Glossary of Terms


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adjuvant: A substance sometimes included in a vaccine formulation to enhance or modify the immune-stimulating properties of a vaccine.
adverse reaction (side effect): In a clinical trial, an unwanted effect detected in participants and attributed to the study vaccine.
AIDS: Acquired Immunodeficiency Syndrome (AIDS) occurs in individuals who have suffered long term infections with the human immunodeficiency virus (HIV) and have compromised immune systems. People with AIDS suffer life threatening diseases from ubiquitous environmental organisms which have limited virulence in normal humans.
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.
antibody-mediated immunity: Also called humoral immunity. Immunity that results from the activity of antibodies in blood and lymphoid tissue.
antigen: Any substance that stimulates the immune system to produce antibodies. Antigens are often foreign substances such as invading bacteria or viruses.
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.
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.
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 cells.
CD4+ T cells: White blood cells that orchestrate the immune response, signaling other cells in the immune system to perform their special functions. Also known as T helper cells, these cells are killed or disabled during HIV infection.
CD8+ T cells: White blood cells that kill cells infected with HIV or other viruses, or transformed by cancer. These cells also secrete soluble molecules that may suppress HIV without killing infected cells directly.
CDC: Centers for Disease Control, part of the U. S. Department of Health and Human Services (HHS), is dedicated to protecting health and promoting quality of life through the prevention and control of disease, injury, and disability.

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.

chicken embryo fibroblast (CEF): MVA is propagated on primary chicken embryo fibroblast cells prepared from embryonated eggs. A fibroblast is a cell that makes the structural fibers and ground substance of connective tissue. It has a branched cytoplasm surrounding an elliptical, speckled nucleus having one or two nucleoli.
clade: Also called subtype. A group of related HIV isolates classified according to their degree of genetic similarity (such as of their envelope proteins). There are currently tow 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.
cytokines: Proteins used for communication by cells of the immune system. Central to the normal regulation of the immune response.
cytoplasm: The living matter within a cell.
cytotoxic T cells (CTLs): A lymphocyte that is able to kill foreign cells marked for destruction by the cellular immune system. CTLs can destroy cancer cells and cells infected with viruses, fungi, or certain bacteria. CTLs can destroy virus-infected cells, whereas antibodies generally target free-floating viruses in the blood. Also known as "killer T cells" and "cytotoxic lymphocytes."
DAIDS: Division of Acquired Immunodeficiency Syndrome, as part of NIAID, was formed in 1986 to develop and implement the national research agenda to address the HIV/AIDS epidemic. Specifically, the mission of DAIDS is to help ensure an end to the HIV/AIDS epidemic by increasing basic knowledge of the pathogenesis and transmission of the human immunodeficiency virus (HIV), supporting the development of therapies for HIV infection and its complications and co-infections, and supporting the development of vaccines and other prevention strategies.
data safety monitoring board (DSMB): An independent group that reviews data during the study and can recommend a study to be stopped if it appears the volunteers are being placed at risk.

dendritic cells: Immune system cells with long, tentacle-like branches. Some of these are specialized cells at the mucosa that may bind to HIV following sexual exposure and carry the virus from the site of infection to the lymph nodes.

DNA (Deoxyribonucleic Acid): DNA is the genetic code for all living matter. DNA vaccines use purified DNA for vaccination. The GeoVax DNA vaccine expresses non-infectious forms of the three major proteins of HIV (Gag, Pol, and Env) and is used as a prime for the GeoVax MVA boost.

DNA immunization: DNA immunization is an experimental technique for protecting an organism against disease by injecting it with naked DNA to produce an immunological response.
double-blinded study: A study in which neither the investigator nor the participant knows whether the participant is receiving a vaccine or a control. Double-blinded studies are designed to prevent bias when conducting the trial or analyzing the results.
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.
enhancing antibody: A type of binding antibody, detected in the test tube and formed in response to HIB 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 antibodies.
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 proteins).

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.
FDA: The U.S. Food and Drug Administration (FDA) has oversight of all new vaccines that enter testing in humans.

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 HIV's capsid or core, the inner protein shell surrounding HIV's strands of RNA.

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.

gp 41: 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 the helper cells. gp120 has been a logical experimental HIV vaccine becasue the outer envelope isthe first part of the virus that encounters antibody.

gp160: Glycoprotein 160. A precursor of HIV envelope proteins gp41 and gp120.

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.

humoral immunity: See antibody-mediated immunity.
HIV: Human Immunodeficiency Virus (HIV), a retrovirus, infects and kills the CD4+ T cells of the human immune system. As CD4+ cells are destroyed, the immune system fails, leading to AIDS.

HVTN: The HIV Vaccine Trials Network is an international collaboration of scientists and educators searching for an effective and safe HIV vaccine. The HVTN's mission is to facilitate the process of testing preventive vaccines against HIV/AIDS, conducting all phases of clinical trials, from evaluating experimental vaccines for safety and the ability to stimulate immune responses, to testing vaccine efficacy.

IAVI: International AIDS Vaccine Initiative's mission is to ensure the development of preventive AIDS vaccines that are not only safe and effective, but also accessible to all people.

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.

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 infectious agent.

immunogencity: 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.

immunotherapy: A treatment that stimulates or modifies the body's immune response.
inactivated vaccine (killed vaccine): A vaccine made from a whole virus or bacterium whose ability to grow or reproduce has been eliminated.
IND: Investigational New Drug applications(IND) are filed for FDA approval prior to the initiation of trials in humans.
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.

intervention: A vaccine (or drug or behavioral therapy) used in a clinical trial to improve health or alter the course of disease.

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.

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 vaccinia.

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.

lymphoid tissue: Tonsils, adenoid, 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.
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.
mosaic vaccine: Mosaic HIV vaccines include inserts made from strings of amino acids (the building blocks of proteins). They are created by a computer program to optimally reflect the known circulating strains of HIV. They are also designed to produce proteins that physically resemble actual HIV proteins so that they will generate immune responses more like those seen in response to a real HIV infection. Mosaic vaccines typically included more than one amino acid sequence to help better cover the range of HIV variability.
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.

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.
MVA: Modified Vaccinia Ankara (MVA) was developed to be a safe smallpox vaccine by further attenuating the standard smallpox vaccine during serial passage in chicken embryos. The MVA component of the GeoVax vaccine is used to deliver genes expressing non-infectious forms of the three major proteins of HIV (Gag, Pol, and Env) and is used as a single component vaccine both priming and boosting, or as a two component vaccine with DNA priming and MVA boosting. The GeoVax MVA vaccine also protects monkeys against smallpox (monkeypox). Thus, GeoVax's MVA vaccine could be a dual-purpose vaccine protecting against both HIV and smallpox. MVA has been used safely in over 120,000 humans including those immunocompromised.

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.

NIAID: U.S. National Institute of Allergy and Infectious Diseases is one of 27 Institutes and Centers of the National Institutes of Health (NIH). A significant part of NIAID research is devoted to the pathogenesis of HIV disease.

NIH: U.S. National Institutes of Health is the nation’s medical research agency, making important discoveries that improve health and save lives.

NK cell (natural killer cell): A non-specific lymphocyte. NK cells, like killter 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.
open-label trial: A clinical trial in which doctors and participants know which vaccine is being administered to all participants.

p24: A protein in HIV's inner core. The p24 antigen test looks for the presence of this protein in a person's blood.

pathogenesis: The origin and development of a disease. More specifically, it is 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 1 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 vaccine's safety in humans, its metabolism and pharmacologic actions, and side effects associated with increasing doses.
Phase 2 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 2b trial: Controlled clinical study, also known as a "proof-of-concept" trial, provides valuable information on the safety and potential efficacy of the vaccine. A Phase 2b trial enrolls fewer volunteers and is less expensive than Phase 3 efficacy trials.

Phase 3 trial: Large controlled study to determine the ability of a vaccine to produce 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 thousand volunteers.

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.

pol: A gene of HIV that codes for the enzymes protease, reverse transcriptase and integrase.
preclinical: Testing of a vaccine or drug in cells or animals before testing in humans.

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 causes at a specified time.

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.
principal investigator: The scientist in charge of a research team conducting clinical trials.

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.

randomized trial: A study in which participants are assigned by chance to one of two or more intervention arms or regimens. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms.

reagent: Any chemical used in a laboratory test or experiment.
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 inserted genes.
recombinant vaccine: Vaccine that uses genetic material from a disease-causing organism to produce an immune response. For instance, an HIV recombinant vector vaccine uses a vector (a weakened virus or bacterium) to transport genetic material from man-made HIV proteins into the body.

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.
screening: The process clinicians use to see if a volunteer is eligible to participate in a clinical trial. Screening usually includes a medical history, including personal questions and laboratory tests.

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.
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 and AIDS-like disease in some species of monkeys.
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, LAI). 

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

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.
tolerability: The body's ability to support or withstand a vaccine or medicine.
toxicity: The extent, quality, or degree of harm to the body.

vaccination: The deliberate induction of protective immunity to a pathogen by administration of non-pathogenic forms of the pathogen or its antigens to induce a memory immune response.

vaccine: An antigenic preparation used to produce active immunity to a disease in order to prevent or ameliorate the effects of infection by any natural or 'wild' strain of the organism.

vaccinia virus: Closely related to the virus that causes cowpox, it is a member of the pox family of viruses which also includes smallpox. Vaccinia is so mild that it is typically asymptomatic in healthy individuals, but may causes a mild rash and fever with an extremely low rate of fatality.

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.
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.