Tumor Immunity In Vivo: Evidence That Immune Destruction of Tumor Leaves “Bystander” Cells Intact

Summary Experiments with mice tested the possibility that immune cell-mediated, tumor-target destruction in vivo involved the elaboration of nonspecific cytotoxic effectors. Moloney sarcoma (MS) regressors were highly immune to a transplantable MS tumor cell line but not to a syngeneic, undifferentiated mammary tumor, EMT6. Limiting numbers of EMT6 cells in suspension were intermixed with 1- to 50-fold more MS cells and transplanted into MS regressors or nonimmune hosts. The incidence of EMT6 tumor growth in mixed tumor sites in MS-immune hosts did not differ significantly from that in sites without admixed MS cells. It is concluded that the effector arm of cell-mediated immunity to MS cells involves specificity in both the recognition and target-cell destruction processes.