Clinical islet transplantation: is the future finally now?

Stem cells in the treatment of diabetes mellitus - Focus on mesenchymal stem cells

Diabetes mellitus type 1 and type 2 have become a global epidemic with dramatically increasing incidences. Poorly controlled diabetes is associated with severe life-threatening complications. Beside traditional treatment with insulin and oral anti-diabetic drugs, clinicians try to improve patient's care by cell therapies using embryonic stem cells (ESC), induced pluripotent stem cells (iPSC) and adult mesenchymal stem cells (MSC). ESC display a virtually unlimited plasticity, including the differentiation into insulin producing β-cells, but they raise ethical concerns and bear, like iPSC, the risk of tumours. IPSC may further inherit somatic mutations and remaining somatic transcriptional memory upon incomplete re-programming, but allow the generation of patient/disease-specific cell lines. MSC avoid such issues but have not been successfully differentiated into β-cells. Instead, MSC and their pericyte phenotypes outside the bone marrow have been recognized to secrete numerous immunomodulatory and tissue regenerative factors. On this account, the term 'medicinal signaling cells' has been proposed to define the new conception of a 'drug store' for injured tissues and to stay with the MSC nomenclature. This review presents the biological background and the resulting clinical potential and limitations of ESC, iPSC and MSC, and summarizes the current status quo of cell therapeutic concepts and trials.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Biomarkers in Islet Cell Transplantation for Type 1 Diabetes

PURPOSE OF REVIEW

Islet transplantation, an important approach to achieve insulin independence for individuals with type 1 diabetes, is limited by the lack of accurate biomarkers to track beta-cell death post islet infusion. In this review, we will discuss existing and recently described biomarkers.

RECENT FINDINGS

As beta cells are killed by the immune system, fragments of beta cell-specific cell-free DNA and proteins are released into the periphery. Several different strategies to identify these fragments have been described. Some circulating, non-coding microRNAs, particularly miRNA-375 are also showing potential to reflect the rate of beta cell loss post-clinical islet transplantation. Recent advances in identifying accurate beta cell-specific biomarkers such as differentially methylated insulin cell-free DNA and circulating miRNA-375 may help predict clinical outcomes. More studies are required to examine the robustness of these biomarkers to detect chronic beta-cell loss in islet transplantation recipients.