Project Summary: Face and limb vascularized composite allograft (VCA) transplantation (Tx) is not only feasible, but can be a superior method of restoring the aesthetics and function of complex structures. Despite the recent strides made in the technical aspects of VCA Tx, there is still an urgent need to develop novel approaches to improve graft function and survival. However, VCAs generate a strong immunological response, and recipients require life-long aggressive immunosuppression to prevent rejection. This places the recipient at substantial risk and shortened life expectancy due to the high toxicity of immunosuppressive drugs. Significantly, immunosuppressives are neurotoxic and can impair neuroregeneration, leading to poorer graft functional recovery. Given this, and because VCA Tx is usually life-changing, but not lifesaving, a principle research goal, and one that is addressed herein, is the development of novel strategies that not only facilitate the use of immunosuppressive sparing regimes but also enable neurogenesis and graft functional recovery. While T cell-mediated rejection is central to graft rejection, studies in solid organ transplant (SOT) have identified the early post-transplant graft injuries of brain death (BD) induced injury and ischemia reperfusion injury (IRI), as key primers of the alloimmune response. Whether BD and IRI play similar roles in VCA has not been investigated. Both BD and IRI are unavoidable early events in the VCA Tx process. We propose to investigate the role of these acute pre and post-transplant injuries on the shaping of an alloimmune response and the consequences thereof on graft rejection, functional recovery, and dose of immunosuppressive required to prevent T-cell mediated rejection. Our working hypothesis is that reducing BD induced injury and IRI will reduce graft alloresponsiveness and improve nerve regeneration and repair, thus enabling the more widespread application of this life-changing procedure. Specifically, we will: 1. Characterize a novel targeting approach for delivery of a complement inhibitor to VCAs, and 2. Determine the role of BD, C and early allograft injury on an acute alloimmune response, the parameters of required immunosuppressive therapy, and functional hindlimb recovery. The potential impact of this proposal is far-reaching as success in reducing early graft injury and rejection, while promoting functional recovery, has the potential to expand the utilization of this life changing procedure. Furthermore, the therapeutic approaches investigated and mechanistic insights gained will likely have implications for multiple transplantation procedures.