Abstract
640 Tolerance after allogeneic bone marrow transplantation is maintained by clonal deletion, clonal anergy and/or suppressor mechanism. In the present work we examined the state of chimerism and immune tolerance of C3H mice conditionned with TBI followed by injection of T cell depleted (TCD) AKR bone marrow (BM) alone or in combination with TCD syngeneic (C3H) BM. METHODS: Recipient C3H (H-2k, Thy1.2, Mls 2a) mice received 9,5 Gy of TBI and one day after irradiation they were reconstitued with TCD (using Thy1.1 mab and complement) AKR (H-2k, Thy1.1, Mls 1a) bone marrow cells(5×106) alone (group 1) or combined with TCD (using Thy1.2 mab and complement) C3H bone marrow cells (5×106) (group 2). Chimerism was determined at various time points by FACS, using Thy1.2 and Thy1.1 mabs. The percentage of CD4+VB6+ T cells and CD4+VB3+ T cells was also determined by FACS. In order to break tolerance, 40×106 host-type spleenocytes were injected (IV) 2 months after bone marrow transplantation(BMT). RESULTS: Both groups of chimeras showed 100% survival without any clinical or histological signs of GVHD. When assayed between 2 weeks and 3months after BM transplantation, the majority of T cells in the thymus and in the periphery (spleen) of group 1 chimeras were from donor-origin (Thy1.1)(90-95%). In contrast in the group2 chimeras donor T cells represented only between 36-60% off all thymocytes or peripheral T cells. In both group of chimeras, donor-reactive T cells (CD4+VB6+) that recognise Mls 1a antigen in AKR donor were completely deleted in both the thymus and the perifery. In contrast, host-reactive T cells (CD4+VB3+) escaped from deletion early (2 weeks) after BMT in the thymus of group 1 and persisted also in the PBL (3%) whereas they were immediately and totaly deleted in the thymus and continously absent in the perifery of group 2 chimeras. Chimerism was easily broken in group 2 chimeras by injection of host type spleen cells but not in group 1 where it was even followed by an expansion of host-reactive T cells. CONCLUSION: Addition of TCD host-type BM cells to a minor mismatched allogeneic BM inoculum results in: 1) lower degree of donor chimerism, 2) a complete and immediate clonal deletion of host-reactive T cells in the thymus and the perifery, 3) a decresed resistance of the mixed chimeras against breaking of tolerance. It is presently examined whether persistent host-reactive T cells in group 1 chimeras play a role in the resistance against breaking of tolerance.
Published Version
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