The Authors' Reply: Organoid Technology: Are Human Cholangiocyte Organoids Immune Protected?

Abstract

We thank Ekser et al1 for reading our commentary2 on the groundbreaking Science publication by Sampaziotis et al3 on repair of bile ducts after transplantation of cholangiocyte organoids in human liver grafts. Ekser et al1 comment that if allogenic cholangiocyte organoids would be used for graft repair, this potentially can provoke an alloimmune response. The authors are “puzzled by the outcome of the original paper3 as nonautologous organoids were used and no protective immunosuppressive medication is used during the normothermic machine perfusion of the liver grafts.” Indeed, cholangiocytes or cholangiocyte organoids, in this matter, are not blinded from the immune system as they normally express major histocompatibility complexes (HLA) on their cell surface. However, in this study, like many studies with human liver normothermic machine perfusion,4 leukocyte-depleted packed red blood cells in gelofusine were used for oxygenation of the graft and therefore completely lacked alloreactive immune cells. Therefore, no acute rejection of the engrafted organoids was observed, even despite no immunosuppressive treatment was given. In case such a cell-therapy repaired graft would be actually transplanted, immunosuppressive medication is inevitably needed to prevent rejection of the donor allograft and the third party allogenic organoid cell alike. Exposing the immune system to extra allogenic cells might nonetheless increase the risk of an alloimmune response. Therefore, as mentioned in our Game Changer commentary: “For graft repair, ideally, autologous cells of the recipient should be used to diminish the risk of alloimmune responses.”2 Safe means to obtain autologous cells for organoid initiation are required. Indeed, cholangiocyte organoids can now be cultured from liver fine-needle aspiration biopsies or from bile, obtained via percutaneous drainage of the gallbladder or via endoscopic retrograde cholangiopancreatography,5 with very limited risks. The future recipient’s cholangiocyte organoids could thus be stored in a biobank at enlistment for liver transplantation, making patient-derived cells directly available for regenerative purposes at the time of a donor liver offer. The bottleneck in using autologous cholangiocyte organoids is not so much culturing the recipient’s own cells but the logistics of having sufficient numbers of cells at the moment of transplantation. Sampaziotis et al3 used approximately 10 million cells for injecting single liver segment 3. To treat the whole graft, at least 10 times this number of cells would be required to treat the entire biliary tree of a full-size liver. To reach high amounts of organoid cells in a short time, more efficient culturing methods are being developed.6 Cryopreservation protocols should be optimized to store large quantities of cholangiocyte organoids, which could be directly administered to the liver after thawing. Taken together, we consider that ideally, autologous cells should be used in graft repair to minimize the risk of an alloimmune response. Logistic problems need to be solved before this regenerative approach can be clinically implemented. We foresee that this way of repairing the biliary tree will evolve from bench to bedside in the upcoming years.