Localized Immunomodulation with PD-L1 Results in Sustained Survival and Function of Allogeneic Islets without Chronic Immunosuppression

Abstract

Allogeneic islet transplantation is limited by adverse effects of chronic immunosuppression used to control rejection. The programmed cell death 1 pathway as an important immune checkpoint has the potential to obviate the need for chronic immunosuppression. We generated an oligomeric form of programmed cell death 1 ligand chimeric with core streptavidin (SA-PDL1) that inhibited the T effector cell response to alloantigens and converted T conventional cells into CD4 + Foxp3 + T regulatory cells. The SA-PDL1 protein was effectively displayed on the surface of biotinylated mouse islets without a negative impact islet viability and insulin secretion. Transplantation of SA-PDL1-engineered islet grafts with a short course of rapamycin regimen resulted in sustained graft survival and function in >90% of allogeneic recipients over a 100-d observation period. Long-term survival was associated with increased levels of intragraft transcripts for innate and adaptive immune regulatory factors, including IDO-1, arginase-1, Foxp3, TGF-b, IL-10, and decreased levels of proinflammatory T-bet, IL-1b, TNF-a, and IFN-g as assessed on day 3 posttransplantation. T cells of long-term graft recipients generated a proliferative response to donor Ags at a similar magnitude to T cells of naive animals, suggestive of the localized nature of tolerance. Immunohistochemical analyses showed intense peri-islet infiltration of T regulatory cells in long-term grafts and systemic depletion of this cell population resulted in prompt rejection. The transient display of SA-PDL1 protein on the surface of islets serves as a practical means of localized immunomodulation that accomplishes sustained graft survival in the absence of chronic immunosuppression with potential clinical implications.

Immunotherapy via PD-L1–presenting biomaterials leads to long-term islet graft survival

“…SA has been used for therapeutic protein delivery both in preclinical ( 31 ) and clinical studies ( 32 ) with no significant adverse effects. Furthermore, the SA-PD-L1 synthetic gene encodes for the extracellular domain of mouse PD-L1 ( 16 ), mitigating concerns of immunogenicity due to interspecies differences. Nevertheless, the delivery of bacterial proteins can lead to antigenicity and subsequently reduced bioavailability.…”

“…Within the context of T1D, the PD-1/PD-L1 axis is pivotal to autoimmunity, as seen by abnormalities in PD-L1 presentation in human patients with T1D ( 14 ) and disease halting in transgenic models expressing PD-L1 ( 15 ). Strategies aimed at using PD-L1 to control disease progression and diabetes reversal have ranged from genetically modifying islets to express PD-L1 ( 16 ) to improve graft survival in allogeneic transplantation models ( 17 ) to the delivery of antigen-presenting cells genetically or chemically modified to overexpress PD-L1 ( 18 ). However, these approaches face barriers to clinical translation or rely on clinically relevant pharmacological interventions that lack evidence of longevity, limiting the long-term effect of the therapeutic strategy.…”

Role of the PD-1/PD-L1 Dyad in the Maintenance of Pancreatic Immune Tolerance for Prevention of Type 1 Diabetes

“…A dimeric form of PD-L1 and Ig fusion protein (PD-L1.Ig) in combination with anti-CD154 blockade prevented cardiac, corneal and pancreatic islet allograft rejection, providing direct evidence for the potential of this pathway to induce allograft tolerance (109)(110)(111). Recently, a recombinant form of PD-L1 chimeric with core streptavidin (SA) (SA-PD-L1) engineered islets approach was evaluated in a preclinical model of allogeneic islet transplantation (112). SA-PDL1-engineered islets survived indefinitely in allogeneic hosts under a short course of rapamycin regimen, demonstrating the significant potential of PD-1 pathway for modulating alloreactive responses to overcome graft rejection.…”

Immunosuppressive PLGA TGF-β1 Microparticles Induce Polyclonal and Antigen-Specific Regulatory T Cells for Local Immunomodulation of Allogeneic Islet Transplants

“…Splenocytes of all allogeneic islet recipients were collected and used in MLR assays to characterize systemic immunotolerance, as previously reported (45). Briefly, splenocytes of recipient mice were labeled with CellTrace Violet dye and co-cultured with mitomycin c treated splenocytes from a naïve C57BL/6 mouse (syngeneic), Balb/c mouse (allogeneic), or C3H mouse (thirdparty stimulators) at a 1:1 ratio.…”