Study Examines Why Merck Vaccine Candidate Might Have Increased Likelihood Of Contracting HIV

Main Category: HIV / AIDS
Also Included In: Immune System / Vaccines
Article Date: 05 Nov 2008 - 8:00 PDT

email to a friend   printer friendly   view / write opinions

Trials of Merck's experimental HIV vaccine were halted in September 2007 because the drug might have increased the likelihood of contracting the virus rather than preventing it, according to a study published Monday in the Journal of Experimental Medicine, AFP/Google.com reports.

The vaccine was based on the idea that a modified form of a common cold virus -- Adenovirus 5 -- would carry elements of HIV into the body, which would then trigger the immune system to start fighting a subsequent HIV infection. An initial concern was that widespread immunity to the vaccine might cause it to be rejected by the body before the body could develop an effective response against HIV. However, three years after the trial began, researchers at the Montpellier Institute of Molecular Genetics in France said that more of the recipients who had prior immunity to the Ad5 virus had contracted HIV than those who had not received the vaccine. The study found that the presence of long-lasting antibodies specific to the Ad5 virus, which were generated during natural infections with the common cold, could have altered the response to the vaccine. Furthermore, HIV spread through cell cultures three times faster in the presence of antibodies from individuals immune to the Ad5 virus because HIV came in contact with an increased amount of CD4+ T cells to infect. In addition, the study found that the problem was not documented during Phase II trials because nonhuman primates, which were used in Phase I trials, do not naturally come into contact with the human common cold (AFP/Google.com, 11/3).

The study is available online.

Reprinted with kind permission from http://www.kaisernetwork.org. You can view the entire Kaiser Daily Health Policy Report, search the archives, or sign up for email delivery at http://www.kaisernetwork.org/dailyreports/healthpolicy. The Kaiser Daily Health Policy Report is published for kaisernetwork.org, a free service of The Henry J. Kaiser Family Foundation.

© 2008 Advisory Board Company and Kaiser Family Foundation.  All rights reserved.