5 research outputs found
Bioabsorption of Subcutaneous Nanofibrous Scaffolds Influences the Engraftment and Function of Neonatal Porcine Islets
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 p p p 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
Molecular Retention Limitations for Prevascularized Subcutaneous Sites for Islet Transplantation
Beta cell replacement therapies utilizing the subcutaneous
space
have inherent advantages to other sites: the potential for increased
accessibility, noninvasive monitoring, and graft extraction. Site
prevascularization has been developed to enhance islet survivability
in the subcutaneous zone while minimizing potential foreign body immune
responses. Molecular communication between the host and prevascularized
implant site remains ill-defined. Poly(ethylene oxide)s (PEOs) of
various hydrated radii (i.e., ∼11–62 Å) were injected
into prevascularized subcutaneous sites in C57BL/6 mice, and the clearance
and organ biodistribution were characterized. Prevascularization formed
a barrier that confined the molecules compared with the unmodified
site. Molecular clearance from the prevascularized site was inversely
proportional to the molecular weight. The upper limit in molecular
size for entering the vasculature to be cleared was determined to
be 35 kDa MW PEO. These findings provide insight into the impact of
vascularization on molecular retention at the injection site and the
effect of molecular size on the mobility of hydrophilic molecules
from the prevascularized site to the host. This information is necessary
for optimizing the transplantation site for increasing the beta cell
graft survival
Developing Hybrid Polymer Scaffolds Using Peptide Modified Biopolymers for Cell Implantation
Polymeric
scaffolds containing biomimics offer exciting therapies
with broad potential impact for cellular therapies and thereby potentially
improve success rates. Here we report the designing and fabrication
of a hybrid scaffold that can prevent a foreign body reaction and
maintain cell viability. A biodegradable acrylic based cross-linkable
polycaprolactone based polymer was developed and using a multihead
electrospinning station to fabricate hybrid scaffolds. This consists
of cell growth factor mimics and factors to prevent a foreign body
reaction. Transplantation studies were performed subcutaneously and
in epididymal fat pad of immuno-competent Balb/c mice and immuno-suppressed
B6 Rag1 mice and we demonstrated extensive neo-vascularization and
maintenance of islet cell viability in subcutaneously implanted neonatal
porcine islet cells for up to 20 weeks of post-transplant. This novel
approach for cell transplantation can improve the revascularization
and allow the integration of bioactive molecules such as cell adhesion
molecules, growth factors, etc
Nanothin Conformal Coating with Poly(N-vinylpyrrolidone) and Tannic Acid (PVPON/TA) Preserves Murine and Human Pancreatic Islets Function
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-Rag1tm1Mom/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
Long-Term Survival and Induction of Operational Tolerance to Murine Islet Allografts by Co-Transplanting Cyclosporine A Microparticles and CTLA4-Ig
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 + and CD8+ cells, p + cells, p IL-6, IL-10, INF-γ, and TNF-α; p CCL2, CCL5, CCL22, and CXCL10; p + 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