Chronic rejection models for vascularized composite tissue allotransplantation

Vascularized composite tissue allotransplantation (VCA) has transformed patients' lives by enabling limb, face, abdominal wall, and penile transplants. Despite advancements in screening and immunosuppression, chronic rejection continues to limit the success of VCA. Lack of reliable preclinical models exacerbates this challenge. Here, we report on new mouse models of chronic rejection following heterotopic hind limb VCA. We employed different levels of MHC mismatch using CD8 knockout C57BL/6 mice as recipients along with BALB/c or B6 H2-Ab1bm12 mice as donors. Transient CD4 T cell depletion was induced to allow graft maturation. Evaluation included gross findings, changes in immune status changes, production of donor-specific antibodies (DSA), C4d levels, and histopathological alterations. Two chronic rejection models displayed common features of clinical chronic graft rejection, such as skin stricture, hair loss, adnexal atrophy, extensive fibrosis and mast cell infiltration without widespread necrotic changes common in acute rejection. Similar to chronic rejection patients, large populations of activated B and plasma cells were detected in the recipient's immune system as well as increased DSA and C4d production. Collectively, our models closely replicate the immunological and histopathological aspects of chronic graft rejection post-VCA, and could provide a new platform for evaluation of novel therapeutic interventions prior to clinical evaluation.