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Researchers provided further data from the trial in 2 late-breaker presentations at the Retrovirus conference. In post hoc analyses, they found no obvious differences in immunological response that could explain the unexpected results, though overall CD4 cell activation was somewhat higher among participants with adenovirus 5 immunity. However, they investigators did determine that the risk of HIV infection was elevated among trial participants outside North America and among men who were not circumcised. In the uncircumcised group, men who received the vaccine had 4 times the infection rate seen in the placebo arm; by contrast, among circumcised men, there was no significant difference in infection rates in the vaccine and placebo arms. Circumcision is not commonly practiced in the study countries outside North America, and immunity to adenovirus 5 is more common in these other countries. In fact, suggested Dr. Susan Buchbinder of the San Francisco Department of Public Health, it may be that the difference in circumcision status can explain the apparent detrimental effect of adenovirus 5 immunity. In support of this hypothesis, the difference in HIV incidence in the circumcised group was most pronounced among men who practiced insertive anal sex - those most likely to benefit from circumcision. The protective effect of circumcision against HIV infection was not established when the STEP trial began, but has since been convincingly demonstrated. The STEP researchers and outside investigators are conducted further analyses, including assessment of sexually transmitted disease status (e.g., herpes simplex type 2), HLA genetic markers, and genotyping of HIV strains to determine whether there are identifiable clusters of sexual transmission. Following the STEP presentations, Dr. Ronald Desrosiers of Harvard Medical School reviewed findings from animal and human vaccine studies to date, concluding that the National Institutes of Health (HIV) vaccine program had "lost its way" and that the vaccine approaches currently in clinical trials are likely to fail. Pharmaceutical companies are right to shun vaccine studies, he suggested, since they are correct in surmising that existing candidates would not work. He concluded that there is "no rational basis" for believing that any vaccine candidates in the pipeline "have any reasonable hope" of being effective. Though not quite so dire, Dr. Neal Nathanson of the University of Pennsylvania Medical Center also sounded a pessimistic note, urging vaccine researchers to go back to the basic science drawing board in an attempt to come up with more promising approaches. In the wake of the recent upheaval in the field, Dr. Anthony Fauci of NIH's National Institute of Allergy and Infectious Diseases will convene a summit of leading vaccine researchers later this month to discuss future strategies. 3/04/08 References M
Robertson, D Mehrotra, D Fitzgerald, and others. Efficacy Results from the STEP
Study (Merck V520 Protocol 023/HVTN 502): A Phase II Test-of-Concept Trial of
the MRKAd5 HIV-1 Gag/Pol/Nef Trivalent Vaccine. 15th Conference on Retroviruses
and Opportunistic Infections (CROI 2008). Boston, MA. February 3-6, 2008. Abstract
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More
Questions than Answers from STEP HIV Vaccine Trials 
Disappointing
results from recent trials fueled considerable discussion at last month's 
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