Islet transplantation is a promising therapy for Type 1 diabetes; however, inflammatory and immune host responses lead to islet dysfunction and destruction. Cell surface PEGylation has been shown to mitigate inflammation and immune recognition via generation of a steric barrier. Blockade of Lymphocyte Function-associated Antigen 1 (LFA-1) has partially prevented murine allograft rejection. In this study, we sought to evaluate the effect of islet PEGylation, alone and in combination with a short-course immunotherapy, on the survival of fully-MHC mismatched islet allografts and the resulting local microenvironment. Islets were coated with a single layer of mPEG using optimized protocols. Chemically-induced diabetic C57BL/6J mice were transplanted with unmanipulated or PEGylated DBA/2 islets in the renal subcapsular space and received either saline or anti-LFA-1 antibody (KBA, 100ug/day, i.p.) on days 0-6. Graft survival rates were evaluated via blood glucose assessment and histopathological evaluation. Mechanistic studies of cellular infiltrates and gene expression within the graft at early time points (< 15 days) were also performed in separate experiments via immunofluorescence and laser capture microdissection for subsequent qRT-PCR analysis (e.g. IFN-Γ, TNF-Α, TGF-Β, and IL-10). While control islet transplants rejected within 60 days (90%), short-course LFA-1 blockade or PEGylation alone resulted in long-term (>100 days) function of the allograft in 50% (P=0.022) or 60% (P=0.0175) of cases, respectively. Combination of PEGylation with LFA-1 blockade resulted in 78% long-term graft function. Nephrectomy of grafts resulted in prompt return to hyperglycemia. Long-term functioning grafts exhibited robust islets with minimal cellular infiltrate. Retrial of long-term functioning KBA-PEG treated mice with unmanipulated donor matched DBA/2 islets resulted in 3 of 4 transplants going long-term (> 100 days), while mice treated with 3^rd party C3H islets rejected (n=3, < 14 days). Results indicate increasing peripheral tolerance with combination treatment. Evaluation of the local graft site microenvironment early post-implantation is currently being evaluated. This study illustrates the synergistic effect of these two treatments and is the first step towards bioactive modification of graft surfaces for immunomodulation of the local microenvironment.

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