Malaria Vaccine Glossary

Primary Sources:

• Centers for Disease Control and Prevention
• National Institute of Allergy and Infectious Diseases/NIH

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

Anopheles: The genus of mosquito that transmits malaria.

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: Immunity that results from the activity of antibodies in blood and lymphoid tissue (also called humoral immunity).

Antigens: Foreign substances in the body that are capable of causing disease. The presence of antigens in the body triggers an immune response, usually the production of antibodies. Antigens may be soluble substances, such as toxins and foreign proteins, or particulate, such as bacteria and tissue cells; however only the portion of the protein of polysaccharide molecule known as the antigenic determinant combines with antibody or a specific receptor on a lymphocyte.

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 or treated in such a way as to decrease the ability of a microorganism (such as parasite or virus) to cause infection or disease.

Attenuated vaccine: A vaccine in which live bacteria or viruses are weakened through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. Attenuated vaccines currently licensed in the United States include measles, mumps, rubella, polio, typhoid, yellow fever, and varicella. Also known as a live vaccine. [Irradiated sporozoites delivered via mosquito bite to volunteers was an investigational attenuated vaccine. The ability of this method of immunization to protect volunteers against challenge by infected mosquitoes is the basis for all current efforts to develop a malaria vaccine.]

B cells: Small white blood cells that help the body defend itself against infection. These cells are produced in bone marrow and develop into plasma cells that produce antibodies. Also known as B-lymphocytes.

Blood meal: Blood taken from a human or other host by a mosquito.

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.

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 lymphocyte: Immune cell that carries a marker on its surface known as "cluster of differentiation 4" (CD4). 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 or person to the infectious agent.

Cytoplasm: The living matter within a cell (excluding the nucleus) that is responsible for the function of the cell (for example, protein synthesis).

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 infected cells, whereas antibodies generally target free-floating organisms in the blood.

Cytotoxicity: Degree to which a substance is poisonous to 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.

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.

Effector arm: The part of the immune system that recognizes and responds to infection.

Efficacy: In vaccine research, the ability of a vaccine to produce a desired clinical effect, such as protection against a specific infection or disease, 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 to a specific antigen (foreign substance in the body) based on a reaction that leads to a detectable color change in the test tube.

Endemic: The continual, sometimes low-level presence of disease in a community.

Epidemic: The occurrence of disease within a specific geographical area or population that is in excess of the normal level.

Epidemiology: The study of the frequency and distribution of disease in human populations.

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

Erythrocyte: A type of red blood cell.

Etiology: Origin or cause.

Exposure: Contact with infectious agents (e.g., bacteria, parasite, and virus) in a manner that promotes transmission and increases the likelihood of disease.

Expression system: In genetic engineering, the cells into which a gene has been inserted to manufacture desired proteins.

Functional antibody: An antibody that binds to an antigen and has an effect that can be demonstrated in laboratory tests.

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Gametocytes: Precursors of the sexual forms of the malaria parasite, which release either male or female gametes within the stomach of the mosquito.

Gene: A unit of genetic material (DNA); a segment of DNA encoding a protein molecule; a segment of DNA that contains the information for a specific function.

Genome: the complete set of genes present in a cell, parasite, or virus, for example.

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.

Hemoglobin: The oxygen-carrying part of the red blood cell.

Hepatocyte: Liver cell.

Host: A plant or animal harboring another organism.

Hypnozoite: A form of the malaria parasite that remains inactive within the liver and can produce relapses.

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 a person.

Immune response: The reaction of the immune system to foreign substances.

Immune system: The complex system (network of specialized cells and organs) in the body responsible for fighting disease. Its primary function is to identify foreign substances in the body (bacteria, viruses, fungi or parasites) and develop a defense against them. This defense is known as the immune response. It involves production of protein molecules called antibodies to eliminate foreign organisms that invade the body.

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. Immunity is indicated by the presence of antibodies in the blood and can usually be determined with a laboratory test.

Immunization: The process by which a person or animal becomes protected against a disease; 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. This term is often used interchangeably with vaccination or inoculation.

Immunogen: A substance capable of provoking an immune response. Also called an antigen.

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.

Incubation period: The time from contact with infectious agents (bacteria, viruses, fungi, or parasites) to onset of disease.

IND (investigational new drug): The pre-approval status of an experimental drug or biologic (e.g. vaccine)after the U.S. Food and Drug Administration (FDA) agrees that it can be tested in people (generally done in order to collect sufficient data for licensure). "IND" often refers to the application to obtain this pre-approval status.

Infectious: Capable of spreading disease. Also known as communicable.

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.

IRB (Institutional Review Board): A committee of physicians, statisticians, community advocates and others that reviews clinical trial protocols before they can be initiated and is responsible for monitoring the safety of clinical trials at that instituition. IRBs ensure that the trial is ethical and that the rights of participants are adequately protected.

Larvae: Immature wingless forms of insects such as mosquitoes.

Leukocyte: A white cell of the blood.

Live-vector vaccine: A vaccine that uses a non-disease-causing organism (virus or bacterium) to transport 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.

Lymphocytes: Small white blood cells that help the body defend itself against infection. These cells are produced in bone marrow and develop into plasma cells, which produce antibodies. Also known as B cells.

Lysine: Bursting (and thereby death) of a cell.

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Macrophage: A large cell that helps the body defend itself against disease by surrounding and destroying foreign organisms (such as viruses or bacteria).

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

Merozoite: The form of the malaria parasite that invades human red blood cells; one of the organisms formed by multiple fission of a sporozoite within the body of the host during the asexual phase of reproduction of a malarial plasmodia and other sporozoa.

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.

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 antigen's absorption and the immune response to that antigen.

Monoclonal antibody: Custom-made, identical antibody that recognizes only one epitope of an antigen.

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 respiratory tract, reproductive tract, gastrointestinal tract and other moist surfaces of the body exposed to the outside environment.

Mucous membrane: The lining of certain cavities, such as the nose and mouth and intestinal tract, that produces a protective layer of mucus.

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 reproduction.

Oocyst: A parasite stage within the mosquito, produced by the union of male and female gametes.

Pandemic: An epidemic occurring over a very large area.

Parasite: An animal (or plant) that must live on or in an organism of another species, from which it draws its nourishment.

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).

Pathogen: An organism (e.g. bacteria, viruses, parasites and fungi) that cause disease in human beings.

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

Pharmacokinetics: The processes of absorption, distribution, metabolism and excretion of a drug or vaccine.

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 vaccine's safety and immunogenicity 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, to collect information additional on its immunogenicity, and to collect initial information on efficacy via live agent challenge of vaccinated volunteers. 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.

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

Plasmodium: The genus of the parasite that causes malaria. The genus includes four species that infect humans: Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale.

Pre-erythrocytic: Prior to entering red blood cells.

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.

Prime-boost: 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).

Prophylaxis: Prevention of disease.

Protein: A type of organic compound that is one of the major components of cells and tissues.

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.

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 immunology 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 inserted genes.

Resistance: The ability of an organism to develop strains that are impervious to specific threats to their existence. The malaria parasite has developed strains that are resistant to drugs such as chloroquine. The Anopheles mosquito has developed strains that are resistant to DDT and other insecticides.

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Schizont: A developmental form of the malaria parasite that contains many merozoites.

Species: Organisms in the same genus that have similar characteristics.

Sporozoite: The infectious form of the malaria parasite, which is injected into people by a feeding mosquito; a spore formed after fertilization; any of the elongated, nucleated cells by division of he encysted zygote of a sporozoon, which undergo multiple fission to give rise to merozoites.

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 begins.

Sterilizing immunity: An immune response that completely prevents the establishment of an infection.

Strain: A genetic variant within a species.

Stratification: Separation of a study cohort into subgroups or strata according to specific characteristics.

Surrogate marker: An indirect measure of disease progression.

T cell: White blood cell critical to the immune response. Among these are CD4⁺ T cells and CD8⁺ T cells.

T lymphocyte proliferation assay: A test used to measure the memory of T cells to antigens.

Titer: The quantity of a substance required to produce a reaction with a given volume of another substance, or the amount of one substance required to correspond with a given amount of another substance.

Vaccination: Injection/introduction of a killed or weakened infectious organism in order to prevent the disease.

Vaccine: A preparation that stimulates an immune response that can prevent an infection or create resistance to an infection.

Vector: The organism, typically an insect, that transmits an infectious agent to its alternate host, typically a vertebrate; in human malaria, the vector of the parasite are mosquitoes, the "carriers" or "hosts" are humans. 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.

Virulent: Able to cause disease and characterized by rapid course or severity.

Virus: A tiny organism that multiples within cells and causes disease such as chickenpox, measles, mumps, rubella, pertussis and hepatitis. Viruses are not affected by antibiotics, the drugs used to kill bacteria.

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