68: Rapid Viability and Potency Assessment of Encapsulated Islets and Insulin-producing Cells

Abstract

Introduction: Diabetes and its insidious complications sicken and kill millions of people worldwide. Our group has developed macroencapsulation devices capable of providing supplemental oxygen to macroencapsulated transplanted tissue. These devices house and protect islets and insulin-producing cells (IPCs) from the immune system, eliminating the need for immunosuppression of the transplant recipient. We predict these devices will facilitate transplant of small footprint devices containing high cell densities of islets or IPCs that can reverse diabetes in humans by fostering increased viability and functionality of transplanted islets and IPCs. However, in order to a) determine the number of cells encapsulation devices can support, b) assess the effects of encapsulation on islets and IPCs, c) meet FDA standards, and d) ensure the quality of a cellular transplant product, the viability and potency of islets and IPCs within encapsulation devices must be determined before clinical application. Materials and Methods: We have developed 2 bioreactor systems integrated with BioRep perifusion machines capable of simultaneous measurement of cellular oxygen consumption rate (OCR) and hormone secretion. One bioreactor can be used to assay free cells and the other, macroencapsulated cells. Each bioreactor contains two integrated FOSPOR oxygen sensors (Ocean Optics) at the inlet and outlet of the bioreactor. Oxygen concentration is derived from the fluorescence lifetime of the sensor measured by fiber optic cables linked to a phase fluorometer (Ocean Optics). Media flow, temperature and collection are controlled by the BioRep perifusion machine. Figure 1 depicts the general design of the integrated bioreactor systems. Results and Discussion: We have determined that cellular density and encapsulation can affect the viability and function of islets. Islet density greater than 500 islet equivalents/cm2 (without supplemental oxygen) was detrimental to islet viability during a 7-day transplant period. In vitro, densely encapsulated islets displayed delayed and diminished glucose-stimulated insulin secretion (GSIS) relative to free islets (Figure 2A), an important consideration for physiological control of glycemia with engrafted tissue. Furthermore, as expected in Krebs Ringer Bicarbonate Buffer, glucose-stimulated insulin secretion (GSIS) was correlated with an increased OCR (Figure 2B) highlighting the link between OCR and GSIS in this medium and the utility of OCR, an inexpensive real time assay as an islet potency indicator. Conclusions: In concert, oxygen consumption and hormone secretion are excellent indicators of islet and IPC health and function. Our bioreactor will allow us to optimize encapsulation densities, cellular function, and supplemental oxygen delivery strategies ensuring a clinical high-grade cellular product and, together with our encapsulation devices, improve the treatment of diabetes. BioRep, Inc. Juvenile Diabetes Research Foundation Award # #2-SRA-2018-685-S-B. NIH Diabetes Impact Award #1DP3DK106933-01.