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 desensitization strategies are imperfect and require a living-donor setting. Here we investigated the impact of sensitization on and the efficacy of a desensitization protocol utilizing syngeneic hematopoietic stem cell transplantation (HSCT) to prevent AMR in VCA. Skin transplants from Dark Agouti (DA) to Lewis rats were performed for sensitization. Orthotopic hind-limb transplants from DA donors were performed to sensitized and non-sensitized recipients, and the animals were treated with either daily tacrolimus or no immunosuppression. A desensitization protocol consisting of total body irradiation (TBI), fludarabine and syngeneic HSCT was applied to sensitized animals. Graft rejection was monitored by clinical assessment and histological analysis. Serum levels of donor-specific antibodies (DSA IgG) were measured using flow-cytometry. Sensitized recipients 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-sensitized recipients, respectively. Serum levels of DSA IgG were markedly elevated (37.3±3.34-fold from baseline) in sensitized recipients after VCA and correlated with histologic evidence of rejection and C4d deposition. Desensitization significantly 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, sensitization leads to accelerated rejection of VCA, and syngeneic HSCT combined with conventional immunosuppression effectively reduces DSA and improves allograft survival in sensitized rats.