The T cell receptor gene usage by simian immunodeficiency virus gag-specific cytotoxic T lymphocytes in rhesus monkeys.

MHC class I-restricted CTL play an important role in limiting the spread of HIV-1 in the infected individual. Elucidating the molecular interactions of CTL with the virus is, therefore, of central importance for characterizing the immune control of this infection. In exploring this CTL response, we have defined the TCR usage by SIVmac Gag-specific CTL in rhesus monkeys. Thirty-nine CTL clones were generated from PBL of three SIVmac-infected monkeys expressing the MHC class I Mamu-A*01 gene product, all of which were shown to recognize a single SIVmac Gag peptide in association with Mamu-A*01. Sixty-six percent of CTL clones derived from two monkeys early after infection expressed TCR genes of the V beta 13 family; 70% of these V beta 13+ CTL clones expressed a TCR heterodimer composed of V alpha 1 and V beta 13 gene products. In addition, there appeared to be a selection of a single conserved amino acid and restricted CDR3 lengths in junctional regions of TCR beta-chains expressed by the V beta 13+ CTL clones. These findings indicate significant structural constraints on the CTL-TCR interaction with the AIDS virus. Interestingly, 55% of the CTL clones derived from the third animal at a later time following infection employed genes of the V beta 6 family in their TCR. Despite the preferential use of TCR V family genes by the CTL clones, the SIVmac Gag-specific CTL response was clearly polyclonal; TCR expressed by these CTL clones displayed varied sequences in their CDR3 regions. Other V gene families, including V beta 23, V alpha 8, and V alpha 20, were used in TCR expressed by SIVmac Gag-specific CTL clones. These studies, therefore, indicate that the TCR repertoire of SIVmac Gag-specific CTL that share a peptide and MHC class I recognition specificity can be diverse. Such a broad CTL-TCR repertoire may be advantageous for the host in containing an AIDS virus infection.

Cytotoxic T lymphocytes do not appear to select for mutations in an immunodominant epitope of simian immunodeficiency virus gag.

Studies to date assessing HIV escape from CTL in vivo have yielded conflicting results. Previous studies have demonstrated that simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys expressing the MHC class I allele Mamu-A*01 reproducibly develop a gag-specific CTL response limited to a 9-amino acid epitope of the SIVmac gag protein (residues 182-190 within peptide 11C). To determine whether CTL have a role in selecting for AIDS virus mutants, we examined mutations in SIVmac proviral DNA encoding this gag CTL epitope in PBL of infected rhesus monkeys. Three Mamu-A*01+ rhesus monkeys were infected with SIVmac and assessed for gag- and peptide 11C-specific CTL responses. This specific CTL response was maintained in two monkeys, but lost in the third animal 2 yr after infection. The generation of proviral gag mutations was then determined by sequencing 500-bp proviral fragments amplified from fresh PBL obtained from the monkeys more than 2.5 yr after infection. Although numerous point mutations were characterized in 131 polymerase chain reaction-generated clones of SIVmac gag, only four mutations within the gag CTL epitope-coding region of the genome were identified. Comparison of synonymous and nonsynonymous nucleotide substitutions in the regions encoding peptide 11C (p11C) and the flanking gag protein indicated a lack of selective pressure for viral mutations in the CTL epitope coding region. Interestingly, a predominant gag mutant encoding a single amino acid change in p11C was found in a monkey which lost its CTL activity. However, even in this setting there was no evidence for selection of mutations in the CTL epitope coding region when compared with the flanking region. Furthermore, synthetic peptides corresponding to all naturally occurring variants in the gag epitope-coding region were recognized by cloned and bulk cultured effector cells of the infected monkeys with persistent CTL. These results indicate that SIVmac gag- and p11C-specific CTL do not select for mutations in the immunodominant epitope-coding region and that the naturally occurring mutants do not appear to escape CTL recognition.

New recombinant HLA-B alleles in a tribe of South American Amerindians indicate rapid evolution of MHC class I loci.

Evidence suggests that the New World was colonized only 11,000-40,000 years ago by Palaeo-Indians. The descendants of these Palaeo-Indians therefore provide a unique opportunity to study the effects of selection on major histocompatibility complex class I genes over a short period. Here we analyse the class I alleles of the Waorani of South America and the Zuni of North America. Four of the Waorani HLA-B alleles were new functional variants which could be accounted for by intralocus recombination. In contrast, all of the Zuni HLA-A and -B molecules were present in caucasians and orientals. This suggests that the new Waorani HLA-B variants arose in South America. The description of four new HLA-B alleles in the Waorani and another five new HLA-B alleles from two other tribes of South American Amerindians indicates that the HLA-B locus can evolve rapidly in isolated populations. These studies underline the importance of gathering genetic data on endangered native human populations.