Introduction: Allogeneic islet transplantation is a potentially curative therapy for individuals with type-1 diabetes (T1D). However, it does not eliminate underlying autoimmunity, and individuals require life-long immunosuppression to prevent rejection. In murine studies, group 2 innate lymphoid cells (ILC2s) prevented islet rejection and group 3 ILCs (ILC3s) supported tolerance within islets, respectively. Here, we assess whether human ILC2s or ILC3s improve islet transplant in humanized models. 
Methods: To assess the potential of harnessing human ILCs to improve islet transplantation, we examined the ability of ILCs to i) support the engraftment of islets and, ii) regulate harmful T cell subsets associated with the pathology of T1D. To assess whether ILCs were able to improve islet survival and engraftment, we performed in vitro co-cultures of allogeneic islets and ILCs and assessed the effects of ILCs on human islet engraftment and function following transplantation into streptozotocin-treated NOD-scidIL2Rgamma^null (NSG) mice. To assess whether ILCs could prevent immune-mediated rejection of islets, we employed an antigen-specific model of islet transplant where HLA-A2⁺ islets are transplanted into NSG mice, and following engraftment HLA-A2-specific CAR T cells are transferred IV to induce islet rejection. The ability of adoptive cell therapy using ILC2s and ILC3s to prevent HLA-A2-specific CAR T cell-mediated rejection was assessed through blood glucose measurements. Additionally, the direct ability of ILC2 and ILC3s to regulate allogeneic T cell cytokine expression, expression of markers of inflammation, proliferation, and killing ability was assessed using in vitro suppression assays.
Results: In vitro and in vivo studies demonstrate ILC2s and ILC3s are not cytotoxic and do not negatively impact the engraftment of allogeneic human islets transplanted into NSG mice. Using an antigen-specific model of islet transplant rejection, we demonstrate the ability of ILCs to prevent CAR T-cell-mediated islet rejection. Cell therapy with both ILC2s and ILC3s suppress antigen-specific rejection by CAR T cells, resulting in sustained normal blood glucose levels. In vitro studies revealed ILC2s suppress both autologous and allogeneic CD4⁺ and CD8⁺ T cell IFN-γ production and decrease expression of apoptosis-inducing molecule FasL on CD8⁺ T cells. ILC3s also display moderate ability to inhibit allogeneic T cells ^{in vitro}, although not as efficiently as ILC2s, suggesting ILC3 effects in vivo may be via indirect T cell interactions.
Conclusion: Collectively, these findings support that adoptive cell therapies with human ILC2s and ILC3s have potential in promoting tolerance in transplantation.