Emergence of cytotoxic T lymphocyte escape mutations in nonpathogenic simian immunodeficiency virus infection

Although CTL escape has been well documented in pathogenic simian immunodef iciency virus (SIV) infection, there is no information on CTL escape in non pathogenic SIV infection in nonhuman primate hosts like the sooty mangabeys . CTL responses and sequence variation in the SIV nef gene were evaluated i n one sooty mangabey and one rhesus macaque inoculated together with the sa me stock of cloned SIVmac239. Each animal developed an immunodominant respo nse to a distinct CTL epitope in Nef, aa 157-167 in the macaque and aa. 20- 28 in the mangabey. Nonsynonymous mutations in their respective epitopes we re observed in both animals and resulted in loss of CTL recognition. These mutations were present in the majority of proviral DNA sequences at 16 week s post infection in the macaque and >2 years post infection in the mangabey . These results document the occurrence of CTL escape in a host that does n ot develop AIDS, and adds to the growing body of evidence that CTL exert si gnificant selective pressure in SIV infection.