Hepatitis C vaccine approaches phase II trial.

The fi rst prophylactic hepatitis C vaccine to reach human trials could enter phase II testing this year, a landmark for a fi eld that has faced many technical challenges since the virus was identifi ed in 1989. If this vaccine — or one of several other candidates — is successful, the public health impact could be substantial. Hepatitis C is a major cause of liver disease, including hepatocellular carci-noma, a leading cause of cancer deaths worldwide. The vaccines being developed are meant to prevent primary infection with the hepatitis C virus. The vaccine in human trials is Chiron Corporation's product, a recom-binant version of the viral envelope proteins E1 and E2. In a phase I trial at St. Louis University Medical School, all 45 healthy volunteers given the vaccine produced neutralizing antibodies to hepatitis C. Phase II planning is under way and should be fi nalized in 2006, according to Michael Houghton, Ph.D., vice president of virology research at Chiron, which is based in Emeryville, Calif. Although Chiron's candidate is the farthest along in development, it is by no means alone in the fi eld. There are at least half a dozen other candidates that take many different approaches to meet the particular challenges of this virus. Challenges One intrinsic diffi culty in developing a vaccine to hepatitis C is that the virus itself does not always stimulate a strong natural immune response in humans. In fact, hepatitis C is " quite clever at evading the immune response, " said T.