REPLIGEN/MERCK AIDS VACCINE CHIMP STUDY

Executive Summary

REPLIGEN/MERCK AIDS VACCINE CHIMP STUDY found that antibodies from one vaccine prototype protected against infection with the AIDS virus, while antibodies from a second vaccine prototype delayed the onset and decreased the severity of infection, Repligen told shareholders in its second quarter report. Merck, which is the development partner for Repligen's AIDS vaccine, conducted the study. The preliminary efficacy study is the first animal study to show that antibodies can protect against the AIDS virus. "We believe this study provides the first indication in an animal model that an AIDS vaccine may provide protection from infection," Repligen said. "Until now, researchers have been unable to demonstrate any protection in virus challenge experiments." The study was conducted by injecting one chimp with an isolate of the AIDS virus combined with a monoclonal antibody to the HIV envelope protein fragment RP135, and a second chimp with an isolate of the AIDS virus combined with a mixture of polyclonal antibodies to the virus. A third control chimp was injected with a mixture of the virus and antibodies from an uninfected chimp. "After six weeks," the company reported, "the control chimpanzee became infected with HIV - a time lapse identical to previous experiments. The chimpanzee with the HIV/RP 135 antibody mixture did not become infected until 12 weeks after injection and, by all testing parameters, this infection was of a lesser degree than that seen in the control animal." The chimp injected with the HIV/polyclonal antibody combination "has shown no signs of infection since it was injected in March 1988," Repligen said. In a note of caution, Repligen pointed out that "while these early results are promising... additional work will be necessary before human trials can be initiated." The firm indicated that it will probably conduct traditional chimp challenge tests before proceeding with clinicals. In addition to the animal efficacy work, Repligen and Merck are also conducting research on the variability of the AIDS virus and methods for increasing immunogenicity of the virus.