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Definitions C through E
CD4+ T cells: White blood cells that carry a marker
on their surface known as "cluster designation 4" (CD4). These cells are the
primary target of HIV. Also known as "T-helper" cells, CD4+ T cells help
orchestrate the immune response.
CD8+ T cells: White blood cells that carry the
"cluster designation 8" (CD8) marker. A subset of these cells are cytotoxic T
lymphocytes, or "killer T cells."
Cell-mediated immunity: The immune response in
which cells such as cytotoxic T lymphocytes fight infection.
Challenge: In vaccine experiments, the exposure of
an immunized animal to the infectious agent.
Clade: a group of related HIV isolates, classified
according to the degree of genetic similarity of their envelope proteins. There are
currently two groups of HIV-1 isolates, M and O. M has eight clades, A through H, and O
may have an equal number of clades. Also called a subtype.
Cohort: Individuals who share one or more
characteristics in a research study.
Complement: Blood proteins that play an important
role in the immune response. Generally, complement proteins amplify the effects of
antibodies.
Control: A way to look at the results seen in
clinical trials of experimental vaccines or drugs. One or more groups of patients are
given experimental compound(s), while a control group is given either the standard
treatment for the disease or an inactive substance.
Correlates of immunity/correlates of protection:
The immune responses that protect an individual from a certain disease. The precise
identities of the correlates of immunity in HIV are unknown.
Cytokines: Proteins used for communication by cells
of the immune system.
Cytoplasm: The living matter within a cell.
Cytotoxic T lymphocytes (CTLs): White blood cells
that can kill foreign cells marked for destruction by the immune system. Also known as
"natural killer" cells.
Deletion: Elimination of a gene either in nature or
in the laboratory.
Domain: A region of a gene or gene product.
Dose-ranging study: A clinical trial in which two
or more doses of an agent are tested against each other to determine which dose works best
and is least harmful.
Dose-response relationship: The relationship
between the dose of some agent, or the extent of exposure, and a physiological response. A
dose-response effect means that as the dose increases, so does the effect.
Double-blind study: A clinical trial in which
neither the researchers nor the participants know who is taking which drug or vaccine
until the trial is over.
DSMB (Data and Safety Monitoring Board): An
independent committee composed of clinical research experts who review data while a trial
is in progress to ensure that participants are not exposed to undue risk. A DSMB may
recommend that a trial be stopped if there are safety concerns or if the trial objectives
have been achieved.
Efficacy: The ability of a drug or vaccine to
elicit a beneficial clinical effect.
ELISA: Enzyme-linked immunoabsorbent assay. A blood
test commonly used to detect the presence of HIV antibodies. A positive ELISA test
generally is confirmed by the Western Blot test.
Empirical: Based on experimental data. Not a
theory.
Emulsion: A suspension of droplets of a liquid in
another liquid. The two liquids do not mix but are suspended within one another.
Enzyme: A protein that accelerates a specific
chemical reaction without itself being altered.
Env: A gene of HIV that codes for gp160, the
precursor of the envelope proteins gp120 and gp41.
Envelope: Outer surface of a virus, also called a
coat.
Epidemiology: The study of the frequency and
distribution of disease in human populations.
Epitope: An area of an antigen molecule that
stimulates production of specific antibodies, and combines with such antibodies.
Expression system: In HIV vaccine production, cells
into which an HIV gene has been inserted to produce desired HIV proteins.
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