PHOTODYNAMIC THERAPY INHIBITS EXPERIMENTAL ALLOGRAFT-REJECTION - A NOVEL-APPROACH FOR THE DEVELOPMENT OF VASCULAR BIOPROSTHESES

Background Biological vascular allografts have proved unsatisfactory b ecause of thrombosis, occlusion, and aneurysmal degeneration during ch ronic rejection. Photodynamic therapy (PDT), a technique that leads to the production of cytotoxic free radicals, was investigated as a nove l method to prepare arterial allografts. Methods and Results Shortly a fter impregnation with the photosensitizer drug chloroaluminum sulfona ted phthalocyanine, infrarenal aortas of ACI rats were PDT-treated and orthotopically grafted in Lewis rats (PDT). The transplanted grafts w ere sequentially analyzed at 2, 4, and 8 weeks by morphometry, immunoh istochemistry, and scanning electron microscopy. Of 25 untreated allog rafts, 4 (16%) developed aneurysms compared with 0 of 33 in PDT or unt reated isografts (ISO, P<.001). PDT treatment of allografts significan tly inhibited intimal hyperplasia (P<.001) and resulted in intimal are as comparable to those in ISO. However, medial thickness in both contr ol allografts and PDT grafts was markedly decreased compared with ISO. External graft diameters of control allografts at 8 weeks were signif icantly enlarged (P<.02) coma pared with PDT or ISO. At all time point s, T lymphocytes were found in a substantially larger number in untrea ted control grafts than in PDT or ISO. Scanning electron microscopy at 4 weeks confirmed complete repopulation with endothelial cells in PDT , which was not seen in the control allografts. Conclusions Our findin gs suggest that local PDT treatment of arterial allografts inhibits in flammatory infiltration, aneurysmal dilatation, and development of int imal hyperplasia and may be used to develop vascular bioprostheses for use in humans.