Multiple clinically relevant immunotherapies prolong the function of microencapsulated porcine islet xenografts in diabetic NOD mice without the use of anti-CD154 mAb.

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.

Dual factor delivery of CXCL12 and Exendin-4 for improved survival and function of encapsulated beta cells under hypoxic conditions.

A bioartifical pancreas (BAP) remains a promising approach for treating insulin-dependent diabetes. Several obstacles to the clinical implementation of a BAP remain, including hypoxia following implantation. Within native pancreatic islets, CXCL12 and glucagon-like peptide-1 (GLP-1) act in a paracrine fashion to promote the survival, function, and proliferation of ß-cells. This work sought to investigate if the presentation of CXCL12 and delivery of a GLP-1 receptor analog, Exendin-4 (Ex-4), alone and in combination, conferred pro-survival and insulinotropic effects on an encapsulated ß-cell line, ßTC-tet, cultured under hypoxic conditions of 7.6 mmHg O2 . Our findings indicate that presentation of CXCL12 in the encapsulation matrix completely abrogated apoptosis under hypoxic conditions. Delivery of Ex-4 increased insulin secretion rate under both normoxic and hypoxic conditions, and additionally reduced apoptosis under hypoxic conditions. Furthermore, presentation of CXCL12 combined with Ex-4 delivery significantly increased insulin secretion rate under hypoxic conditions compared to delivery of Ex-4 alone. These findings demonstrate that the presentation of CXCL12 combined with the delivery of Ex-4 may constitute a promising strategy for supporting ß-cell function and survival following transplantation.