Defining Rejection in Vascularized Composite Allotransplantation: More than Just Arguing Semantics

Vascularized composite allotransplantation (VCA), including upper extremity and face transplantation, is increasingly utilized for reconstruction of devastating and disfiguring injuries, with over 200 transplants performed and more reconstructive teams around the world embarking on these reconstructive endeavors. Targeted, immune-mediated tissue destruction or “rejection” is an inevitable challenge of allotransplantation. Recognizing rejection and distinguishing it from other pathologies is essential in order to prevent damage or loss of the allograft. A better understanding of the mechanisms of VCA rejection will help guide the development of treatment and preventative therapies. The patterns of rejection observed in VCA are not well-defined, and a more standardized use of terminology will further our understanding of the process. Here we discuss the clinical and histological features of allograft rejection that have been described to date and review the use of specific terminology to describe features of VCA rejection. Finally, we conclude with several important questions that are central to our understanding of the rejection process.