Terminology 

AAV (adeno-associated virus) - A viral vector system for gene delivery.

Adenovirus - A group of DNA containing viruses which cause respiratory disease, including one form of the common cold. Adenoviruses can also be genetically modified and used in gene therapy to treat cystic fibrosis, cancer, and potentially other diseases.

Antigens - A substance that when introduced into the body stimulates the production of an antibody. Antigens include toxins, bacteria, foreign blood cells, and the cells of transplanted organs.

Apoptosis - Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.

Adenosine deaminase deficiency (ADA) - A severe immunodeficiency disease that results from a lack of the enzyme adenosine deaminase. It usually leads to death within the first few months of life.

Biologics - A classification of products derived from living sources, such as humans, animals, bacteria and viruses. Vaccines, immune globulin, and anti-toxins are biologics.

Chromosomes - Long strings of genetic material made up of DNA and accessory proteins. The DNA contains the approximately 30,000 to 100,000 genes that make up the human genome. Human cells contain 23 pairs of chromosomes (46 total), with mother and father each contributing one chromosome to each pair.

Clinical Trial - A clinical trial is a research study in human volunteers to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work in people. Trials are in four phases: Phase I tests a new drug or treatment in a small group; Phase II expands the study to a larger group of people; Phase III expands the study to an even larger group of people; and Phase IV takes place after the drug or treatment has been licensed and marketed.

DNA (deoxyribonucleic acid) - Genes are composed of segments of DNA, a very long molecule that carries a cell's genetic information. DNA is made up of two antiparallel strands that are held together by weak chemical bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Eugenic genetic engineering - The ability to modify complex human traits.

ex vivo Gene Therapy - Patient cells are harvested and cultivated in the laboratory and incubated with vectors carrying a corrective or therapeutic gene. Cells with the new genetic information are then harvested and transplanted back into the patient from whom they were derived.

Gene - A segment of DNA found on a chromosome that codes for a particular protein. Humans have approximately 100,000 genes that act as a blueprint for making specific enzymes or other proteins for virtually every biomedical reaction and structure in the body.

Genome - The sum of all genes that code for a particular organism.

Genomics - The study of all of the nucleotide sequences, including structural genes, regulatory sequences, and non-coding DNA segments, in the chromosome of an organism.

Gene Therapy - The treatment of disease by either replacing damaged or abnormal genes with normal ones, or by providing new genetic instructions to help fight disease, e.g., cancer. Therapeutic genes are transferred into the patient either through a weakened virus, a non-viral vector, or through direct delivery of so-called "naked" DNA.

Genetic Engineering - A way of directly manipulating genetic material in a cell or organism to produce desired traits.

Germline therapy - A gene is inserted into the DNA of the germline cells (egg or sperm) so that the offspring of the patient will have the inserted gene.

Hematopoietic stem cell - An unspecialized precursor cell that will develop into a mature blood cell.

Human Genome Project - An international effort to sequence the approximately 30,000 to 100,000 individual genes that constitute a human being.

in situ Gene Therapy - A vector carrying the therapeutic gene(s) is directly administered to the affected tissue.

in vivo Gene Therapy - A vector carrying the therapeutic gene(s) is directly administered to the patient.

Lentivirus - Any of a group of animal viruses that cause diseases having an unusually long incubation period

Mutation - A change in the sequence of DNA that makes up a gene. As a result, the gene no longer makes a normal copy of the protein that it encodes.

Phenotype - The observable traits or characteristics of an organism, for example hair color, weight, or the presence or absence of a disease. Phenotypic traits are not necessarily genetic.

Plasmid - A circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA.

Preclinical Trial - Refers to the testing of experimental drugs in the test tube or in animals - the testing that occurs before trials in humans may be carried out.

Oncogene - A gene that is capable of causing the transformation of normal cells into cancer cells.

Recombinant DNA - A novel DNA sequence formed by the joining, usually in vitro, of two non-homologous DNA molecules.

Retrovirus - A type of virus that contains RNA as its genetic material. The RNA of the virus is translated into DNA, which inserts itself into an infected cell's own DNA. Retroviruses can cause many diseases, including some cancers and AIDS.

RNA (ribonucleic acid) - A molecule that is chemically similar to DNA and carries the same code. When DNA is biochemically read or transcribed, the transcription product is composed of RNA. This RNA is read in turn by the cell's biochemical machinery and converted into a corresponding protein.

Serotype - A group of closely related microorganisms distinguished by a characteristic set of antigens

Somatic Therapy - Involves the manipulation of gene expression in cells that will be corrective to the patient but not inherited by the next generation. Somatic cells include all the non-reproductive cells in the human body.

Suicide gene - A strategy for making cancer cells more vulnerable to chemotherapy. One approach has been to link parts of genes expressed in cancer cells to other genes for enzymes not found in mammals that can convert a harmless substance into one that is toxic to the tumor.

Tropism - The turning or bending movement of an organism or a part toward or away from an external stimulus.

Vectors - Gene therapy delivery vehicles, or carriers, that encapsulate therapeutic genes for delivery to cells. These include both genetically disabled viruses such as adenovirus and nonviral vectors such as liposomes.