Protection of human immunodeficiency virus type 2-exposed seronegative macaques from mucosal simian immunodeficiency virus transmission.

At present it is not known which form of immunity would be most effective against infection with human immunodeficiency virus (HIV). To evaluate the possible role of cellular immunity, we examined whether four HIV type 2-exposed but seronegative macaques developed cellular immune responses and determined whether these exposed macaques were resistant to mucosal transmission of simian immunodeficiency virus (SIV). Following intrarectal challenge with SIV, 2 monkeys were protected against detectable SIV replication and another showed suppressed viral replication compared to 14 persistently infected controls. The two protected monkeys demonstrated SIV-specific cytotoxic T lymphocytes before as well as after SIV challenge. Here we provide evidence that activation of the cell-mediated arm of the immune system only, without antibody formation, can control SIV replication in macaques. The results imply that vaccines that stimulate a strong and broad cellular immune response could prevent mucosal HIV transmission.