Studies on hepatitis A virus. Hepatitis A virus (HAV) is a member of the piconavirus family but is distantly related to other viruses in that family and will be classified into its own genus. While the virus has been cloned and sequenced in several laboratories, useful peptide or polypeptide antigens have not been produced. In earlier work we and others have shown that expressed peptides of HAV are not useful as immunogens for the whole virus indicating that the native antigens of HAV are probably non-linear or conformation dependant. Dr. Jack Stapleton of the University of Iowa has inserted the complete coding region of HAV from our full length clone into a vaccinia virus expression vector. It appears that this construct expresses HAV proteins that are processed and at least partially assembled to form native antigenic particulate structures. This material has been formulated as a vaccine and we will soon be doing preliminary tests with it in chimpanzees. We are studying T-cell immunity to HAV in the chimpanzee model. Following infection by HAV, liver-infiltrating lymphocytes were obtained and specific killer T cell lines have been isolated. Epitopes are being analyzed by use of vaccinia expression clones. HAV specific B cell lines have been established by transformation of the chimpanzee PBL's with EB virus. Helper T-cell lines are being established by stimulating T-cells with purified HAV.