The Overall Picture

The development of an effective HIV/AIDS vaccine has focused on creating either a vaccine that will protect people from HIV infection (preventive vaccine) or a vaccine that will protect people from becoming ill after they have already acquired the virus (therapeutic vaccine). In both approaches, the effectiveness of the vaccine depends on its ability to elicit a protective immune response.

Since the start of HIV vaccine research, scientists have worked to uncover which viral antigens or combinations of viral antigens are capable of stimulating a protective immune response. Initially, scientists focused on outer envelope proteins such as gp120 and gp160. While these antigens stimulated the production of neutralizing antibodies, these antibodies appeared unable to prevent HIV infection. Another seemingly attractive vaccine alternative is the use of attenuated strains of HIV. Attenuated vaccines are weakened forms of viruses that are unable to cause disease, but are still able to provoke a powerful immune response. Recent studies on monkeys indicate that attenuated strains of HIV may be capable of regaining virulence and use of such a vaccine could result in disease instead of protection from disease. Current research has expanded beyond antibody-mediated responses to look at cellular immune responses, including how to stimulate cytotoxic T lymphocytes (CTLs), immune cells that kill HIV-infected cells. CD4 "T-helper" cells appear to be important in maintaining a strong CTL response. The relative importance of CD4, CD8, and antibody responses remains to be determined. At the current time, researchers and policymakers face the choice of beginning large vaccine studies without knowing which approaches are most likely to succeed, or waiting until results from more basic research is available to select which vaccines should be tested in large trials. Since any vaccine trial will take several years to complete, these choices are not easy ones.

Because they are often more effective and affordable than drugs, vaccines play an important role in global public health. As demonstrated by diseases like smallpox, poliomyelitis, rabies, and diptheria, an effective vaccine can reduce the morbidity and mortality associated with a disease as well as limit the spread of the disease. As is true for other treatments, an HIV vaccine can slow the HIV/AIDS pandemic only if it is accessible and affordable. At the moment HIV/AIDS poses the greatest threat to developing countries, where high infection rates have had a detrimental impact on economies and have reversed gains in life expectancy. Because of this it is essential that the issues not only of efficacy, but of accessibility and affordability, be considered in vaccine research.



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