Although the broader topic of the lecture was that of HIV research in South Africa and the challenges and opportunities encountered in that field, ARV therapy was mentioned as a particular success for the country.
However, the lecture, given by Glenda Gray and James McIntyre, executive directors of the Perinatal HIV Research Unit at the University of the Witwatersrand, was also keen to draw attention to the limitations in ARV therapy as a prevention method. Specifically, to research which is beginning to demonstrate the longer-term complications associated with this form of treatment.
Two studies have produced evidence suggesting that even if complete suppression of HIV replication is achieved, this does not mean that virus-shedding in semen will necessarily cease. The implication being that HIV transmission may still be possible in those individuals on ARV therapy. Furthermore, it has become increasingly clear that ARVs alone are unlikely to ensure the total eradication of HIV from infected individuals.
The consequence of these revelations is that new HIV preventative measures, including Pre-Exposure Prophylaxis (PreEP), microbicides and vaccines will remain top priorities for the scientific community. Indeed, this year’s CROI included presentations on encouraging results in the use of microbicides and PreEP, produced during both clinical trials and animal studies.
Sharon Hillier, vice chairman of the Department of Obstetrics, Gynaecology and Reproductive Sciences at the University of Pittsburgh said, ‘It’s an exciting time in the prevention field.’
Researchers are attempting to understand the types of immune responses which could be central to an HIV-vaccine, by studying individuals who are able to control HIV infection successfully. Further evaluation and comprehension of the effectiveness of ARV therapy is needed, according to Robert Siliciano, a professor of biology and genetics at Johns Hopkins University. Although, when taken properly, ARV therapy can often entirely prevent further cycles of viral replication, this is not uniformly the case.
Siliciano also stated that intensifying ARV treatment by adding further potent drugs is unlikely to provide a solution. ‘We will never reduce residual viremia any further with ARV drugs,’ he stated in a lecture given earlier this year.
Two other studies presented to the CROI, concerning the correlation between suppressing HIV in the blood and suppression of the virus elsewhere, suggest that viral shedding in semen can still occur in those on suppressive ARV therapy.
Prameet Sheth of the University of Toronto, presenting one of these studies, said that, ‘Our study shows that even though HAART [highly active ARV treatment] will be able to reduce sexual transmission of HIV on a population level, there is still an individual risk that exists despite long-term HAART.’
The research did not, however, demonstrate any link between particular ARVs used and the frequency of HIV-shedding.
One of the most encouraging presentations at the conference was of a study known as HPTNn 035, which tested the utility and safety of a microbicide gel, PRO 2000, that blocks HIV attachment to host cells. 3 099 women were enrolled in trials in seven centres in Africa and the USA.
The trial had three arms ‘ one received PRO 2000, one received a placebo gel and one received condoms but no gel. At the end of the 3-year trial, women in the PRO 2000 group had 36 HIV infections, compared with 51 in the placebo gel group and 53 in the no-gel group.
Analysis of the study’s data found that women who used PRO 2000 at the last occasion of intercourse at least 85% of the time, had an overall reduction of 44% in HIV infection compared to those using the placebo gel. In women who reported using the PRO 2000 gel at a similar rate, albeit without regularly using condoms, there was a 78% reduction in HIV infection compared to the placebo group.
The leader of the PRO 2000 study, Salim Abdool Karim, a clinical infectious disease specialist, cautioned that additional research would be necessary to ‘conclusively determine whether PRO 2000 is an effective microbicide.’
However, Karim also went on to say that, ‘We need something that gives us hope. The HPTNn 035 trial results represent that hope.’
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