Characterization of Functional and Phenotypic Changes in Anti-Gag Vaccine-Induced T Cell Responses and Their Role in Protection after HIV-1 Infection

Worldwide HIV-1 vaccine efforts are guided by the principle that HIV-specific T cell responses may provide protection from infection or delay overt disease. However, no clear correlates of T cell-mediated immune protection have been identified. Here, we examine in a HLA- B27+HIV seronegative vaccinee persistent HIV-specific vaccine-induced anti-Gag CD4+and CD8+T cell responses. Although these responses exhibited those characteristics (multi-functionality, appropriate memory phenotype, and targeting of epitopes associated with long-term nonprogression) predicted to correlate with protection from infection, the subject became HIV infected. After HIV infection, the vaccine-induced CD8+T cells expanded, but both CD4+and CD8+T cell responses acquired the functional and phenotypic patterns characteristic of chronic HIV infection. The virus quickly escaped the vaccine-induced T cell response, and the subject progressed more rapidly than expected for someone expressing the HLA-B27 allele. These data suggest that control of HIV by vaccine-elicited HIV-specific T cell responses may be difficult, even when the T cell response has those characteristics predicted to provide optimal protection.