Emerging routes to the generation of functional β-cells for diabetes mellitus cell therapy

Abstract

Diabetes mellitus, which affects more than 463 million people globally, is caused by the autoimmune ablation or functional loss of insulin-producing β-cells, and prevalence is projected to continue rising over the next decades. Generating β-cells to mitigate the aberrant glucose homeostasis manifested in the disease has remained elusive. Substantial advances have been made in producing mature β-cells from human pluripotent stem cells that respond appropriately to dynamic changes in glucose concentrations in vitro and rapidly function in vivo following transplantation in mice. Other potential avenues to produce functional β-cells include: transdifferentiation of closely related cell types (for example, other pancreatic islet cells such as α-cells, or other cells derived from endoderm); the engineering of non-β-cells that are capable of modulating blood sugar; and the construction of synthetic 'cells' or particles mimicking functional aspects of β-cells. This Review focuses on the current status of generating β-cells via these diverse routes, highlighting the unique advantages and challenges of each approach. Given the remarkable progress in this field, scalable bioengineering processes are also discussed for the realization of the therapeutic potential of derived β-cells.

Fig. 1 |. Advances in the generation of mature β-cells from hPSCs and their application for diabetes mellitus cell therapy.

Human pluripotent stem cells (hPSCs) include embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs are derived from the inner cell mass of blastocyst stage embryos and induced pluripotent stem cells (iPSCs) are obtained by reprogramming somatic cells of patients such as peripheral blood mononuclear cells (PBMCs) or dermal fibroblasts. hPSCs can be converted to mature β-cells by directed differentiation through modulation of signalling pathways active during human pancreas formation. Efforts from 2015 onwards have focused on further promoting endocrine commitment from bipotential progenitors by inhibition of actin polymerization, YAP^,, Wnt, ITGA5 or Notch, and by adding steps that closely mimic islet formation in vivo to the final stage of differentiation. Isolation of immature endocrine cells and re-aggregation into smaller islet-like assemblies promotes functional and metabolic maturation. New surface markers have been discovered that allow enrichment of endocrine cells. Resizing of clusters and removal of TGFβ inhibitor after re-aggregation causes β-cells to acquire dynamic insulin secretion properties. Ultimately, mature β-cell products need to be manufactured at the clinical scale and transplanted in immunoprotective devices and/or with immunosuppression to reverse diabetes mellitus in patients. hESCs, human ESCs.

Fig. 2 |. Transdifferentiation of closely related endoderm-derived somatic cells to β-like cells.

β-Like cells can be derived from other pancreatic cell types such as: acinar cells, by adenoviral reprogramming with PDX1, MAFA, NGN3 (referred to as the PMN-cocktail) and PAX4 (REFS^–); from α-cells by overexpression of PAX4, MAFA, PDX1 and inhibition of ARX^,,; or from progenitor cells expressing CD133, CD49f^hi, DCLK1 and ALDH^hi lining the ductal tree. Hepatic and associated extrahepatic tissues share similar developmental programmes with the adjacent pancreas, and hence activation of few key pancreatic markers such as PDX1 (REFS^,) or TGIF2 (REF.) or Wnt signalling is sufficient to convert liver or gallbladder tissue to β-like cells. Another source of β-like cell generation are the gut neuroendocrine cells that highly resemble pancreatic endocrine cells. Treatment of gastric endocrine or enteroendocrine cells with the PMN cocktail^, in addition to FOXO1 (REF.) and CDX2 inhibition induces transdifferentiation into cells that possess β-cell characteristics.

Fig. 3 |. Stem cell bioprocessing for pancreatic islet cell manufacturing.

Multiplate systems, roller bottles, bag bioreactors featuring a rocking motion and stirred suspension bioreactors are candidate cultivation modalities for the generation of clinically relevant quantities of islet cells from hPSCs. Stirred suspension bioreactors afford flexibility as cells can be grown and differentiated as aggregates, on microcarriers or following encapsulation. Moreover, these systems allow monitoring and control of the culture environment.