Long-term correction of genetic defect of liver function in rat by transplantation of liver cells after ultraviolet irradiation.

Allograft rejection limits the survival and function of transplanted hepatocytes obtained from allogeneic donors. Presentation of donor antigens by antigen-presenting cells that express class II major histocompatibility antigens (MHC) carried in the graft has been implicated in allograft rejection. Ultraviolet-B (u.v.-B, 280 to 320 nm) irradiation and short-term culture have been shown to modify the function of antigen-presenting cells. In this study, we used u.v.-B irradiation (600 J/m2) of donor hepatocytes isolated from normal inbred Wistar RHA rats, followed by 16 to 20 hours of culture prior to transplantation into histoincompatible genetically analbuminemic rats (Nagase analbuminemic rats, NAR) by intraportal infusion of 10(7) viable hepatocytes. Isolated Wistar RHA hepatocytes without u.v.-B irradiation and/or culture, or NAR rat hepatocytes, were used as control. Survival and function of the transplanted hepatocytes were monitored by serial immunoassay of serum albumin in the recipients. Serum albumin concentration did not increase after transplantation of NAR rat hepatocytes. In NAR rats that received Wistar RHA hepatocytes, serum albumin levels increased from pre-transplantation levels of 0.025 to 0.05 mg/ml to 8 to 10 mg/ml. When freshly isolated liver cells were transplanted with or without u.v.-B-irradiation, but without culturing, serum albumin levels reached a maximum in two weeks and then progressively declined to pretransplantation levels. When the cells were not irradiated but cultured for 16 to 20 hours, elevated serum albumin levels persisted for six weeks, and then progressively declined to baseline concentrations. In contrast, when the isolated normal liver cells were u.v.-B-irradiated and cultured for 16 to 20 hours before transplantation, serum albumin levels persisted at 8 to 10 mg/ml throughout the duration of this study (32 weeks). Immunocytochemistry using anti-rat serum albumin (rabbit) immunoglobulin of liver tissue from NAR rats without transplantation or after transplantation with NAR liver cells showed immunostaining in less than one in 1000 cells. Four to 16 weeks after transplantation of u.v.-B-irradiated and cultured normal allogeneic hepatocytes, one to two per 100 hepatocytes stained positive for albumin. The results indicate that u.v.-B-irradiation followed by short-term culture of allogeneic rat hepatocytes prior to transplantation results in prolonged and perhaps permanent allograft acceptance by NAR rats.