The elusive search for India’s first AIDS vaccine has conquered the roadblock it met when the trial could not proceed to the second phase at the National AIDS Research Institute (NARI) at Bhosari in Pune. Hopes have been rekindled as a fresh round of clinical trials have been planned at NARI and the Tuberculosis Research Centre at Chennai.

The difference this time is that the fresh trials will be “prime-boost vaccine” trials. In the first phase of trials at the Chennai-based centre, researchers had tested an AIDS vaccine based on the vector Modified Vaccinia Ankara (MVA) and the response was encouraging. They will now test a DNA vaccine (which contains five genes of HIV) and boost it with the MVA (six HIV genes), hoping to improve the immune response.

The prime-boost strategy was adopted to improve the immune response and make the vaccine more efficacious, said Dr Kamini Walia, Indian Council of Medical Research’s scientist and programme officer for HIV/AIDS.

Dr V D Ramanathan, head of the clinical pathology department at the Chennai-based centre and principal investigator of the MVA trials, said the results indicated that the vaccine had acceptable levels of safety and was well tolerated.

The volunteers were 32 healthy, HIV-free men and women between 18 and 50 years of age, from all socio-economic strata. Three intra-muscular injections of the vaccine, some high and some low, were administered. Of those who got a low dose, 82 per cent showed an immune response; of those who got a high dose, all registered such a response.

The 100 percent response was greater than that seen with most candidate AIDS vaccines tested in humans so far. However, the strength and diversity of these immune responses were modest, Dr Ramanathan said. It may be possible to boost the immune response, if this vaccine is used in combination with other candidate vaccines.

The new trials, with the DNA-based vaccine as prime and MVA as a boost, will happen simultaneously at NARI and TRC and should start by the year-end, said Dr Walia.

Dr Sanjay Mehendale, deputy director (senior grade) at NARI, said the trials were at the planning stage. Approval is being sought from various bodies. Officials of the International AIDS Vaccine Initiative said further research is required after the success of the first phase. They pointed out that the prime boost regimen should be able to help strengthen the modest immune responses observed in the first phase.