The overall objective of this investigation is the further elucidation of the regulatory mechanisms controlling the primary cytotoxic T-lymphocyte (CTL) response. Two subsets of suppressor T cells have been identified that act at distinct stages in CTL development, one regulating proliferation of CTL and the other their maturation. Studies during the first 2 years of this project have centered on a suppressor T cell that inhibits the proliferative phase of primary CTL development. A number of salient features of the antiproliferative suppressor T cell have been characterized regarding its induction, genetic restriction, antigen specificity, phenotype, properties pertaining to pharmacologic sensitivity and reversibility, and interactions with the cell population that it affects. An objective for the coming year is the establishment of cloned, suppressor T-cell lines. Although our efforts toward this goal in the past year have not been successful, results obtained have suggested ways in which the cloning protocol should be modified. This will include cloning at the single-cell level early on to prevent the outgrowth of more rapidly proliferating nonsuppressor T-cell types and the use of drugs such as Cyclosporin A and pyrilamine, which favor suppressor cell induction. Because we feel that the establishment of cloned suppressor cells would allow a rapid expansion of our understanding of the mechanisms behind suppressor cell function, efforts toward cloning them will continue. Studies in the past year have shown that suppressor cells may exert their effects across a cell-impermeable membrane, thus suggesting the release of a suppressor factor. A second goal for this coming year will thus be the isolation and biological and biochemical characterization of the suppressor factor. Sources of suppressor factor will be supernatants generated from cultures containing active suppressor cells, from T-cell hybridomas made by fusing suppressor T cells with the BW5147 T cell lymphoma, and from successful cloned suppressor T-cell lines. (LB)