In vitro induction of cell-mediated immunity to murine leukemia cells. IV. amplification of the generation of cytotoxic lymphocytes by enzymatically and chemically modified stimulator leukemic cells

Highly reactive cytotoxic lymphoid cells (CTL) to syngeneic murine leukemias (EL4, RBL-5, YAC) were generated in unidirectional mixed leukocyte-tumor cell cultures (MLTC) by the use of enzymatically - and chemically - modified stimulator leukemic cells. The cultures consisted of splenocytes from normal donor mice as responder cells, and mitomycin C-inactivated stimulating leukemia cells either untreated or treated with: trypsin, papain, bromelain, neuraminidase, trinitrobenzene sulfonic acid (TNBS), iodoacetamide, or concanavalin A. Cytotoxic activity of the stimulated lymphoid cells was assayed in vitro against unmodified ⁵¹Cr-labeled leukemic target cells. The specific cytotoxic responsiveness of lymphocytes sensitized to leukemic cells optimally modified with trypsin, bromelain, or TNBS was 3-10 times higher than the reactivity of lymphocytes stimulated with unmodified leukemic cells. The other agents (neuraminidase, papain and iodoacetamide) produced a lesser stimulatory effect, whereas concanavalin A treatment led to a suppressive effect on stimulatory capacity. Heatinactivated enzymes elicited little or no augmentation. The data also suggest that there exists some degree of selectivity in the action of some of these agents. Trypsin was more effective for EL4 than for RBL-5 and YAC cells, whereas bromelain exerted its maximum stimulatory effect on YAC cells. Using a competitive inhibition assay, it was found that unmodified and optimally modified, unlabeled leukemic cells exhibited comparable inhibition of lysis of ⁵¹Cr-labeled target cells.