The subcutaneous space is currently being pursued as an alternative transplant site for ß-cell replacement therapies due to its retrievability, minimally invasive procedure and potential for graft imaging. However, implantation of ß-cells into an unmodified subcutaneous niche fails to reverse diabetes due to a lack of adequate blood supply. Herein, poly (ε-caprolactone) (PCL) and poly (lactic-co-glycolic acid) (PLGA) polymers were used to make scaffolds and were functionalized with peptides (RGD (Arginine-glycine-aspartate), VEGF (Vascular endothelial growth factor), laminin) or gelatin to augment engraftment. PCL, PCL + RGD + VEGF (PCL + R + V), PCL + RGD + Laminin (PCL + R + L), PLGA and PLGA + Gelatin (PLGA + G) scaffolds were implanted into the subcutaneous space of immunodeficient Rag mice. After four weeks, neonatal porcine islets (NPIs) were transplanted within the lumen of the scaffolds or under the kidney capsule (KC). Graft function was evaluated by blood glucose, serum porcine insulin, glucose tolerance tests, graft cellular insulin content and histologically. PLGA and PLGA + G scaffold recipients achieved significantly superior euglycemia rates (86% and 100%, respectively) compared to PCL scaffold recipients (0% euglycemic) (* p < 0.05, ** p < 0.01, respectively). PLGA scaffolds exhibited superior glucose tolerance (* p < 0.05) and serum porcine insulin secretion (* p < 0.05) compared to PCL scaffolds. Functionalized PLGA + G scaffold recipients exhibited higher total cellular insulin contents compared to PLGA-only recipients (* p < 0.05). This study demonstrates that the bioabsorption of PLGA-based fibrous scaffolds is a key factor that facilitates the function of NPIs transplanted subcutaneously in diabetic mice.

One strategy to prevent islet rejection is to create a favorable immune-protective local environment at the transplant site. Herein, we utilize localized cyclosporine A (CsA) delivery to islet grafts via poly(lactic-co-glycolic acid) (PLGA) microparticles to attenuate allograft rejection. CsA-eluting PLGA microparticles were prepared using a single emulsion (oil-in-water) solvent evaporation technique. CsA microparticles alone significantly delayed islet allograft rejection compared to islets alone (p < 0.05). Over 50% (6/11) of recipients receiving CsA microparticles and short-term cytotoxic T lymphocyte-associated antigen 4-Ig (CTLA4-Ig) therapy displayed prolonged allograft survival for 214 days, compared to 25% (2/8) receiving CTLA4-Ig alone. CsA microparticles alone and CsA microparticles + CTLA4-Ig islet allografts exhibited reduced T-cell (CD4⁺ and CD8⁺ cells, p < 0.001) and macrophage (CD68⁺ cells, p < 0.001) infiltration compared to islets alone. We observed the reduced mRNA expression of proinflammatory cytokines (IL-6, IL-10, INF-γ, and TNF-α; p < 0.05) and chemokines (CCL2, CCL5, CCL22, and CXCL10; p < 0.05) in CsA microparticles + CTLA4-Ig allografts compared to islets alone. Long-term islet allografts contained insulin⁺ and intra-graft FoxP3⁺ T regulatory cells. The rapid rejection of third-party skin grafts (C3H) in islet allograft recipients suggests that CsA microparticles + CTLA4-Ig therapy induced operational tolerance. This study demonstrates that localized CsA drug delivery plus short-course systemic immunosuppression promotes an immune protective transplant niche for allogeneic islets.

Beta cell replacement therapies can restore glycemic control to select individuals living with type 1 diabetes. However, the obligation of lifelong immunosuppression restricts cell therapies from replacing exogenous insulin administration. Encapsulation strategies can reduce the inherent adaptive immune response; however, few are successfully translated into clinical testing. Herein, we evaluated if the conformal coating of islets with poly(N-vinylpyrrolidone) (PVPON) and tannic acid (TA) (PVPON/TA) could preserve murine and human islet function while conferring islet allograft protection. In vitro function was evaluated using static glucose-stimulated insulin secretion, oxygen consumption rates, and islet membrane integrity. In vivo function was evaluated by transplanting human islets into diabetic immunodeficient B6.129S7-Rag^1tm1Mom/J (Rag^-/-) mice. The immunoprotective capacity of the PVPON/TA-coating was assessed by transplanting BALB/c islets into diabetic C57BL/6 mice. Graft function was evaluated by non-fasting blood glucose measurements and glucose tolerance testing. Both coated and non-coated murine and human islets exhibited indistinguishable in vitro potency. PVPON/TA-coated and control human islets were able to restore euglycemia post-transplant. The PVPON/TA-coating as monotherapy and adjuvant to systemic immunosuppression reduced intragraft inflammation and delayed murine allograft rejection. This study demonstrates that PVPON/TA-coated islets may be clinically relevant as they retain their in vitro and in vivo function while modulating post-transplant immune responses.

Islet transplantation (ITx) has demonstrated that cellular therapies can improve glycemic control in patients with type 1 diabetes. However, cell death in the acute post-transplant period accounts for the loss of up to 70% of the islets, resulting in the requirement of multiple donors per recipient to achieve normoglycemia. Several studies have targeted apoptosis prevention after ITx; herein, our study explores a novel approach by modulating RIPK1-associated stress pathways using Necrostatin-1 (Nec-1) to enhance human islet survival, engraftment, and function post-transplant. Nec-1 treatment for 24 h prior to transplant significantly reduced the expression of RIPK1 ( p = 0.0021) and RIPK3 ( p = 0.0042), resulting in decreased cell death ( p < 0.0001) and necroptosis ( p < 0.0001), measured as TUNEL ⁺ and pMLKL ⁺ cells, respectively, without affecting basal respiration or insulin secretion in human islets. Nec-1 treatment pre-transplant drastically reduced cytokine ( p = 0.0083), NFκB ( p = 0.0179), TGFβ ( p = 0.0015) and TNF family ( p = 0.0010) signaling pathways at the transcriptional level compared to control. These results correlated with increased diabetes reversal ( p = 0.0200) and decreased reversal time ( p = 0.0011) in the Nec-1-treated group compared to untreated controls. The success of Nec-1 treatment in this study showcases that short-term modulation of RIPK1-associated stress pathways promotes early human marginal mass engraftment post-ITx. In the clinical context, improvement of marginal mass islet function could enable single-donor islet infusion and could aid in future ß-cell replacement therapies, making ITx available to a broader population of individuals living with diabetes.

One strategy to prevent islet rejection, is to create a favorable immune-protective local environment at the transplant site. Herein, we utilize localized cyclosporine A (CsA) delivery to islet grafts via poly(lactic-co-glycolic acid) (PLGA) microparticles to attenuate allograft rejection. CsA microparticles alone significantly delayed islet allograft rejection compared to islets alone (p0.05). CsA microparticles + CTLA4-Ig islet allografts exhibited reduced T-cell (CD4 ⁺ and CD8 ⁺ cells) and macrophage (CD68 ⁺ cells) infiltration compared to islets alone. We observed reduced mRNA expression of proinflammatory cytokines (IL-6, IL-10, INF-γ & TNF-α; p<0.05) and chemokines (CCL2, CCL5, CCL22, and CXCL10; p<0.05) in CsA microparticles + CTLA4-Ig allografts compared to islets alone. Long-term islet allografts contained insulin ⁺ and intra-graft FoxP3 ⁺ T regulatory cells. Rapid rejection of third-party skin grafts (C3H) in islet allograft recipients suggested that CsA microparticles + CTLA4-Ig therapy induced donor specific operational tolerance. This study demonstrates that localized CsA drug delivery plus short-course systemic immunosuppression promotes an immune protective transplant niche for allogeneic islets. Article Highlights: Systemic immunosuppression limits patient inclusion for beta cell replacement therapies Localized islet graft immunosuppression may reduce drug toxicity and improve graft survival Cyclosporine eluting microparticles + CTLA4-Ig therapy induced donor specific operational tolerance Graft localized drug delivery can create an immune protective transplant niche