Enhanced safety and efficacy of live attenuated SIV vaccines by prevaccination with recombinant vaccines

The only vaccines shown to be protective against intravenous challenge with virulent virus in the simian immunodeficiency virus (SIV)/macaque model ar e attenuated live SIVs. However, these vaccines have several disadvantages: 1) they persist indefinitely in vaccinated macaques; 2) they are pathogeni c to neonatal macaques; and 3) they are lethal in some adult macaques. To e nhance the safety and efficacy of these vaccines, we immunized macaques fir st with recombinant vaccines and then inoculated the animals with SIVDelta nef. In the first experiment, preimmunized macaques advanced to disease slo wer than controls after challenge with virulent SIV; five animals survived for 3 years without disease and only the vaccine virus (SIVDelta nef) could be isolated at this time. In the second experiment, preimmunized animals h ad lower virus loads and no disease compared to controls.