Evidence for survival and metabolic activity of encapsulated xenogeneic hepatocytes transplanted without immunosuppression in Gunn rats

Background. Hepatocyte transplantation could be an alternative to whole organ transplantation to correct enzymatic disorders. To this end, it would be of major importance to use xenogeneic cells without immunosuppression. The aim of this study was to investigate the survival and metabolic activity of encapsulated xenogeneic hepatocytes in the absence of immunosuppression. For this purpose, we used Gunn rats genetically incapable of bilirubin conjugation. Methods. Xenogeneic (from guinea pigs) and allogeneic (from Lewis rats) hepatocytes (2 x 10(7)) were isolated, macroencapsulated in hydrogel hollow fibers made with an acrylonitrile-sodium methallyl-sulfonate copolymer, and transplanted into the peritoneum of Gunn rats without any immunosuppression. Plasma bilirubin levels were evaluated weekly, Bilirubin conjugates in bile and cell morphology were studied after 5 and 12 weeks, respectively. Results. In Gunn rats transplanted with xenogeneic hepatocytes, a significant decrease in the serum bilirubin level was observed between 3 and 9 weeks after transplantation when compared with controls transplanted with empty hollow fibers: it fell to 62% of the initial level at weeks 5-7 (P<0.01). A comparable result was observed in Gunn rats transplanted with encapsulated allogeneic cells, Bilirubin conjugates were observed in bile samples of rats transplanted with encapsulated hepatocytes, After explantation, hollow fibers appeared intact with minimal fibrosis. Cell viability and hepatocyte morphology were preserved. Conclusions. These results indicate that macroencapsulated xenogeneic hepatocytes can survive and remain functional for more than 2 months when transplanted in vivo in the absence of any immunosuppression.