CXCL12-delivery by double microcapsules and dual costimulatory blockade synergistically prolong the survival of porcine islet xenografts in diabetic NOD mice

Abstract

Event Abstract Back to Event CXCL12-delivery by double microcapsules and dual costimulatory blockade synergistically prolong the survival of porcine islet xenografts in diabetic NOD mice Susan Safley1, Graham F. Barber1, Stephanie M. Duncanson2, Robert W. Holdcraft3, Lawrence S. Gazda3, Mark C. Poznansky4, Athanassios Sambanis2 and Collin J. Weber1 1 Emory University, Surgery, United States 2 Georgia Institute of Technology, School of Chemical and Biomolecular Engineering, United States 3 The Rogosin Institute, Xenia Division, United States 4 Massachusetts General Hospital, Vaccine and Immunotherapy Center, United States Introduction: Our goal is to improve islet transplantation for patients with Type I diabetes mellitus. Because human donor islets are in short supply, we are studying the efficacy of microencapsulated adult porcine islets (APIs) transplanted intraperitoneally in diabetic NOD mice. We have developed a biocompatible and durable double alginate microcapsule that excludes host IgG and that prevents islets from protruding through the capsule wall. The objective of this study was to test the effectiveness of our double microcapsule for therapeutic delivery of CXCL12 (SDF-1), a chemokine that provides pro-survival signals to islets and also recruits regulatory T cells while repelling effector T cells[1],[2]. In NOD mice, we have evaluated delivery of CXCL12 via our double microcapsule, alone and in combination with: (1) belatacept (CTLA4-Ig)[3], (2) anti-CD154 mAb, and (3) the combination of CTLA4-Ig plus anti-CD154 mAb. Since CD4+ T cells are the primary effectors in the rejection of islet xenografts[4],[5], we also have assessed the efficacy of a non-depleting anti-CD4 mAb (YTS177.9) that spares regulatory T cells[6], alone and in combination with CXCL12. Materials and Methods: APIs were isolated from adult pig pancreata, prepared as described[7], encapsulated in our double capsules as described[8] and transplanted i.p. in diabetic NOD mice (9,000 IEQ/mouse) given no immunosuppresssion, CTLA4-Ig (Orencia, Bristol-Myers Squibb, New York, NY,400 mg i.p. on day 0, QOD for 21 days, then once weekly), anti-CD154 mAb (BioXCell, West Lebanon, NH, 500 mg i.p. days 0, 2, 4, and 6 then once weekly), or non-depleting anti-CD4 mAb (YTS177.9, BioXCell, 250 mg i.p. days -3, -2, -1, then weekly). CXCL12 (Preprotech, Rocky Hill, NJ) was incorporated into the matrix of our double capsule (1μg/mL alginate). Graft function was monitored by measuring random blood glucose (BG) and histologic analyses of graft biopsies. Results and Discussion: APIs in double capsules functioned for 45 ± 33 days in diabetic NOD mice given no immunosuppression (n=24). Intracapsular CXCL12 alone prolonged graft survival for 90 ± 123 days (n=10), similar to the effects of CTLA4-Ig alone (77 ± 66, n=9), and not significantly longer than survival in untreated mice. The combination of CXCL12 and CTLA4-Ig (n=5) has augmented graft survival for 105 ± 52 days to date (n=5) with two animals still living with functioning grafts on day 146 post-transplant. Anti-CD4 mAb (YTS177.9) alone yielded significantly prolonged graft survival compared to untreated controls (217 ± 56, p<0.001, n=6). The addition of CTLA4-Ig to YTS177.9 did not further improve graft function (168 ± 44, n=6). Dual costimulatory blockade (CTLA4-Ig plus anti-CD154 mAb) (n=25) significantly prolonged graft function to 144 ± 74 days (p<0.001, vs no treatment). The most durable and consistent results to date were found when NOD mice were treated with CTLA4-Ig and anti-CD154 mAb plus CXCL12 (n=5), which resulted in encapsulated API xenograft function for 438 ± 133 days. Conclusions: Single therapy with a non-depleting anti-CD4 mAb (YTS177.9) significantly augmented API xenograft function in diabetic NOD mice for up to 301 days, suggesting that our double capsule may allow reduced immuno-suppression. Notably, CXCL12 plus CTLA4-Ig and anti-CD154 mAb has resulted in robust graft function for >300 days in all mice tested, up to 645 days in one animal. Both CXCL12 and YTS177.9 enhance regulatory T cell responses, and therefore we hypothesize that recruitment of these immunoregulatory T cells may be an important mechanism for the survival and function of encapsulated porcine islet xenografts. Our data suggest that combining CXCL12 or YTS177.9 with CTLA4-Ig and anti-CD154 mAb may be an effective means of augmenting the survival and function of encapsulated APIs. Funding from the Juvenile Diabetes Research Foundation