Activation and Growth of Murine Tumor-specific T-Cells Which Have in Vivo Activity with Bryostatin l

We examined the ability of bryostatin 1 (Bryo), a novel protein kinase C activator, plus ionomycin (Io), a calcium ionophore, to activate T-cells with specific antitumor activity. Lymphocytes from the draining lymph nodes (DLN) of MCA-105 tumor-bearing host mice were stimulated with Bryo/Io, either fresh or after in vitro stimulation with autologous tumor, and then were incubated in interleukin-2 at 20 units/ml. Lymphocytes sensitized with tumor cells in vitro and then stimulated with Bryo/Io exhibited significant expansion (12-fold) after a total of 3 weeks in culture and moderate cytolytic activity (40% at an effectontumor cell ratio of 80:1) and were exclusively CD8+ T-cells. DLN cells activated immediately with Bryo/Io, without tumor antigen sensitization in vitro, displayed marked growth (130-fold expansion) over 3 weeks in culture, had weak cytolytic activity (8% at an effectontumor ratio of 80:IX and were a mixed population of CD8* and CD4+ cells. Despite the differences in phenotypes and in cytotoxicity, both groups of DLN cells were highly effective in vivo against MCA-105 pulmonary metastases. Bryo/Io-acti-vated DLN cells from MCA-105 tumor-bearing hosts had no therapeutic efficacy against B16 melanoma or MCA-203 sarcoma metastases. Lymph node cells from normal mice and non-draining lymph node cells from tumor-bearing hosts could be expanded with Bryo/Io to a degree similar to that of DLN cells but had no antitumor activity. Phenotypic analyses and in vitro and in vivo depletion studies demonstrate that CD8+ cells mediated tumor regression.