iPrEx update, bone mineral density study highlighted at day three of 18th CROI

The 18th Conference on Retroviruses and Opportunistic Infections is being held at the Hynes Convention Center in Boston from February 27 through March 2. Day three of this major HIV/AIDS research conference included the following selected presentations from scientists supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

Robert M. Grant, M.D., of the J. David Gladstone Institutes in San Francisco, presented an update on the results of the iPrEx study. As reported in November 2010, this placebo-controlled clinical trial found that daily oral Truvada (tenofivir plus emtricitabine) was safe and 44 percent effective at preventing HIV infection in the nearly 2,500 HIV-negative gay and bisexual men and transgender women in the trial.

Kathleen Mulligan, Ph.D., of the University of California, San Francisco, presented the findings of the DEXA study, which examined the effects of daily oral Truvada on bone mineral density using data from a subgroup of 503 participants enrolled in the iPrEx study. The DEXA study found small but significant decreases in bone mineral density among the individuals who took daily Truvada compared with those who took a placebo pill. Given the known association between tenofovir and decreases in the bone mineral density of HIV-infected individuals taking this antiretroviral therapy, the new finding can help scientists begin to determine whether the cause of the observed effect on bone mass is tenofovir, the virus, a host-virus interaction or other factors.

Vanessa Hirsch, D.V.M., D.Sc., of NIAID in Bethesda, Md., described how variations in the TRIM5 gene affect the level of simian immunodeficiency virus (SIV), the monkey counterpart of HIV, in rhesus macaques infected with sooty mangabey-derived SIV (SIVsm). SIVsm is a strain commonly used in animal model studies of vaccine candidates. Rhesus macaques can have five different forms of TRIM5 that vary in the degree to which they control virus replication. Dr. Hirsch reported how variations in the TRIM5 protein potentially influence the observed protective effects of vaccine candidates tested in rhesus macaques that are challenged with SIVsm.