Factors contributing to the lack of human immunodeficiency virus type 1 (HIV-1) transmission in HIV-1-discordant partners

Correlates of resistance to infection by human immunodeficiency virus type 1 (HIV-I) are important for defining potential therapeutic interventions and for prophylactic vaccination. In this study, Ii couples discordant in their HIV-1 infection status were prospectively evaluated for the presence of protective factors. Behavioral characteristics of all subjects entailed a high risk of transmission, Cytotoxic T lymphocyte (CTL) responses against viruses isolated from the infected partner, and against laboratory virus isolates, were detected in 5 (45%) of ii HIV-negative partners, including a CCR5 Delta 32-homozygous and a heterozygous subject. No CTL responses were observed in 6 control unexposed subjects. Marked variation in lymphocyte susceptibility to viral infection was noted, Resistance attributable to major histocompatibility complex discordance or anti-major histocompatibility complex antibodies was not identified. These results suggest that a combination of factors, including cellular immunity, viral characteristics, and coreceptor integrity, may be involved in the persistent nontransmission of HIV.