This study was approved by the research ethics board at the Toronto General Hospital Research Institute, University Health Network (Toronto, ON, Canada) and was performed in compliance with relevant guidelines. Informed consent was obtained from all patients. Typical immunosuppression regimen includes steroids, cyclosporine (Cyclosporin, Novartis, USA) and/or azathioprine (Imuran, Prometheus Laboratories Inc, USA). Specimens were obtained from one upper extremity transplant (below elbow) and one patient who underwent solid organ transplantation and a sentinel flap. Procured specimens included multiple samples of skin and subcutaneous tissue obtained by 3-mm punch biopsies. Local anesthetic was provided (1% xylocaine with 1:200,000 epinephrine) before chlorohexidine prep of area of biopsy. At least three samples were collected from different areas on the extremity transplant and the sentinel flap at each time point. Regular timepoints were the following: 1 week, 2 weeks, 1 month, 2 months, 3 months, 6 months, 9 months, 12 months, 1 year, 2 years, and 3 years posttransplantation. Additional samples were also collected whenever skin changes were observed, such as a rash or discoloration. Collected specimens included up to 3 years following transplantation. Samples were graded by a trained dermatopathologist. Episodes of acute rejection were treated with steroids and possible increase in baseline medication.