AIDS Vaccine Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

adjuvant: a substance sometimes included in a vaccine formulation to enhance or modify the immune-stimulating properties of a vaccine.

AIDS (acquired immunodeficiency syndrome): the late stage of HIV disease, characterized by a deterioration of the immune system and a susceptibility to a range of opportunistic infections and cancers.

antibody: an infection-fighting protein molecule in blood or secretory fluids that tags, neutralizes and helps destroy pathogenic microorganisms (e.g. bacteria, viruses) or toxins. Antibodies known generally as immunoglobulins, are made and secreted by B lymphocytes in response to stimulation by antigens. Each specific antibody binds only to the specific antigen that stimulated its production. (See also neutralizing antibody.)

antigen: any substance that stimulates the immune system to produce antibodies. Antigens are often foreign substances such as invading bacteria or viruses. (See also immunogen.)

attenuated: weakened. Attenuated viruses are often used as vaccines because they can no longer produce disease but still stimulate a strong immune response, like that to the natural virus. Examples of attenuated virus vaccines include oral polio, measles, mumps and rubella vaccines.

B lymphocyte (B cell): one of the two major classes of lymphocytes, B lymphocytes are white blood cells of the immune system that are derived from the bone marrow and spleen. B cells develop into plasma cells, which produce antibodies.

baseline: the time point in a study just before initiation of intervention (vaccination) when starting measurements are taken. Measurements taken at later time points may be compared with those taken at baseline to study variations.

binding antibody: an antibody that attaches to some part of HIV. Binding antibodies may or may not lead to the killing of the virus.

blinded study: a clinical trial in which participants are not aware whether or not they are in the experimental or control arm of the study. (See also double-blind study.)

booster: a second or later vaccine dose given after the primary dose(s) to increase the immune response to the original vaccine antigen(s). The vaccine given as the booster dose may or may not be the same as the primary vaccine. (See also prime-boost.)

canarypox: a virus that infects birds and is used as a live vector for HIV vaccines. It can carry a large quantity of foreign genes. Canarypox virus cannot grow in human cells, an important safety feature. (See also ALVACHIV™; vector.)

CD4+ T lymphocyte: immune cell that carries a marker on its surface known as “cluster of differentiation 4” (CD4). These cells are the primary targets of HIV. Also known as helper T-cells, CD4+ T-cells help orchestrate the immune response, including antibody responses as well as killer T-cell responses. (See also T-cell.)

cell-mediated immunity (cellular immunity): the immune response coordinated by active T-cells rather than by antibodies. This branch of the immune system targets cells infected with microorganisms such as viruses, fungi and certain bacteria.

challenge: in vaccine experiments, the deliberate exposure of an immunized animal to the infectious agent. Challenge experiments are never done in human HIV vaccine research.

clade: also called a subtype. A group of related HIV isolates classified according to their degree of genetic similarity (such as of their envelope proteins). There are currently two groups of HIV- 1 isolates, M and O. M consists of at least nine clades, A through I. Group O may consist of a similar number of clades (See also isolate).

clinical trial: any precisely controlled test of an experimental drug, vaccine or other intervention, performed on human volunteers.

correlates of protection: the immune responses that must be present to protect an individual from a certain infection.The precise correlates of immunity in HIV transmission are unknown.

cytokine: a soluble, hormone-like protein produced by white blood cells that acts as a messenger between cells.Cytokines can stimulate or inhibit the growth and activity of various immune cells. Cytokines are essential for a coordinated immune response and can be used also as immunologic adjuvants. HIV replication is regulated by a delicate balance among cytokines.

DNA (deoxyribonucleic acid): the double-stranded, helical molecular chain found within the nucleus of each cell. DNA carries the genetic information that encodes proteins and enables cells to reproduce and perform their functions.

DNA vaccine: a vaccine that uses the strategy of direct injection of a gene(s) coding for a specific antigenic protein(s), resulting in direct production of such antigen(s) within the vaccine recipient in order to trigger an appropriate immune response.

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efficacy: in vaccine research, the ability of a vaccine to produce a desired clinical effect, such as protection against a specific infection, at the optimal dosage and schedule in a given population. A vaccine may be tested for efficacy in Phase III trials if it appears to be safe and shows some promise in smaller Phase I and II trials.

elite controllers: Elite controllers or long-term non-progressors are people infected with HIV whose bodies have kept the microbe at undetectable levels in their bloodstreams without treatment.

empirical: based on experience or observational information and not necessarily on proven scientific data. In the past, AIDS vaccine trials have been performed based exclusively on empirical data and without a full understanding of the disease processes or correlates of immunity.

envelope (Env): outer surface of a virus, also called the coat. Not all viruses have an envelope. (See also virus.)

epitope: a specific site on an antigen that stimulates specific immune responses, such as the production of antibodies or activation of immune cells.

genome: the complete set of genes present in a cell or virus.

gp: abbreviation for glycoprotein. A protein molecule that is glycosylated, that is, coated with a carbohydrate, or sugar. The outer coat proteins of HIV are glycoproteins. The number after the gp (e.g., 160, 120, 41) is the molecular weight of the glycoprotein.

gp120: glycoprotein 120. One of the proteins that forms the envelope of HIV. gp120 projects from the surface of HIV and binds to the CD4 molecule on helper T-cells. gp120 has been a logical experimental HIV vaccine because the outer envelope is the first part of the virus that encounters an antibody.

host: a plant or animal harboring another organism.

hypothesis: a tentative statement or supposition, which may then be tested through research.

immunity: natural or acquired resistance provided by the immune system to a specific disease. Immunity may be partial or complete, specific or nonspecific, long-lasting or temporary.

immunogen: a substance capable of provoking an immune response.

immunogenicity: the ability of an antigen or vaccine to stimulate immune responses.

incidence: the rate of occurrence of some event, such as the number of individuals who get a disease divided by a total given population per unit of time. (Contrast with prevalence.)

informed consent: an agreement signed by prospective volunteers for a clinical research study that indicates their understanding of (1) why the research is being done, (2) what researchers want to accomplish, (3) what will be done during the study and for how long, (4) what risks are involved, (5) what, if any, benefits can be expected from the study, (6) what other interventions are available, and (7) the participant’s right to leave the study at any time.

isolate: a particular strain of HIV-1 taken from a person.

lymphoid tissue: tonsils, adenoids, lymph nodes, spleen and other tissues that act as the body’s filtering system, trapping invading microorganisms and presenting them to squadrons of immune cells that congregate there.

memory cell: a subset of T-cells and B-cells that have been exposed to specific antigens and can then proliferate (recognize the antigen and divide) more readily when the immune system re-encounters the same antigens.

mucosal immunity: resistance to infection across the mucous membranes. Mucosal immunity depends on immune cells and antibodies present in the linings of the reproductive tract, gastrointestinal tract and other moist surfaces of the body exposed to the outside world.

neutralizing antibody: an antibody that keeps a virus from infecting a cell, usually by blocking receptors on the cells or the virus.

open-label trial: a clinical trial in which doctors and participants know which vaccine is being administered to all participants.

opportunistic infection: an illness caused by an organism that usually does not cause disease in a person with a normal immune system. People with advanced HIV infection suffer opportunistic infections of the lungs, brain, eyes and other organs.

pathogen: any disease-causing organism.

pathogenesis: the origin and development of a disease. More specifically, it’s the way a microbe (bacteria, virus, etc.) causes disease in its host.

peptide: a short compound formed by linking two or more amino acids. Proteins are made of multiple peptides.

Phase I vaccine trial: a closely monitored clinical trial of a vaccine candidate conducted in a small number of healthy volunteers. A Phase I trial is designed to determine the safety of the vaccine candidate in a few dozen healthy people. They may also assess the immunogenicity of the vaccine, or its basic ability to generate an immune response.

Phase II vaccine trial: a controlled clinical study of a vaccine candidate to identify common short-term side effects and risks associated with the vaccine candidate and to collect information on its immunogenicity. Phase II trials enroll some volunteers who have the same characteristics as persons who would be enrolled in an efficacy (Phase III) trial of a vaccine. Phase II trials enroll up to several hundred participants and have more than one arm.

Phase IIb vaccine trial: a possible intermediate step is a Phase IIb test-of-concept trial. A test-of-concept trial is about finding out if the vaccine concept or the type of vaccine candidate being tested will be effective. A test-of-concept trial is not designed to establish the efficacy of a particular candidate but rather to help researchers decide if a candidate is worth testing in larger Phase III trials. These intermediate studies are also referred to as proof-of-concept trials. The number of volunteers required for such trials is smaller, around 2,000 to 5,000 volunteers, compared to over 10,000 for Phase III trials.

Phase III vaccine trial: a large controlled study to determine the ability of a vaccine candidate to produce a desired clinical effect on the risk of a given infection, disease or other clinical condition at an optimally selected dose and schedule. These trials also gather additional information about safety needed to evaluate the overall benefit-risk relationship of the vaccine candidate and to provide adequate basis for labeling. For AIDS vaccines, Phase III trials usually involve thousands of volunteers and can take several years to complete.

placebo: an inactive substance administered to some study participants while others receive the agent under evaluation, to provide a basis for comparison of effects.

preventive HIV vaccine (or AIDS vaccine): a vaccine designed to prevent HIV infection or AIDS .

prime-boost: in HIV vaccine research, administration of one type of vaccine, such as a live-vector vaccine, followed by or together with a second type of vaccine, such as a recombinant subunit vaccine. The intent of this combination regimen is to induce different types of immune responses and enhance the overall immune response, a result that may not occur if only one type of vaccine were to be given for all doses.

priming: giving one vaccine dose(s) first to induce certain immune responses, followed by or together with a second type of vaccine. The intent of priming is to induce certain immune responses that will be enhanced by the booster dose(s).

protocol: the detailed plan for a clinical trial that states the trial’s rationale, purpose, vaccine dosages, routes of administration, length of study, eligibility criteria and other aspects of trial design.

reagent: any chemical used in a laboratory test or experiment.

receptor: a molecule on the surface of a cell that serves as a recognition or binding site for antigens, antibodies or other cellular or immunologic components.

retroviruses: HIV and other viruses that carry their genetic material in the form of RNA rather than DNA and have the enzyme reverse transcriptase that can transcribe it into DNA. In most animals and plants, DNA is usually made into RNA, hence “retro” is used to indicate the opposite direction.

serostatus: positive or negative results of a diagnostic test for a specific antibody.

SHIV: genetically engineered hybrid virus having an HIV envelope and an SIV core.

SIV (simian immunodeficiency virus): an HIV-like virus that infects and causes an AIDS-like disease in some species of monkeys.

strain: one type of HIV. HIV is so heterogeneous that no two isolates are exactly the same. When HIV is isolated from an individual and worked on in the lab, it is given its own unique identifier, or strain name (i.e., MN, LAI).

Screening Test of Concept Trial (STOC). A STOC trial is an approach developed by IAVI to obtain efficacy data from human subjects in a shorter time frame and with fewer volunteers. STOC trials involve relatively small cohorts (300-600 individuals from higher-risk communities) and expedite preliminary indications of potential efficacy, helping guide product development for new vaccine candidates that represent a marked improvement over existing candidates.

subtype: also called a clade. With respect to HIV isolates, a classification scheme based on genetic differences.

therapeutic HIV vaccine: a vaccine designed to boost the immune response to HIV in a person already infected with the virus. Also referred to as an immunotherapeutic vaccine.

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vaccine: a preparation that stimulates an immune response that can prevent an infection or create resistance to an infection.

vaccinia: a cowpox virus, formerly used in human smallpox vaccines. Employed as a vector in HIV vaccines to transport HIV genes into the body.

vector: in vaccine research, a bacterium or virus that does not cause disease in humans and is used in genetically engineered vaccines to transport genes coding for antigens into the body to induce an immune response. (See also vaccinia and canarypox.)

virus: a microorganism composed of a piece of genetic material—RNA or DNA—surrounded by a protein coat.To replicate, a virus must infect a cell and direct its cellular machinery to produce new viruses.

This Glossary has been adapted from the Office of Communications and Public Liaison. National Institutes of Health. HIV Vaccine Glossary. 2007. (accessed June 28, 2008).