T cell responses to peptides covering the gag p24 region of HIV -1 occur in HIV -1 seronegative individuals

We demonstrate that peptides (16 amino acids long) covering the sequence of the HIV-1 core protein p24 induce significant proliferation in peripheral blood mononuclear cells (PBMC) of several (>50%) healthy seronegative volunteers as well as seronegative homosexual men. The nature of this response was characterized and compared with those of HIV-infected patients. Several peptides induced responses; however, the most frequent responses in both seropositive and seronegative individuals were noted to the following peptides: 1 and 2 (aa 133–157); 6 and 7 (aa 183–207); 15 (aa 273–287); and 17 and 18 (aa 293–317). The response pattern was related to the disease stage of the patients; seronegative individuals as well as asymptomatic seropositive individuals (CDC II/III) responded to low concentrations of several peptides, but symptomatic patients (CDC IV) only responded to high concentrations of a few peptides. Cell separation studies of PBMC from healthy volunteers showed that the responding cells were CD4+ and expressed the CD45RO differentiation antigen. Furthermore, cord-blood mononuclear cells with