MECHANISMS OF PROTECTION INDUCED BY ATTENUATED SIMIAN IMMUNODEFICIENCY VIRUS .1. PROTECTION CANNOT BE TRANSFERRED WITH IMMUNE SERUM

To evaluate its role in protection, immune serum was collected from fo ur macaques which were chronically infected with live attenuated simia n immunodeficiency virus (SIVmacC8) and had resisted challenge with wi ld-type SIVmacJ5. The immune serum was transferred to two naive cynomo lgus macaques by intraperitoneal injection (11 ml/kg). Four control ma caques received an intraperitoneal injection of normal saline. One day later, all macaques were challenged with 10 MID50 of the J5M challeng e stock of SIV. After challenge, all macaques became infected as deter mined by virus co-culture and diagnostic PCR. Virus loads in PBMC at 2 weeks post-challenge were indistinguishable between the two groups of macaques. Thus, the failure of passive immunization to transfer prote ction indicates that serum components alone are not sufficient to medi ate the potent protection obtained using live attenuated vaccines. Thi s is the first time that serum has been transferred from animals known to be protected against superinfection.