B. J. Swearingen1,2, S. S. Graves2,3, R. F. Storb2,3, D. W. Mathes1,2 1University Of Colorado Denver,Plastic And Reconstructive Surgery,Aurora, CO, USA 2Fred Hutchinson Cancer Research Center,Clinical Research Division,Seattle, WA, USA 3University Of Washington,School Of Medicine,Seattle, WA, USA
Introduction:
Vascularized Composite Allograft (VCA) transplantation is a clinical reality but limited by toxicities of chronic immunosuppression and rejection. Current clinical tolerance protocols rely on recipient conditioning and donor cell mobilization that limits use to living donor transplants. We sought to design a clinically relevant protocol applicable to cadaveric organs. We modified our existing non-myeloablative stem cell canine VCA transplant model to use AMD3100 (Plerixafor) for stem cell mobilization.
Methods:
5 DLA-haploidentical, related canine recipients [Group I] received conditioning with 350cGy TBI, AMD3100-mobilized donor stem cells and VCA transplantation with a short course of immunosuppression (MMF:56 days/CSP 70 days +/- taper). 4 DLA-haploidentical, related canine recipients [Group II] underwent identical conditioning plus an infusion of Bone Marrow (BM) Aspirate in addition to AMD3100. CD34+ hematopoietic progenitor cells were quantified via flow cytometry. Peripheral blood chimerism was evaluated by PCR techniques weekly. VCA graft survival was followed clinically and histologically.
Results:
All 9 canines tolerated the conditioning regimen. 4 [Group I] and 3 [Group II] were followed long-term. Stem cell engraftment and donor chimerism were seen in all dogs. Median COBE apheresis counts were 6.21×10^8 (Group I) and 3.08×10^8 (Group II) cells/kg, respectively. Bone Marrow aspirate counts were 1.47×10^8 cells/kg (Group II). No acute rejection nor evidence of GVHD was seen. An unexpected finding of persistent thrombocytopenia that resolved on loss of donor cell chimerism seen in Group I led to addition of BM aspirate for Group II in an attempt to address this.
Conclusion:
This study demonstrates proof of principle for AMD3100 as a single-dose stem cell mobilizing agent for a clinically relevant tolerance protocol. Use of AMD3100 led to stem cell engraftment in all animals transplanted with no evidence of acute rejection in the VCA. Current application of AMD3100 is limited by thrombocytopenia that may be resolved with the addition of BM Aspirate.
