Engineering a Hybrid Thymus to Unravel the Tolerogenic Properties of Vascularized Composite Allotransplants

Vascularized composite allotransplantation (VCA) refers to the utilization of multiple types of tissue as a single functional transplantation unit for the management severe injury and tissue defects (face, amputated limb, etc.) in the recipients. In the past 20 years, VCA has shown its potential in helping patients with injuries and defects to achieve functional restoration that was unattainable using conventional reconstructive techniques. However, the clinical practice of VCA is hindered by several factors such as unvalidated criteria for assessing complications, and most importantly, the risks of lifelong immunosuppressive therapy. This thesis proposes an innovative strategy for the promotion of VCA acceptance. We introduce a novel term called “hybrid thymus” in which we inject donor-derived thymic epithelial cells (TECs) into the thymus of the recipient. We try to re-engineer the recipient thymic environment and achieve long-lasting coexistence of donor and recipient TECs, and hope that the engrafted donor TECs can fully train the developing T cells to accept and protect the allotransplant in the recipient. The first contribution of this thesis is the refinement in current TEC isolation and engraftment protocol. We improve the yield and viability of donor TECs by precisely controlling the conditions during the purification process. We also determine the best donor age in our mouse model to achieve the best TEC engraftment results in the recipients. The second contribution of this thesis is the analysis of the effectiveness of using different combinations of post-TEC engraftment treatments in promoting the survival of allogeneic donor TECs. We show that appropriate treatment of the recipient protects the engrafted donor TECs from rejection for a significant longer period. The third contribution is the examination of the effects of allogeneic TECs on hindlimb-transplantation survival and the thymic environment of the recipient after donor TEC engraftment. Together we attempt to incorporate TECs, which play a pivotal role in thymocyte development and immune tolerance, into overcoming graft rejection after VCA in the absence of immune suppression