With donor xenoislet microencapsulation and host immunosuppression, APIs corrected hyperglycemia after ip transplantation in STZ-diabetic NHPs in the short term. The islet xenografts lost efficacy gradually, but at graft failure, some viable islets remained, substantial porcine C-peptide was detected in the peritoneal graft site, and there was very little evidence of a host immune response. We postulate that chronic effects of non-immunologic factors, such as in vivo hypoxic and hyperglycemic conditions, damaged the encapsulated islet xenografts. To achieve long-term function, new approaches must be developed to prevent this damage, for example, by increasing the oxygen supply to microencapsulated islets in the ip space.

Antibody-mediated immune checkpoint blockade is a transformative immunotherapy for cancer. These same mechanisms can be repurposed for the control of destructive alloreactive immune responses in the transplantation setting. Here, we implement a synthetic biomaterial platform for the local delivery of a chimeric streptavidin/programmed cell death-1 (SA-PD-L1) protein to direct “reprogramming” of local immune responses to transplanted pancreatic islets. Controlled presentation of SA-PD-L1 on the surface of poly(ethylene glycol) microgels improves local retention of the immunomodulatory agent over 3 weeks in vivo. Furthermore, local induction of allograft acceptance is achieved in a murine model of diabetes only when receiving the SA-PD-L1–presenting biomaterial in combination with a brief rapamycin treatment. Immune characterization revealed an increase in T regulatory and anergic cells after SA-PD-L1-microgel delivery, which was distinct from naïve and biomaterial alone microenvironments. Engineering the local microenvironment via biomaterial delivery of checkpoint proteins has the potential to advance cell-based therapies, avoiding the need for systemic chronic immunosuppression.

Background Adult porcine islets (APIs) constitute a promising alternative to human islets in treating Type 1 diabetes. The intrahepatic site has been used in pre-clinical primate studies of API xenografts; however, an estimated two-thirds of donor islets are destroyed after intraportal infusion due to a number of factors, including the instant blood mediated inflammatory reaction (IBMIR), immunosuppressant toxicity, and poor reestablishment of extracellular matrix connections. Intraperitoneal (i.p.) transplantation of non-vascularized encapsulated islets offers several advantages over intrahepatic transplantation of free islets, including avoidance of IBMIR, immunoprotection, accommodation of a larger graft volume, and reduced risk of hemorrhage. However, there exists evidence that the peritoneal site is hypoxic, which likely impedes islet function. Methods We tested the effect of hypoxia (2-5% oxygen or pO2: 15.2-38.0 mmHg) on free and encapsulated APIs over a period of 6 days in culture. Free and encapsulated APIs under normoxia served as controls. Islet viability was evaluated with a viability/cytotoxicity assay using calcein AM and ethidium bromide on days 1, 3 and 6 of culture. Alamar blue assay was used to measure the metabolic activity on days 1 and 6. Insulin in spent medium was assayed by ELISA on days 1 and 6. Results Viability staining indicated that free islet clusters lost their integrity and underwent severe necrosis under hypoxia; encapsulated islets remained intact, even when they began to undergo necrosis. Under hypoxia, thae metabolic activity and insulin secretion (normalized to metabolic activity) of both free and encapsulated islets decreased relative to islets cultured under normoxic conditions. Conclusions Hypoxia (2-5% oxygen or pO2: 15.2-38.0 mmHg) affects the viability, metabolic activity and insulin secretion of both free and encapsulated APIs over a 6-day culture period. Encapsulation augments islet integrity under hypoxia, but it does not prevent loss of viability, metabolic activity, or insulin secretion.

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Background Our goal was to identify clinically relevant immunotherapies that synergize with microencapsulation to protect adult porcine islet (API) xenografts in diabetic NOD mice. We have shown previously that dual costimulatory blockade (CTLA4‐Ig plus anti‐CD154 mAb) combined with encapsulation protects APIs long‐term in NOD mice. Since no anti‐CD154 mAbs currently are approved for use in humans, we tested the efficacy of other targeted immunosuppression regimens that might be used for diabetic patients receiving encapsulated islets. Methods Microencapsulated APIs were transplanted i.p. in diabetic NOD mice given either no immunosuppression or combinations immunosuppressive reagents. Graft function was monitored by blood glucose levels, i.p. glucose tolerance tests, and histology. Mechanisms of rejection were investigated by phenotyping host peritoneal cells and measuring graft site cytokine and chemokine levels. Results New immunosuppressive therapies were compared to CTLA4‐Ig plus anti‐CD154 mAb, used here as a control. The most effective was triple treatment with CTLA4‐Ig, anti‐CD154 mAb, and intracapsular CXCL12, and the next most effective was a non‐depleting anti‐CD4 mAb (YTS177.9) plus intracapsular CXCL12. Three additional regimens (CTLA4‐Ig plus YTS177.9, YTS177.9 alone, and anti‐OX40‐Ligand mAb alone) significantly prolonged encapsulated API function. Dual treatment with CTLA4‐Ig plus anti‐CD40 mAb was as effective as CTLA4‐Ig plus anti‐CD154 mAb. Five other monotherapies and three combination therapies did not augment encapsulated API survival. Most peritoneal cytokines and chemokines were either absent or minimal. At necropsy, the capsules were intact, not fibrosed, and clean when function was maintained, but were coated with host cells if rejection had occurred. Conclusions Multiple different immunotherapies which specifically inhibit CD4+ T cells, modulate T‐cell trafficking, or interfere with antigen presentation can substitute for anti‐CD154 mAb to prolong encapsulated islet xenograft function in diabetic NOD mice.