Non-T-cell resistance against a mouse Moloney lymphoma.

We have previously shown that spleen cells from normal mice contain lymphocytes that kill certain in vitro-grown Moloney lymphoma lines in a 51Cr release test. The killing activity shows a marked dependence on the genotype of the donor mouse. In vivo rejection studies with a Moloney lymphoma line in various normal semisyngeneic F1 hybrids showed a clear positive correlation between in vitro natural cytotoxicity and in vivo rejection. Thus mice can be grouped as high- or low-reactive according to their in vitro cytolytic behavior as well as their in vivo rejection potential. A lymphoid cell without detectable T- or B-cell markers is responsible for the in vitro killing effect. The present study also shows that the in vivo growth inhibitory function is T-cell-independent. Lymphoid cells depleted of T- and B-cells and transferred together with Moloney lymphoma cells into an irradiated syngeneic recipent were highly efficient in delaying tumor growth. Furthermore, syngeneic or semisyngeneic thymecto-mized, irradiated, fetal-liver-reconstituted mice showed if anything an increased in vivo resistance to a Moloney lymphoma compared to control mice. In contrast, tumor cells histoincompatible with regard to the H-2 locus showed the expected preferential growth in the thymectomized animals. We thus conclude that the major in vivo resistance against transplantation of the syngeneic or semisyngeneic Moloney lymphoma used in this study is T-independent.