Immunosuppressive treatment of aortic allografts.

Immunosuppression with cyclosporine (CsA) was explored as a means of preventing arterial allograft rejection and failure. Aortic allografts across the major histocompatibility barrier were studied in Brown-Norway and Lewis inbred rats. Grafts 1 cm long were interposed into the infra-abdominal aorta of Lewis recipients; five groups included two groups of untreated isograft and allograft control animals and three groups had allograft-CsA treatment regimens. The grafts were examined at 30, 60, and 100 days for patency, aneurysmal dilation, gross structural changes, inflammatory responses, and infiltration of W3/25- and OX8-positive lymphocytes. Only three allograft controls became occluded; the rest showed significant dilation (p less than 0.01), medial thinning and necrosis, intimal proliferation, and prominent cellular infiltration at 30 days. With all CsA regimens, aneurysmal dilation was significantly reduced or prevented (p less than 0.01), correlating with medial smooth muscle cell preservation. Cellular infiltration was delayed by an average daily dose of 5 to 10 mg/kg subcutaneous CsA for 30 days and was suppressed at 100 days by a continuous 5 mg/kg dose every 4 days. Intimal thickening in the graft was delayed but not prevented. We conclude that a low maintenance dose of CsA provides effective immunosuppression, thereby preventing aneurysm formation, and that the potential use of arterial allografts in vascular surgery may need to be readdressed.