cellular cytotoxicity): an immune response in
which an infected target cell that is coated with
antibody is destroyed by an immune cell.
adjuvant: a substance sometimes
included in a vaccine formulation to enhance or
modify the immune-stimulating properties of a
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.
adverse reaction (side effect): in a
clinical trial, an unwanted effect detected in
participants and attributed to the study 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.
ALVAC-HIV™: a genetically
engineered HIV vaccine composed of a live,
weakened canarypox virus (ALVAC™) into
which parts of genes for non-infectious
components of HIV have been inserted. When ALVAC™
infects a human cell, the inserted HIV genes
direct the cell to make HIV proteins. These
proteins are packaged into HIV-like particles
that bud from the cell membrane. These particles
are not infectious but fool the immune system
into mounting an immune response to HIV.
ALVAC™ can infect but not grow in human
cells, an important safety feature. (See also
amino acid: any of the 26 chemical
building blocks of proteins.
anamnestic response: the heightened
immunologic reaction elicited by a second or
subsequent exposure to a particular pathogenic
microorganism (e.g., bacterium, fungus, virus),
toxin, or antigen. (See also memory cells.)
anergy: the loss or weakening of immune
response to an irritating agent or antigen.
Anergy can be thought of as the opposite of
allergy, which is an overreaction to a substance.
The strength of the immune response is often
quantitatively evaluated by standardized skin
tests. A small amount of solution containing an
antigen known to cause a response, such as
tetanus, mumps, or candida, is injected under the
skin and the area checked for a localized skin
reaction after 48 to 72 hours. Healthy people
will develop a measurable area of redness at the
injection site; people who are immune suppressed,
such as people with AIDS, will have no measurable
response to these skin tests.
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 immunoglobulin;
binding antibody; enhancing
antibody; functional antibody;
antibody-mediated immunity: also called
humoral immunity. Immunity that results from the
activity of antibodies in blood and lymphoid
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.)
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. (See also dendritic cell; macrophage.)
anti-idiotype: an antibody that
recognizes and binds to the antigen-binding site
of another antibody. In HIV vaccines,
anti-idiotype vaccines are made from antibodies
generated against antibodies to the virus.
apoptosis: cellular suicide, also known
as programmed cell death. A possible mechanism
used by HIV to suppress the immune system. HIV
may cause apoptosis in both HIV-infected and
HIV-uninfected immune system cells.
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.
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
autoimmunity: in HIV
vaccination, a theoretical adverse effect in
which the vaccine causes immune responses that
are inappropriately directed at a persons
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
baculovirus: an insect virus used in
the production of subunit vaccines. By splicing a
specific HIV gene(s) into the baculovirus genome,
and then combining this construct with insect
cells, mass quantities of the purified HIV
protein(s) coded for by these two HIV gene(s) can
be made by the cells for use as a vaccine. (See
also expression system.)
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
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 unaware as to 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.)
bDNA (branched DNA) assay: laboratory
test for measuring the amount of virus in blood
plasma. The test detects an amplified luminescent
signal whose brightness depends on the amount of
viral RNA present.
breakthrough infection: an infection,
which the vaccine is intended to prevent, that
occurs in a volunteer during the course of a
vaccine trial. Such an infection is caused by
exposure to the infectious agent and may occur
before or after the vaccine has taken effect or
all doses have been given.
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 ALVAC- HIV™; vector.)
CD: abbreviation for "cluster of
differentiation," referring to cell surface
molecules that are used to identify stages of
maturity of immune cells, for example, CD4+ T
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.)
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. (See also cytotoxic T lymphocyte (CTL);
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.
CHO (Chinese hamster ovary) cell: a
cell used as a "factory" in genetic
engineering to make certain subunit vaccines. CHO
cells are derived from mammals and are
advantageous because they add carbohydrates (a
sugar coat) to the protein, much like naturally
infected human cells do.
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.)
cohort: groups of individuals who share
one or more characteristics in a research study
and who are followed over time. For example, a
vaccine trial might include two cohorts, a group
at low risk for HIV and a group at higher risk
complement: blood proteins that play an
important role in the immune response. Generally,
complement proteins amplify the effects of
antibodies and inflammation.
control: in vaccine clinical trials,
the control group is given either the standard
treatment for the disease or an inactive
substance called a placebo. The control group is
compared with one or more groups of volunteers
given experimental vaccines to detect any effects
of the vaccines.
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.
HIVs 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.
cytoplasm: the living matter within a
cell (excluding the nucleus) that is responsible
for the function of the cell (for example,
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. (See also CD8+ T lymphocyte.)
deletion: elimination of a gene either
in nature or in the laboratory.
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. (See
also antigen-presenting cell.)
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
DNA vaccine (nucleic acid vaccine):
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.
domain: a region of a gene or gene
product. A neutralizing domain is a specific site
on the virus to which a neutralizing antibody is
dose-ranging study: a clinical trial in
which two or more doses (starting at a lower dose
and proceeding to higher doses) of a vaccine are
tested against each other to determine which dose
works best and has acceptable side effects.
dose-response relationship: the
relationship between the dose of a vaccine and an
immune or physiologic response. In vaccine
research, a dose-response effect means that as
the dose of the vaccine increases, so does the
level of the immune response (antibodies and CTL
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 researchers
and volunteers expectations about the
experimental vaccine do not affect the outcome.
DSMB (Data and Safety Monitoring Board):
a committee of independent clinical research
experts who review data while a clinical trial is
in progress. The DSMB ensures that participants
are not exposed to undue risk and looks for any
differences in effectiveness between the
experimental and control groups. The DSMB may
review the data in such a way that they know
which group received the vaccine and which group
did not. This group may also recommend that a
trial be modified or stopped if there are safety
concerns or if the trial objectives have been
EBV (Epstein-Barr Virus) cell line: a
herpesvirus; in vaccine research, used to make
target cells for CTL assays.
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.
ELISA (enzyme-linked immunoabsorbent assay):
a blood test that detects antibodies based on a
reaction that leads to a detectable color change
in the test tube. The HIV ELISA is commonly used
as the initial screening test because it is
relatively easy and inexpensive to perform.
Because the HIV ELISA is designed for optimal
sensitivity -- that is, it detects all persons
with HIV antibodies as well as some who
dont have them (false positives) -- a
positive HIV ELISA test must be confirmed by a
second, more specific test such as an HIV Western
empirical: based on experience or
observational information and not necessarily on
proven scientific data. In the past, vaccine
trials have been performed based exclusively on
empirical data and without a full understanding
of the disease processes or correlates of
emulsion: a suspension of droplets of
one liquid in another liquid (such as oil and
water). The two liquids do not actually combine
but are instead suspended within one another.
endpoint: the results of an
intervention such as vaccination compared among
different study groups in a clinical trial. In
early vaccine trials, common endpoints are safety
and specific types and intensities of immune
responses (neutralizing antibodies, CTL
enhancing antibody: a type of binding
antibody, detected in the test tube and formed in
response to HIV infection, that may enhance the
ability of HIV to produce disease. Theoretically,
enhancing antibodies could attach to HIV virions
and enable macrophages to engulf the viruses.
However, instead of being destroyed, the engulfed
virus may remain alive within the macrophage,
which then can carry the virus to other parts of
the body. It is currently unknown whether
enhancing antibodies have any effect on the
course of HIV infection. Enhancing antibodies can
be thought of as the opposite of neutralizing
enzyme: a protein produced by cells to
accelerate a specific chemical reaction without
itself being altered. Enzymes are generally named
by adding the ending "-ase" to the name
of the substance on which the enzyme acts (for
example, protease is an enzyme that acts on
env: a gene of HIV that codes
for gp160, the precursor molecule that breaks
down into the envelope proteins gp120 and gp41.
(See also gp.)
envelope: outer surface of a virus,
also called the coat. Not all viruses have an
envelope. (See also virus; env.)
epidemiology: the study of the
frequency and distribution of disease in human
epitope: a specific site on an antigen
that stimulates specific immune responses, such
as the production of antibodies or activation of
expression system: in genetic
engineering, the cells into which a gene has been
inserted to manufacture desired proteins. Chinese
hamster ovary (CHO) cells and baculovirus/insect
cells are two expression systems that are used to
make recombinant HIV vaccines.
functional antibody: an antibody that
binds to an antigen and has an effect that can be
demonstrated in laboratory tests. For example,
neutralizing antibodies are functional antibodies
that inactivate HIV or prevent it from infecting
gag: a gene of HIV that
codes for p55, the core protein. p55 is the
precursor of HIV proteins p17, p24, p7 and p6
that form HIVs capsid or core, the inner
protein shell surrounding HIVs strands of
genetic engineering: the laboratory
technique of recombining genes to produce
proteins used for drugs and vaccines.
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., gp160, gp120, gp41) is
the molecular weight of the glycoprotein.
gp41: glycoprotein 41. A protein
imbedded in the outer envelope of HIV that
anchors gp120. gp41 plays a key role in HIV's
infection of CD4+ T cells by
facilitating the fusion of the viral and cell
membranes. Antibodies to gp41 can be detected on
a screening HIV ELISA.
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 antibody.
gp160: glycoprotein 160, a precursor of
HIV envelope proteins gp41 and gp 120.
half-life: the time required for half
the amount of a substance to be eliminated from
the body or to be converted to another
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. (See also CD4+ T lymphocyte.)
homologous: similar in appearance,
structure and usually function. For HIV, the same
strain of the virus.
host: a plant or animal harboring
HLA (human leukocyte antigen): two
major classes of molecules on cell surfaces.
HLA class I: molecules that exist on
all nucleated cells and identify the cell as
"self." In addition, if the cell is
infected by a virus or other microbe, the cell
displays the invaders antigens in
combination with the cells HLA class I
molecules. The presence of the foreign peptide
antigen with the HLA class I molecule activates
CD8+ CTLs specific for that antigen.
HLA class II: molecules that are found
on antigen-presenting cells such as macrophages.
These cells process soluble antigens such as
toxins or other proteins made by microbes and
then display them on their surface as peptide
antigens in combination with HLA Class II
molecules. Helper T cells specific for these
antigens are then able to be activated and
respond to the presence of the invading microbe.
humoral immunity: see antibody-mediated
hypothesis: a tentative statement or
supposition, which may then be tested through
immune complex: the result of a
reaction between an antigen and a specific
antibody. This combination of antigen bound by
antibody may or may not cause adverse effects in
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
immunization: the process of inducing
immunity by administering an antigen (vaccine) to
allow the immune system to prevent infection or
illness when it subsequently encounters the
immunogen: a substance capable of
provoking an immune response. Also called an
immunocompetent: capable of developing
an immune response; possessing a normal immune
immunogenicity: the ability of an
antigen or vaccine to stimulate immune responses.
immunoglobulin: a general term for
antibodies, which bind to invading organisms,
leading to their destruction. There are five
classes of immunoglobulins: IgA, IgG, IgM, IgD
and IgE. (See also antibody.)
immunotherapy: a treatment that
stimulates or modifies the body's immune
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.)
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.
IND (investigational new drug): the
status of an experimental drug after the FDA
agrees that it can be tested in people.
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
participants right to leave the trial at
intervention: a vaccine (or drug or behavioral therapy)
used in a clinical trial to improve health or alter the course
in vitro: an artificial environment
created outside a living organism (e.g., in a
test tube or culture plate) used in experimental
research to study a disease or biologic process.
in vivo: testing within a living
organism, e.g., human or animal studies.
IRB (Institutional Review Board): a
committee of physicians, statisticians, community
advocates and others that reviews clinical trial
protocols before they can be initiated. IRBs
ensure that the trial is ethical and that the
rights of participants are adequately protected.
isolate: a particular strain of HIV-1
taken from a person.
LAI: an HIV-1 isolate used in HIV
vaccine development. LAI is also referred to as
IIIB or LAV. LAI belongs to clade B, the clade to
which most HIV-1 found in America and Europe
belongs. (See also clade.)
live-vector vaccine: a vaccine that
uses a non-disease-causing organism (virus or
bacterium) to transport HIV or other foreign
genes into the body, thereby stimulating an
effective immune response to the foreign
products. This type of vaccine is important
because it is particularly capable of inducing
CTL activity. Examples of organisms used as live
vectors in HIV vaccines are canarypox and
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. (See also B
cell and T cell.)
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.
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.
mean: the arithmetic average, or the
sum of all the values divided by the number of
median: the midpoint value obtained by
ranking all values from highest to lowest and
choosing the value in the middle. The median
divides a population into two equal halves.
memory cell: memory cells are 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. (See also anamestic response.)
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. (See also HLA.)
microencapsulated: surrounded by a thin
layer of biodegradable substance referred to as a
microsphere. A means of protecting a drug or
vaccine antigen from rapid breakdown.
Microencapsulation may also enhance an
antigens absorption and the immune response
to that antigen.
MN: an HIV-1 strain belonging to clade
B, the clade to which most HIV-1 found in North
America and Europe belong. MN is used in vaccine
development. (See also clade.)
monoclonal antibody: custom-made,
identical antibody that recognizes only one
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.
monovalent vaccine: a vaccine that
contains only one antigen.
mucosal immunity: resistance to
infection across the mucous membranes. Mucosal
immunity depends on immune cells and antibodies
present in the linings of reproductive tract,
gastrointestinal tract and other moist surfaces
of the body exposed to the outside world.
nef: a gene of SIV and HIV that
regulates the production of the virus. Vaccines
made of SIV virions from which nef has
been removed (nef-deleted) have shown
promise in monkeys.
neutralizing antibody: an antibody that
keeps a virus from infecting a cell, usually by
blocking receptors on the cells or the virus.
neutralizing domain: a section of HIV
(most commonly on the envelope protein gp120)
that elicits antibodies with neutralizing
activity. (See also V3 loop.)
NK cell (natural killer cell): a
non-specific lymphocyte. NK cells, like killer T
cells, attack and kill cancer cells and cells
infected by microorganisms. NK cells are
"natural" killers because they do not
need to recognize a specific antigen in order to
attack and kill.
nucleus: the central controlling body
within a living cell, usually a spherical unit
enclosed in a membrane and containing genetic
codes for maintaining life systems of the
organism and for issuing commands for growth and
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.
p24: a protein in HIV's inner core. The
p24 antigen test looks for the presence of this
protein in a person's blood.
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
pathogenesis: the origin and
development of a disease. More specifically,
its the way a microbe (bacteria, virus,
etc.) causes disease in its host.
PBMC (peripheral blood mononuclear cell):
cells in the bloodstream that have one round
nucleus; e.g., lymphocytes and monocytes.
Usually, the majority of circulating PBMCs are
PCR (polymerase chain reaction): a
sensitive laboratory technique used to detect and
repeatedly copy small amounts of RNA or DNA. Some
PCR tests can also quantify the amount of RNA or
DNA. PCR is used to measure viral load in persons
infected with HIV.
peptide: a short compound formed by
linking two or more amino acids. Proteins are
made of multiple peptides.
PHA (phytohemagglutinin): a plant
chemical used to stimulate the multiplication
(proliferation) of T lymphocytes in laboratory
Phase 1 vaccine trial: a closely
monitored clinical trial of a vaccine conducted
in a small number of healthy volunteers. A Phase
1 is designed to determine the vaccines
safety in humans, its metabolism and
pharmacologic actions, and side effects
associated with increasing doses.
Phase 2 vaccine trial: controlled
clinical study of a vaccine to identify common
short-term side effects and risks associated with
the vaccine and to collect information on its
immunogenicity. Phase 2 trials enroll some
volunteers who have the same characteristics as
persons who would be enrolled in an efficacy
(Phase 3) trial of a vaccine. Phase 2 trials
enroll up to several hundred participants and
have more than one arm.
Phase 3 vaccine trial: large
controlled study to determine the ability
of a vaccine 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 and to provide adequate basis for
labeling. Phase 3 trials usually include several
hundred to several thousand volunteers.
pharmacokinetics: the processes of
absorption, distribution, metabolism and
excretion of a drug or vaccine.
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
pol: a gene of HIV that
codes for the enzymes protease, reverse
transcriptase and integrase.
polymerase: an enzyme that creates
genetic material, either RNA or DNA, from
polyvalent vaccine: a vaccine that is
produced from multiple viral strains, or is made
to induce immune responses against multiple
prevalence: the number of people in a
given population affected with a particular
disease or condition at a given time. Prevalence
can be thought of as a snapshot of all existing
cases at a specified time. (Contrast with incidence.)
preventive HIV vaccine: a vaccine
designed to prevent HIV infection.
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).
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.
prophylaxis: prevention of disease.
protease inhibitor: one of a class of
anti-HIV drugs designed to inhibit the enzyme
protease and interfere with virus replication.
Protease inhibitors prevent the cleavage of HIV
precursor proteins into active proteins, a
process that normally occurs when HIV replicates.
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.
pseudovirion: a virus-like particle
that resembles a virus but does not contain its
genetic information and cannot replicate. In some
viral diseases pseudovirions can interfere with
infection by the real infectious virus.
randomized trial: a study in which
participants are assigned by chance to one of two
or more intervention arms or regimens.
Randominization minimizes the differences among
groups by equally distributing people with
particular characteristics among all the trial
reactogenicity: the capacity of a
vaccine to produce adverse reactions.
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.
recombinant DNA technology: the
technique by which genetic material from one
organism is inserted into a foreign cell in order
to mass produce the protein encoded by the
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.
reverse transcriptase: the enzyme
produced by HIV and other retroviruses that
enables them to direct a cell to synthesize DNA
from their viral RNA.
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.
seroconversion: the development of
antibodies to a particular antigen. When people
develop antibodies to HIV or an experimental HIV
vaccine, they "seroconvert" from
antibody-negative to antibody-positive.
Vaccine-induced seroconversion does not represent
an infection. Instead, vaccine-induced
seroconversion is an expected response to
vaccination that may disappear over time.
serostatus: positive or negative
results of a diagnostic test, such as an ELISA,
for a specific antibody.
SF-2: an HIV-1 strain used in vaccine
development. SF-2 belongs to clade B, the clade
to which most HIV-1 strains found in North
America and Europe belong. (See also clade.)
SHIV: genetically engineered hybrid
virus having an HIV envelope and an SIV core.
side effect: (See adverse reaction.)
SIV (simian immunodeficiency virus): an
HIV-like virus that infects and causes an AIDS-like disease in some species of monkeys.
statistical significance: the
probability that an event or difference occurred
as the result of the intervention (vaccine)
rather than by chance alone. This probability is
determined by using statistical tests to evaluate
collected data. Guidelines for defining
significance are chosen before data collection
sterilizing immunity: an immune
response that completely prevents the
establishment of an infection.
strain: one type of HIV. HIV is so
heterogeneous, 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,
stratification: separation of a study
cohort into subgroups or strata according to
subtype: also called a clade. With
respect to HIV isolates, a classification scheme
based on genetic differences.
subunit vaccine: a vaccine that
contains only part of the virus or other
microorganism. HIV subunit vaccines produced by
genetic engineering are referred to as
recombinant subunit HIV vaccines.
surrogate marker: an indirect measure
of disease progression. In HIV disease, the
number of CD4+ T cells per cubic
millimeter of blood is often used as a surrogate
syncytia: giant cells formed by the
fusion of an HIV-infected blood cell with one or
more uninfected ones.
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. (See also lymphocyte.)
T lymphocyte proliferation assay: a
test used to measure the memory of T cells to
antigens or microbes, such as HIV.
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.
V3 loop: a section of the HIV gp120
surface protein that appears to be important in
stimulating neutralizing antibodies. (See also neutralizing
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
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.)
viremia: the presence of virus in the
virion: a mature infectious virus
particle existing outside a cell.
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.
Western blot: a blood test to detect
antibodies to several specific components of a
virus such as HIV. This test is most often used
to confirm a positive ELISA.