HIV Gene Sequence In India
Unlike That Anywhere Else
By Maggie Fox
Reuters Health and Science Correspondent
WASHINGTON (Reuters) - Scientists who have mapped all the genes of an Indian subtype of the HIV virus said Friday it had a frightening knack for swapping genes with other strains, which will make it extremely hard to develop a vaccine against it.
They found major differences in genes throughout the virus -- not surprising in a bug known to mutate quickly. But it shows just how hard HIV is going to be to fight in the long run.
Writing in the Journal of Virology, the team at Johns Hopkins University in Baltimore and the AIDS Research Institute in Pune, India, said they had sequenced the HIV genes taken from six patients recently infected with the virus.
The most common strain of HIV in India is known as HIV-C. It is slightly different from the strain found in the United States, known as HIV-B. There are 10 known subtypes, named from A to J.
But subtype C is the most commonly transmitted form, both in India, which is a growing center of HIV infection, with an estimated 3 million to 4 million people infected with HIV, and in Africa, the current center of the AIDS epidemic.
Dr. Bob Bollinger of Johns Hopkins, who worked on the study, said researchers had found that the Indian C subtype was different from C subtypes found elsewhere in the world. And one patient had a virus that contained bits of both the A subtype and the C subtype.
``These recombinant viruses are becoming increasingly important and have a lot of importance for the design and testing of potential vaccines,'' Bollinger said in a telephone interview.
``We may have to deal with not only multiple subtypes but with multiple subtypes that combine with each other.''
Especially notable is that the surface envelopes of the different strains had different genes.
Most HIV vaccines being worked on target these surface proteins, because the outside layer of an invader is where the immune system looks first to check to see whether it should attack.
But the C strain, and the one combined A/C virus, had big genetic differences in their surface proteins. So a vaccine using these proteins might not work against different subtypes.
``We should probably look to other places in the virus for a vaccine,'' Dr. Stuart Ray, who led the study, said.
If a person has a recombinant virus -- one that contains elements from two or more strains -- it means that patient was infected with more than one subtype.
Unless he or she was infected with two at once, it means the patient was infected first with one, then later with another. As HIV is transmitted mostly through heterosexual sex in India and Africa, this in not an unlikely scenario.
But this is significant for vaccine efforts, Ray said. ``If prior infection is not protective, what are our chances for making a vaccine?'' he asked.
The idea behind a vaccine is to ``prime'' the immune system. That is the same reason that someone who is infected with a disease such as smallpox can never be reinfected with it.
But just like the influenza virus, HIV mutates into so many types that vaccination is made more difficult.
``That's why we need a new influenza vaccine every year,'' Bollinger said.
Bollinger and Ray said they hoped the study would help Indian health officials develop a suitable vaccine for their country and would shed light on where vaccine efforts elsewhere should be heading.
Most AIDS experts agree that a vaccine is the only answer to the epidemic. But Ray said the findings indicated that any vaccine might have to be combined with some way of stimulating the immune system.