Chemical enhancement of tumor immunogenicity

C57BL/6 spleen cells immunized in vitro against syngeneic methylcholanthrene-induced sarcoma cells (MC-1 cells) modified with various chemical reagents show cytotoxic activity against unmodified MC-1 cells in a short-term ⁵¹Cr release assay, whereas unmodified MC-1 cells are nonimmunogenic. The effector cells cross-react widely with many other fibroblastic and epithelioid tumors, even those that are not H-2 matched, as well as with some nonneoplastic cells. Priming mice in vivo with a hapten leads to enhanced anti-tumor cytotoxicity developed by spleen cells from these mice immunized in vitro against tumor cells modified with the same hapten. Cytotoxic activity is largely, but not completely, removed by treatment with anti-θ serum and C. The existence of suppressor cells that can inhibit an anti-tumor response is demonstrated in in vitro immunizations of mixtures of spleen cells from normal mice and mice primed with mitomycin-treated cells, the latter suppressing the former.