As described above, the prevailing hypothesis is that HLA-B*27 is protective against HIV disease progression because the immunodominant response, Gag KK10, is highly efficacious, killing virus-infected target cells very soon after viral entry (8), and escape mutants are typically selected late in the course of infection (5) because of the crippling impact of the R264K or R264G mutation in the absence of a simultaneous compensatory mutation at S173T or E260D, respectively (22, 23). The gene discussed is HLA-B; the disease is infection.