Leukaemogenesis and regeneration of lymphoid system in (C3H × AKR/tiald)F1 hybrids restored with parental bone marrow and thymic cells

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Abstract
Leukaemogenesis and repopulation of the lymphoid system have been studied in sub‐lethally irradiated (C3H × AKR/TIALD) F1 hybrids which have been restored with parental Bone Marrow (BM) cells with or without thymic cells. The metacentric marker of the TIALD sub‐strain made it possible to identify the host or donor origin of leukaemias. Leukaemias occur either in the thymus (lymphosarcomas) or in the other lymphoid tissues (extra‐thymic leukaemias). After irradiation, the percentage of lymphosarcomas increases from 5 to 95%. The rate of leukaemias in hybrids which have been restored only with BM cells is 55, 56 and 100% respectively depending on the origin of BM: syngenic, C3H and AKR. In this last group 75% of the lymphosarcomas originate from donor cells. The inhibitory efficiency of the three kinds of BM on leukaemogenesis seems to be related to their respective abilities to spontaneous malignant transformation. When AKR or C3H thymic cells are injected together with BM cells, leukaemogenesis is altered. The effect is indirect as these cells are not actually concerned by the malignant transformation. The percentage of LS is significantly reduced and the mean survival improved in hybrids restored with C3H thymic, mixed with AKR or C3H BM cells. AKR thymic cells are less efficient. In both cases, the percentage of extra thymic leukaemias increases at the expense of lymphosarcomas. Thymic cells do not change the kinetics of repopulation in thymus and lymph‐node by the BM cells, except when C3H thymic cells are mixed with TIALD BM cells; in this case, the lymph‐node repopulation is temporarily enhanced. Different hypotheses might explain the effect of thymic cells on leukaemogenesis: enhanced recovery of the post‐irradiation immunological deficiency, transfer of virus by the AKR thymic cells, and more probably influence of the thymic cells on the maturation or/and differentiation of the lymphoid cells.