Background
Vascularized composite allotransplantation (VCA), including hand and face transplantation, is increasingly utilized for reconstruction of disfiguring injuries. Immune rejection is a problem inherent to allotransplantation and must be recognized early to prevent graft injury/loss. Skin biopsy is required to confirm rejection however this approach may further promote rejection through tissue injury. Thermal imaging has been used to non-invasively detect inflammation and ischemia in other disease states but has not been evaluated in VCA rejection. The purpose of this study was to evaluate the utility of non-invasive thermal imaging in the detection of rejection in a swine VCA model.
Methods
Osteomyocutaneous hindlimb transplantation was performed in 9 MGH miniature swine across a full SLA mismatch. The positive rejection control group (3 pigs) did not receive any form of immunosuppression. The treated group (6 pigs) received non-myeloablative conditioning with 50cGy total body and 350cGy thymic irradiation prior to transplantation, daily tacrolimus (20–25 ng/ml) until POD 30, and IV steroids on POD 4–6. Allografts were assessed daily for erythema, edema, blistering, and ulceration. Daily infrared images were acquired using a thermal camera (FLIR E8 #63903-0303) and thermal emission intensities from graft and contralateral flank control were analyzed using Image.
Results
In the untreated group, erythema was observed by POD 4 and progressed to epidermolysis by POD 8 in 3/3 animals. In the treated group, rejection was observed at POD 5–7 in 6/6 animals and was reversed by POD 10 with steroids in 5/6 animals. The sixth animal developed severe rejection on POD 5 that progressed to necrosis despite steroids. Interestingly, infrared imaging did not distinguish these episodes of rejection in the early post-operative period (<POD 30) despite clinical signs of inflammation and biopsy-proven rejection (Banff II–IV). At later post-operative periods (>POD 60), there was a trend toward cooler graft temperatures even in the absence of clinical rejection.
Conclusions
Despite signs of inflammation, infrared imaging did not reliably detect graft rejection. The finding that grafts become cooler over time suggests there may be long-term changes in graft perfusion. This may represent chronic graft injury and is the subject of on-going studies.