Evidence for recombination of live, attenuated immunodeficiency virus vaccine with challenge virus to a more virulent strain

Live, attenuated immunodeficiency virus vaccines, such as nef deletion muta nts, are the most effective vaccines tested in the simian immunodeficiency virus (SIV) macaque model. In two independent studies designed to determine the breadth of protection induced by live, attenuated SN vaccines, we noti ced that three of the vaccinated macaques developed higher set point viral load levels than unvaccinated control monkeys, Two of these vaccinated monk eys developed AIDS, while the control monkeys infected in parallel remained asymptomatic. Concomitant with an increase in viral load, a recombinant of the vaccine virus and the challenge virus could be detected. Therefore, th e emergence of more-virulent recombinants of live, attenuated immunodeficie ncy viruses and less-aggressive wild-type viruses seems to be an additional risk of live, attenuated immunodeficiency virus vaccines.