India stops further trials of HIV vaccine

New Delhi, Dec 5 (IANS) Human trials of a US-produced HIV/AIDS vaccine have been halted in India after it was found to induce poor immune responses.



The vaccine, developed by the US-based Targeted Genetics Corporation, uses the adeno-associated virus (AAV) as a vector to deliver an AIDS vaccine against subtype C, the dominant HIV subtype in India, Scidev.net reported.



India's National AIDS Research Institute (NARI) tested the vaccine on 30 volunteers and announced its decision in November.



'The vaccine met safety criteria, but did not induce immune responses in a sufficient number of the volunteers to meet the criteria for advancement. At present there are no plans to test it further,' Pat Fast, executive director of medical affairs at the International AIDS Vaccine Initiative (IAVI), told SciDev.Net.



Fast said the vaccine showed a 20 percent immune response in the phase I trials - IAVI generally looks for 60 percent immune response before moving on to phase II. The vaccine has shown a similar response in trials in Belgium and Germany.



The halt comes at a time when animal studies of AAV are suggesting that the virus may pose a risk to human health.



A study, led by the University of Pennsylvania and published in the November issue of the Journal of Clinical Investigation (JCI), reports that AAV affects the ability of a crucial group of immune cells - CD8 cells, a type of T cell - to proliferate in vaccinated mice.



CD8 cells play a key role in the immune response to HIV infection, killing the infected cells.



'I am relieved that the trial is halted in India. Although our work centred on mice we cannot rule out a similar impairment in human vaccine recipients,' said Hildegund Ertl, professor at the university's Wistar Institute and one of the authors of the JCI study.



In July 2007, a study published in the journal Science showed links between a disabled AAV vector and tumour growth in mice. It concluded that further research into AAV is needed to determine its long-term safety in humans.



However, Fast points out there are fundamental differences between the immune responses of mice and humans, particularly with regards to HIV. Additionally, the mice received a very high dose of the vaccine - which is known to impair immune response.



India's hopes for a HIV vaccine now rest on an ongoing trial at the Tuberculosis Research Centre (TRC) in Chennai, on a modified vaccinia Ankara virus, one of the pox viruses, as a vector.