Hepatocyte transplantation in Swine using prevascularized polyvinyl alcohol sponges

Hepatocyte transplantation shows promise as therapy to support liver function. We have shown that hepatocytes can be transplanted into prevascularized synthetic polymers in rat models. While there are many studies in rats showing the benefits of hepatocyte transplantation, there are few in larger animal models more akin to humans. Therefore, we developed a swine model of hepatocyte transplantation using prevascularized synthetic polymers. Polyvinyl alcohol sponges measuring 2 x 3 x 0.5 cm were implanted in preperitoneal, mesenteric, and subcutaneous spaces for prevascularization as a transplantation bed. On postimplantation day 0, 4, 8, or 12 the sponges were removed and examined histologically. New tissue ingrowth was quite satisfactory on day 8 and 12 in preperitoneal and mesenteric sites, but the sponges in subcutaneous tissue were compressed, leaving little space for hepatocyte engraftment. Mesenteric sponges were irritating to intraabdominal organs and induced peritoneal adhesions. Thus, the preperitoneal sponges seemed to be best for hepatocyte transplantation. Hepatocytes isolated from donor livers using collagenase perfusion were transplanted into the preperitoneal sponges prevascularized for 0, 4, 8, or 12 days as allografts with cyclosporine immunosuppression, and the number of hepatocytes was evaluated on posttransplantation day 4. The optimal period for prevascularization for subsequent hepatocyte implantation was 8 days. The number of hepatocytes implanted in the preperitoneal sponges prevascularized for 8 days was counted on day 0, 1, 4, or 8 after transplantation. Hepatocytes were lost mainly in the first day after implantation, but still many hepatocytes maintained their shape histologically and there were mitotic figures confirming growth of the transplanted hepatocytes. Areas of hepatocytes within the sponge devices showed tissue remodeling with plates of hepatocytes lined with sinusoid-like capillaries and evidence of early tubular formation. Positive staining by immunohistochemical examination using antipig albumin indicated albumin production by implanted hepatocytes. The effect of a portacaval shunt as a hepatotrophic stimulation to maintenance of the implanted hepatocytes was evaluated on day 4, 8, or 12 after implantation. Total hepatocyte number in sponges was significantly increased by portacaval shunt compared to controls treated by a sham operation. These results suggest that significant numbers of hepatocytes can engraft and function using a prevascularized polymer bed as a site for transplantation and ongoing hepatotrophic stimulation with portacaval shunting.