Sentinel flaps reflect key inflammatory aspects of human face transplant rejection

Early diagnosis and treatment of immune rejection is critical for maintaining the viability of face transplants, a type of vascularized composite allograft (VCA). Surveillance currently involves multiple skin biopsies that leave scars. Fasciocutaneous sentinel flaps have been proposed as remote-site monitors of rejection, but the molecular immune events in sentinel flaps (SF) during rejection have never been compared to those in facial allografts (FA). We used transcriptional profiling, immunostaining, and high throughput T cell receptor sequencing (HTS) to study 14 matched skin SF and FA biopsies during rejection and non-rejection. SF and FA shared common signatures of rejection, including pro-inflammatory and immunoregulatory genes we previously identified as key indicators of VCA rejection. SF and FA both exhibited antigen-specific T cell activation and T cell granzyme B-mediated cytotoxic injury. HTS of CDR3 TCRβ genes from 4 matched pairs during rejection revealed shared T cell clones in both tissues, indicating that shared antigens were driving rejection at both sites. Our results suggest that sentinel flaps reflect inflammation and clinically significant (grade 2-3) rejection in VCA, with less specificity for distinguishing mild (grade 1) changes from non-rejection.

Allografts and sentinel flaps were stained for CD3, CD8, granzyme B (GZMB), and DAPI during grade 0 non-rejection (bottom two rows) and grade 3 rejection (top two rows).