Participants in February’s Fifteenth Conference on Retroviruses and Opportunistic Infections (CROI) and Microbicides 2008 conference heard both sobering updates and promising reports from important HIV prevention studies.

At CROI, researchers from the STEP trial of Merck’s failed adenovirus-vector vaccine candidate reported that the vaccine appeared to increase HIV susceptibility in IV risk in inuncircumcised men with strong pre-existing immunity to adenovirus. Results from the federally funded study sparked fierce debate over the wisdom of continuing to fund expensive trials that have yet to produce an effective vaccine, and the future remains uncertain for the PAVE 100 trial of a different adenovirus-vector vaccine candidate. Vaccine researchers agree that if the study proceeds, adenovirus-immune volunteers should be excluded as a safety precaution.

Also disappointing were results from a large study evaluating treatment for herpes simplex virus type 2 (HSV-2)—a known cofactor in HIV transmission—as an HIV prevention approach: No reduction in HIV incidence was observed in participants receiving twice-daily doses of the HSV-2 suppression drug acyclovir (Zovirax) compared with those on placebo. Ongoing analyses will hopefully reveal factors (such as the effect of suboptimal nutrition on acyclovir absorption) that may have handicapped an intervention expected by many to be a “slam dunk” for biomedical HIV prevention.

Microbicides 2008 offered an update on the next generation of microbicide candidates—including UC-781, the first to be tested rectally in humans. Dr. Peter Anton reported that the candidate appears to be safe and well tolerated, based on both participant reports and markers of tissue inflammation. A novel trial design incorporating both in vivo gel application and explant technology also suggests anti-HIV activity in human tissue, although Dr. Anton stressed that the data have not yet been unblinded.

These developments and other conference news will be covered in depth in the Summer 2008 issue of BETA, the San Francisco AIDS Foundation’s treatment and prevention magazine. For a free subscription, sign up at www.ga4.org/sfaf/join or call 415-487-8060.