Immune Response Corp. shares fell $7.25 to $52 on Fridaybefore recovering to close at $59.50, up 25 cents, after Kidder,Peabody analyst Robert Kupor said a rival AIDS vaccine maygain quicker Food and Drug Administration approval.

The stock (NASDAQ:IMNR) had jumped $19.50 since Oct. 28,based on favorable reports about its AIDS therapeutic vaccine.

Privately held MicroGeneSys Inc. of Meriden, Conn., andAmerican Home Products Corp. (NYSE:AHP) are developing avaccine using a genetically engineered version of gp160, aprecursor to the coat protein of HIV. Immune ResponseLsvaccine is an inactivated virus from which the envelope hasbeen removed.

"I conclude that the FDA will be much more willing to considerapproval of AHP unless their clinical efficacy is lower," Kuportold BioWorld. "My very strong sense is that the twopreparations look similar in efficacy. This would give AHP themuch more attractive product license application for review."

Kupor said the larger size and randomized, placebo-controlleddesign of the MicroGeneSys trials put them ahead of ImmuneResponse.

While both trials are using surrogate end points, theMicroGeneSys trials are using a more widely accepted T4 celldecline surrogate, Kupor said. Immune Response is using apolymerase chain reaction measure of the virus number inblood cells. Kupor said that the marker "is very interesting, buthasnLt been validated."

Kupor also noted the MicroGeneSys vaccine uses a standardalum adjuvant, while Immune Response is using an unapprovedadjuvant.--- Karen Bernstein

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