PD-L1 Deficiency within Islets Reduces Allograft Survival in Mice

Ex vivo anchored PD‐L1 functionally prevent in vivo renal allograft rejection

Organ transplantation is the optimal treatment for patients with end‐stage diseases. T cell activation is a major contributing factor toward the trigger of rejection. Induction therapy with T cell depleting agent is a common option but increases the risk of severe systemic infections. The ideal therapy should precisely target the allograft. Here, we developed a membrane‐anchored‐protein PD‐L1 (map‐PD‐L1), which effectively anchored onto the surface of rat glomerular endothelial cells (rgEC). The expression of PD‐L1 increased directly with map‐PD‐L1 concentration and incubation time. Moreover, map‐PD‐L1 was even stably anchored to rgEC at low temperature. Map‐PD‐L1 could bind to PD‐1 and significantly promote T cell apoptosis and inhibited T cell activation. Using kidney transplantation models, we found that ex vivo perfusion of donor kidneys with map‐PD‐L1 significantly protected grafts against acute injury without using any immunosuppressant. We found map‐PD‐L1 could reduce T cell graft infiltration and increase intragraft Treg infiltration, suggesting a long‐term effect in allograft protection. More importantly, modifying donor organs in vitro was not only safe, but also significantly reduced the side effects of systemic application. Our results suggested that ex vivo perfusion of donor organ with map‐PD‐L1 might provide a viable clinical option for organ‐targeted induction therapy in organ transplantation.

Xenogeneic Sertoli cells modulate immune response in an evolutionary distant mouse model through the production of interleukin-10 and PD-1 ligands expression

BACKGROUND

Immunomodulatory mechanisms of Sertoli cells (SCs) during phylogeny have not been described previously. This study attempted to reveal mechanisms of SC immune modulation in an evolutionary distant host.

METHODS

The interaction of the SC cell line derived from Xenopus tropicalis (XtSC) with murine immune cells was studied in vivo and in vitro. The changes in the cytokine production, the intracellular and surface molecules expression on murine immune cells were evaluated after co-culturing with XtSCs. Migration of XtSCs in mouse recipients after intravenous application and subsequent changes in spleen and the testicular immune environment were determined by flow cytometry.

RESULTS

The in vitro co-culture model was established, allowing the study of XtSCs interaction with murine immune cells. Intracellular staining of interleukin (IL-)10 revealed a significant increase in its expression in macrophages and B cells co-cultured with XtSCs, compared to both unstimulated cells and xenogeneic control. On the contrary, a significant decrease in Th lymphocytes expressing interferon-gamma was observed. The expression of both PD-1 ligands (PD-L1 and PD-L2) was upregulated on the macrophage surfaces after co-culture with XtSCs, but not with the controls. XtSCs migrated specifically to testes when administered intravenously and modulated systemic and local testicular microenvironment; this was detected by the expression of molecules associated with suppressive phenotype by CD45⁺ cells in both spleen and testes.

CONCLUSION

We have demonstrated for the first time that SCs can migrate and modulate immune response in a phylogenetically distant host. It was further observed that SCs induce expression of molecules associated with immunosuppression, such as IL-10 and PD-1 ligands.

Current Topics of Relevance to the Xenotransplantation of Free Pig Islets

Pig islet xenotransplantation is a potential treatment for patients with type 1 diabetes. Current efforts are focused on identifying the optimal pig islet source and overcoming the immunological barrier. The optimal age of the pig donors remains controversial since both adult and neonatal pig islets have advantages. Isolation of adult islets using GMP grade collagenase has significantly improved the quantity and quality of adult islets, but neonatal islets can be isolated at a much lower cost. Certain culture media and coculture with mesenchymal stromal cells facilitate neonatal islet maturation and function. Genetic modification in pigs affords a promising strategy to prevent rejection. Deletion of expression of the three known carbohydrate xenoantigens (Gal, Neu5Gc, Sda) will certainly be beneficial in pig organ transplantation in humans, but this is not yet proven in islet transplantation, though the challenge of the '4th xenoantigen' may prove problematic in nonhuman primate models. Blockade of the CD40/CD154 costimulation pathway leads to long-term islet graft survival (of up to 965 days). Anti-CD40mAbs have already been applied in phase II clinical trials of islet allotransplantation. Fc region-modified anti-CD154mAbs successfully prevent the thrombotic complications reported previously. In this review, we discuss (I) the optimal age of the islet-source pig, (ii) progress in genetic modification of pigs, (iii) the immunosuppressive regimen for pig islet xenotransplantation, and (iv) the reduction in the instant blood-mediated inflammatory reaction.

The Fetal-Maternal Immune Interface in Uterus Transplantation

Uterus transplants (UTxs) have been performed worldwide. Overall frequencies have been low, but globally initiated UTx programs are expected to increase clinical implementation. The uterus constitutes a unique immunological environment with specific features of tissue renewal and a receptive endometrium. Decidual immune cells facilitate embryo implantation and placenta development. Although UTx adds to the complexity of immunity during pregnancy and transplantation, the procedure provides a unique clinical and experimental model. We posit that understanding the distinct immunological properties at the interface of the transplanted uterus, the fetus and maternal circulation might provide valuable novel insights while improving outcomes for UTx. Here, we discuss immunological challenges and opportunities of UTx affecting mother, pregnancy and healthy livebirths.

Immune Protection of Stem Cell-Derived Islet Cell Therapy for Treating Diabetes

Insulin injection is currently the main therapy for type 1 diabetes (T1D) or late stage of severe type 2 diabetes (T2D). Human pancreatic islet transplantation confers a significant improvement in glycemic control and prevents life-threatening severe hypoglycemia in T1D patients. However, the shortage of cadaveric human islets limits their therapeutic potential. In addition, chronic immunosuppression, which is required to avoid rejection of transplanted islets, is associated with severe complications, such as an increased risk of malignancies and infections. Thus, there is a significant need for novel approaches to the large-scale generation of functional human islets protected from autoimmune rejection in order to ensure durable graft acceptance without immunosuppression. An important step in addressing this need is to strengthen our understanding of transplant immune tolerance mechanisms for both graft rejection and autoimmune rejection. Engineering of functional human pancreatic islets that can avoid attacks from host immune cells would provide an alternative safe resource for transplantation therapy. Human pluripotent stem cells (hPSCs) offer a potentially limitless supply of cells because of their self-renewal ability and pluripotency. Therefore, studying immune tolerance induction in hPSC-derived human pancreatic islets will directly contribute toward the goal of generating a functional cure for insulin-dependent diabetes. In this review, we will discuss the current progress in the immune protection of stem cell-derived islet cell therapy for treating diabetes.

Immune-evasive human islet-like organoids ameliorate diabetes

While stem cell-derived islets hold promise as a therapy for insulin-dependent diabetes, challenges remain in achieving this goal^1–6. Here we generate human islet-like organoids (HILOs) from induced pluripotent stem cells (iPSCs) and show that non-canonical WNT4 signaling drives the metabolic maturation necessary for robust ex vivo glucose-stimulated insulin secretion. These functionally mature HILOs contain endocrine-like cell types that, upon transplantation, rapidly re-establish glucose homeostasis in diabetic NOD-SCID mice. Overexpression of the immune checkpoint protein PD-L1 protected HILO xenografts such that they were able to restore glucose homeostasis in immune-competent diabetic mice for 50 days. Furthermore, ex vivo interferon gamma stimulation induced endogenous PD-L1 expression and restricted T cell activation and graft rejection. The generation of glucose-responsive islet-like organoids able to avoid immune detection provides a promising alternative to cadaveric and device-dependent therapies in the treatment of diabetes.

New onset diabetes with ketoacidosis following nivolumab immunotherapy: A case report and review of literature

Introduction

Immune-checkpoint inhibitors have become an increasingly popular form of systemic therapy for cancer treatment. Their use has proven to be so effective that certain regimens have gained approval as first-line therapy for various solid tumor types. The most common and well-studied forms of immunotherapy include agents that target cytotoxic T-lymphocyte antigen-4, programmed death-1, and programmed death ligand-1. These therapies act by blocking signaling between immune cells and cancer cells which subsequently augment T cell-mediated destruction of tumor cells.

Case report

Here, we report a case of a 77-year-old black male with no history of or risk factors for diabetes mellitus who presented with acute onset of diabetic ketoacidosis after beginning immunotherapy with nivolumab for metastatic high-grade neuroendocrine tumor of the lung. He was admitted and treated for diabetic ketoacidosis but required prolonged use of an insulin infusion with frequent need of intravenous dextrose due to labile blood sugars. The patient was eventually discharged and discontinued further immunotherapy with nivolumab.

Discussion

Due to the unique mechanisms by which immune-checkpoint inhibitors cause immune-mediated destruction of tumor cells, clinicians may be challenged with their associated autoimmune complications referred to as immune-related adverse events. In particular, the incidence of endocrine dysfunction following immune-checkpoint inhibitor therapy is approximately 12%, with the development of insulin-dependent diabetes mellitus being a rare complication. Increasing awareness of immune-related adverse events is essential for the early recognition and effective management of patients who present with life-threatening complications related to immune-checkpoint inhibitor therapy.

Early T cell infiltration is modulated by programed cell death-1 protein and its ligand (PD-1/PD-L1) interactions in murine kidney transplants

Allogeneic transplants elicit dynamic T cell responses that are modulated by positive and negative co-stimulatory receptors. Understanding mechanisms that intrinsically modulate the immune responses to transplants is vital to develop rational treatment for rejection. Here, we have investigated the impact of programed cell death-1 (PD-1) protein, a negative co-stimulatory receptor, on the rejection of MHC incompatible kidney transplants in mice. T cells were found to rapidly infiltrate the kidneys of A/J mice transplanted to C57BL/6 mice, which peaked at six days and decline by day 14. The T cells primarily encircled tubules with limited infiltration of the tubular epithelium. Lipocalin 2 (LCN2), a marker of tubular injury, also peaked in the urine at day six and then declined. Notably, flow cytometry demonstrated that most of the T cells expressed PD-1 (over 90% of CD8 and about 75% of CD4 cells) at day six. Administration of blocking antibody to PD-L1, the ligand for PD-1, before day six increased T cell infiltrates and urinary LCN2, causing terminal acute rejection. In contrast, blocking PD-1/PD-L1 interactions after day six caused only a transient increase in urinary LCN2. Depleting CD4 and CD8 T cells virtually eliminated LCN2 in the urine in support of T cells injuring tubules. Thus, our data indicate that PD-1/PD-L1 interactions are not just related to chronic antigenic stimulation of T cells but are critical for the regulation of acute T cell responses to renal transplants.

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

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-β, IL-10, and decreased levels of proinflammatory T-bet, IL-1β, TNF-α, and IFN-γ 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.

Costimulation Blockade in Transplantation

T cells play a pivotal role in orchestrating immune responses directed against a foreign (allogeneic) graft. For T cells to become fully activated, the T-cell receptor (TCR) must interact with the major histocompatibility complex (MHC) plus peptide complex on antigen-presenting cells (APCs), followed by a second "positive" costimulatory signal. In the absence of this second signal, T cells become anergic or undergo deletion. By blocking positive costimulatory signaling, T-cell allo-responses can be aborted, thus preventing graft rejection and promoting long-term allograft survival and possibly tolerance (Alegre ML, Najafian N, Curr Mol Med 6:843-857, 2006; Li XC, Rothstein DM, Sayegh MH, Immunol Rev 229:271-293, 2009). In addition, costimulatory molecules can provide negative "coinhibitory" signals that inhibit T-cell activation and terminate immune responses; strategies to promote these pathways can also lead to graft tolerance (Boenisch O, Sayegh MH, Najafian N, Curr Opin Organ Transplant 13:373-378, 2008). However, T-cell costimulation involves an incredibly complex array of interactions that may act simultaneously or at different times in the immune response and whose relative importance varies depending on the different T-cell subsets and activation status. In transplantation, the presence of foreign alloantigen incites not only destructive T effector cells but also protective regulatory T cells, the balance of which ultimately determines the fate of the allograft (Lechler RI, Garden OA, Turka LA, Nat Rev Immunol 3:147-158, 2003). Since the processes of alloantigen-specific rejection and regulation both require activation of T cells, costimulatory interactions may have opposing or synergistic roles depending on the cell being targeted. Such complexities present both challenges and opportunities in targeting T-cell costimulatory pathways for therapeutic purposes. In this chapter, we summarize our current knowledge of the various costimulatory pathways in transplantation and review the current state and challenges of harnessing these pathways to promote graft tolerance (summarized in Table 10.1).

An update on potentials and promises of T cell co-signaling molecules in transplantation

The promising outcomes of immune-checkpoint based immunotherapies in cancer have provided a proportional perspective ahead of exploiting similar approaches in allotransplantation. Belatacept (CTLA-4-Ig) is an example of costimulation blockers successfully exploited in renal transplantation. Due to the wide range of regulatory molecules characterized in the past decades, some of these molecules might be candidates as immunomodulators in the case of tolerance induction in transplantation. Although there are numerous attempts on the apprehension of the effects of co-signaling molecules on immune response, the necessity for a better understanding is evident. By increasing the knowledge on the biology of co-signaling pathways, some pitfalls are recognized and improved approaches are proposed. The blockage of CD80/CD28 axis is an instance of evolution toward more efficacy. It is now evident that anti-CD28 antibodies are more effective than CD80 blockers in animal models of transplantation. Other co-signaling axes such as PD-1/PD-L1, CD40/CD154, 2B4/CD48, and others discussed in the present review are examples of critical immunomodulatory molecules in allogeneic transplantation. We review here the outcomes of recent experiences with co-signaling molecules in preclinical studies of solid organ transplantation.

Human regulatory macrophages are potent in suppression of the xenoimmune response via indoleamine-2,3-dioxygenase-involved mechanism(s)

BACKGROUND

For xenotransplantation to truly succeed, we must develop immunomodulatory strategies to suppress the xenoimmune response but by minimizing immunosuppression over the long term. Regulatory macrophages (Mreg) have been shown to suppress polyclonal T-cell proliferation in vitro and prolong allograft survival in vivo. However, the question of whether they are capable of suppressing xenoimmune responses remains unknown. This study assessed the potential of human Mreg to be used as an effective immunomodulatory method in xenotransplantation.

METHODS

CD14+ monocytes selected from human peripheral blood mononuclear cells (PBMC) were cultured with macrophage colony-stimulating factor (M-CSF) for 7 days with IFN-γ added at day 6 for Mreg induction. Mreg phenotyping was performed by flow cytometric analysis, and the in vitro suppressive function was assessed by mixed lymphocyte reaction (MLR) using irradiated pig PBMC as the xenogeneic stimulator cells, human PBMC as responder cells, and autologous Mreg as suppressor cells. To assess mRNA expression of Mreg functional molecules indoleamine-2,3-dioxygenase (IDO), IL-10, inducible nitric oxide synthase (iNOS) and TGF-β were measured by real-time PCR. Supernatants were collected from the MLR cultures for IDO activity assay by high-performance liquid chromatography (HPLC). The effects of the IDO inhibitor 1-D/L-methyl-tryptophan (1-MT), iNOS inhibitor N^G -monomethyl-l-arginine (L-NMMA), and anti-IFN-γ or anti-TGF-β monoclonal antibody (mAb) treatment on Mreg suppressive capacity were tested from the supernatants of the MLR assays.

RESULTS

We demonstrated that induced Mreg with a phenotype of CD14^low CD16^-/low CD80^low CD83^-/low CD86^+/hi HLA-DR^+/hi were capable of suppressing proliferating human PBMC, CD4+, and CD8+ T cells, even at a higher responder:Mreg ratio of 32:1 in a pig-human xenogeneic MLR. The strong suppressive potency of Mreg was further correlated with their upregulated IDO expression and activity. The IDO upregulation of Mreg was associated with an increased production of IFN-γ, an IDO stimulator, by xenoreactive responder cells in the xenogeneic MLR. While no effect on Mreg suppressive potency was detected by addition of the iNOS inhibitor L-NMMA or anti-TGF-β mAb into the MLR assays, inhibition of IDO activity by neutralizing IFN-γ or by IDO inhibitor 1-MT substantially impaired the capacity of Mreg to suppress the xenogeneic response, indicating the importance of upregulated IDO activity in Mreg-mediated suppression of the xenogeneic response in vitro.

CONCLUSION

This study demonstrates that human Mreg are capable of suppressing the xenoimmune response in vitro via IDO-involved mechanism(s), suggesting their potential role as an effective immunomodulatory tool in xenotransplantation.