Molecular analysis differentiates inflammatory dermatoses from skin rejection in face transplant recipients

Face transplantation is a life-transforming procedure for severely disfigured patients. Clinical challenges include differentiating skin rejection from inflammatory dermatoses. Using skin biopsies from the largest cohort of face transplant patients at a single center worldwide, we characterized the molecular changes specific for rejection compared to inflammatory dermatoses. Using NanoString gene expression profiling, we analyzed 36 human face transplant skin biopsies collected during acute cellular rejection (n=25) and non-rejection (n=11), and compared with biopsies from non-transplanted patients with rosacea (n=3) and delayed type hypersensitivity reaction (DTH; n=4), or healthy skin (n=4). Gene expression findings were validated at the protein level using immunofluorescence staining of biopsies. Genes overexpressed in rejection compared to non-rejection included ones involved in T cell signaling, interferon-γ (IFNG) expression, and cytotoxicity. Strikingly, rejection was associated with overexpression of inhibitors such as CTLA4 and PDL1. A set of 142 genes was differentially expressed (adjusted p value <0.05) exclusively in rejection but not in inflammatory dermatoses or healthy facial skin. In pathway analysis, the top canonical pathways included Th1 and Th2 activation and T helper cell differentiation. Upstream regulator analysis suggests that the genes overexpressed in rejection are potentially activated by IFNG, while IL17 is implicated for activating genes overexpressed in DTH and rosacea. This is the most comprehensive study to date to identify the molecular signature of face transplant rejection: T cell receptor triggering in effector T cells leading to IFNG expression, with an unexpected prominence of co-inhibitory signaling between the effector T cells and antigen presenting cells, raising the possibility of active negative control within the rejecting transplants. Our data indicate that skin rejection, although indistinguishable on histology from inflammatory dermatoses, reveal extensive differences at the molecular level.