Cell-mediated immunity to antigens associated with murine sarcoma virus-induced tumors: augmentation of cytolytic T lymphocyte activity by successive specific and nonspecific stimulationin vitro

Abstract
It has been shown previously that lymphoid cells from mice which have rejected a tumor induced by the Moloney sarcoma virus-leukemia virus (MSV-MLV) complex develop high levels of specific H-2-restricted cytolytic T lymphocyte (CTL) activity after in vitro stimulation with syngeneic, irradiated MLV-induced lymphoma cells in mixed leukocyte-tumor cell cultures (MLTC). Attempts to further increase lytic activity by restimulating long-term MLTC cells with syngeneic, irradiated lymphoma cells have met but with limited success. This report shows that, in contrast to the lack of increased activity observed after specific stimulation with lymphoma cells, nonspecific stimulation of long-term MLTC cells either with supernatants from secondary mixed leukocyte cultures (2º MLC SN) or with supernatants from concanavalin A-stimulated spleen cells leads, on a per cell basis, to a further 5 to 10-fold increase in CTL activity. The stimulatory activity of 2º MLC SN is due to a factor(s) of apparent mol. wt. of 25 000 to 40 000. The activity of the CTL populations formed under these conditions is at least 100-fold higher against syngeneic as compared to allogeneic MLV-induced or unrelated tumor cells.

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