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  BASIC SCIENTIFIC DICTIONARY
 
A
 
adjuvant: a substance sometimes included in a vaccine formulation to enhance or modify the immune-stimulating properties of a vaccine.
 
adverse event: in a clinical trial, an unwanted effect detected in participants. The term is used whether or not the effect can be attributed to the vaccine under study.
 
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.
 
antigen: any substance that stimulates the immune system to produce antibodies. Antigens are often foreign substances such as invading bacteria or viruses.
 
antigen-presenting cell (APC): B cell, macrophage, dendritic cell or other cell that ingests and processes foreign bodies such as viruses and displays the resulting antigen fragments on its surface to attract and activate the CD4+ T cells that respond specifically to that antigen.
 
arm: a group of participants in a clinical trial, all of whom receive the same treatment, intervention or placebo. The other arm(s) receive(s) a different treatment.
 
B
 
binding antibody: an antibody that attaches to some part of HIV. Binding antibodies may or may not lead to the killing of the virus.
 
C
 
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.
 
CD8+ T lymphocyte: immune cell that carries the "cluster of differentiation 8" (CD8) marker. CD8 T cells may be cytotoxic T lymphocytes or suppressor T cells.
 
cell-mediated immunity (cellular immunity): the immune response coordinated by helper T cells and CTLs. 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.
 
core: the protein capsule surrounding a virus' DNA or RNA. In HIV, p55, the precursor molecule to the core, is broken down into the smaller molecules p24, p17, p7 and p6. HIV's core is primarily composed of p24.
 
correlates of immunity (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 also be used as immunologic adjuvants. HIV replication is regulated by a delicate balance among cytokines.
 
cytotoxic T lymphocyte (CTL): immune system cell that can destroy cancer cells and cells infected with viruses, fungi or certain bacteria. CTLs, also known as killer T cells, carry the CD8 marker. CTLs kill virus-infected cells, whereas antibodies generally target free-floating viruses in the blood. CTL responses are a proposed but unproven correlate of HIV immunity.
 
D
 
dendritic cell: immune cell with threadlike tentacles called dendrites used to enmesh antigen, which they present to T cells. Langerhans cells, found in the skin, and follicular dendritic cells, found in lymphoid tissues, are both types of dendritic cells.
 
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.
 
double-blind study: a clinical trial in which neither the study staff nor the participants know which participants are receiving the experimental vaccine and which are receiving a placebo or another therapy. Double-blind trials are thought to produce objective results, since the researcher's and volunteer's expectations about the experimental vaccine do not affect the outcome.
 
E
 
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 3 trials if it appears to be safe and shows some promise in smaller Phase 1 and 2 trials.
 
env: a gene of HIV that codes for gp160, the precursor molecule that breaks down into the envelope proteins gp120 and gp41.
 
envelope: outer surface of a virus, also called the coat. Not all viruses have an envelope.
 
epitope: a specific site on an antigen that stimulates specific immune responses, such as the production of antibodies or activation of immune cells.
 
H
 
helper T cell: lymphocyte bearing the CD4 marker. Helper T cells are the chief regulatory cells of the immune response. They are responsible for many immune system functions, including turning antibody production on and off, and are the main target of HIV infection.
 
I
 
immune deficiency: a breakdown or inability of certain parts of the immune system to function, thus making a person susceptible to diseases that they would not ordinarily develop.
 
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.
 
immunogenicity: the ability of an antigen or vaccine to stimulate immune responses.
 
inclusion/exclusion criteria: the medical or social reasons why a person may or may not qualify for participation in a clinical trial. For example, some trials may exclude people with chronic liver disease or with certain drug allergies; others may include only people with a low CD4+ T-cell count.
 
informed consent: an agreement signed by prospective volunteers for a clinical research trial 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 trial and for how long, (4) what risks are involved, (5) what, if any, benefits can be expected from the trial, (6) what other interventions are available, and (7) the participant's right to leave the trial at any time.
 
isolate: a particular strain of HIV-1 taken from a person.
 
L
 
lymphocyte: a type of white blood cell produced in the lymphoid organs that is primarily responsible for immune responses. Present in the blood, lymph and lymphoid tissues.
 
M
 
macrophage: a large immune system cell in the tissues that devours invading pathogens and other intruders. Macrophages stimulate other immune cells by presenting them with small pieces of the invaders. Macrophages also can harbor large quantities of HIV without being killed, acting as reservoirs of the virus.
 
MHC (major histocompatibility complex): the gene cluster that controls certain aspects of the immune response. Among the products of these genes are the histocompatibility antigens, such as HLA class I antigens, which are present on every cell with a nucleus and serve as markers to distinguish self from non-self.
 
monoclonal antibody: custom-made, identical antibody that recognizes only one epitope.
 
monocyte: a large white blood cell in the blood that ingests microbes or other cells and foreign particles. When a monocyte passes out of the bloodstream and enters tissues, it develops into a macrophage.
 
N
 
neutralizing antibody: an antibody that keeps a virus from infecting a cell, usually by blocking receptors on the cells or the virus.
 
O
 
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.
 
P
 
parenteral: administered intravenously or by injection. For example, medications or vaccines may be administered by injection into the fatty layer immediately below the skin (subcutaneous), or into the muscle (intramuscular). Medications, but not vaccines, can also be administered into a vein (intravenously).
 
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.
 
placebo: an inactive substance administered to some study participants while others receive the agent under evaluation, to provide a basis for comparison of effects.
 
plasmid: an extrachromosomal ring of DNA, especially of bacterial origin, that replicates autonomously.
 
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.
 
R
 
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.
 
regulatory gene: HIV genes (nef, rev, tat, vpr) that regulate viral replication in infected cells.
 
retrovirus: 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.
 
RNA (ribonucleic acid): a single-stranded molecule composed of chemical building blocks, similar to DNA. The RNA segments in cells represent copies of portions of the DNA sequences in the nucleus. RNA is the sole genetic material of retroviruses.
 
S
 
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.
 
sterilizing immunity: an immune response that completely prevents the establishment of an infection.
 
subtype: also called a clade. With respect to HIV isolates, a classification scheme based on genetic differences.
`
T
 
Tat: a gene of HIV that regulates the production of the virus.
 
T cell: white blood cell critical to the immune response. Among these are CD4+ T cells and CD8+ T cells. The "T" stands for the thymus, where T lymphocytes mature.
 
V
 
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.
 
viremia: the presence of virus in the bloodstream.
 
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.
 

 

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