Background: Previous studies have demonstrated that composite tissue allotransplantation (CTA) is restricted primarily because of the lifelong immunosuppressive requirements dictated by the skin component (1-4). Therefore, in light of the unexpected death of the first face/bilateral upper extremity (UExt) transplant recipient, we aimed to scientifically quantify the size of the antigenic skin component accompanying this type of CTA. Methods: A total of five cadavers were studied. All dissections were performed to mimic sizes and levels according to published reports (n=25). Two-dimensional surface area was calculated for all limbs and comparative analysis was performed based on our laboratory's previously-published facial/scalp alloflap data (n=5). Results: The mean cadaver age, height, weight, and body mass index (BMI) was 69±15.9 years, 70±4.4 inches, 175±49.8 lbs, and 25±4.5 kg/m2, respectively. The mean skin quantity accompanying unilateral UExt transplants ranged from 335±58.4 to 787±81.7 cm2 depending on the required level of reconstruction, and from 670±116.8 to 1575±163.4 cm2 in bilateral. Facial alloflaps without a scalp component (675±22.3, as per our group's previous study) were found to be nearly identical in skin quantity to both unilateral proximal forearm and bilateral wrist transplants (675±101.7 and 670±116.8, respectively). Concomitant facial/scalp with bilateral UExt transplants were found to contain up to 2766 ±201.6 cm2 of antigenic skin. Conclusion: This study, to our knowledge, is the first to demonstrate the antigenic skin quantity accompanying simultaneous face and UExt transplantation to be bewteen 1010±80.7 to 2766±201.6 cm2. In addition, we found that face transplants (without scalp) have the identical skin quantity as compared to unilateral proximal forearm and bilateral wrist extremity transplants. Further research is undoubtedly warranted to identify 1) whether or not this large antigenic skin load is safe for concomitant transplantation 2) to investigate if currently available immunosuppressive protocols should be adjusted for CTA with large skin components and 3) to investigate if human skin found in different anatomical areas has the same antigenicity? References 1. Lee WP, Yaremchuk MJ, Pan YC, Randolph MA, Tan CM, Weiland AJ. Relative antigenicity of components of a vascularized limb allograft. Plast Reconstr Surg 1991;87(3):401-11. 2. Gordon CR, Nazzal J, Lee WPA, et al. From Experimental Rat Hindlimb to Clinical Face Composite Tissue Allotransplantation: Historical Background and Current Status. Microsurg 2006;26(8):566-72. 3. Gordon CR, Siemionow M, Zins J. Composite tissue allotransplantation: A proposed classification system based on relative complexity. Transplant Proc 2009;41(2):481-4. 4. Gordon CR, Siemionow M, Papay F, et al. The world's experience with facial transplantation: What have we learned thus far? Ann Plast Surg 2009;63(5):121-7.