936-85 Intrathymic Injection of Donor Splenocytes Prolongs Rat Cardiac Allograft Survival but Does not Inhibit Graft Arteriosclerosis

Abstract

Chronic rejection , manifested by the development of graft arteriosclerosis, remains the leading cause of late death in cardiac transplant recipients. Immunologic mechanisms have been implicated in both experimental and clinical studies, yet the pathogenesis of chronic allograft rejection remains poorly understood. Recent studies have shown that intrathymic (i.t.) injection of donor cells or processed allo-MHC antigens with or without transient immunosuppression induces specific systemic T cell tolerance and prevents acute allograft rejection in several experimental transplantation models. In this study we examined the effects of i.t. injection of donor cells with or without systemic anti-lymphocyte serum (ALS) on the development of chronic rejection in the Lewis-to-F344 rat cardiac allograft model. Recipients were divided into 4 groups: control group A was pre-treated with saline i.t., group B was pre-treated with a one-time dose of ALS (1 mI) via intraperitoneal injection (i.p.). group C received donor (Lewis) splenocytes i.t. (2 × 10 6 ), and group D received both the splenocytes i.t. and a one-time dose of ALS i.p. two weeks prior to transplantation. Allografts were followed by daily palpation and graded from 0–4 (grade 0 = rejection, grade 4 = normal heartbeat). Graft survival on post-op day 90 for all three experimental groups was 100% vs. 33% for the control (n = 6/group). Moreover, mean heartbeat grade for the three experimental groups (B = 2.83 ± 0.17, C = 2.0 ± 0.41, D = 2.67 ± 0.21) was significantly higher (p < 0.01) than that of the control group (A = 0.4 ± 0.24). Histologic and immunocytochemical analysis of 90-day old grafts revealed the following results: GROUPS Inflammation % Vessels Diseased % Luminal Occlusion Intima:Media Ratio Control(A) severe 89 ± 1 64 ± 5 0.97 ± 0.33 Splenocyte only (C) moderate-severe 79 ± 8 57 ± 7 068 ± 0.16 ALS only (B) minimal 25 ± 7 ** 8 ± 3 ** 0.09 ± 0.04 * Splenocyte + ALS (D) minimal 27 ± 4 ** 8 ± 3 ** 0.07 ± 0.03 * * p < 0.02. ** p < 0.003 vs. Control (1) The induction of systemic unresponsiveness with donor splenocyte i.t. plus ALS i.p. or ALS i.p. alone markedly reduced inflammation and inhibited graft arteriosclerosis indicating that the immune response and graft inflammation playa critical role in the pathogenesis of chronic allograft rejection. (2) The donor cells i.t. alone significantly prolonged graft survival and prevented rejection as measured by functional criteria but did not significantly inhibit graft inflammation or graft arteriosclerosis. These results suggest that partial suppression of the immune response without significant inhibition of graft inflammation prolongs rat cardiac allograft survival but does not prevent graft arteriosclerosis.