Characterising differential maturation of stem cell‐derived islets in mice: Graft function and transcriptomic analysis

AIMS: Stem cell-derived islets (SC-islets) offer the potential to revolutionise type 1 diabetes treatment. However, functional maturation in vivo is variable, suggesting that specific, but as-yet undefined, environmental cues are critical. We aimed to identify pathways associated with SC-islet in vivo maturation in mice, assess early functional markers of this, and determine whether a hyperglycaemic graft environment impairs this. METHODS: Mice transplanted with 800 SC-islets but exhibiting differing glycaemic outcomes (cured, semi-cured, uncured) were selected and glucose tolerance and human C-peptide concentrations over time were measured. Single-cell transcriptomic analysis of the graft from the cured mouse was compared with in vitro-maintained SC-islets. The impact of hyperglycaemia on in vivo maturation was assessed by comparing mouse recipients of SC-islet grafts which were either hyperglycaemic or normoglycaemic for 1 month post-transplantation. RESULTS: Superior SC-islet in vivo maturation was broadly associated with progressive improvements in C-peptide and glucose tolerance. In vivo maturation was associated with a distinct transcriptomic pattern (including increased MAFA and INS expression) compared with SC-islets maintained in vitro. Finally, a hyperglycaemic post-transplant environment did not affect long-term SC-islet maturation, with no impairment in plasma human C-peptide seen at 6 months, and no changes in gene expression of β-cell maturity markers after SC-islets were transplanted into diabetic mice. CONCLUSION: Longitudinal plasma C-peptide and glucose tolerance can be used to characterise in vivo SC-islet maturation, which is associated with transcriptomic changes not observed in vitro. Additionally, elevated blood glucose does not impair long-term functional maturation. These findings support the importance of in vivo cues for SC-islet maturation to inform future preclinical studies.