High dose bone marrow transplantation induces deletion of antigen-specificT cells in a Fas-independent manner

Background. Monoclonal antibody induced tolerance to high doses of multiple lymphocyte stimulating (MLS)+minor mismatched bone marrow has recently bee n associated with clonal deletion, as reported in fully allogeneic models o f bone marrow transplantation. Fast-induced apoptosis has been shown to med iate antigen-specific T cell deletion after antigenic stimulation in wild-t ype and T cell receptor transgenic mice. Therefore, we investigate a role f or the Fas pathway in deletional tolerance to high dose bone marrow. Methods. Fas mutant and control mice (H-2(k), MLS-1(b)) were tolerized unde r the cover of monoclonal antibodies to high dose (5 x 10(7) cells) AKR (H- 2(k), MLS-1(a)) bone marrow, Tolerance was confirmed by AKR skin grafting a fter antibody clearance, Antigen-reactive cell deletion was monitored by V beta 6(+) T cell elimination, measured by flow cytometry of peripheral bloo d throughout the experiment. Donor T cell (Thy1.1(+)) chimerism was assesse d in a similar manner. Results. Fas mutant mice infused with high dose AKR bone marrow under the c over of antibody were tolerant, as demonstrated by indefinite survival of A KR skin grafts. When high levels of donor cell chimerism were established i n Fas mutant mice, peripheral deletion of antigen-reactive cells was observ ed to be independent of signaling through Fas. Conclusions, Apoptosis mediated by Fas receptor signaling is not the mechan ism of clonal deletion of antigen-reactive cells after antibody facilitated high dose marrow transplantation. However, the Fas mutation does impair th e development of adequate donor chimerism.