Group M-based HIV-1 Gag peptides are frequently targeted by T cells in chronically infected US and Zambian patients.

<p><b>BACKGROUND: </b>The enormous sequence diversity of HIV-1 has been a major obstacle in the development of a globally useful vaccine for AIDS. The consensus and ancestral sequence-based immunogens minimize the genetic distance between contemporary isolates and vaccine strains. Hence these sequences may be promising candidates for HIV vaccines or serve as a universal reagent set for evaluating Gag-specific responses.</p><p><b>METHODS: </b>In this study, we measured the T-cell reactivity to consensus (subtype A, B, C and group M), ancestral (group M and subtype B) and HXB2 Gag peptides (15-mers overlapping by 11) in HIV-1-infected subjects from two reference populations. We evaluated the Gag-specific T-cell responses in 43 chronically infected US (subtype B) and 13 Zambian (subtype C) subjects using an interferon-gamma enzyme-linked immunosorbent spot assay.</p><p><b>RESULTS: </b>Our findings demonstrate a broad cross-reactivity of nearly 70% among all the seven Gag immunogens evaluated. Consensus M sequences elicited similar levels of responses as did the consensus B, ancestral subtype B and HXB2 peptides in subtype B-infected US patients. In subtype C-infected Zambian subjects, responses of similar breadth and magnitude were elicited by consensus C, consensus M and ancestral M peptides.</p><p><b>CONCLUSION: </b>Our data demonstrate that peptide pools based on consensus or ancestral M-based sequences can be used to evaluate Gag-specific responses elicited by subtype B or subtype C-based immunogens.</p>