42: Molecular Pathways in Support of Allogenic Human Amnion Epithelial Cell Transplantation for Liver Disease Without Immunosuppression

Placenta is a non-controversial and readily available source of stem cells for regenerative medicine. We previously reported that human amnion epithelial cells (hAEC) from term placenta are not tumorigenic, have immunomodulatory and anti-inflammatory properties and are able to differentiate into functional hepatocyte-like cells. In preclinical studies with immune-competent mice, hAEC engrafted and survived without administration of immunosuppressive drugs, resulting in correction of metabolic liver diseases or the reversal of acute liver failure. In clinical settings allogenic hAEC have been transplanted without immunosuppression, and during the last year we studied and identified molecular pathways through which hAEC can drive immunoacceptance by the host immune system. We performed a complete surface screening of hAEC, profiling all the molecules commonly described on other stem as well as somatic cells. Amnion characteristically lacks HLA class 2 expression and expresses both class 1a and non-polymorphic class 1b (responsible for maternal immune-toleration of the fetus). We quantified the level of expression of HLA-G and HLA-E molecules both as membrane-bound and soluble forms. Recently, purinergic mediators, hydrolyzed by plasma membrane nucleotidases, have also been identified to regulate immune cell response, thus we quantified the level of expression of all ecto-enzymes in hAEC preparations. hAEC constitutively express all known ecto-enzymes. In addition, we proved constitutive expression of of CD47 (‘don’t-eat-me’ signal) and complement system (CD55/CD59). We measured immunogenicity of hAEC on purified immune effector cells involved in disease pathogenesis (with particular attention to Th1/Th2 and M1/M2 switch and Treg/Breg induction). We measured amnion-derived cells to actively interact and crosstalk with innate and adaptive immune cells not only by cell-to-cell interactions but also through soluble mediators and vesicles with characteristic surface profile. Conclusions: High level expression of ecto-enzymatic axis and non-canonical HLA molecules likely play a key role in immunological tolerance and long-term acceptance of the human xeno-cell graft in immunocompetent mice. The ability to treat the most common (liver) diseases with one stem cell therapy without the administration of immunosuppressive drugs could be a “game changer” and will greatly expand the number of patients who could receive cellular therapy. Based on their safety and the successful preclinical studies, approval was granted to begin banking of hAEC under cGMP condition at Karolinska Institutet, and to perform hAEC transplants on 10 patients with liver disease without immunosuppression.