PRIOR INFECTION WITH A NONPATHOGENIC CHIMERIC SIMIAN-HUMAN IMMUNODEFICIENCY VIRUS DOES NOT EFFICIENTLY PROTECT MACAQUES AGAINST CHALLENGE WITH SIMIAN IMMUNODEFICIENCY VIRUS

Prior infection with a nef-deleted simian immunodeficiency virus (SIV) protects macaques not only against a homologous pathogenic SIV challe nge but also against challenge with a chimeric SIV expressing a human immunodeficiency virus type 1 env gene (SHIV). Since this SHIV is itse lf nonpathogenic, we sought to explore the use of a nonpathogenic SHIV as a live, attenuated AIDS virus vaccine. Four cynomolgus monkeys inf ected for greater than 600 days with a chimeric virus composed of SIVm ac 239 expressing the human immunodeficiency virus type 1 HXBc2 env, t at, and rev genes were challenged intravenously with 100 animal infect ious doses of the J5 clone of SIVmac 32H, an isolate derived by in viv o passage of SIVmac 251. Three of the four monkeys became infected wit h SIVmac. This observation underlines the difficulty, even with a live virus vaccine, in protecting against an AIDS virus infection.