At the Conference on Retroviruses and Opportunistic Infections in Denver today, a presentation by CDC researcher Walid Heinene at showed that a combination of injected antiretroviral drugs (tenofovir and FTC, commercially available in pill form as Truvada) protected macaques against infection with an HIV/SIV hybrid called SHIV162p3. The study used a series of weekly low dose intrarectal challenges with SHIV162p3 which, unlike other available SHIVs, mimics primary HIV isolates in that it utilizes the CCR5 co-receptor to gain entry into CD4 T cells. Six macaques received once daily injections of tenofovir and FTC while six animals served as controls. Four controls became infected after four challenges (5/6 controls were infected by the 10th challenge) while none of the recipients of tenofovir/FTC became infected even after 14 challenges. The results were highly statistically significant. Heinene noted that the dose of FTC used in the trial was considered equivalent to that used in humans, but that the dose of tenofovir was "somewhat higher." A seperate ongoing study is evaluating FTC alone and Heinene reported that of the six macaques in that study, one became infected after five challenges and another after 10. So while FTC alone is less effective, it still offered statistically significant protections against SHIV162p3 challenge and is thus thought to have contributed to the complete protection seen in the tenofovir/FTC combination study. Heinene also noted that the animal in the FTC study that became infected after five weeks displayed a viral load peak that was three logs lower than that seen in controls. There was also no sign of FTC resistance in this animal. Follow up of this study continues. The results offer hope that Pre-Exposure Prophylaxis (or PreP) may be a feasible means of preventing HIV infection in humans. A number of studies of tenofovir PreP are ongoing and these data are likely to generate interest in conducting studies using Truvada.
This story was picked up by Maggie Fox at Reuters.