Passive immunization of macaques against SIV infection.

Passive immunization with plasma from an inactivated-whole SIVmac vaccine protected monkey conferred complete or partial protection to rhesus macaques challenged intravenously 4 or 18 hours later with 10 AID50 of homologous cell-free virus. In contrast, passive immunization with inactivated plasma or purified immunoglobulin (Ig) from SIVmac infected asymptomatic monkeys failed to protect any recipients similarly challenged and may have enhanced infection and accelerated disease. Administered 24 hours post challenge, anti-SIV Ig may also have enhanced the infection.