Background
Vascularized composite allotransplantation (VCA) is a promising option for patients with devastating injuries from severe burn or trauma The initial management of this patient population frequently requires blood transfusions or skin allografts, leading to formation of alloantibodies and a high degree of sensitization Sensitized recipients are at risk for antibody-mediated rejection (AMR) and poor graft outcomes Our group has established a model of AMR in sensitized rats and demonstrated accelerated rejection of the hind-limb allograft The aim of this study is to establish a desensitization protocol using haematopoietic stem cell transplantation (HSCT) to prevent AMR in the setting of VCA.
Methods
Sensitization was established by performing skin transplants from Dark Agouti (DA) donors to Lewis rat recipients Sensitized controls received skin transplant only, whereas the experimental group underwent a desensitization protocol including a 7-day course of fludarabine, myeloablative total body irradiation (12Gy) and syngeneic HSCT Serum donor specific antibody (DSA) levels of both groups were measured using flow cytometry after skin transplant and again after desensitization Orthotopic hind-limb transplantation from DA donors was then performed, and daily tacrolimus (05 mg/kg) was administered thereafter Graft rejection was defined as grade 3 rejection and was assessed by clinical monitoring and histology Complement deposition was examined by performing immunohistochemistry for C4d.
Results
Sensitization with DA skin transplants resulted in marked elevation in the levels of serum DSA, 115 ± 53-fold compared to baseline levels, in all animals At 30 d after desensitization, the experimental group had a significantly lower level of serum DSA titers compared to the sensitized controls (255-fold vs 599-fold p < 005) After hind-limb transplantation, the sensitized control animals rejected their grafts by 102 ± 15 days despite tacrolimus administration In comparison, all animals in the desensitized group maintained graft survival beyond 30 d (p < 001) Furthermore, C4d deposition was detected in the vascular endothelium of the skin and muscle components of sensitized controls but not the desensitized animals.
Conclusions
Desensitization with HSCT and Fludarabine led to improved control of VCA rejection in sensitized recipients. Future work will focus on elucidating the mechanism of action and optimizing the protocol to minimize adverse effects.