Targeting Metabolism as a Platform for Inducing Allograft Tolerance in the Absence of Long-Term Immunosuppression

Immunometabolic Approaches Mitigating Foreign Body Response and Transcriptome Characterization of the Foreign Body Capsule

Directing immunometabolism presents new opportunities to modulate key cell types associated with the formation of foreign body response (FBR) capsule. Contrasting approaches directing immunometabolism are investigated to mitigate FBR: a broadly suppressive metabolic inhibitor (MI) cocktail comprised of 2-deoxyglucose (2-DG), metformin, and 6-diazo-5-oxo-l-norleucine (DON) with daily systemic dosing regimen, and local weekly injection of the more narrowly focused tryptophan catabolizing IDO-Gal3 fusion protein. Treatments significantly decrease FBR capsule formed around subcutaneously implanted cellulose disks. MI cocktail results in a substantially thinner FBR capsule (40% of control), while weekly local injection of IDO-Gal3 also results in a thinner FBR capsule (69% of control). RNA-sequencing capsule transcripts reveal MI cocktail promotes quiescence, with decreased antigen processing and presentation, T helper subset differentiation, and cytokine-cytokine receptor pathway. IDO-Gal3 promotes pro-regenerative, alternatively activated M2-like macrophages and T helper 2 cells, with increased expression of type 2 response-associated genes (Il4, Il13, Arg1, Mrc1, Chil3, Gata3). IDO-Gal3 decreases pro-inflammatory innate sensing pathways, and C-type lectin receptor, NOD-like receptor, RIG-I-like receptor, and Toll-like receptor signaling. This work helps define key gene targets and pathways concomitantly regulated in the FBR capsule during immunometabolic modulation compared to control FBR capsule.

Glycolysis Changes in Alloreactive Memory B Cells in Highly Sensitized Kidney Transplant Recipients Undergonig Desensitization Therapy

Despite the growing use of desensitization strategies, hyperimmune patients remain at high risk of antibody-mediated rejection suggesting that, even when donor-specific antibodies (DSA) are effectively depleted, anti-donor specific B cells persist. We included 10 highly sensitized recipients that underwent desensitization with plasmapheresis and B cell depletion prior to kidney transplantation. We quantified changes in DSA (luminex), total B-cell subsets (flow cytometry), anti-donor HLA B cells (fluorospot), and single-cell metabolism in serially collected samples before desensitization, at the time of transplant, and at 6 and 12 months thereafter. Desensitization was associated with a decrease in DSA and total memory B cell and naive B cell percentage, while plasma cells and memory anti-donor HLA circulating B cells persisted up to 12 months after transplant. At 12-month post-transplantation, memory B cells increased their glycolytic capacity, while proliferative KI67+ plasma cells modified their metabolism by increasing fatty acid and amino acid oxidation capacity and decreasing their glucose dependence. Despite effective DSA depletion, anti-donor B cells persist in kidney transplant recipients. Due to the reliance of these cells on glycolysis, glycolysis-targeting therapies might represent a valuable treatment strategy.

Harnessing Immune Cell Metabolism to Modulate Alloresponse in Transplantation

Immune cell metabolism plays a pivotal role in shaping and modulating immune responses. The metabolic state of immune cells influences their development, activation, differentiation, and overall function, impacting both innate and adaptive immunity. While glycolysis is crucial for activation and effector function of CD8 T cells, regulatory T cells mainly use oxidative phosphorylation and fatty acid oxidation, highlighting how different metabolic programs shape immune cells. Modification of cell metabolism may provide new therapeutic approaches to prevent rejection and avoid immunosuppressive toxicities. In particular, the distinct metabolic patterns of effector and suppressive cell subsets offer promising opportunities to target metabolic pathways that influence immune responses and graft outcomes. Herein, we review the main metabolic pathways used by immune cells, the techniques available to assay immune metabolism, and evidence supporting the possibility of shifting the immune response towards a tolerogenic profile by modifying energetic metabolism.

Metabolic reprogramming of myeloid-derived suppressor cells in the context of organ transplantation

Myeloid-derived suppressor cells (MDSCs) are naturally occurring leukocytes that develop from immature myeloid cells under inflammatory conditions that were discovered initially in the context of tumor immunity. Because of their robust immune inhibitory activities, there has been growing interest in MDSC-based cellular therapies for transplant tolerance induction. Indeed, various pre-clinical studies have introduced in vivo expansion or adoptive transfer of MDSC as a promising therapeutic strategy leading to a profound extension of allograft survival due to suppression of alloreactive T cells. However, several limitations of cellular therapies using MDSCs remain to be addressed, including their heterogeneous nature and limited expansion capacity. Metabolic reprogramming plays a crucial role for differentiation, proliferation and effector function of immune cells. Notably, recent reports have focused on a distinct metabolic phenotype underlying the differentiation of MDSCs in an inflammatory microenvironment representing a regulatory target. A better understanding of the metabolic reprogramming of MDSCs may thus provide novel insights for MDSC-based treatment approaches in transplantation. In this review, we will summarize recent, interdisciplinary findings on MDSCs metabolic reprogramming, dissect the underlying molecular mechanisms and discuss the relevance for potential treatment approaches in solid-organ transplantation.

Inhibition of hexokinase 2 with 3-BrPA promotes MDSCs differentiation and immunosuppressive function

The adoptive transfer of ex vivo generated myeloid-derived suppressor cells (MDSCs) may be a promising therapeutic strategy for preventing allograft rejection after solid organ transplantation. Currently, the precise role of immune-metabolic pathways in the differentiation and function of MDSCs is not fully understood. Hexokinase 2 (HK2) is an isoform of hexokinase and is a key enzyme involved in the increased aerobic glycolysis of different immune cells during their activation and function. Here, we demonstrate that the addition of HK2 inhibitor 3-Bromopyruvic acid (3-BrPA) into traditional MDSCs induction system in vitro significantly promoted MDSCs production and enhanced their immunosuppressive function. Treatment with 3-BrPA increased the expression of MDSC-related immunosuppressive molecules, such as iNOS, Arg1, and CXCR2. Moreover, the adoptive transfer of 3-BrPA-treated MDSCs significantly prolonged the survival time of mouse heart allografts. This study provides a novel strategy to solve the problems of harvesting enough autologous cells for MDSC production from sick patients, and producing functionally enhanced MDSCs for preventing graft rejection and inducing tolerance.

Targeting inflammation and immune activation to improve CTLA4-Ig-based modulation of transplant rejection

For the last few decades, Calcineurin inhibitors (CNI)-based therapy has been the pillar of immunosuppression for prevention of organ transplant rejection. However, despite exerting effective control of acute rejection in the first year post-transplant, prolonged CNI use is associated with significant side effects and is not well suited for long term allograft survival. The implementation of Costimulation Blockade (CoB) therapies, based on the interruption of T cell costimulatory signals as strategy to control allo-responses, has proven potential for better management of transplant recipients compared to CNI-based therapies. The use of the biologic cytotoxic T-lymphocyte associated protein 4 (CTLA4)-Ig is the most successful approach to date in this arena. Following evaluation of the BENEFIT trials, Belatacept, a high-affinity version of CTLA4-Ig, has been FDA approved for use in kidney transplant recipients. Despite its benefits, the use of CTLA4-Ig as a monotherapy has proved to be insufficient to induce long-term allograft acceptance in several settings. Multiple studies have demonstrated that events that induce an acute inflammatory response with the consequent release of proinflammatory cytokines, and an abundance of allograft-reactive memory cells in the recipient, can prevent the induction of or break established immunomodulation induced with CoB regimens. This review highlights advances in our understanding of the factors and mechanisms that limit CoB regimens efficacy. We also discuss recent successes in experimentally designing complementary therapies that favor CTLA4-Ig effect, affording a better control of transplant rejection and supporting their clinical applicability.

Sedative and Immunosuppressive Effects of Dexmedetomidine in Transplantation

Dexmedetomidine, an α2-adrenergic receptor agonist, is used as an anti-anxiety medication. It exerts a cholinergic effect, thereby reducing the release of tumor necrosis factor alpha (TNF-α). We hypothesized that the use of dexmedetomidine as a sedative agent in transplantation would also protect allografts. We examined our patients who underwent living donor liver transplantation. Subsequently, we generated a series of mouse models to investigate the effect of dexmedetomidine on sedation-based tolerance post transplantation. A total of 49 liver recipients were enrolled in this study, of which 23 (47%) were administered dexmedetomidine through 24 h infusion on postoperative day 1. A trend toward the improvement of hepatocyte injury along with better liver function was observed in the dexmedetomidine-treated group during the first postoperative week. In animal models, dexmedetomidine inhibited the proliferation of CD4+ and CD8+ T cells and TNF-α production in a dose-dependent manner. We used dexmedetomidine to treat skin-transplanted mice and observed a significantly prolonged graft survival in mice that were administered a higher dose of dexmedetomidine. Our results revealed that dexmedetomidine exerts a dual effect of sedation and immunosuppression. This light-sedation approach will not only make patients calmer in the intensive care unit but also protect allografts from injury.