(A) Human C-peptide concentrations in mouse sera collected in the fasting state. Error bars represent standard deviation. (B) Measurement of human C-peptide levels in mouse sera prior to and after excision of the transplants. Mice transplanted with GCK mutant cells (GCKG299R/+) are shown. Error bars represent standard deviation. (C and D) Immunohistochemistry of explants isolated 4 months after transplantation of GCK mutant cells (GCKG299R/+). GCG, glucagon; SST, somatostatin; INS, insulin; UCN-3, urocortin-3; ZNT8, zinc transporter 8. Scale bar: 10 μm (C); 100 μm (D). (E) Scatter plots showing fold change in C-peptide concentration (30 minutes after glucose injection versus 16 hours of fasting) versus the change in capillary blood glucose concentration (30 minutes after glucose injection minus 16 hours of fasting) during intraperitoneal glucose tolerance tests.