Spleen as an Ectopic Site for Human Stem Cell-derived Hepatocyte and Islet Transplantation in an Operational Immunodeficient Pig Model

Background. Extensive efforts in cell transplantation have focused on identifying effective transplantation sites, including autologous and ectopic options. Intraportal transplantation of pancreatic islets into the liver has produced favorable outcomes. We examined whether the spleen, which possesses a sinusoidal vascular structure similar to that of the liver, could serve as an alternative transplantation site for human progenitor cell-derived hepatocyte- or islet-like cells, using the same clinically relevant transplantation procedure. Methods. The operational immunodeficient pig (OIDP) model has been used for transplantation of human stem cell-derived cells. In accordance with the OIDP protocol, recipients underwent thymectomy and received tacrolimus, mycophenolate mofetil, and prednisolone via a gastric tube, while the spleen was not removed. Instead, splenic immune cells were inactivated by perfusing mitomycin C using a temporal extracorporeal circuit that isolated the spleen from systemic circulation. After thorough rinsing, human-induced pluripotent stem cell-derived hepatocyte-like cells (iPSC-HLCs) or induced tissue progenitor cell-derived islets (iTPC-derived islets) were transplanted into the spleen through this route. Results. Administration of tacrolimus, mycophenolate mofetil, and prednisolone reduced concanavalin A-induced lymphocyte activation. Splenic lymphocytes treated with mitomycin C under extracorporeal circulation similarly reduced activation in response to concanavalin A. Human albumin was detectable in pig serum 2 wk after iPSC-HLC transplantation. After harvesting the spleen at 4-wk posttransplantation, colonies of cells positive for human albumin and vimentin were identified. Similarly, after transplantation of quantum-dot-labeled human iTPC-derived islets, human C-peptide was detected in the serum after a glucose tolerance test. Histological analysis confirmed differentiation of pancreatic progenitor cells into insulin-producing cells in the spleen. Conclusions. This exploratory study using pigs demonstrated the feasibility of intrasplenic cell transplantation via the splenic artery.