Induction of long-term protective effects against heterologous challenge in SIVhu-infected macaques

A group of three rhesus macaques were inoculated with SIV isolated from a h uman (SIVhu) accidentally exposed and infected with SIVsm. Extensive sequen ce analyses of SIVhu obtained from the human and macaques following infecti on indicated the presence of truncated nef. Not only did nei fail to repair itself in vivo postinfection (p.i.), but instead, further mutations added additional stop codons with increasing time p.i. Infection of these animals was associated with minimal acute viral replication, followed by undetecta ble plasma viral loads and only intermittent PCR detection up to 5 years p. i. The three SIVhu infected and three control monkeys were then challenged with the heterologous highly pathogenic SHIV89.6p. All three controls becam e infected and showed rapid declines in peripheral CD4(+) lymphocytes, dise ase, and death at 10 and 32 weeks p.i., respectively. In contrast, all thre e animals previously infected with SIVhu are healthy and exhibit stable CD4 (+) lymphocyte levels and undetectable plasma viral loads at >20 months pos t-SHIV89.6p challenge. Only transient, low levels of SHIV replication were noted in these animals. Whereas responses to SIVgag/pol were noted, no evid ence for SIV/SHIV envelope cross-reactivity was detected by antibody or CTL analyses, suggesting that the protective immune mechanisms to the heterolo gous challenge isolate were most likely not directed to envelope but rather to other viral determinants. (C) 2000 Academic Press.