Positive correlation between in vitro NK activity and in vivo resistance towards AKR lymphoma cells

The possible in vivo relevance of murine natural killer (NK) cells in resistance towards grafted lymphoma was analyzed. The system comprised two AKR T lymphomas having similar behavior as to growth patterns but significant differences in vitro with regard to susceptibility to NK-cell-mediated lysis. These tumor cells were grafted into (AKRxCBA)F1 hybrids which had been lethally irradiated and then protected with bone marrow of CBA or AKR origin. Some adult animals were thymectomized before irradiation. The F1 chimeras could be shown to be repopulated with donor cells at the level of peripheral white blood cells and displayed high or low NK levels if coming from CBA and AKR donors respectively. Thymectomy resulted in a significant increase in the final levels of NK activity in the recipients. The in vivo growth patterns of the two AKR lymphomas were in a strikingly positive manner correlated with the NK activities of the recipients. Thus, high NK activity in the recipients resulted in a significant increase in resistance towards the outgrowth of the NK-sensitive AKR lymphoma but had only marginal impact on the relatively NK resistant lymphoma. This was true irrespective of whether or not the recipients were thymectomized before marrow reconstitution and in general the T-deficient mice were thus more resistant towards tumor grafting than their non-thymectomized counterparts. In all, the results would thus further suggest an important role for NK cells in mediating in vivo resistance towards NK-susceptible tumors, and they fail to provide any evidence for T lymphocytes in tumor protection in the same system.