Characterization of a conserved T cell epitope in HIV-1 gp41 recognized by vaccine-induced human cytolytic T cells

A human CTL epitope located in a region of the HIV-1 envelope protein gp41 that is highly conserved among various HIV-1 strains was identified. This epitope was recognized by CD4+ CTL clones that were induced in seronegative humans by immunization with recombinant gp160. Fusion proteins carrying portions of the HIV-1 env gene and synthetic peptides were used to localize this epitope to amino acids 584-595 of the HIV-1 BRU env sequence. Only two positions within this epitope showed variation among North American HIV-1 isolates, and the substitutions were conservative in nature. The Lys to Arg substitution at position 593 abolished recognition, probably by interfering with the peptide-MHC interactions. This epitope was recognized in association with at least one subtype of the widely distributed human class II MHC specificity DPw4, namely DPw4.2. The relatively high frequency of this allele (27.2% among Caucasians) makes it likely that a larger fraction of the population would generate a response directed at this epitope than would be the case for epitopes recognized in the context of gene products of most other class II and class I loci. Interestingly, the closely related DP beta-chain allele types 4.1 and 2.1, which differ from 4.2 by 3 and 1 amino acids, respectively, were unable to present this gp41 peptide to DPw4.2-restricted clones. Comparison of the structure of this epitope with that of other peptides recognized in the context of DPw4.2 led to the identification of a consensus sequence for DPw4.2 binding peptides. Because the gp41 CTL epitope 584-595 identified here is highly conserved and is recognized in the context of a common DP allele, it may represent an important target region for vaccine development. Our results indicate that vaccines containing this epitope may induce in a significant fraction of those immunized CTL active against at least half of all HIV-1 strains.