Haemopoietic stem cells and progenitors of functional T-lymphocytes in the bone marrow of 'nude' mice.

The stem cell potential of thymusless mice measured in terms of CFU ratio and the capacity to reprieve lethally irradiated mice was similar to that of /+ and CBA mice. The thymus of →T6T6 rediation chimaeras was repopulated by donor cells. Proliferation of donor cells, presumed to be T-lymphocytes, was observed in regional lymph nodes 3 days after sensitization with oxazolone. T6T6 thymus grafts implanted subcutaneously in mice restored the response to C57BL skin grafts. The mitotic figures in the thymus implant 30 and more days after grafting were almost exclusively of host karyotype. The high proportion of host cells dividing in the lymph nodes of thymus-grafted mice suggested that T-cells derived originally from bone marrow were present. Allogeneic thymus grafts partially restored the response of mice to oxazolone. It is concluded that the failure of thymic development in mice is not due to an absence of thymocyte precursors in the bone marrow or to anything in the general physiological environment which prevents their differentiation to thymocytes and T-lymphocytes. It is presumably the result of defective embryonic development of the epithelial rudiment.