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The trial demonstrated that the vaccine regimen was safe and modestly effective in preventing HIV infection.
The Thai HIV vaccine efficacy trial, known as RV144, tested the “prime-boost” combination of two vaccines: ALVAC® HIV vaccine (the prime) and AIDSVAX® B/E vaccine (the boost). The vaccine combination was based on HIV strains that commonly circulate in Thailand.
The trial demonstrated that the vaccine regimen was safe and modestly effective in preventing HIV infection. The results show that the prime-boost combination lowered the rate of HIV infection by 31.2 percent compared to placebo based on the modified intent-to-treat (mITT) population (n=51 vs. n=74, respectively; p=0.04).
This study results, announced by the Army in 2009, showed that a preventive HIV vaccine is possible and is providing scientific direction to help guide future vaccine development and testing. Since then, MHRP researchers—in collaboration with partners worldwide—have made substantive progress in understanding what it will take to develop a more efficacious HIV vaccine.
Building on Success
In April, 2012 the New England Journal of Medicine published a paper co-authored by MHRP scientists that detailed clues to why the vaccine tested in the RV144 trial protected some volunteers. This unprecedented collaboration, led by researchers at Duke University and MHRP, brought together investigators from around the world to study those who became infected compared to those who did not. One finding was that immunoglobulin G antibodies that bind to the V1/V2 region of HIV’s Envelope protein correlated with lower infection rates among those who were vaccinated.
Next, scientists examined whether those vaccine-induced antibody responses selectively blocked certain HIV variants. They examined HIV genome sequences from 110 volunteers who participated in RV144, and who subsequently became infected with HIV. The findings, published in September 2012 in Nature, reinforced that antibodies directed at the V1V2 region reduced the risk of infection. “Taken together the work suggests that the Env-V2 region could be a critical target for future HIV vaccines,” noted Col. Jerome Kim, MHRP Principal Deputy Director and senior author on the study.
In the May 2012 issue of The Lancet Infectious Diseases, MHRP researchers reported that vaccine efficacy seemed to peak early—cumulative vaccine efficacy was estimated to be 60.5% (95% CI 22–80)—through the 12 months after initial vaccination, after which it declined quickly. This early, high protective immune response suggests an additional boost or other augmentation of immune response would improve efficacy.
RV144 is generating a wealth of scientific data through secondary studies with collaborators around the globe.
Follow-up Clinical Research
MHRP began a small clinical study, RV305, in April 2012 in Thailand to evaluate re-boosting in volunteers who participated in the RV144 study. Another clinical study, RV306, began in September 2013 using the RV144 vaccine regimen to compare additional vaccine boosts and gather more immunogenicity data in 360 new volunteers.
A public-private collaborative team, called the Pox-Protein Public-Private Partnership (P5), is planning follow-up clinical studies using a similar vaccine regimen in Southern Africa as well as Thailand. Researchers are working to improve and prolong the level of protection by using an extra vaccine boost and better adjuvants in these studies, which are slated to begin in 2016/17.
The RV144 study was sponsored by the U.S. Army and conducted by the Thailand Ministry of Public Health. MHRP provided overall project leadership, and the Armed Forces Research Institute of Medical Sciences (AFRIMS) helped execute the trial.
The study was made possible by an international collaboration involving numerous partners from the Thai and U.S. governments, private companies, non-profit organizations and more than 16,000 volunteers. It was supported by a cooperative agreement with the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc.
It is important to note that a vaccine must be seen as part of a comprehensive approach to prevention of HIV infection. The true public health benefits of any vaccine, and particularly of an experimental vaccine that has not yet been licensed, can only be realized if vaccine recipients continue to control HIV risk-taking behavior.
provided “new clues” to how the RV144 vaccine regimen may have provided protection from HIV.
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