The Friend murine leukemia virus (F-MuLV) is a replication competent retrovirus that is capable of causing erythroleukemia in newborn mice and can induce acute erythroleukemia in adult mice in association with replication defective spleen focus forming virus (SFFV). Previous studies have demonstrated that vaccinia viruses can be utilized as vectors for efficient expression of foreign glycoprotein genes when placed under vaccinia virus transcriptional regulatory signals. The expressed glycoproteins have been demonstrated to be properly processed and glycosylated and when used as live virus vaccines have been shown to protect animals against challenge with virulent virus. Using F-MuLV as a model for examining the expression of retroviral glycoproteins in vaccinia, we propose to construct different recombinant vaccinia viruses expressing either intact or secreted forms of the gp70/p15E of F-MuLV and mink cell focus forming virus (F- MCFV). We will also construct and express in vaccinia virus a chimeric glycoprotein in which the transmembrane and cytoplasmic domains of F-MuLV p15E are replaced with the corresponding region from the hemaggltinin (HA) of influenza virus. We immunize mice with each recombinant vaccinia viruses expressing intact, secreted, or chimeric F-MuLV and F-MCFV glycoproteins and monitor the immune response to these antigens using standard virus neutralization and cytotoxic T-lymphocyte assays. We also immunize mice with the various recombinant vaccinia viruses expressing F-MuLV and F-MCFV antigens to determine whether newborn and adult mice can be protected from erythroleukemia by challenge with F-MuLV and F-MuLV/SFFV, respectively. In addition, we will construct recombinant vaccinia viruses expressing cell associated or secreted forms of the F- MuLV glycoproteins in which the majority of the immunosuppressive region localized in the p15E protein is deleted. The immune response to cell associated and secreted gp70/p15E, with or without the immunosuppressive region, will be compared by in vitro proliferation assays, neutralization and cytotoxic T- lymphocyte assays, as well as in challenge experiments with F- MuLV and F-MuLV/SFFV. We also generate infectious F-MuLV clones with deleted immunosuppressive domain to determine its role in pathogenicity. The results from the research will provide useful information about several aspects of immunity to retroviral glycoproteins that should be applicable to the construction of vaccines to human retroviruses such as HTLV-III, the causative agent of acquired immune deficiency syndrome.