Local, Controlled Release In Vivo of Vascular Endothelial Growth Factor Within a Subcutaneous Scaffolded Islet Implant Reduces Early Islet Necrosis and Improves Performance of the Graft

Islet transplantation remains the only alternative to daily insulin therapy for control of type 1 diabetes (T1D) in humans. To avoid the drawbacks of intrahepatic islet transplantation, we are developing a scaffolded islet implant to transplant islets into nonhepatic sites. The implant test bed, sized for mice, consists of a limited (2-mm) thickness, large-pore polymeric sponge scaffold perforated with peripheral cavities that contain islets suspended in a collagen hydrogel. A central cavity in the scaffold holds a 2-mm diameter alginate sphere for controlled release of the angiogenic cytokine vascular endothelial growth factor ( VEGF). Host microvessels readily penetrate the scaffold and collagen gel to vascularize the islets. Here, we evaluate the performance of the implant in a subcutaneous (SC) graft site. Implants incorporating 500 syngeneic islets reversed streptozotocin-induced diabetes in mice approximately 30 d after SC placement. Controlled release of a modest quantity (20 ng) of VEGF within the implant significantly reduced the time to normoglycemia compared to control implants lacking VEGF. Investigation of underlying causes for this effect revealed that inclusion of 20 ng of VEGF in the implants significantly reduced central necrosis of islets 24 h after grafting and increased implant vascularization (measured 12 d after grafting). Collectively, our results demonstrate (1) that the scaffolded islet implant design can reverse diabetes in SC sites in the absence of prevascularization of the graft site and (2) that relatively low quantities of VEGF, delivered by controlled release within the implant, can be a useful approach to limit islet stress after grafting.

Inhibition of hyaluronan synthesis restores immune tolerance during autoimmune insulitis

We recently reported that abundant deposits of the extracellular matrix polysaccharide hyaluronan (HA) are characteristic of autoimmune insulitis in patients with type 1 diabetes (T1D), but the relevance of these deposits to disease was unclear. Here, we have demonstrated that HA is critical for the pathogenesis of autoimmune diabetes. Using the DO11.10xRIPmOVA mouse model of T1D, we determined that HA deposits are temporally and anatomically associated with the development of insulitis. Moreover, treatment with an inhibitor of HA synthesis, 4-methylumbelliferone (4-MU), halted progression to diabetes even after the onset of insulitis. Similar effects were seen in the NOD mouse model, and in these mice, 1 week of treatment was sufficient to prevent subsequent diabetes. 4-MU reduced HA accumulation, constrained effector T cells to nondestructive insulitis, and increased numbers of intraislet FOXP3+ Tregs. Consistent with the observed effects of 4-MU treatment, Treg differentiation was inhibited by HA and anti-CD44 antibodies and rescued by 4-MU in an ERK1/2-dependent manner. These data may explain how peripheral immune tolerance is impaired in tissues under autoimmune attack, including islets in T1D. We propose that 4-MU, already an approved drug used to treat biliary spasm, could be repurposed to prevent, and possibly treat, T1D in at-risk individuals.

Inhibition of hyaluronan synthesis restores immune tolerance during autoimmune insulitis

We recently reported that abundant deposits of the extracellular matrix polysaccharide hyaluronan (HA) are characteristic of autoimmune insulitis in patients with type 1 diabetes (T1D), but the relevance of these deposits to disease was unclear. Here, we have demonstrated that HA is critical for the pathogenesis of autoimmune diabetes. Using the DO11.10xRIPmOVA mouse model of T1D, we determined that HA deposits are temporally and anatomically associated with the development of insulitis. Moreover, treatment with an inhibitor of HA synthesis, 4-methylumbelliferone (4-MU), halted progression to diabetes even after the onset of insulitis. Similar effects were seen in the NOD mouse model, and in these mice, 1 week of treatment was sufficient to prevent subsequent diabetes. 4-MU reduced HA accumulation, constrained effector T cells to nondestructive insulitis, and increased numbers of intraislet FOXP3+ Tregs. Consistent with the observed effects of 4-MU treatment, Treg differentiation was inhibited by HA and anti-CD44 antibodies and rescued by 4-MU in an ERK1/2-dependent manner. These data may explain how peripheral immune tolerance is impaired in tissues under autoimmune attack, including islets in T1D. We propose that 4-MU, already an approved drug used to treat biliary spasm, could be repurposed to prevent, and possibly treat, T1D in at-risk individuals.

Inhibition of hyaluronan synthesis restores immune tolerance during autoimmune insulitis (THER5P.919)

We recently reported that abundant deposits of the extracellular matrix polysaccharide hyaluronan (HA) characterize autoimmune insulitis in human type 1 diabetes (T1D) but the significance of these deposits was unclear. Here, we demonstrate that HA is critical for the pathogenesis of autoimmune diabetes. Using the DO11.10xRIPmOVA (DORmO) mouse model of T1D, we show that HA deposits are temporally and anatomically associated with the development of insulitis. Moreover, treatment with an inhibitor of HA synthesis, 4‑methylumbelliferone (4-MU), halted progression to diabetes even after the onset of insulitis. 4-MU reduced HA accumulation, constrained effector T-cells to non-destructive insulitis, and increased numbers of intra-islet Foxp3+ regulatory T-cells (Treg). Consistent with this, Treg differentiation was inhibited by HA and anti-CD44 antibodies and rescued by 4-MU in an ERK1/2-dependent manner. These data may explain how peripheral immune tolerance is impaired in tissues under autoimmune attack, including islets in T1D. We propose that 4-MU, already an approved drug used to treat biliary spasm, could be repurposed to prevent, and possibly treat, T1D in at-risk individuals.

Antigen-specific immunomodulation for type 1 diabetes by novel recombinant antibodies directed against diabetes-associates auto-reactive T cell epitope

The trimolecular complex composed of autoreactive T-cell receptor, MHC class II, and an autoantigenic peptide plays a central role in the activation of pathogenic Islet-specific CD4+ T cells in type 1 diabetes (T1D). We isolated and characterized novel antibodies against autoreactive T-cell epitopes associated with T1D. Our antibodies mimic the specificity of the T-cell receptor (TCR), while binding MHC class II/peptide complexes in an autoantigen peptide specific, MHC-restricted manner. The isolated TCR-like antibodies were directed against the minimal T-cell epitope GAD-555-567 in the context of the HLA-DR4-diabetic-associated molecule. A representative high-affinity TCR-like antibody clone (G3H8) enabled the detection of intra- and extra-cellular DR4/GAD-555-567 complexes in antigen presenting cells. I561M single mutation at the central position (P5) of the GAD-555-567 peptide abolished the binding of G3H8 to the DR4/GAD complex, demonstrating its high fine TCR-like specificity. The G3H8 TCR-like antibody significantly inhibited GAD-555-567 specific, DR4 restricted T-cell response in vitro and in vivo in HLA-DR4 transgenic mice. Our findings constitute a proof-of-concept for the utility of TCR-like antibodies as antigen-specific immunomodulation agents for regulating pathogenic T-cells and suggest that TCR-like antibodies targeting autoreactive MHC class II epitopes are valuable research tools that enable studies related to antigen presentation as well as novel therapeutic agents that may be used to modulate autoimmune disorders such as T1D.

Reversal of diabetes in mice with a bioengineered islet implant incorporating a type I collagen hydrogel and sustained release of vascular endothelial growth factor

We have developed a bioengineered implant (BI) to evaluate strategies to promote graft survival and function in models of islet transplantation in mice. The BI, sized for implantation within a fold of intestinal mesentery, consists of a disk-shaped, polyvinyl alcohol sponge infused with a type I collagen hydrogel that contains dispersed donor islets. To promote islet vascularization, the BI incorporates a spherical alginate hydrogel for sustained release of vascular endothelial growth factor (VEGF). BIs that contained 450-500 islets from syngeneic (C57Bl/6) donors and 20 ng of VEGF reversed streptozotocin (STZ)-induced diabetes in 100% of mice (8/8), whereas BIs that contained an equivalent number of islets, but which lacked VEGF, reversed STZ-induced diabetes in only 62.5% of mice (5/8). Between these "+VEGF" and "-VEGF" groups, the time to achieve normoglycemia (8-18 days after implantation) did not differ statistically; however, transitory, postoperative hypoglycemia was markedly reduced in the +VEGF group relative to the -VEGF group. Notably, none of the mice that achieved normoglycemia in these two groups required exogenous insulin therapy once the BIs began to fully regulate levels of blood glucose. Moreover, the transplanted mice responded to glucose challenge in a near-normal manner, as compared to the responses of healthy, nondiabetic (control) mice that had not received STZ. In future studies, the BIs described here will serve as platforms to evaluate the capability of immunomodulatory compounds, delivered locally within the BI, to prevent or reverse diabetes in the setting of autoimmune (type 1) diabetes.

IL-10 induction from implants delivering pancreatic islets and hyaluronan

Local induction of pro-tolerogenic cytokines, such as IL-10, is an appealing strategy to help facilitate transplantation of islets and other tissues. Here, we describe a pair of implantable devices that capitalize on our recent finding that hyaluronan (HA) promotes IL-10 production by activated T cells. The first device is an injectable hydrogel made of crosslinked HA and heparan sulfate loaded with anti-CD3/anti-CD28 antibodies and IL-2. T cells embedded within this hydrogel prior to polymerization go on to produce IL-10 in vivo. The second device is a bioengineered implant consisting of a polyvinyl alcohol sponge scaffold, supportive collagen hydrogel, and alginate spheres mediating sustained release of HA in fluid form. Pancreatic islets that expressed ovalbumin (OVA) antigen were implanted within this device for 14 days into immunodeficient mice that received OVA-specific DO.11.10 T cells and a subsequent immunization with OVA peptide. Splenocytes harvested from these mice produced IL-10 upon re-challenge with OVA or anti-CD3 antibodies. Both of these devices represent model systems that will be used, in future studies, to further evaluate IL-10 induction by HA, with the objective of improving the survival and function of transplanted islets in the setting of autoimmune (type 1) diabetes.

CD44 costimulation promotes FoxP3+ regulatory T cell persistence and function via production of IL-2, IL-10, and TGF-beta

Work by our group and others has demonstrated a role for the extracellular matrix receptor CD44 and its ligand hyaluronan in CD4(+)CD25(+) regulatory T cell (Treg) function. Herein, we explore the mechanistic basis for this observation. Using mouse FoxP3/GFP(+) Treg, we find that CD44 costimulation promotes expression of FoxP3, in part through production of IL-2. This promotion of IL-2 production was resistant to cyclosporin A treatment, suggesting that CD44 costimulation may promote IL-2 production through bypassing FoxP3-mediated suppression of NFAT. CD44 costimulation increased production of IL-10 in a partially IL-2-dependent manner and also promoted cell surface TGF-beta expression. Consistent with these findings, Treg from CD44 knockout mice demonstrated impaired regulatory function ex vivo and depressed production of IL-10 and cell surface TGF-beta. These data reveal a novel role for CD44 cross-linking in the production of regulatory cytokines. Similar salutary effects on FoxP3 expression were observed upon costimulation with hyaluronan, the primary natural ligand for CD44. This effect is dependent upon CD44 cross-linking; while both high-molecular-weight hyaluronan (HA) and plate-bound anti-CD44 Ab promoted FoxP3 expression, neither low-molecular weight HA nor soluble anti-CD44 Ab did so. The implication is that intact high-molecular weight HA can cross-link CD44 only in those settings where it predominates over fragmentary LMW-HA, namely, in uninflamed tissue. We propose that intact but not fragmented extracellular is capable of cross-linking CD44 and thereby maintains immunologic tolerance in uninjured or healing tissue.