VACCINE PROTECTION AND REDUCED VIRUS LOAD FROM HETEROLOGOUS MACAQUE-PROPAGATED SIV CHALLENGE

The efficacy of vaccine protection afforded by live attenuated vaccine s was tested by heterologous SIVtno8980 challenge following successful protection against homologous SIVmac32H challenge. Animals immunized with the attenuated SIVmacBK28 molecular clone were asymptomatic and v irus isolation negative by quantitative virus isolation pries to chall enge. Two groups of four animals previously immunized 5 years and 4 mo nths (respectively) were challenged with 100 MID(50) of SIVtno8980, as was a third group of four naive controls. All control animals that we re challenged developed high levels of plasma antigenemia within 2 wee ks of challenge and developed rapid T-h/m cell loss whereas vaccinated animals did not. Quantitative virus isolation from peripheral blood m ononuclear cells revealed that one of four animals in each group becam e virus isolation positive but that the virus load in the two vaccinat ed animals was markedly lower than in nonvaccinated controls. Studies are underway to determine the duration and immunological correlates of protection from AIDS.