Co-Transplantation of Marginal Mass Allogeneic Islets with 3D-Culture-Derived Adult Human Skin Cells Improves Glycemia in Diabetic Mice

Background. Pancreatic islets transplantation represents a promising therapeutic option for severe type 1 diabetes (T1D). Maintenance of long-term viability of transplanted islets still requires improvement. Stem cell use represents an option to repair and replace damaged islets or, alternatively, b cells in T1D. Mesenchymal stem cells (MSC) have been proposed as adjuvants for islet transplantation, facilitating grafting and improving their functionality. Aggregation of stem cells has gained interest in providing physiological interactions between cells and enhancing the in situ concentration of modulators of inflammation and immunity.Methods. We established a hanging-drop culture by the spontaneous aggregation of adult human skin fibroblast-like cells as spheroids. Adult skin spheroid-derived cells (SphCs) were characterized in vitro and in vivo. We assessed the potential benefit of SphCs as adjuvants to improve islet functionality by cotransplantation with a marginal mass of allogeneic islets in an experimental diabetic mouse model. We characterized the secretome of SphCs by mass spectrometry-based proteomics.Results. SphCs were characterized as multipotent progenitors by their surface expression of markers analyzed by flow cytometry and multilineage germ differentiation capacity. Coculture of SphCs with anti-CD3-stimulated mouse splenocytes diminished the proliferation of T-CD4+ lymphocytes and biased splenocyte cytokine secretion through an increase in the Th2/Th1 ratio. SphCs conditioned media attenuated apoptosis of islets induced by inflammatory cytokine challenge in vitro. Administration (i.t.) of SphCs showed the absence of tumorigenicity in immune-deficient mice.SphCs improved glycemic control when cotransplanted with a marginal mass of allogeneic islets in an experimental diabetic mouse model without pharmacological immunosuppression. SphCs’ protein secretome differed from its paired skin fibroblast-like counterpart in containing 70% of up- and downregulated proteins and biological processes that overall positively influence islets such as cytoprotection, cellular stress, metabolism, and survival.Conclusions. Hanging-drop cell culture methodology might contribute to the development of an efficient way to improve transplantation outcome by reducing undesirable consequences of pharmacological immunosuppression as well as the number of allogeneic islets required to achieve normoglycemia in T1D transplanted patients. Further studies might determine whether the identified proteins sustain immunomodulation and/or cytoprotective effects in transplanted allogeneic islets.