AIDS Research Reaches Turning Point
"I don't think the lesson is that this is the only vaccine regimen that will work -- what this shows is that if you have a certain level of memory cells [before infection], there seems to be a good outcome," Ahmed says. "I think several candidate vaccines now in the pipeline may very well be able to demonstrate this kind of CTL response in humans."
In a commentary article accompanying the study, Johns Hopkins researcher Robert F. Siliciano, MD, PhD, suggests that it might be possible to elicit this kind of immune response in HIV-infected people receiving the AIDS drug combinations known as highly active antiretroviral therapy, or HAART.
"I think this is a very exciting demonstration that vaccines that ... fail to protect against HIV infection might still have a huge beneficial effect," Siliciano tells WebMD. "This would be helpful both in terms of preventing people from getting sick and in reducing transmission by holding down the amount of virus in the blood."
Siliciano warns that it remains to be seen how long vaccine-elicited immune responses can keep HIV in check. "The vaccination gives the immune system a head start on the virus," he says. "It's not entirely clear that this vaccine-induced head start will have a significant effect over the long term. It is hard to know. On the one hand, you might say that because you are able to protect against such a highly pathogenic virus in the monkeys, the vaccine may do well against HIV. But another way to look at it is that over the long course of HIV infection, the little head start isn't going to make that much of a difference."
Ahmed, however, believes that what works in monkeys against the fast-acting monkey/human virus is likely to work against the slower HIV in people. "For something to work against a strong virus and not to work against a wimpy virus -- that goes against everything we know about vaccinology," he says.
Also impressed by the Letvin team's results is Harriet Robinson, PhD, chief of microbiology and immunology at Yerkes Regional Primate Research Center in Atlanta. "I think it's a very solid study -- and very encouraging," Robinson tells WebMD.