No AIDS Vaccines on the Near Horizon
Nov. 29, 1999 (Philadelphia) -- Vaccination against AIDS is still years away, so a primary focus of research is still treatment, according to investigators who spoke here recently at the 37th Annual Meeting of the Infectious Diseases Society of America (IDSA).
Neal Nathanson, MD, presented reasons why developing an AIDS vaccine is more complex than developing vaccines for other viruses. "It's going to be a long time [before an AIDS vaccine] is developed," he tells WebMD. "Clinical trials are extremely slow to do compared to efficacy trials of other vaccines. It really takes three to five years to do a trial of an AIDS vaccine. ... The best time frame we're looking at is 10 years, and it could be longer." Nathanson is director of the office of AIDS research at the National Institutes of Health.
According to Nathanson, there are several problems associated with developing an AIDS vaccine. For instance, it is hard to find antibodies that will completely neutralize or destroy HIV. Suppressing viral levels below a certain critical point during the initial phase of a viral infection is how most viral vaccines work; they don't kill the entire virus, but just enough to make it ineffective.
In HIV, however, such a vaccine would offer little or no protection against any remaining infection because the infection typically leads to continued drops in the number of all-important immune cells called CD4 cells. Eventual fatality from opportunistic infections or other complications will ultimately result when enough of those immune cells are destroyed.
In addition, vaccines that use a "live" form of HIV, much like some flu vaccines do, cannot be used because primate tests have shown that such a vaccine would, in and of itself, most likely eventually lead to full-blown AIDS. Targeting a combination of immune responses will probably be necessary to contain the virus.
Primate studies indicate that initial HIV exposure offers some, but not complete, protection against HIV reinfection, suggesting that a vaccine would similarly be able to offer only partial immunity. Therefore, the best case scenario for an AIDS vaccine would be one that keeps the virus at bay for a lifetime.
"We're going to have to depend on therapy for the time being," Nathanson tells WebMD.
The next presenter, Joseph J. Eron, MD, adds that improvements to available therapies are therefore in order. These improved therapies should have less side effects while being easier to take on a daily basis. They should also have increased potency, especially with respect to resistant HIV strains. Eron is an associate professor of medicine at the University of North Carolina at Chapel Hill.
"We're developing agents to simplify therapy in each of the current existing classes [of drugs]," Eron tells WebMD. "I think the biggest focus has been on the development of drugs that are active against resistant HIV. ... The other focus is new agents [for] new targets, and while there's a lot of interest in that area, [the number of] really practical drugs that are going to be in our hands in a short period of time is quite limited."