Protection from secondary human immunodeficiency virus type 1 infection inchimpanzees suggests the importance of antigenic boosting and a possible role for cytotoxic T cells

Recent evidence suggests a much higher prevalence of human immunodeficiency virus type 1 (HIV-1) recombinants than previously anticipated. These recom binants arise from secondary HIV infections in individuals already infected with the virus. It remains unclear why some individuals acquire secondary HIV-1 infections and others do not. To address this question, a study was u ndertaken of a small cohort of chimpanzees with well-defined HIV-1 infectio n. After exposure to an infectious dose of heterologous primary isolate, 4 of 8 HIV-1 seropositive chimpanzees resisted secondary infection, whereas 2 naive controls became readily infected. Only animals who were immunologica lly boosted were protected. Protection from heterologous secondary exposure appeared to be related to the repertoire of the cytolytic CD8(+) T cell re sponses to HIV-1. Data suggested that immunologic boosting by HIV-1 antigen s or exposure to subinfectious doses of virus may be important events in su staining sufficient immunity to prevent secondary infections from occurring .