GCG and type 2 diabetes mellitus: In fact, the nonclinical–clinical translation of results has been a limiting factor in β-cell research in general—e.g., the GLP1 agonist exenatide was shown to cause β-cell regeneration in vitro and in rat models33 but was recently shown to not cause any β-cell regeneration in humans.34 The absence of data on therapies known to cause β-cell changes in T2DM patients limits our ability to apply anything but the simplest level of interpretation to model predictions.