Primary and secondary <i>in vitro</i> generation of cytolytic T lymphocytes in the murine sarcoma virus system

Abstract

Abstract Cell‐mediated cytotoxic responses in vitro to surface antigens associated with murine sarcoma virus (MSV)‐induced tumors were investigated using mixed leukocyte‐tumor cell cultures (MLTC). The source of responding cells was either spleens from normal C57BL/6 mice (primary MLTC) or spleens of C57BL/6 mice carrying or having rejected a MSV‐induced tumor (secondary MLTC). Graffi virus‐induced GiL‐4 leukemia cells, Rauscher virus‐induced RBl‐5 leukemia cells, and MSV‐induced MSV‐B16 sarcoma cells were used as stimultating syngeneic tumor cells and/or target cells. Under appropriate culture conditions, cytolytic T lymphocytes (CTL) were generated in both primary and secondary MLTC. As assessed by a quantitative short‐term 51 Cr release assay system, CTL activity in secondary MLTC populations was at least 10‐fold higher than that in primary MLTC populations, and 100‐fold higher than that in spleen cells taken at the peak of the in vivo response of MSV‐infected mice. The ability of spleen cells to mount a secondary CTL response in vitro could be observed as early as 5 days after virus injection, increased up to the time of maximum tumor size and persisted long after tumor regression. This suggests the development of increased numbers of CTL progenitors and/or the formation of “memory” CTL in spleens of MSV‐injected mice.