Biological considerations in the development of a human immunodeficiency virus vaccine

Over the last 12 years, many human immunodeficiency virus (HIV) vaccine candidates have been tried in humans, with disappointing results. In particular, recombinant envelope proteins have failed to elicit strong cellular immune responses or neutralizing antibody against many wild-type isolates of HIV-1. Attenuated strains of simian immunodeficiency virus (SIV), although capable of protecting against virulent strains of SIV, often retain residual pathogenicity. These difficulties suggest that it will be necessary to address a number of biological questions that underpin the rational development of an AIDS vaccine: (1) Will natural infection with HIV protect against superinfection? (2) Is partial protection induced by an HIV vaccine adequate to prevent AIDS? (3) What are the immune correlates of protection for an AIDS vaccine? (4) Will a monotypic HIV-1 vaccine confer cross-clade immunity? (5) Is mucosal immunity important for an effective AIDS vaccine? (6) Is there a rationale for therapeutic immunization? Ongoing research that is addressing these questions should lead to the formulation of a safe and effective AIDS vaccine.