EARLY HELPER T-CELL DYSFUNCTION IN SIMIAN IMMUNODEFICIENCY VIRUS BUT NOT IN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-2-INFECTED MACAQUES

Both naive and vaccinated macaques acquired a virus-specific prolifera tive helper T-cell reactivity in response to infection with the nonpat hogenic human immunodeficiency virus type 2 (HIV-2). In contrast, maca ques infected with the pathogenic simian immunodeficiency virus of the macaque strain (SIVmac) did not develop a helper T-cell response. Fur thermore, a vaccine-induced preexisting T-cell reactivity was abrogate d after SIVmac infection in vaccine failures. These differences may re flect the different pathogenicity of the two closely related viruses.