THE IMMUNOSURVEILLANCE OF HYPOIMMUNOGENIC IPSC-DERIVED PANCREATIC ISLETS: IMPACT OF VIRAL INFECTIONS.

Abstract

Background & Aim

Immune-evasive induced pluripotent stem cell (iPSC)-derived islets are being developed as a promising cell therapy for type 1 diabetes (T1D). While abrogation of MHC-I prevents CD8⁺ T cell killing, it exposes the graft to natural killer (NK) cell destruction via missing-self recognition. Prior strategies attempted to mitigate NK responses by expressing inhibitory ligands but yielded inconsistent results due to the heterogeneity of NK cell populations. We devised an alternative strategy targeting NK cell activation by genetically ablating B7-H3 and CD155 ligands in MHC-I^-/- iPSCs (triple knockout, T-KO). Differentiated T-KO pancreatic islets successfully evaded both T and NK cell-mediated rejection and restored glycemic control in diabetic mice. However, the safety of hypoimmune iPSC-islets in the context of infection remains uncertain. To investigate this, we evaluated in vivo immunosurveillance by challenging T-KO islets with lymphocytic choriomeningitis virus (LCMV-WE).

Methodology

hIL-15 NOG mice transplanted with luciferase-expressing T-KO islets were humanized with NK cells (day 10) and infected with 1 × 10e6 ffu/mouse of LCMV-WE (day 24). Non-humanized and uninfected mice were used as controls. Acute infection was assessed by platelet count 7 days post-infection (p.i.), while viral titers, immunophenotyping, and hC-peptide levels were evaluated 3 and 7 days p.i.. Graft survival was analyzed by IVIS and explanted organs examined at the endpoint.

Results

Thrombocytopenia indicated acute LCMV-WE infection. Viral titers were higher in NK-humanized mice compared to controls. Interestingly, hC-peptide significantly decreased in humanized mice, correlating with the bioluminescence decrease of T-KO islets. Importantly, we found that NK cells were responsible for graft rejection, as we detected CD56⁺ cells at the graft site. Mechanistic evaluations confirmed that NK cell activation and recognition of islet cells were NKG2D-dependent, with LCMV-WE infection causing the upregulation of the NKG2D-activating ligands MICA/B and ULBP3 in T-KO islets.

Conclusion

This study highlights that the upregulation of activating ligands other than B7-H3 and CD155 enables NK cells to re-engage in missing-self recognition, targeting infected cells. Considering the potential for viral escape, further investigations are warranted using viruses with pancreatic islet tropism to comprehensively assess the safety of hypoimmune iPSC-islets for clinical applications.