Human pluripotent stem cell-derived insulin-producing cells: A regenerative medicine perspective

Abstract

Tremendous progress has been made over the last two decades in the field of pancreatic beta cell replacement therapy as a curative measure for diabetes. Transplantation studies have demonstrated therapeutic efficacy, and cGMP-grade cell products are currently being deployed for the first time in human clinical trials. In this perspective, we discuss current challenges surrounding the generation, delivery, and engraftment of stem cell-derived islet-like cells, along with strategies to induce durable tolerance to grafted cells, with an eye toward a functional cellular-based therapy enabling insulin independence for patients with diabetes.

Figure 1:. Schematic showing differentiation of human pluripotent stem cells to pancreatic lineages.

Directed differentiation of human pluripotent stem cells (hPSCs) to pancreatic cells is achieved through a series of sequential steps that recapitulate in vivo development. Such protocols lead to the formation of definitive endoderm (DE, characterized by expression of the transcription factors FOXA2 and SOX17 and the cell surface marker CXCR4), patterning of the posterior foregut (PF) to generate PDX1-expressing endoderm and specification of the PDX1+ endoderm to pancreatic progenitors (PP) expressing PDX1 and NKX6-1. Endocrine commitment, leading to the formation of endocrine progenitors (EP), is characterized by the up-regulation of transcription factors NGN3 and NKX2-2, followed by the expression of lineage-specific gene, including the hormones insulin (INS) expressed by beta-like cells, glucagon (GCG) expressed by alpha-like cells, and somatostatin (SST) expressed by delta-like cells. Each developmental step is controlled by activation (black) and/or inhibition (red) of specific signalling pathways. Activin/Nodal and Canonical Wnt signaling are required for definitive endoderm formation. Retinoic Acid and FGF10 signaling are important for PDX1 induction. PKC activation or EGF and Nicotinamide treatment are required for the formation of PP cells. Endocrine lineage commitment is achieved in the presence of BMP/TGF-β/NOTCH inhibition.

Figure 2:. Strategies for beta cell replacement using human pluripotent stem cells (hPSCs).

Cell Generation: hPSCs can be differentiated in vitro to generate pancreatic progenitors (PPs) or islet-like cells for functional restoration of euglycemia. Potential sources of hPSCs include allogeneic hESC or iPSC lines, autologous iPSCs derived from the patient’s own cells, and hESC or hiPSC lines that have been genetically engineered to be hypoimmunogenic. Cell Delivery: To protect the graft from allorejection and/or autoimmunity, allogeneic and autologous cells can be delivered inside micro- or macroencapsulating devices, possibly supplemented with accessory niche cells to improve engraftment and functionality. Hypoimmunogenic pancreatic cells could be transplanted in the absence of immunoprotective devices but may still require scaffolds and/or accessory cells to facilitate engraftment. Transplantation: Potential anatomical sites for transplantation include the subcutaneous, omental/intra-peritoneal, intramuscular, or intraportal locations. Target patient populations include patients living with type 1 diabetes (T1D), type 2 diabetes (T2D), pancreatitis, or cystic fibrosis. This figure was created using BioRender.com