In?. zyxwvutsrqpo J. Cancer: 17, zyxwvutsr 275-281 (1976) zyxwvuts NON-T-CELL RESISTANCE AGAINST A MOUSE MOLONEY LYMPHOMA Rolf KIESSLING, Gyozo PETRANYI,' George KLEIN and Hans WIGZELL Department zyxwvuts of Tumor Biology, Karolinska Institute, zyxwvu 104 01 Stockholm 60, Sweden zyx Summary. We have previously shown that spleen cells floni 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 iymphonia line in various normal setnisyngeneic F, 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 jimction is T-cell-independent. Lymphoid cells depleted of T- and B-cells and transferred together with Moloney lymphoma cells into an irradiated syngeneic recipient were highly eficient 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 0)" the syngeneic or semisyngeneic Moloney lymphoma used in this study is T-independent. Thymus-derived lymphocytes are known to play a major role in cell-mediated transplant rejection directed against major (Miller and Mitchell, 1969) or minor (Allison and Taylor, 1967) antigenic dif- ferences. Alternative mechanisms involve antibody- dependent cell-mediated cytolysis mediated by non-T lymphoid cells (Perlmann et al., 1972). Activated macrophages can also exert significant growth- inhibitory activity (Evans and Alexander, 1972). Additional subpopulations of effector cells probably exist, capable of inhibiting the growth of certain target cells. Naturally occurring cytolytic effector cells have been demonstrated in several in vitro systems (Gomard et al., 1974; Greenberg and Playfair, 1974; Herberman et al., 1975a; Kay and Sinkovic, 1974; Petranyi et al., 1974; Pross and Jondal, 1975; Rosenberg et al., 1974; Skurzak et al., 1973; Takasugi et al., 1973). In some systems the effector cells appear to be lymphocytes, not yet defined with regard to subclass (Herberman et al., 1975b; Kiessling et al., 1975a). We have previously analyzed one such naturally occurring killer cell type in the mouse, capable of lysing certain in vitro- maintained Moloney lymphoma lines with a high efficiency (Kiessling et al., 19756). While this effector cell has the appearance of a small lymphocyte, it has neither T- nor B-lymphocyte markers and has weak adhesive properties. It does not function in antibody-dependent cell-mediated lysis (Kiessling et al., 1975a), and aggregated IgG fail to inhibit its killer effect (Herberman et al., 19756; Kiessling et al., 1975~). This natural killer cell (abbreviated as NK) is under genetic control. High reactivity is dominant over low reactivity in F, crosses. Back- cross tests showed the involvement of a strong H-2 linked factor, although other minor factor(s) appeared to contribute as well (Petranyi et al., 1975a). A comparison between in vitro high-reactive and low-reactive F, hybrids showed a clear corre- lation between NK activity and resistance to the growth of small tumor-cell numbers in vivo. In vivo, the resistance was also influenced by an H-2-linked factor(s) (Kiessling et al., 1975d). Since the NK effector cell is a non-T-cell it was of interest to test whether in vivo resistance was also thymus-independent in the same system. Two experimental systems were used to investigate this question. In the neutralization test different lymphoid cell fractions were admixed to tumor cells and implanted to irradiated syngeneic recipients. In another experimental series, thymectomized or congenitally athymic mice were tested for in vivo resistance against small numbers of Moloney lymphoma cells or against a H-2 incompatible methylcholanthrene-induced sarcoma. Received: June zyxw 12, 1975, and in revised form November 11, 1975. lFellow of the UICC; present address: National Institute of Haematology and Blood Transfusion, Budapest, Hungary. Department of Immunology, Uppsala University, Uppsala, Sweden. Abbreviations: FCS zyxw = fetal calf serum; NK = natural killer cell; HRBC = horse red blood cell.