences separated by spacers derived from nucleic acid of viruses and plasmids. The spacers are used as recognition elements to find matching virus genomes and destroy them. CRISPR-associated protein 9 (Cas9) enzymes, together with CRISPR sequences, form the basis of a technology known as CRISPR–Cas9 that can be used to edit genes within organisms.
Cobalamin disorders
Disorders of intracellular cobalamin metabolism that can result from deficient synthesis of the coenzymes derived from vitamin B12.
Cofactor
A non-protein chemical that assists with a biological chemical reaction.
Complement
A heat-labile component of normal plasma that causes the opsonization and killing of bacteria. The complement system refers to a series of >20 proteins, circulating in the blood and tissue fluids. Most of the proteins are normally inactive; however, in response to the recognition of molecular components of microorganisms, they become sequentially activated in an enzyme cascade.
Complementary DNA
A DNA copy of a messenger RNA (mRNA) molecule produced by reverse transcriptase, a DNA polymerase that can use either DNA or RNA as a template.
Complex disease
A disease caused by a combination of genetic, environmental, and lifestyle factors.
Compounding
The process of combining, mixing, or altering ingredients to produce a medication tailored to the needs of an individual patient.
Congenital enzyme deficiencies
Enzyme deficiencies, usually inherited in a recessive fashion, caused by loss-of-function mutations. They may be autosomal recessive or X-linked recessive.
Copy number variation
A type of structural variation in the DNA in which the number of copies of a particular gene or multiple genes vary from one individual to the next. If the genes involved are sensitive to dosage, it may impact disease risk.
CpG island
A stretch of DNA 500–1500 base pairs long with a cytosine-guanine base composition greater than 60%. CpG islands are normally found at promoter regions and contain the 5’ end of the transcript.
Crigler–Najjar syndrome
A genetic severe disorder characterized by hyperbilirubinemia. It is inherited in an autosomal recessive manner and caused by mutations in the UGT1A1 gene.
CRISPR-associated protein 9 (Cas9)
An enzyme that uses clustered regularly interspaced short palindromic repeat (CRISPR) sequences as a guide to recognize and cleave specific strands of DNA that are complementary to the CRISPR sequence. Cas9 enzymes, together with CRISPR sequences, form the basis of a technology known as CRISPR–Cas9 that can be used to edit genes within organisms.
Cross-contamination
Inadvertent transfer of bacteria or other contaminants from one surface, substance, etc., to another especially because of unsanitary handling procedures.
Cross-reactivity (T cell)
The recognition of two or more peptide-bound major histocompatibility complexes (MHCs) by a T-cell receptor (TCR).
Cyclin-dependent kinase (CDK)
Protein kinase that plays a key role in controlling cell division and modulating transcription in response to cues that can be both intracellular and extracellular.
Cystic fibrosis (CF)
A genetic disease characterized by the build-up of thick, sticky mucus that can damage many of the body's organs. It is inherited in an autosomal recessive manner and is caused by mutations in the CFTR gene. The CFTR gene encodes cystic fibrosis transmembrane conductance regulator proteins.
Cytidine
A pyrimidine nucleoside containing a cytosine bound to ribose. It is a precursor for uridine and is used in RNA synthesis.
Cytokine
Small secreted proteins released by cells that have a specific effect on the interactions and communications between cells. They can be made by immune and non-immune cells. Examples of cytokines include interleukins, interferons, and colony-stimulating factors.
Cytokine release syndrome (CRS)
A condition that may occur after treatment with some types of immunotherapy, such as monoclonal antibodies and chimeric antigen receptor T cells (CAR-T cells). Cytokine release syndrome is caused by a large, rapid release of cytokines into the blood from immune cells affected by the immunotherapy. Signs and symptoms of cytokine release syndrome include fever, nausea, headache, rash, rapid heartbeat, low blood pressure, and trouble breathing. Most patients have a mild reaction, but sometimes, the reaction may be severe or life-threatening.
Cytomegalovirus (CMV)
A common virus that is usually harmless. If the mother is infected during pregnancy, it can be passed to the baby (congenital CMV) and can cause them health problems such as rash, jaundice, microcephaly, low birth weight, hepatosplenomegaly, seizures, and retinitis; it may even lead to death of the unborn baby.
Cytopenia
A condition in which the number of blood cells is lower than normal.
Cytosine
It is one of four chemical bases that, together with phosphate and a deoxyribose sugar, form the fundamental building blocks of DNA; it is a pyrimidine base that pairs with guanine.
Cytotoxic agent
A substance that kills cells, including cancer cells.
Deletion
A type of genetic alteration involving the removal of a piece of DNA, resulting in a reduction in the number of DNA base pairs. It can occur within one gene, resulting in the loss of base pairs in that gene, or could result in deletion of a section of a chromosome, resulting in the removal of one or several neighboring genes.
Dendritic cell
A bone marrow-derived leukocyte that is the most potent type of antigen-presenting cell. Named for their probing, “tree-like” or dendritic shapes, dendritic cells are responsible for the initiation of adaptive immune responses and function as the “sentinels” of the immune system.
Diffuse large B-cell lymphoma (DLBCL)
The most common type of non-Hodgkin lymphoma, marked by rapidly growing tumors in the lymph nodes, spleen, liver, bone marrow, or other organs.
Diploid cells
Cells that contain two copies of each chromosome.
Direct delivery
Direct injection of viral vector into the patient. Also referred to as in vivo gene therapy.
Disinfection
A process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects.
DNA overhang 
A stretch of single-stranded nucleotides that is created as a result of asymmetric cleavage of double-stranded DNA by an endonuclease.
DNA vaccine
It involves the introduction into the patient’s cells of a plasmid or viral vector that contains DNA encoding an antigen in order to trigger an immune response to this antigen. Cells directly produce the antigen, causing a protective immunological response.
Dominant negative receptor
A receptor protein that blocks the downstream functions of an associated receptor that requires dimerization for activity. A dominant negative receptor is usually missing an intracellular enzymatic region but has an intact ligand binding region instead. This results in the prevention of downstream signaling following ligand binding.
Dominant-negative (mutation)
A mutation whose gene product adversely affects the normal, wild-type gene product within the same cell. This usually occurs if the product can still interact with the same elements as the wild-type product, but blocks some aspect of its function.
Double-strand break (DSB) 
A break in both strands of the DNA duplex that can be repaired by homologous recombination or non-homologous end joining. DSBs are deleterious, as the DNA ends can lead to potentially lethal chromosomal rearrangements.
Duchenne muscular dystrophy (DMD)
A rare muscular dystrophy, but one of the most frequent genetic conditions in boys, caused by mutations of the DMD gene on the X chromosome that regulates the production of dystrophin, a protein found in the membrane of skeletal and cardiac muscle cells.
Duplication
A type of genetic alteration that consists of a piece of DNA being copied once or many more times. This duplication could occur within the same gene or result in duplication of a section of a chromosome (chromosomal duplication), resulting in multiple copies of genes within that chromosomal region.
Dystrophinopathies
A group of dystrophies resulting from mutations in the dystrophin (DMD) gene, located on the short arm of the X chromosome in the Xp21 region. They cover a spectrum of X-linked muscle diseases ranging from mild to severe that includes Duchenne muscular dystrophy, Becker muscular dystrophy, and DMD-associated dilated cardiomyopathy (DCM).
Ebola virus (Zaire ebolavirus species)
A virus belonging to the Zaire ebolavirus species that causes Ebola virus disease, an acute and serious disease that frequently causes death if untreated.
Ebola virus (Zaire ebolavirus species)
A virus belonging to the Zaire ebolavirus species that causes Ebola virus disease, an acute and serious disease that frequently causes death if untreated.
Electroporation (or electropermeabilization)
A molecular biology technique in which a high-voltage electrical pulse is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, or DNA to be introduced into the cell.
Endoplasmic reticulum (ER)
A cellular organelle found in the cytoplasm that is comprised of a network of sac-like structures and tubes. Its outer surface is either covered with ribosomes, producing proteins (known as the rough endoplasmic reticulum), or is smooth, producing other substances such as lipids and carbohydrates (known as the smooth endoplasmic reticulum).
Enzyme
A biological catalyst, almost always a protein, that speeds up the rate of a specific chemical reaction in the cell.
Epigenetic modification
A heritable alteration that changes DNA accessibility and chromatin structure, thereby regulating patterns of gene expression.
Episome
In bacterial genetics, an extrachromosomal DNA molecule that can exist and replicate autonomously in the cytoplasm or as a part of a chromosome. In gene therapy, this can also refer to genetic material introduced into a cell by a vector that does not integrate into the host DNA but instead persists in an extrachromosomal form.
Epistasis
A phenomenon in which the expression of a gene is impacted by the expression of other independently inherited genes.
Epitope
Also called antigenic determinant. It is a portion of a foreign protein, or antigen, that is capable of stimulating an immune response. An epitope is the part of the antigen that binds to a specific antigen receptor on the surface of a B cell.
Esophageal squamous cell cancer
A type of cancer that occurs in the squamous cells that line the surface of the esophagus.
Ex vivo gene therapy
The genetic modification of cells outside the body. Also referred to as cell-based therapy.
Exocytosis
The release of cellular substances (such as secretory products) contained in cell vesicles by fusion of the vesicular membrane with the plasma membrane and subsequent release of the contents to the exterior of the cell.
Exon
Part of a gene sequence that is expressed in the mature messenger RNA, encoding the amino acids of a protein.
Exon skipping
The process of skipping exons with disease-causing mutations and/or nearby exons to restore the reading frame, which results in an internally truncated, partially functional protein.
Exosome
A type of cell-derived extracellular vesicle formed through the fusion of an intermediate endocytic compartment with the plasma membrane. 
Expression cassette
A component of vector DNA comprising the gene (or genes) of interest and regulatory sequences controlling transgene expression.
Fabry disease
A genetic disorder that results from the build-up of globotriaosylceramide in the body's cells. It is inherited in an X-linked pattern and caused by mutations in the GLA gene. The GLA gene encodes the enzyme galactosidase alpha.
Facioscapulohumeral muscular dystrophy (FSHD)
An inherited condition characterized by muscle weakness and wasting (atrophy). There are two types of FSHD (FSHD1 and FSHD2), both caused by overexpression of the DUX4 gene (due to hypomethylation in the D4Z4 region of chromosome 4). FSHD1 is caused by a shorter D4Z4 region and is inherited in an autosomal dominant manner. FSHD2 is inherited in a digenic pattern (two independent genetic changes are necessary) and occurs as a result of mutations in the SMCHD1 gene and the presence of a “permissive” chromosome 4 that allows for production of DUX4 protein.
Familial adenomatous polyposis (FAP)
An inherited disorder characterized by cancer of the colon and rectum. It can be inherited in an autosomal dominant or recessive manner when caused by mutations in the APC or MUTYH gene, respectively.
Familial hypercholesterolemia (FH)
A genetic disorder caused by a defect in chromosome 19, leading to high cholesterol. The condition begins at birth and can cause heart attacks at an early age.
Familial lipoprotein lipase deficiency
A genetic condition that disrupts the normal breakdown of fats in the body, resulting in an increase in certain kinds of fats. It is inherited in an autosomal recessive manner and is caused by mutations in the LPL gene, encoding lipoprotein lipase.
Fanconi anemia
A genetic disorder that mainly affects many parts of the body. It may lead to bone marrow failure, physical abnormalities, organ defects, and an increased risk of certain cancers. It is mainly inherited in an autosomal recessive manner, but it can also be X-linked. It can be caused by mutations in at least 15 genes.
Ferritin
A ubiquitous protein found in all cells and the primary site of iron storage in the cell. Ferritin concentrates cellular iron and protects cells from its toxic effects.
Follicular lymphoma
A type of B-cell non-Hodgkin lymphoma where cells slowly grow in groups to form nodules.
Gain-of-function mutation
A mutation that confers new or enhanced activity on a protein.
Galactosemia
A group of autosomal recessive inherited disorders that impair the body's ability to process and produce energy from galactose due to the deficiency of any of three enzymes, caused by mutations in different genes.
Galactosialidosis
A genetic condition that affects many areas in the body. There are three forms of galactosialidosis that are distinguished by the age at which symptoms develop and the pattern of features. Galactosialidosis is an autosomal recessive lysosomal storage disorder caused by mutations in the CTSA gene.
Gammaretroviruses
Also known as onco-retroviruses. These consist of a large number of leukemia and sarcoma viruses of mice, cats, primates, and other mammals.
Gastric cancer
A type of cancer that occurs when cancer cells form in the lining of the stomach.
Gaucher disease
An autosomal recessive inherited disorder caused by mutations in the GBA gene, resulting in the build-up of a fatty substance called glucocerebroside and related substances, and subsequent damage to tissues and organs.
Gene editing
The use of engineered or bacterial nucleases for targeted modifications of the genome to prevent or treat a disease.
Gene gun
Also called biolistic gene transfer. This technique involves bombarding target cells with DNA-coated gold particles driven by pressurized inert gas, such as helium, or by high-voltage electronic discharge.
Gene inhibition
Deactivating or “silencing” the expression of a mutated gene that is not functioning properly.
Gene replacement
The introduction of a complementary DNA construct or modified gene that expresses a functional protein that is absent, reduced, or non-functional due to a mutated gene in an effort to correct the disease.
Gene silencing
A process that involves the interruption or suppression of the expression of a gene at the transcriptional or translational level.
Gene therapy
The introduction of genetic material into an individual, or the modification of the individual’s genetic material, in order to achieve a therapeutic objective.
Gene transfer
The insertion of exogenous genetic information in the form of DNA into cells.
Genetic modulation of immune cells
The introduction of a complementary DNA construct or modified gene that promotes a stronger immune response to attack diseased cells.
Genome editing 
A mechanism that uses engineered or bacterial nucleases for targeted modifications of the genome to prevent or treat a disease.
Germline gene therapy
Direct manipulation of genetic material in oocytes, sperm, zygotes, or embryos. It affects all tissues of the developing fetus, including germ cells, and therefore the genetic alteration would be passed on to future generations.
Glial cell line–derived neurotrophic factor (GDNF)
A growth factor that plays a role in the organogenesis of several different bodily systems. It supports cellular functions, such as survival, proliferation, differentiation, maturation, and neurite outgrowth.
Glioblastoma (glioblastoma multiforme [GBM])
A fast-growing type of central nervous system tumor that forms from glial (supportive) tissue of the brain and spinal cord. Also called Grade IV astrocytoma.
Glioma
A type of tumor that originates in the glial cells that surround and support the nerve cells of the brain.
Graft-versus-host disease
A complication of bone marrow transplants in which T cells in the donor bone marrow graft attack the host's tissue. It often occurs when the blood marrow donor is unrelated to the patient or not a perfect match. There are two forms: an early acute form and a chronic form.
Granulocyte–macrophage colony-stimulating factor (GM-CSF) 
A cytokine and type of hematopoietic agent that stimulates the growth and function of white blood cells, such as granulocytes, macrophages, and platelet precursor cells. 
Granzyme
A family of serine proteases released by cytoplasmic granules within cytotoxic T cells and natural killer (NK) cells. They can play an important role in the apoptosis of the target cell.
Guanine 
It is one of four chemical bases that, together with phosphate and a deoxyribose sugar, form the fundamental building blocks of DNA; it is a purine base that pairs with cytosine.
Gyrate atrophy
A genetic condition characterized by progressive degeneration of the choroid and pigment epithelium of the retina, leading to progressive vision loss. Gyrate atrophy is inherited in an autosomal recessive manner and it is caused by mutations in the OAT gene.
Hairpin (loop) structure
A hairpin loop (usually in messenger RNA [mRNA]) forms when an mRNA strand folds and forms base pairs with another section of the same strand.
Haploinsufficiency
A situation in which the total level of a gene product (a particular protein) produced by the cell is about half of the normal level and is not sufficient to permit the cell to function normally. It can also be defined as a condition that arises when the normal phenotype requires the protein product of both alleles, and reduction of 50% of gene function results in an abnormal phenotype.
Head and neck cancer
A collective term used to describe tumors, usually originating in squamous cells, that line the head and neck (for example: mouth, throat, etc).
Helper virus
A virus that enables genetically modified viruses to replicate or to form a protein coat by complementing the missing gene function of the defective virus.
Hematologic disease 
A disorder of the blood or blood-forming organs.
Hematological malignancies
Cancers that affect the blood, lymph nodes, or bone marrow.
Hematopoietic stem cells (HSCs)
Cells residing in the bone marrow that have the capacity to regenerate all the different types of blood cells.
Hemophilia
A bleeding disorder that slows the blood-clotting process. It is inherited in an X-linked recessive pattern and can be caused by mutations in the F8 gene (hemophilia A), or F9 gene (hemophilia B).
Hepatitis B
An infection of the liver caused by the hepatitis B virus that can spread through blood and body fluids.
Hepatitis B
A liver disease caused by the hepatitis B virus (HBV). Most people do not experience any symptoms but a small subset of people with acute hepatitis can develop acute liver failure and even death. People with chronic hepatitis can later develop cirrhosis or liver cancer.
Hepatitis C
A liver disease caused by the hepatitis C virus (HCV). It can be acute or chronic, with symptoms ranging mild to very severe. It is a major cause of liver cancer.
Herpes simplex virus (HSV)
A virus that causes herpes, a lifelong infection. There are two types of herpes simplex virus: HSV type 1 (HSV-1) and HSV type 2 (HSV-2).
Heterodimer
A protein composed of two polypeptide chains differing in composition in the order, number, or kind of their amino acid residues.
Hodgkin lymphoma
A type of cancer in which B lymphocytes begin to multiply abnormally and collect in parts of the lymphatic system, such as the lymph nodes.
Homeostasis
The balanced state of the bodily systems that is required for correct functioning of the body.
Homology-directed repair (HDR) 
A mechanism to repair double-strand breaks in DNA. HDR uses a template with regions of homology to the sequence surrounding the double-strand break.
Human immunodeficiency virus (HIV)
A virus that damages the cells in the immune system and weakens their ability to fight everyday infections and disease. Acquired immune deficiency syndrome (AIDS) is the name used to describe a number of potentially life-threatening infections and illnesses that happen when the immune system has been severely damaged by HIV.
Human papillomavirus
A group of related viruses that can cause warts on different parts of the body. Some types of the human papillomavirus can be spread through direct sexual contact. Some types of the human papillomavirus can cause cancer.
Humoral immunity
A type of adaptive immune response that is mediated by antibody molecules that are secreted by plasma cells. In this response, antibodies produced by B cells cause the destruction of extracellular microorganisms and prevent the spread of intracellular infections.
Huntington’s disease (HD)
A progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition). It is inherited in an autosomal dominant pattern and caused by mutations in the huntingtin gene (HTT).
Hypoxia-inducible factor (HIF)
A transcription factor that regulates the expression of genes that mediate the response to low levels of oxygen.
Immune-privileged (site)
Specific sites in the mammalian body, such as the eyes, brain, testis, and placenta, that are able to tolerate the introduction of antigens without eliciting an inflammatory immune response.
Immunogenicity
The ability of a molecule or substance to provoke an immune response, or the strength or magnitude of an immune response.
Immunosuppressant
An agent that can suppress or prevent the immune response. Immunosuppressants can be used to prevent rejection of a transplanted organ and to treat autoimmune diseases.
Immunotherapy
A type of therapy that uses substances to stimulate or suppress the immune system to help the body fight cancer, infection, and other diseases.
In vivo gene therapy
Direct injection of viral vector into the patient. Also referred to as direct delivery.
Infectious disease
A disease caused by pathogenic microorganism(s), such as bacteria, viruses, parasites, or fungi; the disease can be spread, directly or indirectly, from one person to another.
Inflammasome
A multiprotein intracellular complex that detects pathogenic microorganisms and sterile stressors, and that activates the highly pro-inflammatory cytokines interleukin (IL)-1b and IL-18. Inflammasomes also induce a form of cell death termed pyroptosis.
Inflammatory diseases
A vast array of disorders and conditions that are characterized by inflammation. Examples include allergy, asthma, autoimmune diseases, celiac disease, glomerulonephritis, hepatitis, inflammatory bowel disease, preperfusion injury, and transplant rejection.
Influenza
An acute viral infection of the respiratory tract frequently caused by influenza virus A or B subtypes. 
Innate immune response
A rapid, non-specific immune response that develops hours after an infection. It is crucial for the initiation of an adaptive immune response.
Inosine 
A product formed by the deamination of adenosine in DNA. This event is premutagenic and gets blocked by DNA repair enzymes, which remove inosine. It preferentially pairs with cytosine.
Insertional mutagenesis
The process by which an exogenous DNA sequence integrates within the genome of a host organism. It can result in the disruption of the host gene(s) and lead to perturbation of the cellular phenotype.
Integrating viral vector
Viral DNA from integrating viral vectors translocates into the nucleus and integrates into the host genome, leading to stable, long-lasting transgene expression.
Interferon (IFN)
A natural substance that helps the body’s immune system fight infection and other diseases, such as cancer. An interferon is a type of cytokine and type of immunomodulating agent. There are three main types of interferon: alpha, beta, and gamma.
Interleukin (IL)
One of a group of related proteins made by leukocytes (white blood cells) and other cells in the body that regulate immune responses. An interleukin is a type of cytokine.
Interleukin (IL)-4 
A type of cytokine made by T lymphocytes. IL-4 stimulates the growth and activation of B lymphocytes and the production of T lymphocytes. 
Interleukin-12 (IL-12)
A type of cytokine that is made mainly by B lymphocytes and macrophages. It causes other immune cells to make cytokines and increases the growth of T lymphocytes. It may also block the growth of new blood vessels.
Interleukin-2 (IL-2)
A type of cytokine that is made by a type of T lymphocyte. It increases the growth and activity of other T lymphocytes and B lymphocytes and affects the development of the immune system.
Intramuscular
Referring to situated in, occurring in, or administered by entering a muscle.
Intravenous
Referring to situated, performed, or occurring within or entering by way of a vein.
Intron
Non-coding regions of a gene, not expressed in the mature messenger RNA, that are in between exons in the gene.
Inversion
A type of genetic alteration that occurs when two breaks occur in one chromosome and the region between the breaks flips 180 degrees before rejoining with the two end fragments, thereby resulting in the sequence being reversed. Inversions can occur within a single gene or can occur across several genes in one chromosome.
Inverted terminal repeat
A sequence of nucleotides that is repeated nearly without change except in the opposite direction, usually at some point distant from the original sequence; often associated with gene insertion.
Junctional epidermolysis bullosa (JEB)
A group of genetic conditions that cause the skin to be very fragile and to blister easily. It is inherited in an autosomal recessive pattern and most commonly results from mutations in the LAMA3, LAMB3, LAMC2, and COL17A1 genes.
Keratinocyte
An epidermal cell that produces keratin. It is formed in the basal layer of the skin and migrates into the outer protective layers of the skin, where it undergoes final differentiation into a corneocyte.
Krabbe disease
Also called globoid cell leukodystrophy. It is a severe neurological condition that is part of a group of disorders known as leukodystrophies, which result from the loss of myelin in the nervous system. It is inherited in an autosomal recessive pattern and caused by mutations in the GALC gene.
Laminar flow biological safety cabinet
A laboratory enclosure designed to carefully direct high-efficiency particulate (HEPA) filtered air.
Latency
Referring to the property of a virus to persist indefinitely in their host after a primary or secondary infection.
Leber congenital amaurosis (LCA)
An eye disorder that primarily affects the retina. It can result from mutations in at least 14 genes (including RPE65). It usually has an autosomal recessive pattern of inheritance.
Lentivirus
A subclass of retroviruses characterized by long incubation periods and persistent infection. Lentiviruses have the ability to integrate into the genome of both dividing and non-dividing cells.
Leukapheresis
Removal of the blood to collect specific blood cells. The remaining blood is returned to the body.
Leukemia
A type of cancer that occurs when the bone marrow produces too many abnormal white blood cells (lymphocytes) affecting the blood and the bone marrow. The types of leukemia include acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), acute myeloid leukemia (AML), and chronic myeloid leukemia (CML).
Leukocyte adhesion deficiency (LAD)
A defect of cellular adhesion molecules resulting in clinical syndromes. It is a combined (B cell) and cellular (T cell) immunodeficiency disorder. There are three different types of LAD (types I, II, and III). It is inherited in an autosomal recessive manner and it can be caused by mutations in at least seven genes.
Library (genetic)
A population of DNA molecules containing all the sequence information necessary for DNA propagation in a host cell.
Limb-girdle muscular dystrophy (LGMD)
A group of diseases that cause weakness and wasting of the muscles in the arms and legs. It can have different inheritance patterns and be caused by mutations in many different genes.
Lipid nanoparticle (LNP)
A type of lipophilic delivery system made of a lipid core, stabilized in aqueous media by a single layer of surfactants (phospholipids, poly(ethylene glycol)-based [PEGylated] surfactants, etc.)
Lipoplex (cationic liposomes)
Non-viral (synthetic) lipid carriers of DNA. Due to their positive surface charge, they can form complexes with negatively charged DNA.
Liposome
An artificial vesicle composed of one or more concentric phospholipid bilayers that is often used to deliver microscopic substances (such as drugs or DNA) to target tissues.
Liver cancer
A type of cancer that affects the liver. There is more than one kind of primary liver cancer; hepatocellular carcinoma (HCC) is the most common form of primary liver cancer in adults.
Long-chain fatty acid oxidation disorder
Also called long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. It is a rare condition that prevents the body from converting certain fats to energy, particularly during fasting. It is inherited in an autosomal recessive manner and caused by mutations in the HADHA gene.
Loss-of-function (mutation)
A mutation that results in reduced or abolished protein function.
Lung cancer
A type of cancer that affects the lungs. There are two main forms of primary lung cancer: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC).
Lymph node
A small structure that filters substances travelling through the lymphatic fluid. They contain lymphocytes that help the body fight against infection and disease.
Lymphoblastic leukemia
A type of leukemia that develops in early (immature) forms of lymphocytes found mainly in the bone marrow and blood. It can be either acute (fast growing) or chronic (slow growing).
Lymphocyte
A type of white blood cell (leukocyte) and one of the body's main types of immune cells. Lymphocytes are made in the bone marrow and are found in the blood and in lymph tissue. There are two categories of lymphocytes known as B lymphocytes (or B cells) and T lymphocytes (or T cells).
Lymphoma
A type of cancer that begins in the immune system and affects the lymph nodes and lymphocytes. There are two types of lymphomas: Hodgkin lymphoma and non-Hodgkin lymphoma.
Lysosomal acid lipase deficiency
An inherited metabolic lipid storage disorder caused by mutations in the LIPA gene encoding for lysosomal acid lipase (LAL) protein, which is needed for the breakdown of lipids and cholesterol in the cells. Two conditions have been described: Wolman disease and cholesteryl ester storage disease. Lysosomal acid lipase deficiency is inherited in an autosomal recessive manner.
Macrophage
A specialized cell involved in the detection, phagocytosis, and destruction of bacteria and other harmful organisms. Macrophages can also present antigens to T cells and initiate inflammation by releasing cytokines that activate other cells. Macrophages originate from blood monocytes that leave the circulation to differentiate in different tissues.
Magnetofection
A process that involves attaching DNA to supramagnetic iron oxide nanoparticles coated with a cationic polymer, in the presence of a magnetic field, to mediate the delivery of the attached DNA into the target organ.
Major histocompatibility complex (genes) (MHC)
A group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances. In humans, the major histocompatibility complex is also called the human leukocyte antigen (HLA) system.
Major histocompatibility complex class I (MHC I)
A set of proteins expressed on the surface of nucleated cells that present processed antigen peptides to CD8+ T cells.
Major histocompatibility complex class II (MHC II)
A set of proteins expressed on the surface of antigen-presenting cells and other cells that present processed antigen peptides to CD4+ T cells.
Mantle cell lymphoma (MCL)
A type of non-Hodgkin lymphoma that occurs when abnormal B-cells are produced from a region of the lymph node called the mantle zone.
Maple syrup urine disease
A genetic disorder in which the body is unable to process amino acids properly, giving a distinctive sweet odor of affected infants' urine, and characterized by poor feeding, vomiting, lack of energy (lethargy), abnormal movements, and delayed development. It is inherited in an autosomal recessive pattern, and caused by mutations in the BCKDHA, BCKDHB, or DBT gene.
Marfan syndrome
An autosomal dominant disorder that affects the connective tissue in many parts of the body. It is caused by mutations in the FBN1 gene.
Melanoma
A form of skin cancer that begins in cells called melanocytes. While most cases of melanoma are not inherited, some are inherited in an autosomal dominant manner.
Mesothelioma
A type of cancer that develops in the lining that covers the outer surface of some of the body’s organs. It is usually linked to asbestos exposure.
Metabolic diseases
Diseases that occur when abnormal chemical reactions in the body disrupt the process of converting food to sugars and acids, the main sources of energy for the body. Metabolic diseases can develop when organs such as the liver or pancreas become diseased or do not function normally.
Metachromatic leukodystrophy
A genetic disorder characterized by the accumulation of fats called sulfatides in cells affecting mainly the white matter of the brain and causing progressive deterioration of intellectual functions and motor skills, such as the ability to walk. It is inherited in an autosomal recessive manner and caused by mutations in the ARSA or PSAP gene.
Metastatic melanoma
A type of melanoma (skin cancer) that has spread to other parts of the body.
Methylmalonic aciduria/acidemia
A genetic disorder in which the body is unable to process certain proteins and lipids properly. It is inherited in an autosomal recessive pattern and is caused by mutations in the MMUT, MMAA, MMAB, MMADHC, or MCEE gene.
Microfluidization
A process where harvested cells are mechanically disrupted with a very high efficiency. It can be used to collect viruses for large-scale manufacturing of adeno-associated virus (AAV) vectors.
MicroRNA (miRNA)
A small non-coding RNA molecule (~22 nucleotides) that functions in RNA silencing and post-transcriptional regulation of gene expression.
Minicircle DNA
An episomal DNA vector that is produced as a circular expression cassette lacking any bacterial plasmid DNA backbone.
Modifier gene
A gene that influences the expression of another gene and impacts the phenotype.
Monoclonal antibody (mAb)
Laboratory-made antibody that binds to only one substance or epitope.
Monogenic disease
A genetic disease that results from modifications in a single gene occurring in all cells of the body.
Mucopolysaccharidosis
A group of inherited conditions in which the body is unable to properly break down mucopolysaccharides. As a result, these sugars build up in cells, blood, and connective tissue, which can lead to a variety of health problems.
Multiple myeloma
A type of cancer that occurs due to abnormal and uncontrolled growth of plasma cells in the bone marrow. It is generally not inherited but arises from somatic mutations in plasma cells. The risk of developing multiple myeloma appears to increase in some families, but the inheritance pattern is unknown.
Muscular dystrophy (MD)
A group of genetic diseases that cause the weakening of muscles over time. Muscular dystrophies are caused by mutations in genes responsible for the structure and functioning of a person’s muscles, and often inherited.
Muscular skeletal disorders
Disorders that affect muscles, tendons, joints, cartilage, and/or spinal discs.
Myelodysplastic syndrome (MDS)
A type of cancer originating in the bone marrow resulting in low numbers of healthy blood cells (white blood cells, red blood cells, and platelets).
Myeloid leukemia
A type of leukemia that originates in the early myeloid cells that eventually become white blood cells, red blood cells, or platelet-making cells. It can be either acute (fast growing) or chronic (slow growing).
Myocardial ischemia
A disorder that occurs when blood flow to the heart is reduced, preventing the heart muscle from receiving enough oxygen. The reduced blood flow is usually the result of a partial or complete blockage of the heart's arteries (coronary arteries). It is also called cardiac ischemia.
Natural killer (NK) cell
A type of lymphocyte that plays a major role in the host rejection of both tumor cells and virally infected cells. Natural killer cells serve to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells that can clear the infection.
Neoantigen
A mutated antigen that is only expressed in tumor cells.
Netherton syndrome
A genetic disorder that affects the skin, hair, and immune system. It is inherited in an autosomal recessive pattern and is caused by mutations in the SPINK5 gene.
Neuroblastoma
A type of cancer that forms from immature nerve cells. It usually begins in the adrenal glands but may also begin in the abdomen, chest, or in nerve tissue near the spine.
Neurodegenerative disease 
A group of diseases caused by loss of function, and ultimately death, of nerve cells of the nervous system.
Neurological disease
A disease of the central and peripheral nervous system (i.e. brain, spinal cord, cranial nerves, peripheral nerves, nerve roots, autonomic nervous system, neuromuscular junction, and muscles).
Neurotoxicity
This occurs when exposure to natural or man-made toxic substances (neurotoxicants) alters the normal activity of the nervous system. This can eventually disrupt or even kill neurons (key cells that transmit and process signals in the brain and other parts of the nervous system).
Neutralizing antibody
A binding antibody that is capable of keeping an infectious agent, usually a virus, from infecting a cell by neutralizing or inhibiting its biological effect, for example by blocking the receptors on the cell or the virus.
Neutrophil
One of the first white blood cells that travels to the site of an infection. Neutrophils help fight infection by ingesting microorganisms and releasing enzymes that kill the microorganisms. A neutrophil is a type of granulocyte and a type of phagocyte.
Niemann–Pick disease type C
A rare, progressive genetic disorder characterized by an inability of the body to transport cholesterol and other fatty substances (lipids) inside of cells. It is inherited in an autosomal recessive manner and caused by mutations in the NPC1 or NPC2 gene.
Non-Hodgkin lymphoma
A type of cancer that develops in the lymphatic system, a network of vessels and glands spread throughout the body.
Non-homologous end joining (NHEJ) 
A mechanism to repair double-strand breaks in DNA. In the absence of a donor template, NHEJ can introduce small base insertions or deletions that can result in gene disruption.
Non-integrating viral vector
The genetic material of non-integrating vectors remains in the cytoplasm in episomal form and does not integrate into the host genome.
Non-viral delivery systems
Comprise all the physical and chemical systems for delivery of gene therapy except viral systems, and generally include either chemical methods (such as cationic liposomes and polymers) or physical methods (such as gene gun, electroporation, particle bombardment, ultrasound utilization, and magnetofection).
Nonsense mutation
The substitution of a single base pair that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid. The presence of this premature stop codon results in the production of a shortened, and likely non-functional, protein.
Normoxic
Used to describe oxygen levels in tissues that are within normal ranges.
Nuclease
An enzyme that hydrolyzes DNA and RNA.
Nucleoside 
It is composed of a purine or pyrimidine base and a ribose or deoxyribose sugar that are connected via a β-glycosidic linkage. They are associated with DNA and RNA structure.
Off-target effect
Negative effect that can result from the modulation of targets different from the targets of interest.
Off-target genome editing
Non-specific genetic modifications as a result of a designed genome editing process, including point mutations, deletions, insertions, inversions, and translocations of unexpected genes.
On-target off-effect tumor
A process that results from a direct attack on normal tissues that have the shared expression of the targeted antigen. It occurs when the chimeric antigen receptor (CAR) T cell recognizes the correct antigen, but the antigen is expressed on healthy, non-pathogenic tissue.
Oncogenesis
The process through which healthy cells become transformed into cancer cells. Oncogenesis is characterized by a series of genetic and cellular changes, including oncogene activation, that lead cells to divide in an uncontrolled manner.
Oncolytic virus
A form of immunotherapy that uses viruses to infect and destroy cancer cells.
Opportunistic infections
Infections caused by non-pathogenic microorganisms that become pathogenic when the immune system is weakened by an unrelated disease.
Opsonization
A process where microorganisms and inanimate colloids (e.g. liposomes, particulates) are coated with host-produced proteins and lipids (immunoglobulins, complement factors), thus facilitating the binding of the opsonized bacteria or particle to specific receptor molecules present on phagocytes (i.e. neutrophils, macrophage, dendritic cells).
Organic acidemias
A group of metabolic disorders resulting from enzymatic deficiencies in the catabolic pathway of branched-chain amino acids and lysine, leading to the accumulation of organic acids in the body fluids and tissues. Most organic acidemias have autosomal recessive inheritance patterns.
Ornithine transcarbamylase deficiency
A genetic disorder characterized by complete or partial lack of the enzyme ornithine transcarboxylase, resulting in accumulation of ammonia in the blood. It is an X-linked disorder caused by mutations in the OTC gene.
Pancreatic cancer
A type of cancer that starts in the pancreas. Pancreatic adenocarcinoma is the most common type of pancreatic cancer.
Parvovirus
Any of a family (Parvoviridae) of single-stranded DNA viruses that include the causative agents of fifth disease in humans, panleukopenia in cats, and parvovirus in dogs.
Pathogen-associated molecular patterns (PAMPs)
Molecules that activate innate immune responses, protecting the host from infection, by the recognition of some conserved non-self molecules on pathogens.
Pemphigus vulgaris
An autoimmune disease that causes blistering and erosion of the skin and mucous membranes. The exact cause of pemphigus vulgaris is unknown, but several potential factors have been identified including genetic factors, age, and disease association, and even certain medications, e.g. angiotensin-converting enzyme inhibitors, chelating agents, non-steroidal anti-inflammatory drugs, and antibiotics.
Persistence
A state in which the virus is not cleared but remains in specific cells of infected individuals.
Persistence (viral infection)
A state in which the virus is not cleared but remains in specific cells of infected individuals.
Persistence (viral infection)
A state in which the virus is not cleared but remains in specific cells of infected individuals.
Personal protective equipment (PPE)
Equipment that will protect the user against health or safety risks at work, such as safety helmets, gloves, eye protection, high-visibility clothing, safety footwear, safety harnesses, and respiratory protective equipment (RPE).
Phage (bacteriophage)
A type of virus that infects bacteria.
Phagocyte
A type of leukocyte capable of phagocytosis (a specific form of endocytosis by which cells internalize solid matter, including microbial pathogens). Macrophages, neutrophils, and immature dendritic cells are types of phagocytes.
Phagocytosis
The process by which certain living cells called phagocytes ingest or engulf other cells or particles. The phagocyte may be a free-living one-celled organism, such as an amoeba, or one of the body cells, such as a white blood cell.
Phenotype
The observable physical properties of an organism, such as appearance, development, and behavior. Phenotype is determined by genotype and environmental influences.
Phenylketonuria (PKU)
An inherited disorder that increases the levels of the amino acid phenylalanine in the blood, which can lead to intellectual disability and other serious health problems. It is inherited in an autosomal recessive manner and caused by mutations in the PAH gene.
Plasmid
A small extrachromosomal ring of DNA, especially of bacteria, that can replicate independently and can be taken from one organism and inserted into another.
Polymer
A large molecule formed of multiple chemical units called monomers. Proteins, cellulose, and nucleic acids are made of polymers.
Polyneuropathy
The simultaneous malfunction of many peripheral nerves throughout the body.
Polyplex
A complex of a polymer and DNA designed to carry genetic material and protect DNA from degradation during delivery into target tissue.
Pompe disease
A genetic disorder caused by the build-up of glycogen in the body's cells. The accumulation of glycogen in certain organs and tissues, especially muscles, impairs their ability to function normally. Pompe disease is inherited in an autosomal recessive manner and caused by mutations in the GAA gene.
Premature stop codon
A mutation that results in the coding of a stop codon prematurely in the protein-coding gene sequence.
Primary barrier
The primary means of physical containment include laboratory practices and the use of containment equipment within the laboratory.
Primary mediastinal large B-cell lymphoma (PMBCL)
An aggressive type of B-cell non-Hodgkin lymphoma that develops from B cells in the mediastinum.
Programmed cell death protein 1 (PD-1)
A cell-surface receptor that is expressed on T cells, B cells, antigen-presenting cells, and in some non-lymphoid tissues. When activated by its ligands, it triggers a pathway that results in immunosuppression.
Promoter
A DNA sequence typically located directly upstream or at the 5' end of the transcription initiation site that defines where transcription of a gene by RNA polymerase begins.
Propionic aciduria
Also known as propionic acidemia or propionyl-CoA carboxylase deficiency. A genetic disorder in which the body is unable to process certain parts of proteins and lipids properly, leading to an abnormal build-up of organic acids in the blood, urine, and tissues. Propionic aciduria is inherited in an autosomal recessive pattern and caused by mutations in the PCCA or PCCB genes.
Prostate cancer
A type of cancer that begins when cells in the prostate gland start to grow out of control.
Protamine
Any of various low-molecular weight proteins rich in arginine that are found combined with DNA in place of histone in animal sperm cells.
Protease
An enzyme that hydrolyzes proteins and is classified according to the most prominent functional group (such as serine or cysteine) at the active site.
Proteostasis
The interconnection of processes within the cell that ensure the production of functioning proteins. Processes include protein synthesis, localization, quality control, and degradation.
Proto-oncogene
A normal gene that, when altered by mutation, becomes an oncogene that can contribute to cancer. Mutations in proto-oncogenes are typically dominant in nature, and the mutated version of a proto-oncogene is called an oncogene.
Protospacer adjacent motif (PAM) 
A short signature sequence of 2–5 base pairs that is critical for clustered regularly interspaced short palindromic repeats (CRISPR)-based immune systems.
Protospacer sequence
A sequence of DNA in the target genome that is complementary to the RNA guide in the CRISPR–Cas9 genome editing system.
Pseudotyping
A process of producing viruses or viral vectors in combination with foreign viral envelope proteins.
Reading frame
One of the three possible ways to read a nucleotide sequence in DNA, depending on whether reading starts with the first, second, or third base in a triplet.
Recombinant DNA (technology)
A technology that involves either the combining of DNA from different genomes or the insertion of foreign DNA into a genome.
Refractory
Applies to a disease that does not respond to treatment. A refractory cancer can become resistant at the beginning or during treatment.
Regulatory T cell (Treg)
A T cell that has a role in regulating or suppressing other cells in the immune system. Regulatory T cells control the immune response to self and foreign particles (antigens) and help prevent autoimmune disease.
Relapse
A recurrence of symptoms of a disease after a period of improvement.
Replication-competent
In viral vectors, it enables each cell infected to become a vector-producing cell that gives rise to more vectors and thus more efficient transduction.
Replication-deficient
In viral vectors, characterized by being defective in one or more functions that are essential for viral genome replication or synthesis and assembly of viral particles.
Respiratory disorders
Include diseases that affect the lungs and may lead to respiratory failure.
Retinal dystrophies
A complex set of hereditary diseases of the retina that result in the degeneration of photoreceptors, rods, and/or cones.
Retinitis pigmentosa
A group of genetic related eye disorders that cause progressive vision loss. More than 60 genes are known to cause retinitis pigmentosa. It can be inherited in an autosomal dominant or recessive manner, or it can be X-linked.
Retrovirus
A type of RNA virus that reverse transcribes its RNA into DNA and inserts this DNA copy into the genome of the host cell. Retroviruses only infect dividing cells.
Rett syndrome
A neurodevelopmental disorder that affects girls almost exclusively. Nearly all cases are caused by a mutation in the methyl CpG-binding protein 2 or MECP2 gene.
Ribonuclease (RNase)
A type of nuclease that catalyzes the hydrolysis of RNA.
Risk groups
Classifications that describe the relative hazard posed by infectious agents or toxins in the laboratory.
RNA interference (RNAi)
Sequence-specific “post-transcriptional inhibition” of gene expression mediated by small double-stranded RNAs.
RNA polymerase
An enzyme that catalyzes DNA template-directed extension of the 3' end of an RNA strand, one nucleotide at a time. RNA polymerase can initiate the synthesis of a chain de novo. In eukaryotes, there are three distinct types of RNA polymerases.
RNA vaccine
It involves the direct introduction into the host’s cells of an RNA sequence encoding an antigen against which an immune response is needed to fight the disease. Cells directly produce the antigen, causing a protective immunological response.
RNA-induced silencing complex (RISC)
A multiprotein complex, specifically a ribonucleoprotein, which incorporates one strand of a single-stranded RNA fragment, such as microRNA (miRNA), or double-stranded small interfering RNA (siRNA) and uses the RNA as a template for recognizing complementary messenger RNA. When it finds a complementary strand, the RNA-induced silencing complex activates RNase and cleaves the RNA.
Same-sense mutation
A phenotypically silent mutation caused by a point mutation that gives rise to a different codon, which is transcribed as a “synonymous” codon. The same amino acid is incorporated into the growing polypeptide as would have been incorporated by the original, non-mutated codon and the protein remains unchanged.
Sanitation
The promotion of hygiene and prevention of disease by maintenance of sanitary conditions (as by removal of sewage and trash).
Sarcoma
A type of cancer affecting soft tissues of the body that connect or support other tissues such as cartilage, fat, muscle, blood vessels, and fibrous tissues. Different types of sarcoma are based on where the cancer forms.
Seroconversion
The development of detectable antibodies in the blood that are directed against an infectious agent.
Seroprevalence
The proportion of a population that is seropositive (i.e. has been exposed to a particular pathogen or immunogen).
Serostatus
The state of either having (seropositive) or not having (seronegative) detectable antibodies against a specific antigen, as measured by a blood test (serologic test).
Serotype
A group of intimately related microorganisms, e.g. viruses, within a single species that share distinctive surface structures.
Severe combined immunodeficiency (SCID)
A group of genetic disorders caused by mutations in genes involved in the development and function of infection-fighting immune cells. More than a dozen genes have been implicated in SCID. SCID is often inherited in an autosomal recessive pattern, but X-linked SCID can also occur. The best-known form of autosomal recessive SCID is caused by adenosine deaminase (ADA) deficiency, in which infants lack the ADA enzyme necessary for T-cell survival.
Short hairpin RNA or small hairpin RNA (shRNA)
A short sequence of RNA that makes a tight hairpin turn and can be used to silence gene expression.
Sickle cell anemia
A disorder in which atypical hemoglobin S molecules distort red blood cells into a sickle, or crescent, shape. It is inherited in an autosomal recessive manner and caused by mutations in the HBB gene.
Single nucleotide change
A type of genetic alteration that involves a change in a DNA base pair in the gene, causing a change in the amino acid encoded by the surrounding DNA sequence. A single nucleotide change can result in altered function of the resulting protein.
Small interfering RNA (siRNA)
Short, double-stranded RNA molecules usually 21–23 nucleotides in length, with a phosphate group at the 5’ end and a hydroxyl group at the 3’ end of each strand, and with a two-nucleotide overhang at the 3’ end of both strands. Small interfering RNAs target complementary messenger RNA for degradation.
Solid tumor
An abnormal growth of tissue that does not contain cysts or fluid areas. Sarcomas, carcinomas, and lymphomas are examples of solid tumors.
Somatic gene therapy
The alteration of genetic material in diploid cells. It targets cells of individual organs or tissues and the effects are only maintained for the lifespan of the individual and not passed on to their offspring.
Somatic mutation
A non germ-line mutation acquired by a cell after conception, therefore not inherited.
Spinal muscular atrophy
A group of genetic disorders that affects the lower motor neurons of the spinal cord and leads to progressive muscle weakness and paralysis. The most common form of spinal muscular atrophy is inherited in an autosomal recessive manner and is caused by mutations in both copies of the survival motor neuron 1 gene (SMN1) located on the long arm (q) of chromosome 5.
Squamous cell carcinoma (SCC)
A type of non-melanoma skin cancer that begins in the squamous cells.
Squamous cell non-small cell lung carcinoma
A type of non-small cell lung cancer (NSCLC) that forms the thin, flat cells that cover the inside of the lungs.
Staff exposure log
A centrally held record of staff exposure to a gene therapy product within an institution.
Standard microbiological practice
Provides protection for laboratory workers and other employees in the building at Biosafety Level 1.
Stargardt disease (Stargardt macular dystrophy)
A genetic eye disorder that causes progressive vision loss. It can have different inheritance patterns and can be caused by mutations in different genes (ABCA4, ELOVL4).
Stem cell
A cell that possesses self-renewal capacity as well as the ability to differentiate into one or more mature cell types.
Sterilization
A process that destroys or eliminates all forms of microbial life and is carried out in healthcare facilities by physical or chemical methods.
Stromal cell 
A connective tissue cell that provides support to tissues and organs. 
Substrate
A molecule acted upon by an enzyme.
Suicide gene
A gene whose expression can lead to death of cells.
Synovial sarcoma
A type of cancer that can arise from soft tissues, such as muscle or ligaments. It usually affects the arm, leg, or foot, and near joints such as the wrist or ankle, but it can also affect the lung or abdomen.
Systemic
Involves a treatment that affects the body as a whole or that acts specifically on systems that involve the entire body.
T lymphocytes (or T cells)
One of the two types of lymphocytes that help to destroy infected or cancerous cells. T cells are involved in adaptive immunity and determine the specificity of the immune response to antigens in the body. T cells originate in the bone marrow and mature in the thymus, where they multiply and differentiate into helper, regulatory, or cytotoxic T cells or become memory T cells.
Targeted cancer therapy
A type of treatment that interferes with molecular targets that are involved in the growth and spread of cancer.
Tay–Sachs disease
A genetic disorder that progressively destroys neurons in the brain and spinal cord. The most common form of Tay–Sachs disease becomes apparent in infancy. It is inherited in an autosomal recessive pattern and is caused by mutations in the HEXA gene.
Thalassemia
A group of inherited conditions that affect the production of hemoglobin. There are two main types of thalassemia: alpha and beta thalassemia.
Thymidylate kinase
A protein that catalyzes the conversion of thymidine 5'-monophosphate (dTMP) to thymidine 5'-diphosphate (dTDP).
Thymine 
It is one of four chemical bases that, together with phosphate and a deoxyribose sugar, form the fundamental building blocks of DNA; it is a pyrimidine base that pairs with adenine.
Toll-like receptor (TLR)
A pattern recognition receptor that plays a crucial role in the initiation of innate immune response by detecting potential harmful pathogens.
Tonic signaling
A constitutive or chronic activation of T cells in the absence of a ligand. 
Transcription
The transference of information in DNA to a messenger RNA (mRNA) molecule.
Transcription activator-like effector nuclease (TALEN) 
A protein used to introduce double-strand breaks and achieve genome editing. TALENs are composed of the DNA-binding domain of the transcription activator-like effector protein fused to the FokI cleavage domain.
Transcription factor
A protein involved in the process of converting, or transcribing, DNA into RNA.
Transcription termination signal
A section of nucleic acid sequence that marks the end of a gene or operon in genomic DNA during transcription.
Transcriptional start site
The location where transcription starts at the 5’ end of a gene sequence.
Transduction
The process by which DNA is introduced into cells (by viral vectors).
Transfection
A procedure that introduces foreign nucleic acids (DNA or RNA) into cells to produce genetically modified cells.
Transforming growth factor (TGF)
One of several proteins secreted by transformed cells that can stimulate the growth of normal cells. TGF alpha (TGF-α) binds the epidermal growth factor receptor (EGFR) and stimulates the growth of endothelial cells. TGF-beta (TGF-β) is found in hematopoietic (blood-forming) tissue and initiates a signaling pathway that suppresses the early development of cancer cells.
Transgene
A gene or a segment of DNA that is introduced into the genome of another organism by artificial techniques.
Translation
The process of translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis.
Translational readthrough
The continuation of translation beyond a stop codon by the use of a special transfer RNA (tRNA) that recognizes the UAG and UGA codons as modified amino acids, rather than as termination codons.
Transposable element
Discrete segments of DNA that can excise and reintegrate to another site in the genome.
Transthyretin-mediated amyloidosis
A genetic, slowly progressive condition characterized by the build-up of abnormal deposits of a protein called amyloid (amyloidosis) in the body's organs and tissues. It is inherited in an autosomal dominant manner and caused by mutations in the TTR gene.
Tropism
Determines which cells or tissues can become infected by any given pathogen (e.g. a virus).
Tumor
An abnormal mass of tissue that can be benign or malignant (cancerous).
Tumor lysis syndrome
A complication commonly observed in hematological cancers that occurs when tumor cells release their contents into the bloodstream, either spontaneously or in response to therapy, leading to hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia.
Tumor microenvironment
The environment around a tumor, consisting of tumor cells, immune cells, endothelial cells, and components of the extracellular matrix such as collagen and fibronectin, among others.
Tumor necrosis factor (TNF)
A type of cytokine made by white blood cells in response to an antigen or infection. It may boost a person’s immune response, and also may cause necrosis (cell death) of some types of tumor cells.
Tumor suppressor gene
A gene involved in the regulation of cell growth. Mutations in tumor suppressor genes can result in cancer.
Tumorigenesis
The process by which normal cells gain malignant properties that result in accelerated proliferation and metastasis, and evasion of apoptosis and immunosurveillance.
Tyrosine kinase
An enzyme that catalyzes the transfer of a phosphate group from adenosine triphosphate (ATP) to a tyrosine residue of specific proteins.
Tyrosinemia
A genetic disorder characterized by disruptions in the multistep process that breaks down tyrosine. It is inherited in an autosomal recessive pattern and caused by mutations in the FAH, TAT, or HPD gene.
U.S. Pharmacopeia General Chapter 800
Practice and quality standards for handling hazardous drugs to promote patient safety, worker safety, and environmental protection.
Ultrasound + microbubble
A non-invasive, site-specific technique, also known as sonoporation, which utilizes ultrasound waves to temporarily permeabilize the cell membrane to allow cellular update of DNA. Genetic material of interest is incorporated within microbubbles and administered into systemic circulation, followed by external application of ultrasound.
Untranslated region (UTR)
A non-protein coding section of the messenger RNA that can be recognized by specific RNA-binding proteins. Untranslated regions are important for the post-transcriptional regulation of gene expression. They can be located at the 5’ end of the coding region (5' UTR) or at the 3’ end of the coding region (3’ UTR).
Uracil
A naturally occurring pyrimidine nucleobase that pairs with adenine in RNA and replaces thymine during DNA transcription.
Urea cycle disorder (UCD)
A disorder that results from genetic mutations causing defects in the metabolism of the extra nitrogen produced by the breakdown of protein and other nitrogen-containing molecules.
V1V2 loop of the human immunodeficiency virus type 1 (HIV-1) envelope gp120 protein
A hypervariable region of the HIV-1 envelope protein that contributes to viral stability, cellular attachment, and entry. The HIV-1 envelope protein is the only viral protein that is exposed to the immune system prior to HIV infection.
Variant
An alteration in the most common DNA nucleotide sequence. The term “variant” can be used to describe an alteration that may be benign, pathogenic, or of unknown significance. The term “variant” may be used in place of the term “mutation”.
Vascular endothelial growth factor
A growth factor involved in developing and maintaining the blood and lymphatic vascular systems.
Vector (cloning)
A genetically engineered carrier that delivers genetic material into target cells or tissues.
Vector shedding
The dissemination of the vector through secretions and/or excreta of the patient.
Viral envelope
The lipid and protein bilayer that surrounds the capsid in some viruses.
Viral genome integration
The insertion of viral DNA into the host cell.
Viral vector
A naturally occurring virus that has been modified to deliver genetic material into cells.
Virucidal
Having the capacity to or tending to destroy or inactivate viruses.
Visual cycle
A chain of biochemical reactions that regenerate visual pigment following exposure to light.
von Gierke disease (glycogen storage disease type Ia)
An inherited disorder caused by the build-up of glycogen in the body’s cells. It is inherited in an autosomal recessive pattern and is caused by mutations in the G6PC gene.
White blood cell (leukocyte or white corpuscle)
A cellular component of the blood that lacks hemoglobin, has a nucleus, is capable of motility, and defends the body against infection and disease by ingesting foreign materials and cellular debris, by destroying infectious agents and cancer cells, or by producing antibodies. White blood cells are grouped into three major classes—lymphocytes, granulocytes (neutrophils, eosinophils, and basophils), and monocytes—each of which carries out somewhat different functions.
X-linked adrenoleukodystrophy
A genetic disorder affecting the nervous system and the adrenal glands that is characterized by the progressive loss of myelin in the nervous system (reducing the ability of the nerves to relay information to the brain) and a shortage of certain hormones caused by damage to the outer layer of the adrenal glands (which may cause weakness, weight loss, skin changes, vomiting, and coma). It is inherited in an X-linked manner and caused by mutations in the ABCD1 gene.
X-linked dominant disorder
A disorder caused by mutations in genes on the X chromosome. In females, a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder. In males, a mutation in the only copy of the gene in each cell causes the disorder. In most cases, males experience more severe symptoms of the disorder than females.
X-linked recessive disorder
A disorder caused by mutations in genes on the X chromosome. In females, a mutation would have to occur in both copies of the gene to cause the disorder. In males, one altered copy of the gene in each cell is sufficient to cause the condition. Males are affected by X-linked recessive disorders much more frequently than females.
X‐linked myotubular myopathy
An X-linked recessive condition that primarily affects skeletal muscles and occurs almost exclusively in males. It is inherited in an X-linked recessive pattern and is caused by mutations in the MTM1 gene.
Yeast
A type of fungi that grow as single cells, producing daughter cells either by budding or fission.
Zinc-finger nuclease (ZFN) 
A protein used to introduce double-strand breaks and achieve genome editing. ZFNs consist of a custom-designed zinc-finger protein that is fused to the cleavage domain of the FokI restriction endonuclease.