Immunization and Vaccines

Definitions

Active immunization: administration of antigen with the intent of eliciting the immune response

Passive immunization: transfer of preformed antibodies; first used in infectious diseases and venom exposures

antibodies used to be derived from immunized animals, now can produced in laboratory

Adoptive immunotherapy: transfer of previously activated immune cells (usually T); new mode of therapy

Adjuvent: substance that non-specifically boosts the immune response and may affect the quality of that response (i.e. the cells involved)

Properties of desirable vaccine

safe, immunogenic, effective, long-lasting, cost-effective

requirement of ‘safe’ is very subjective and controversial Þ leads to fewer people being vaccinated

Goals of vaccination

Types of Vaccines

live-attenuated: pathogen that can still infect but has somehow been rendered less virulent

illicits a stronger and broader response than killed organism
this type can be dangerous for immunodeficent patients (i.e. oral polio vaccine)

killed whole organism: incapable of causing disease but still triggers immune response (safe for immunodificient)

subunit: purified component(s) of the pathogen (i.e. inactivated toxins, usually polysaccharides or proteins)

synthetic: man-made subunit

live-subunit: use a vector to carry a gene segment encoding an antigen into the host

genetic: directly inject DNA into host to be taken up and expressed

surrogate: use a distinct, nonvirulent substance that mimics the antigen

DNA vaccines are currently under investigation; surrogates currently show little promise

production of antibodies is central to the effectiveness of any vaccine

Difficulties in Vaccine Design

vaccine may interrupt one phase of the pathogen’s life cycle but may not protect against other stages

i.e. intracellular forms vs. extracellular forms (require activation of different lymphoid cells)

mechanisms of pathogens that permit evasion of host response

human genetic variation, especially in MHC I and II can make vaccine formulation difficult

minimal requirements for activating B cells

minimal requirements for activating T cells

Current Vaccines

In Use

Under Development

AIDS, malaria, schistosomiasis, tuberculosis, helminthic infestations, diarrheal diseases, respiratory diseases