Growth of transplantable melanoma and leukaemia and prevention of virus-induced leukaemia in long lived radiation chimeras constructed with unmanipulated bone marrow.

Haemopoietic radiation chimeras across the H-2 barrier (BALB/c----C57Bl/6; H-2d----H-2b chimeras and vice versa) have been studied for their capacity to suppress the growth, or to reject, transplantable B16 melanotic melanoma and radiation leukaemia virus-induced, transplantable leukaemia. Also, radiation leukaemia virus (RadLV) obtained from the thymus of leukaemic C57Bl/6 mice was injected i.p. into established chimeras (H-2d----H-2b). As expected, long lived, graft versus host disease free allogeneic chimeras constructed with intact bone marrow were unable to reject the tumours both when recipients were BALB/c----C57Bl/6 or C57Bl/6----BALB/c chimeras. However, also inoculation of a large number of immunocompetent cells from normal BALB/c mice into BALB/c----C57Bl/6 chimeras, failed to promote a rejection of the tumours. On the contrary, the same amount of syngeneic (BALB/c) immunocompetent cells prevented growth of melanoma when transferred into athymic nude BALB/c mice, while the tumour grew unimpaired in untreated athymic nude BALB/c mice. The same type of H-2d----H-2b chimeras displayed complete resistance to inculation of leukaemogenic H-2b restricted RadLV while all H-2b----H-2b, syngeneically reconstituted mice developed disseminated leukaemia. These findings demonstrate that: (a) a powerful suppressive principle operates in the chimeras which does not allow effector function and anti-tumour activity of passively transferred normal, mature T cells from resistant BALB/c mice. Thus, no H-2 restriction of donor T cells can be advocated for suppression of anti-tumour effector functions in the chimeras. (b) New donor (BALB/c, H-2d) marrow character in the H-2d----H-2b chimeras prevents expression of the H-2b restricted viral activity and leukaemogenic transformation and/or proliferation.