By Karen Bernstein

Rhône-Poulenc Rorer on Friday decided to relinquish its 50 percent share of the HIV immunotherapeutic it has been developing jointly with The Immune Response Corp. since 1988. RPR returned all manufacturing, distribution and marketing rights to IMNR in a transaction that involved no cash.

IMNR shares fell 81.3 cents to $3.563 on Friday. The stock now is down 45 percent from Jan. 23 when it peaked in anticipation of an FDA advisory panel review that resulted in a tepid endorsement of Phase III trials for the vaccine.

The Carlsbad, Calif., company still hopes to start the Phase III studies within the two- to four-month timeframe it outlined in late January. The company still needs to submit to the FDA certain data from assays used to validate steps in the manufacturing process, as well as the final clinical trial protocols.

Key assumption

When IMNR and RPR began work on the vaccine, an inactivated HIV depleted of its envelope, the assumption was that the product would undergo accelerated development and would be a candidate for accelerated FDA approval based on Phase II data, said RPR spokesperson Bob Pearson.