The first expanded Phase II clinical trial of experimentalprophylactic AIDS vaccines in high-risk subjects has begun atfive U.S. test sites. The trials, which the National Institute ofAllergy and Infectious Diseases (NIAID) announced last week,will test the safety and immune-stimulating ability of twogenetically engineered gp120 vaccine candidates, fromGenentech Inc. (NYSE:GNE) of South San Francisco, Calif., andBiocine Co. of Emeryville, Calif., a joint venture between ChironCorp. (NASDAQ:CHIR) and Swiss-based Ciba-Geigy.

The two vaccines were chosen because they have caused noserious adverse effects in Phase I trials and they have shownpromising evidence that they induce antibodies that canneutralize several different HIV strains. Moreover, both gp120viral envelope subunits were engineered from two of the mostprevalent HIV strains circulating in the U.S. -- MN and SF-2 --and "there's fairly good cross-reactivity between these twostrains," said Patricia Fast, chief of the clinical section of theNIAID's division of AIDS vaccine research and development."They're the only two vaccines available with thosecharacteristics," Fast told BioWorld.

(The gp160 therapeutic vaccine VaxSyn, produced byMicroGenesis Inc. of Meriden, Conn., is derived from alaboratory rather than field strain of the virus. Also, VaxSyn isproduced in insect cells, whereas both the gp120 vaccines aremade in mammalian cells.)

But the difference between Genentech's version and Biocine'sresides in the choice of adjuvant: Genentech's uses alum, whichhas a long history of safety in humans, while Biocine's usesMF59, a novel microemulsified squalene formulation that isstill fairly experimental, explained Larry Kurtz, Chiron's vicepresident of corporate communications.

About 330 volunteers will be recruited for the multicentertrial. Of these, "143 will get the Biocine vaccine, 143 will getGenentech's and the remainder will receive one of the twoadjuvants," Kurtz told BioWorld.

The individuals, men and women between the ages of 18 and60, will include minorities and those from several differentpopulations hardest hit by the epidemic. By including high-riskindividuals in the trial, "we anticipate that this trial willgenerate valuable data for planning large-scale efficacy trialsfor those populations that will derive the greatest benefit fromeffective vaccines to prevent HIV infection," explained AnthonyFauci, director of NIAID.

However, NIAID's Fast cautions that "the fact that we are goingahead with these two vaccines for Phase II trials is not anassumption that they will be going into Phase IIIs." NIAID hasemphasized that it will "continue to work with themanufacturers of these and other products to identify the bestcandidate vaccines for such large-scale efficacy trials asmodified formulations and other vaccine preparations becomeavailable."

-- Jennifer Van Brunt Senior Editor

(c) 1997 American Health Consultants. All rights reserved.