CHARACTERIZATION OF HUMAN AND NON-HUMAN PRIMATE COMPOSITE TISSUE ALLOGRAFT REJECTION.

Abstract

O127* Introduction: Composite tissue allotransplants (CTAs) differ from other vascularized allografts in their embryologically diverse tissues. Given the infrequent application of CTA, it has not been established whether rejecting tissues have an immunological hierarchy. Aims: We have examined specimens from transplanted human limbs in various stages of rejection and compared them with a more controlled evaluation of rejecting non-human primate limb CTAs to determine the temporal progression of CTA rejection and evaluate the relative degree to which CTA elements are targeted for immune destruction. Methods: Human tissues were received from international transplant centers for histological evaluation. A primate radial forearm flap model was developed for serial histological and transcript RT-PCR analysis. Primate autografts (n=5) and allografts with (n=7) and without (n=4) subtherapeutic immunosuppression have been studied with protocol incisional and excisional biopsies. Primate CTA components studied included native and donor skin, skeletal muscle, artery, vein, nerve and tendon. Results: Human CTA rejection under immunosuppression presented as a rash localized to the allograft, and was characterized by a prominent dermal infiltrate. Given that biopsies were prompted by skin signs, this could indicate that rejection begins in the dermis, or that rejection becomes clinically evident after the infiltrate reaches the dermis. Primates evaluated without immunosuppression had an infiltrate arising within 3 days in the perivenular tissue leading to graft congestion and failure without a prominent dermal infiltrate. Dermal findings were consistent with ischemic injury referable to the early vascular injury. Subtherapeutically immunosuppressed animals rejected in 2 weeks with a marked dermal lymphocytic infiltrate similar to human cases. The inflammatory lesions in the engrafted tissues were primarily perivascular and CD3+. Levels of mRNA of most composite tissues showed constituative expression of the regulatory cytokines IL-10 and TGF-B. These increased in native tissues exposed to trauma and in rejecting tissues suggestive of local regulation in response to tissue injury. Allografts were unique in their expression of CD80, CD25, and T-bet consistent with a cytotoxic T-cell mediated event. This was most evident in transplanted artery and skin. Conclusions: Thus, the clinical appearance of a rash occurs relatively late as an extension of vascular alloimmune egress. These data suggest that protocol surveillance of CTAs may be of some benefit in detecting occult alloimmune activity.