Cellulose Sulfate: Two Times More HIV, or Not

The reason for searching out more focused anti-HIV microbicides is the failure of the cellulose sulfate (CS) microbicide testing effort (see HHSWatch March 2007). CS is a broadly active charged molecule that interferes with viral coatings and cellular membranes. Two major cellulose sulfate efficacy trials, taking place mainly in Africa, were closed down prematurely last January. One was sponsored by Family Health International (FHI) in North Carolina, the other by Virginia-based CONRAD. Preliminary results from the CONRAD trial appeared to show that cellulose sulfate was paradoxically linked to a higher rate of new HIV than placebo. Researchers presented both trials' complete results at the IAS conference, but they still do not have an explanation for what went wrong.

In the CONRAD trial, the HIV rate was 60% to 120% higher in the cellulose sulfate arm than in the placebo arm, depending on how you count the results. In contrast, the FHI cellulose sulfate trial observed no effect on HIV transmission from cellulose sulfate. HIV rates among the cellulose sulfate recipients were actually less than among those who used the placebo gel, although the trial stopped too early to tell whether this difference was statistically significant.

The contrasting results might be related to differences in the two trial populations: the CONRAD enrollees were somewhat older (30 years versus 23 years for the FHI group) and had sex more often (11 times per week compared with 6 times per week in the FHI trial). If cellulose sulfate causes minor vaginal disruption, it might have been aggravated by very frequent sex plus older age. This in turn would have led to more susceptibility to HIV.

Such possibilities are under investigation. Meanwhile, major trials of two similar-acting microbicides continue without reported difficulty.

Back to September 2007 issue of HHS Watch