Dramatic rise in plasma viremia after CD8(+) T cell depletion in simian immunodeficiency virus-infected macaques

To determine the role of CD8(+) T cells in controlling simian immunodeficie ncy virus (SIV) replication in vivo, we examined the effect of depleting th is cell population using an anti-CD8 monoclonal antibody, OKT8F. There was on average a 99.9% reduction of CD8 cells in peripheral blood in six infect ed Macaca mulatta treated with OKT8F. The apparent CD8 depletion started 1 h after antibody administration, and low CD8 levels were maintained until d ay 8. An increase in plasma viremia of one to three orders of magnitude was observed in five of the six macaques. The injection of a control antibody to an infected macaque did not induce a sustained viral load increase, nor did it significantly reduce the number of CD8(+) T cells. These results dem onstrate that CD8 cells play a crucial role in suppressing SIV replication in vivo.