In vivo administration to rhesus monkeys of a CD4-specific monoclonal antibody capable of blocking AIDS virus replication.

Monoclonal antibodies (mAbs) specific for CD4 are potent inhibitors of HIV replication in vitro. These agents may be useful prophylactically or in chronic HIV infection if they can be administered without inducing immunosuppression. In the present study, we explored the safety of a CD4-specific murine mAb in rhesus monkeys. The mAb 5A8, which binds to domain 2 of the CD4 molecule, inhibits AIDS virus replication noncompetitively at a postvirus binding step. This antibody, which had a similar affinity for rhesus monkey and human CD4 cells, efficiently inhibited in vitro replication of both HIV-1 and the simian immunodeficiency virus of macaques. A single 3-mg/kg injection of mAb 5A8 into normal rhesus monkeys coated all circulating and lymph node CD4 cells for 4-6 days. CD4 cells were not cleared from circulation nor was the CD4 molecule modulated from the lymphocyte surface. In fact, administration of mAb 5A8 resulted in an approximately one-to twofold increase in absolute number of circulating CD4 cells. Repeated administration in normal rhesus monkeys resulted in CD4 lymphocyte coating with mAbs for > 9 days without CD4 cell clearance or modulation. While coated with mAbs, PBLs of these monkeys retained normal in vitro proliferative responses to mitogens and these animals generated normal humoral responses in vivo to tetanus toxoid. Loss of cell coating with mAbs in normal monkeys corresponded to the appearance of anti-mouse immunoglobulin antibodies. Thus, administration of certain anti-CD4 mAbs capable of blocking HIV replication can achieve coating of the entire CD4 cell pool in rhesus monkeys without inducing significant cell loss or immunosuppression.