TRANSPLANTATION OF HEPATOCYTES - AN IN-VITRO AND IN-VIVO STUDY IN CANINES

Highly purified perinatal rat islets, isolated by a nonenzymic in vitr o culture technique, have been successfully transplanted across comple te MHC barriers without immunosuppression. Acceptance of these allogen eically transplanted islets is hypothesized to result from an absence of antigen presenting cells (APCs) within the islets. This study was d esigned to examine the effects of organ transplantation and cyclospori ne (CsA) therapy on the development of immunological unresponsiveness in recipients receiving a graft of culture-isolated islets. Kidneys we re successfully allotransplanted into unilaterally nephrectomized rats , across a complete MHC barrier (Rt1lv1 to Rt1u) using CsA therapy ini tiated on the day of transplantation (7.5 mg/kg, orally for 14 days). Remaining native kidneys were removed 14 days following renal allotran splantation. Limited mononuclear cell (MNC) infiltrates were observed in biopsies of renal allografts, taken 30 days posttransplant, but fai lure of the renal allograft was not observed. Animals bearing establis hed renal allografts (n = 10) received allografts of almost-equal-to 2 00 highly purified perinatal islets (ACI, n = 5; F-344, n = 5), transp lanted to the kidney subcapsule of the established renal allograft at least 30 days following renal allotransplantation (at least 16 days fo llowing termination of CsA). Islet allografts were not rejected, and, as expected, did not initiate rejection of the renal allograft. Simila r results were observed in renal allograft recipients rendered diabeti c by a single injection of streptozotocin (STZ, 65 mg/kg, n = 5) and r eceiving islet allografts of sufficient mass (almost-equal-to 1200-140 0 islets) to reverse STZ-induced hyperglycemia. Further, neither islet nor renal allografts were rejected following challenge by 1 x 10(7) d onor-strain dendritic cells (DCs). Control animals not bearing a renal allograft, which began CsA therapy either 30 days prior to, or on the day of islet allotransplantation, did reject their islet grafts follo wing challenge with 1 x 10(7) donor-strain DCs. Further, recipients of perinatal islets not receiving CsA did not develop donor-specific tol erance at any time up to 300 days posttransplant. Islet allografts wer e rapidly rejected following challenge with as few as 5 x 10(5) donor- specific whole spleen cells. Transplantation of isolated perinatal isl ets, MHC-identical to the renal donor, neither compromised the establi shed renal allograft, nor did the immune activity observed in the rena l allograft affect the subsequent MHC-identical islet allograft. The i nability to initiate rejection of the renal and islet allografts by DC challenge represents development of donor-specific immunological unre sponsiveness in response to kidney allotransplantation and concomitant CsA therapy, although CsA therapy concomitant with transplantation of isolated perinatal islets did not induce development of donor-specifi c unresponsiveness. These observations suggest a possible requirement for donor-derived APCs, present in the renal allograft and absent from the islet allograft, in the establishment of immunological unresponsi veness in transplantation with concomitant CsA therapy.