In further support of a lentiviral selective sweep driving the near fixation of −21T in Pan, the −21 T/T HLA-B phenotype in humans is associated with NK cells that are more effective in resisting HIV infection, as well as the disease progression to AIDS, compared to NK cells in individuals with the M/M or M/T phenotype (34, 37, 101, 102). The gene discussed is HLA-B; the disease is AIDS.