Stem Cell Therapies for Treating Diabetes: Progress and Remaining Challenges

Abstract

Restoration of insulin independence and normoglycemia has been the overarching goal in diabetes research and therapy. While whole-organ and islet transplantation have become gold-standard procedures in achieving glucose control in diabetic patients, the profound lack of suitable donor tissues severely hampers the broad application of these therapies. Here, we describe current efforts aimed at generating a sustainable source of functional human stem cell-derived insulin-producing islet cells for cell transplantation and present state-of-the-art efforts to protect such cells via immune modulation and encapsulation strategies.

Figure 1

Strategies for generating human pluripotent stem cell (hPSC)-derived pancreatic islets for transplantation. A) The pancreas is comprised of both an exocrine and an endocrine compartment. The latter is composed of small spherical mini-organs called the islets of Langerhans (inset). Each islet contains insulin-producing beta cells, along with other hormone-producing endocrine cells (alpha, delta, epsilon, and PP cells). A subset of beta cells are so-called “hub” cells, which orchestrate the coordinated release of insulin across the islet in response to glucose. The endocrine cells do not exist in isolation, but rather in the context of various types of niche cells, including stromal, neural, endothelial, and perivascular cells. B) The generation of beta-like cells from hPSCs involves the promotion of pluripotent cells through a series of intermediate progenitor stages. At the completion of directed differentiation, the clusters of beta-like cells can be dissociated and reaggregated into islet-like clusters of defined size and composition. The reaggregation with other endocrine cell types (themselves potentially derived from hPSCs) may lead to improved glucose homeostatic function, potentially through the specialization of some hPSC-derived beta-like cells into hub cells. Lastly, endocrine cells can be reaggregated along with niche cells to more closely recapitulate interactions with the local microenvironment that are critical for beta cell function.

Figure 2

Cell encapsulation strategies for islet transplantation. While encapsulation with expanded polytetrafluoroethylene (ePTFE) and alginate have been the conventional approaches, more recent advances include the use of microfabricated silicon and nanotemplated polymer thin films, such as polycaprolactone (PCL). A hybrid approach utilizes an oxygen depot to enhance cell viability. Pros and cons of the various strategies center around ease of implantation (injectable or not), ability for retrieval (if needed), getting oxygen to and insulin from the cells, and protection provided by the membrane to cells from attack by the patient’s immune system.