The effects of natural altered peptide ligands on the whole blood cytotoxic T lymphocyte response to human immunodeficiency virus

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Abstract
Cytotoxic T lymphocytes (CTL) directed against human immunodeficiency virus (HIV)‐1 are detectable in the majority of infected individuals, and their early appearance as the initial viremia is suppressed is thought to represent a potent antiviral response. Variation which arises in CTL epitopes can affect recognition by CTL, and we have observed previously that variant epitopes in HIV‐1 gag which arise in HIV‐1‐seropositive donors may act as T cell receptor (TCR) antagonists of their own CTL (Klenerman et al., Nature 1994. 369: 403). The most important question arising from these observations is the extent of these immune escape mechanisms in vivo. Here we show that fresh, uncultured lymphocytes taken directly from HIV‐1‐infected patients are susceptible to TCR antagonism by variants present within their own virus. In contrast to HLA Class II‐restricted T cell responses, where anergy may be induced, we find that in vitro, natural variants may stimulate and sustain growth of CTL. These CTL lines retain lytic specificity exclusively for the original peptide. If this represents events in vivo, natural HIV altered peptide ligands (APL) have the capacity to inhibit the range of CTL directed against an epitope, not simply those clones selected in vitro. Partial activation of CTL by APL could also act to drive an ineffectual CTL response incapable of lysing infected cells bearing these natural antigenic variants. Distortion of lymphocyte populations and function by APL might represent a further mechanism of immune evasion by HIV.