Infused Bone Marrow Fails to Prevent Vascularized Composite Allograft Rejection in Nonhuman Primate

Abstract

Vascular composite allografts (VCA) are highly antigenic as demonstrated by near universal rejection rates. Nonetheless, substantial immunosuppressive therapy has permitted VCA to survive currently between 10 (face) and 15 (hand) years. The field of VCA has placed major emphasis on investigating in preclinical and clinical trials whether infused bone marrow combined with standard immunosuppression may improve immunologic outcomes. In contrast to solid organ transplant protocols utilizing bone marrow cells (BMC) and nonmyeloblative conditioning, tolerance (or even the absence of rejection on immunosuppression) has not been observed in any VCA trials (1.Schneeberger S Gorantla VS Brandacher G Upper-extremity transplantation using a cell-based protocol to minimize immunosuppression.Ann Surg. 2013; 257 (et al): 345-351Crossref PubMed Scopus (146) Google Scholar, 2.Devauchelle B Badet L Lengele B First human face allograft: Early report.Lancet. 2006; 368 (et al): 203-209Abstract Full Text Full Text PDF PubMed Scopus (475) Google Scholar, 3.Kawai T Sachs DH Sprangers B Long-term results in recipients of combined HLA-mismatched kidney and bone marrow transplantation without maintenance immunosuppression.Am J Transplant. 2014; 14 (et al): 1599-1611Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar). The lack of controlled trials directly evaluating infused BMC as a cellular adjunct leads to ongoing ambiguity regarding the role of BMC infusion without preconditioning in VCA (4.Khalifian S Brazio PS Mohan R Facial transplantation: The first 9 years.Lancet. 2014; 384 (et al): 2153-2163Abstract Full Text Full Text PDF PubMed Scopus (193) Google Scholar). We have previously shown in a nonhuman primate (NHP) facial transplantation model that cotransplanted vascularized bone marrow (VBM) in the allograft improved outcomes when compared to VCA without VBM (5.Barth RN Rodriguez ED Rodriguez GS Vascularized bone marrow-based immunosuppression inhibits rejection of vascularized composite allografts in nonhuman primates.Am J Transplan. 2011; 11 (et al): 1407-1416Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). We have further investigated whether infused BMC could protect VCA by performing facial VCA without VBM but with donor BMC infusion Briefly, marrow was harvested from the donor lumbar vertebrae immediately following euthanasia and stored overnight using a method adapted from clinical and primate protocols. The infused marrow was analyzed for viability, cell number and percent of CD34+ hematopoietic stem and progenitor cells (HSPCs), and compared to the mandibular marrow compartment excised from the facial segment. Total nucleated cell count of hemimandibles ranged between 42.5 and 56.5 × 106 cells/kg of donor weight. Donor vertebrae yielded between 250 and 341 × 106 cells/kg donor. Viability of HSPCs immediately after processing was greater than 92.4%, with survival to postoperative day (POD) 1 of 94.8%. On POD 1, BMC were infused at a dose of 200 × 106 cells/kg of recipient weight guaranteeing greater than 2 106 HSPCs. Grafts with BMC infusion underwent early significant rejection (Banff grade II), similarly to grafts with no bone marrow component (Figure 1). Alloantibody was positive, although reduced compared to VCA without bone marrow, and in contrast to animals receiving VBM that did not produce alloantibody. One animal in the BMC infusion group progressed to complete rejection and graft loss at POD 28. A second animal progressed to chronic rejection with vessel wall thickening and C4D positivity by POD 50. The third animal resolved rejection but developed posttransplant lymphoproliferative disease (PTLD) likely secondary to LCV-mismatch. No animal with infused BMC demonstrated any evidence of chimerism, in contrast to three of four VCA + VBM animals that demonstrated transient chimerism. These data do have shortcomings, including an N of only 3, comparison to historical controls and the confounding occurrence of PTLD. However, these results suggest that VBM can protect VCA compared to BMC when performed without preconditioning. Minimal preconditioning could lead to further immunologic benefit for VBM that has the benefit of containing both cellular and stromal compartments. These data suggest that compared to infused bone marrow, VBM may improve VCA outcomes by minimizing pretransplant conditioning and chronic immunosuppression requirements, and reducing rejection episodes. The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation. This work was performed at the University of Maryland School of Medicine, Baltimore, MD.