An effective vaccine to prevent HIV-1 infection may need to generate diverse and multifaceted immunologic responses. Required parts of the immune response may include: humoral antibodies, which broadly neutralize non-syncytium-inducing strains of HIV-1; T cell help provided by both CD4 and CD8 positive subsets; and a class I-restricted cytotoxic lymphocyte response. Other effector responses, such as the generation of antibody-dependent cellular cytotoxicity, cytokines, chemokines, or other antiviral factors may also be critical in mounting protective immunity. Given the lack of a surrogate immunologic marker, the most practical approach for possible efficacy trials would be to evaluate a candidate vaccine that elicits as many of these responses as possible.