LA JOLLA- While a successful AIDS vaccine continues to elude researchers, several new developments suggest progress is being made towards fulfilling what remains one of the key goals of medical research.

A Food and Drug Administration advisory committee has now recommended that an AIDS vaccine developed by Dr. Jonas Salk undergo further clinical trials. The Vaccine and Related Biological Products Advisory Committee based its decision on the results of preliminary clinical trials with the vaccine.

Pending final FDA approval, the new trials would involve about 1,000 patients. The clinical trials, would be double-blind and adjuvant-controlled to study surrogate markers and clinical endpoints in large patient populations. The trials would be divided into two groups: (1) patients with CD4 T cell counts above 550 per cubic millimeter of blood, and (2) those with CD4 T cell counts between 300 and 549.

The FDA decision appears to be something of a vindication for Dr. Salk. It was three years ago at the International AIDS Conference in Amsterdam when Dr. Salk first proposed an alternative hypothesis on the pathogenesis of HIV disease, and suggested a contrarian approach to developing an AIDS vaccine. At the time, most leading researchers dismissed his ideas out of hand. Dr. Salk went ahead with his own studies anyway. The next year at the International AIDS Conference in Berlin, Dr. Salk presented the first clinical results of his vaccine to a capacity crowd, while other researchers also reported findings which appeared to provide support for the Salk approach.

Dr. Salk maintains that it may be more effective to prime the cell mediated side of the immune response rather than attempt to modulate the humoral immune response to HIV. The goal of this approach would be to inhibit the progression of disease in patients already infected with the virus

The Salk immunogen is based on a killed HIV preparation with the gp-120 envelope protein depleted, in an Incomplete Freunds Adjuvant. HIV positive patients receiving the immunogen in a preliminary clinical trial demonstrated significant increases in humoral and cell mediated immunity, as well as decreases in viral burden, compared to those receiving placebo.

"This study confirms that the immune system can be manipulated and that this immunogen does produce an immune response, including an effect on HIV infected cells. The field of AIDS vaccine research is wide open and we now have ample reason to go forward with our research," said Jonas Salk, M.D., Founder of the Salk Institute for Biological Studies, La Jolla, CA., at the time.

In another AIDS vaccine development, researchers at the National Institutes of Health announced the development of a genetically altered version of HIV containing a "suicide gene". The researchers inserted an extra gene from the herpes virus into the HIV genome. The strategy proposed by the researchers would involve giving patients the attenuated form of the virus to prime the immune response, then give the patients ganciclovir, a potent anti-herpes drug to selectively destroy the modified AIDS virus.

Considerable basic research will be needed before that approach is ready for clinical trials, emphasized Dr. Stephen Smith of the National Institute of Allergy and Infectious Diseases, at a conference of the American Society of Microbiology.

Several recent studies involving patients with apparent immunity to HIV are also causing optimism among vaccine developers. Another group of researchers is about to begin a trial using a gene therapy-based vaccine. In addition, large scales trials with subunit vaccines based on the envelope protein of HIV are expected to begin in Africa within the next year or two. (See stories in Science Update)

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