Engineering human stem cell-derived islets to evade immune rejection and promote localized immune tolerance

Immunological protection of transplanted stem cell-derived islet (SC-islet) cells is yet to be achieved without chronic immunosuppression or encapsulation. Existing genetic engineering approaches to produce im-mune-evasive SC-islet cells have so far shown variable results. Here, we show that targeting human leuko-cyte antigens (HLAs) and PD-L1 alone does not sufficiently protect SC-islet cells from xenograft (xeno)-or allograft (allo)-rejection. As an addition to these approaches, we genetically engineer SC-islet cells to secrete the cytokines interleukin-10 (IL-10), transforming growth factor b (TGF-b), and modified IL-2 such that they promote a tolerogenic local microenvironment by recruiting regulatory T cells (Tregs) to the islet grafts. Cyto-kine-secreting human SC -b cells resist xeno-rejection and correct diabetes for up to 8 weeks post -transplan-tation in non-obese diabetic (NOD) mice. Thus, genetically engineering human embryonic SCs (hESCs) to induce a tolerogenic local microenvironment represents a promising approach to provide SC-islet cells as a cell replacement therapy for diabetes without the requirement for encapsulation or immunosuppression.