Tolerogenic Human Placental Trophoblast Survival and Engraftment in a Xenograft Model

Cell and tissue transplantation is hindered by graft rejection, which necessitates lifelong chronic systemic immunosuppression. Placental pregnancy is the only natural state of de novo tolerance against allogeneic tissue in adult mammals, and is mediated by placental trophoblast cells, which use diverse mechanisms to induce antigen-specific tolerance. Understanding trophoblast tolerogenic mechanisms holds potential implications for eliminating immunosuppression in allogeneic transplantation.
In this study we aimed to evaluate the potential of human trophoblast model cell line, JAR, to evade graft rejection via tolerogenic soluble factors in an immune competent xenograft model (C57BL/6 recipient). To conduct this, we validated the survival of JAR cells macroencapsulated in spiral devices via live/dead imaging and metabolic activity in vitro over 7 days of culture. To evaluate successful engraftment in vivo in the absence of immune rejection, encapsulated and unencapsulated JAR cells transfected with Nanoluciferase were transplanted into immune deficient NSG mice in the subcutaneous (SUBQ) or epididymal fat pad (EFP) sites with a vasculogenic VEGF-delivering degradable hydrogel to enhance local vascularization. Unencapsulated groups maintained higher luminescent signal than encapsulated groups, increasing gradually over time, and formed palpable tumors SUBQ over 3 weeks. Overall, encapsulated JAR cells exhibited highest signal relative to day 0 in the EFP (~213%) compared to the SUBQ (~74%). Next, we evaluated unencapsulated and encapsulated nanoluciferase JAR survival in an immune competent C57BL/6 xenograft model. JAR were transplanted in SUBQ and EFP sites, with and without vasculogenic degradable hydrogel. The EFP groups experienced rapid rejection, with a reduction to near-baseline signal in all groups by day 10. In the SUBQ groups, rejection was observed between day 14-28, except for the encapsulated with vasculogenic hydrogel group, which demonstrated significantly elevated signal comparable to the NSG group out to day 63. Encapsulated non-tolerogenic control human HEK cell controls were rapidly rejected within 10 days, suggesting that trophoblast-secreted soluble factors contributed to JAR survival.
Overall, trophoblast in vivo imaging survival demonstrated high cell survival in immune compromised mice and comparable survival in immune competent mice in the SUBQ site. Ongoing studies are evaluating mechanisms of trophoblast survival and immune modulation via histology and flow cytometry.