New Human AIDS Vaccine Tests Rejected : Health: Federal researchers decide that expanded studies on two products are not justified. Possible devastating psychological effect feared.

Federal AIDS researchers decided Friday against expanding human studies of two experimental AIDS vaccines but agreed to allow current trials to continue.

The decision came moments after a key federal advisory committee recommended that course to the National Institute of Allergy and Infectious Diseases, the government’s lead AIDS research agency.

The 26-member AIDS Research Advisory Committee, made up of AIDS experts from around the country, said after a daylong meeting that the trials should proceed but not on a large-scale basis.

Panel members unanimously agreed that preliminary results indicated that the vaccines did not show enough promise to justify a larger effort at this time.

The panel rejected several proposals, among them that the studies be widened to include up to 30,000 participants. Another approach would expand the studies initially to 4,500 patients and ultimately to 9,000 after several years. Currently, the trials involve 296 patients.

Dr. Anthony S. Fauci, the director of the institute and a leading U.S. AIDS researcher, immediately accepted the recommendation. “I think this approach, given the uncertainties with the current candidates, is quite reasonable and reflects my own views,” he said in an interview.

He said he agreed that the results thus far from the two experimental vaccines “had not been an overwhelming success.”

There has already been some indication that the two vaccines do not fully protect humans against infection. At least six people in the trial have become infected with the human immunodeficiency virus, although most had not received the full series of inoculations.

The infections appear to be the result of high-risk behaviors and are not believed to be caused by the vaccine itself, the institute said.

Fauci said that conducting a large-scale trial on the vaccines “runs the danger that people will go in and think they are protected,” and could engage in high-risk behaviors that resulted in their becoming infected.

He added that a large-scale trial could have devastating psychological impact if it turned out to be “a big flop.”

Both vaccines contain genetically engineered versions of gp120, the major protein on the envelope--or outer coat--of the human immunodeficiency virus. The vaccines are based on two closely related strains of HIV that are representative of most infections in North America and Europe.

The vaccines have been developed by Biocine Co., a joint venture of Chiron and CIBA-Geigy in Emeryville, Calif., and Genentech Inc., of South San Francisco.

Currently, these are the only experimental vaccines being studied in a Phase II, institute-sponsored clinical trial. Other vaccines are under study but have not progressed as far in the evaluation process.

Phase I studies typically involve small numbers of participants and are designed to evaluate only the safety of the product. Phase II and Phase III studies examine whether the vaccine can actually prevent infection. Typically, Phase III trials involve much larger numbers of participants.

Fauci said that he thought it would be another one to three years before another candidate vaccine would be ready for expanded testing.

The panel’s recommendation appeared to contradict last April’s conclusions of an institute working group, whose members said they believed that additional scientific information about the approach of using a viral envelope protein as a basis for a vaccine could be obtained from advancing the trials to a larger scale.

In all the studies, researchers have been trying to determine whether experimental vaccines can elicit immune responses in the body, such as the production of so-called neutralizing antibodies, and whether these antibodies would prevent infection.

Researchers believe that it will take many years and tens of thousands of participants to prove the effectiveness of an AIDS vaccine, because it would be highly unethical to deliberately expose anyone to the virus to see if a potential vaccine works.

The gp120 vaccines have produced antibodies but they have neutralized HIV only in the laboratory. They have failed to work in tests against virus found outside the lab. And although the vaccines appear to have protected chimpanzees, researchers said that these results cannot be extrapolated to humans.

The institute launched the gp120 studies in its five national AIDS vaccine evaluation units in December, 1992.

“Regardless of the decision . . . vaccine research and the preparedness for clinical trials will continue,” Fauci said in remarks to the advisory committee. “The commitment of resources to vaccine research is substantial.”