Bone marrow transplantation into recipients sensitized against donor-type T cells

Immunization of prospective bone marrow recipients with thymocytes of the marrow donor strain prevented subsequent hemopoietic engraftment of the marrow. Immunization with thymocytes of a third party strain sharing the marrow donor's theta alloantigen but not his histocompatibility antigens permitted chimaerism and suppressed GVH in mice. Bone marrow of rat strains of the Th-1.1 group did not take in mice sensitized against mouse Th-1.1 thymocytes. This observation lead to the conclusion that hemopoietic stem cells of rats but not of mice express an early thymic and even prethymic antigen. This antigen is not restricted to the Th-1.1 specificity: rabbit anti-rat thymocyte globulin absorbed in a way which removed stem cell toxicity from a rabbit anti-mouse thymocyte globulin prevented hemopoietic engraftment when incubated with rat bone marrow before transfer to irradiated mice. Serologically this antiserum reacted with thymocytes as well as lymphocytes in the rat bone marrow but less with lymph node cells. An antiserum against rat lymph node cells was rendered T cell specific by absorption. It defined a postthymic T antigen lacking on stem cells, bone marrow lymphocytes and thymus. It labeled lymphocytes in the interfollicular T dependent area of lymph nodes by an immunohistochemical method. T cells in rats were thus found to express a prethymic and/or a postthymic antigen. Implications of theta alloantigens for the suppression of GVH in polytransfused bone marrow grafted patients are discussed.