Desensitization and prevention of antibody-mediated rejection in vascularized composite allotransplantation by syngeneic hematopoietic stem cell transplantation

Candidates for vascularized composite allotransplantation(VCA) are frequently sensitized, putting them at risk for antibody-mediated rejection (AMR). Current desensitizationstrategies are imperfect and require a living-donor setting. Here we investigated the impact of sensitizationon and the efficacy of a desensitizationprotocol utilizing syngeneichematopoietic stem cell transplantation (HSCT) to prevent AMR in VCA. Skin transplantsfrom Dark Agouti (DA) to Lewis rats were performed for sensitization. Orthotopic hind-limb transplants from DA donors were performed to sensitizedand non- sensitizedrecipients, and the animals were treated with either daily tacrolimusor no immunosuppression. A desensitizationprotocol consisting of total body irradiation(TBI), fludarabineand syngeneicHSCT was applied to sensitizedanimals. Graft rejection was monitored by clinical assessment and histological analysis. Serum levels of donor-specific antibodies (DSA IgG) were measured using flow-cytometry. Sensitizedrecipients exhibited accelerated rejection by 5.5±1.2 days without immunosuppression and 10.2±3.6 days with daily tacrolimus, compared to 8.7±1.2 days and >30 days in non- sensitizedrecipients, respectively. Serum levels of DSA IgG were markedly elevated (37.3±3.34-fold from baseline) in sensitizedrecipients after VCA and correlated with histologic evidence of rejection and C4d deposition. Desensitizationsignificantly reduced DSA compared to sensitized-controls (2.6±0.5-fold vs 6.0±1.2-fold, p 30 days without evidence of C4d deposition (n=6). In summary, sensitizationleads to accelerated rejection of VCA, and syngeneicHSCT combined with conventional immunosuppression effectively reduces DSA and improves allograft survival in sensitizedrats.