Tolerance to Composite Tissue Allografts is Dependent on the Administration of Hematopoietic Stem Cells but not Long-Term Engraftment
David Mathes1,2, Jeff Chang1,2, Scott Graves2, Billana Huang2, Tiffany Miwongtum2, Rainer Storb2
1Department of Surgery, Division of Plastic and Reconstructive Surgery, University of Washington; 2Transplantation Biology Research Center, Fred Hutchinson Cancer Research Center; Seattle, Washington, USA
Introduction: Composite tissue allografts (CTA) are a clinical reality. However, the survival of these transplants is dependent on immunosuppression. This experiment sought to develop a large animal model for the simultaneous transplantation of hematopoietic stem cells (HSC) and CTA using our mixed chimerism protocol and to examine the role of the HSC infusion.
Methods: 4 transplants were performed across a DLA matched, minor mismatch barrier. All dogs received 200 cGy of radiation and a CTA transplant with injection of HSC. 3 dogs underwent the protocol except without an HSC infusion. All dogs received 35 days of post-grafting immunosuppression and were followed for donor cell chimerism and underwent biopsies. Tolerant animals underwent a donor and third-party skin graft. Finally, they were followed for levels of FoxP3 and GranzymeB in the transplanted muscle and skin.
Results: All of the experimental animals demonstrated long-term tolerance to the CTA (497, 467, 465, and 400 days). 3 of 4 dogs had long-term detectable donor chimerism. One dog lost its chimerism at 10 weeks post-transplant but remained tolerant to the CTA. The expression of CD3+ FoxP3 was stable in the tolerant transplanted muscle and skin. It was also noted to be elevated in the draining lymph node. The three dogs transplanted without an HSC infusion rejected their transplants at 45 days after the cessation of post-grafting immunosuppression. All of the tolerant dogs accepted the donor skin graft and promptly rejected the third-party graft.
Conclusion: The simultaneous transplant of HSC and CTA leads to tolerance. This tolerance induction appears to be dependent on the administration of HSC but not its long-term engraftment. This finding suggests that modifications to the protocol that promote initial engraftment but not long-term presence of donor cells will be key to the development of a protocol that can used on complete mismatched transplants.