Molecular and functional analysis of a conserved CTL epitope in HIV-1 p24 recognized from a long-term nonprogressor: Constraints on immune escape associated with targeting a sequence essential for viral replication

It has been hypothesized that sequence variation within CTL epitopes leadin g to immune escape plays a role in the progression of HIV-1 infection. Only very limited data exist that address the influence of biologic characteris tics of CTL epitopes on the emergence of immune escape variants and the eff iciency of suppression of HIV-1 by CTL. In this report, we studied the effe cts of HIV-1 CTL epitope sequence variation on HIV-1 replication. The highl y conserved HLA-B14-restricted CTL epitope DRFYK-TLRAE in HIV-1 p24 was exa mined, which had been defined as the immunodominant CTL epitope in a long-t erm nonprogressing individual. We generated a set of viral mutants on an HX 10 background differing by a single conservative or nonconservative amino a cid substitution at each of the P1 to P9 amino acid residues of the epitope , All of the nonconservative amino acid substitutions abolished viral infec tivity and only 5 of 10 conservative changes yielded replication-competent virus. Recognition of these epitope sequence variants by CTL was tested usi ng synthetic peptides, All mutations that abrogated CTL recognition strongl y impaired viral replication, and all replication-competent viral variants were recognized by CTL, although some variants with a lower efficiency. Our data indicate that this CTL epitope is located within a viral sequence ess ential for viral replication. Targeting CTL epitopes within functionally im portant regions of the HIV-1 genome could limit the chance of immune evasio n.