PRE-TRANSPLANT INFUSION OF EXTRACORPOREAL PHOTOPHERESIS (ECP) TREATED DONOR SPLENOCYTES LEADS TO LONG-TERM LIVER ALLOGRAFT SURVIVAL AND DONOR SPECIFIC TOLERANCE IN RATS

Aim of Study: To test effect of ECP-treated donor splenocyte (ECP-DSp) in inducing donor-specific tolerance after allogenic liver transplantation (LTx). Methods: Allogeneic LTx was orthotopically performed from ACI to Lewis. Rats were divided into Iso group (Lewis→Lewis), Untreated group (no treated), ECP group (infuse100×106 of ECP-DSp 7 days before LT, IV), Reci-group (infuse 100×106 of ECP treated Lewis splenocytes 7 days before LT, IV), TAC group (tacrolimus, 1mg/kg, ip.day 0-21), and Depl-Tregs group (inject total 700ug of anti-rat CD25 on post-operative days 20(POD20),6 times, ip.). Survival time, function and pathology of graft were measured. Skin transplantation was performed for testing whether donor specific tolerance was achieved. Proliferation of T cell, chimeric phenotyping and FoxP3+ Tregs in blood and Donor-specific antibodies were analysed by FCM. Results: Median survival time(MST) of allografts with ECP-DSp (MST=180 days) was significant longer than that of Untreated group (MST=12days, P<0.001), TAC (MST=60days, P<0.01). AST and ALT in ECP group were better than those of Untreated and TAC group on day 7 and 14(all P<0.05). Mean Fluorescence intensity of IgM, IgG, IgG1, and IgG2b, proliferation of CD4+ and CD8+ cells on POD7 in ECP group were lower than those of untreated group (all P<0.05). Interestingly, ECP-DSp mediated graft protection was coincided with increased numbers of Tregs in ECP treated recipients compared to Untreated and TAC group (both P<0.05), and graft function in Depl-tregs group were lowered after depleting Tregs(P<0.05). Percentage of chimeric CD3, CD11b/c and CD161 in ECP group were significant higher than those of Iso, Untreated and TAC group (all P<0.05). Importantly, ECP-DSp treated allografts (POD100) accepted donor-type (ACI) skin grafts but not third-party skin grafts, and recipients of reci-group died from 10 to 12 days, significantly inferior to ECP group, suggesting that ECP could successfully induce donor specific tolerance. Conclusions: Pre-transplant infusion of ECP-DSp facilitated long-term liver allograft survival and led to donor specific tolerance, demonstrating a novel role of ECP in induction of transplant tolerance, which may cause by generation of Tregs and chimera via ECP-DSp infusion.