NEW YORK (Reuters) Sept 21 - Merck & Co has halted testing of its experimental HIV vaccine -- long considered one of the most promising vaccines in development -- after a monitoring board found it was ineffective, the company said on Friday.
The failed tests represent a major setback in the global effort to stem HIV infections. Merck had expressed great optimism for the vaccine, which it has been testing for a decade.
The independent Data Safety Monitoring Board, after reviewing interim results of the study of the vaccine, recommended discontinuing vaccinations of volunteers as the trial was headed for failure, Merck said.
"No one really knows when and if we will ever have an effective HIV vaccine because the virus is such a great challenge," Mark Feinberg, vice president of medical affairs at Merck's vaccine unit, said in an interview.
The vaccine consisted of a common cold virus expressing three HIV proteins.
Asked if Merck would attempt to develop other HIV vaccines in the wake of the failed trial, Keith Gottesdiener, another senior Merck research executive, said, "At this point, we can't give an answer; we're just starting to look at this data and all its implications."
The New Jersey-based company, which was developing the product in partnership with the federally funded HIV Vaccine Trials Network, said two other early-stage trials of the vaccine had also been discontinued.
Study investigators have been instructed to discontinue vaccinating volunteers and to monitor them, Merck said.
Merck's discontinued international trial, called STEP, involved 3,000 HIV-negative volunteers from diverse backgrounds, between the ages of 18 and 45, at high risk of HIV infection.
An interim efficacy analysis, involving about 1,500 volunteers expected to have the best response to the vaccine, showed it was ineffective.
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Source: http://www.sciencedaily.com/releases/2007/10/071012080135.htm
Science Daily — The search for a vaccination against HIV has been in progress since 1984, with very little success. Traditional methods used for identifying potential cellular targets can be very costly and time-consuming.
The key to creating a vaccination lies in knowing which parts of the pathogen to target with which antibodies. A new study by David Heckerman and colleagues from Massachusetts General Hospital, publishing in PLoS Computational Biology, has come up with a way to match pathogens to their antibodies.
At the core of the human immune response is the train-to-kill mechanism in which specialized immune cells are sensitized to recognize small peptides from foreign pathogens (e.g., HIV). Following this sensitization, these cells are then activated to kill cells that display this same peptide. However, for sensitization and killing to occur, the pathogen peptide must be "paired up" with one of the infected person's other specialized immune molecules--an HLA (human leukocyte antigen) molecule. The way in which pathogen peptides interact with these HLA molecules defines if and how an immune response will be generated.
Heckerman's model uses ELISpot assays to identify HLA-restricted epitopes, and which HLA alleles are responsible for which reactions towards which pathogens. The data generated about the immune response to pathogens fills in missing information from previous studies, and can be used to solve a variety of similar problems.
The model was applied to data from donors with HIV, and made 12 correct predictions out of 16. This study, says David Heckerman, has "significant implications for the understanding of...vaccine development." The statistical approach is unusual in the study of HLA molecules, and could lead the way to developing an HIV vaccine.
Citation: Listgarten J, Frahm N, Kadie C, Brander C, Heckerman D (2007) A statistical framework for modeling HLA-dependent T cell response data. PLoS Comput Biol 3(10): e188. doi:10.1371/journal.pcbi.0030188
Note: This story has been adapted from material provided by Public Library of Science.
Fausto Intilla
www.oloscience.com
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