Human hand transplantation is complicated by skin rejection. To better define the characteristics of infiltrating cells, biopsies from human hand transplants have been investigated for expression of Foxp3 and indoleamine 2,3-dioxygenase (IDO), a key regulatory enzyme to induce T-lymphocyte unresponsiveness. A total of 104 skin biopsies taken from three bilateral hand transplant recipients over 6 years posttransplant were assessed by hematoxylin-eosin histology (graded 1-4b) and immunohistochemistry for IDO and Foxp3 according to a three-grade classification and correlated with the grade of rejection as well as time after transplantation. Overall, rejection ranged between grades 0 and 4a with an average score of 0.94. IDO was expressed in the endothelium independent of rejection. Upon rejection, IDO staining within the cellular infiltrate was significantly increased. Foxp3 in regulatory T cells was mainly found in samples undergoing severe rejection. Expression of IDO and Foxp3 compared well to each other, although the overall expression of Foxp3 was lower when compared to IDO. An increased expression of IDO as well as Foxp3 during rejection late after transplantation was observed. Characteristics of the cellular infiltrate indicate tolerogenic properties of a proportion of the cells and therefore a tendency toward self-limitation of the alloimmune response during skin rejection after hand transplantation.