Targeting NFATc1-regulated MTHFD2 one-carbon metabolism to suppress sustained T-cell-mediated inflammation in rheumatoid arthritis

Signal Transduction and Targeted Therapy ARTICLE www.nature.com/sigtrans OPEN Targeting NFATc1-regulated MTHFD2 one-carbon metabolism to suppress sustained T-cell-mediated inflammation in rheumatoid arthritis Theodora Manolakou 1 ✉, Jianyu Shen1, Sanjaykumar Boddul2, Martina Samiotaki3, Michail Angelos Panagias1, George Sentis4, Tarcília Aparecida Silva5, Alexandra Argyriou2, Dionysis Nikolopoulos2, Kumar Sanjiv1, Karine Chemin 2, Fredrik Wermeling2, Martin Henriksson1, Ana Slipicevic1,6, Per-Johan Jakobsson 2, Katerina Chatzidionysiou2 and Thomas Helleday 1,7 ✉ 1234567890();,: T cells are central drivers of inflammation across autoimmune and inflammatory diseases, yet current therapies inadequately target pathogenic T-cell pathways, limiting durable disease control. Here, we identified a novel, targetable transcriptional-metabolic axis that sustains inflammatory T-cell responses, characterized by NFATc1-regulated activation of MTHFD2-dependent one-carbon metabolism. We demonstrate that NFATc1 directly binds the MTHFD2 promoter region, driving metabolic reprogramming in activated T cells from rheumatoid arthritis (RA) patients as well as in experimental arthritis models. Pharmacological inhibition of MTHFD1/2 using the novel small molecule TH9619 suppresses proinflammatory cytokine production, expands Foxp3⁺ regulatory T cells and protects against cartilage and bone damage in vivo. Proteomic profiling reveals that TH9619 elicits a distinct molecular response in patients’ T cells, divergent from the currently used anti-folate therapy, particularly in inadequate responders. These findings use RA as the proving ground to establish NFATc1-mediated MTHFD2 activation as a critical regulator of sustained T-celldriven inflammation and support selective MTHFD1/2 inhibition as a novel, mechanism-based therapeutic strategy for RA. Signal Transduction and Targeted Therapy (2026)11:226 INTRODUCTION T cells are essential orchestrators of immune responses, enabling host defense while maintaining tissue homeostasis. However, dysregulated T-cell activation and effector function can drive persistent inflammation, tissue destruction, and autoimmunity. Rheumatoid arthritis (RA), a chronic autoimmune disease affecting approximately 1% of the global population, exemplifies the consequences of aberrant T-cell activity, leading to persistent synovial inflammation, progressive joint destruction, and systemic complications if not treated early.1 Despite the availability of conventional synthetic, biological, and targeted synthetic disease-modifying antirheumatic drugs (DMARDs), including methotrexate (MTX) and tumor necrosis factor (TNF) inhibitors, a substantial fraction of patients exhibits inadequate or incomplete responses, and a significant minority develop treatment-refractory disease.2,3 These limitations stem from mechanisms of action of the drugs that do not exploit the disease characteristics and adverse effects, underscoring the urgent need for more precise therapeutic targets, personalized approaches and predictive biomarkers of treatment response. In RA and other T-cell-driven autoimmune conditions, T cells are subjected to proliferative pressures and amplify their proinflammatory and tissue-invading behavior, aided by heightened folate 1 ; https://doi.org/10.1038/s41392-026-02752-y and nucleotide production.4 Specifically, CD4+ T-cell subsets, including Th1, Th17, and peripheral helper T cells (Tph), infiltrate the synovium and produce proinflammatory cytokines such as IFNγ, IL-17, CXCL13 and TNFα.5–9 These cytokines amplify inflammation, promote cartilage degradation, and stimulate autoantibody production. Tph cells are proposed to support B-cell responses and autoantibody production, further exacerbating the disease.8 These T-cell subsets interact with other immune cells, including B cells and innate immune cells, forming a complex network that perpetuates the inflammatory response. The imbalance between effector T cells and regulatory T cells (Tregs), whose suppressive functions can be undermined in inflammatory environments, further exacerbates immune dysregulation.10 However, the molecular mechanisms underlying sustained pathogenic T-cell activation and resistance to therapeutic suppression in chronic inflammation remain incompletely understood. One-carbon (1C) metabolism is a key metabolic pathway supporting nucleotide synthesis, redox balance, and epigenetic regulation.11–13 Enzymes involved in one-carbon metabolism, such as SHMT1, SHMT2, MTHFD1, and MTHFD2, are reported to be induced upon T-cell activation.14 Among the enzymes involved in this pathway, methylenetetrahydrofolate dehydrogenase 2 Department of Oncology-Pathology, Science for Life Laboratory, Karolinska Institutet, Solna, Sweden; 2Division of Rheumatology, Department of Medicine, Center for Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden; 3Institute for Bioinnovation, Biomedical Sciences Research Centre “Alexander Fleming”, Vari, Greece; 4Clinical, Experimental Surgery & Translational Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece; 5Department of Oral Surgery, Pathology and Clinical Dentistry, School of Dentistry, Federal University of Minas Gerais, Belo Horizonte, Brazil; 6One-carbon Therapeutics AB, Stockholm, Sweden and 7 Department of Oncology and Metabolism, Medical School, Sheffield, UK Correspondence: Theodora Manolakou () or Thomas Helleday () These authors contributed equally: Jianyu Shen, Sanjaykumar Boddul Received: 4 July 2025 Revised: 30 March 2026 Accepted: 16 April 2026 © The Author(s) 2026 Targeting MTHFD2-dependent one-carbon metabolism in rheumatoid arthritis Manolakou et al. 2 (MTHFD2) has emerged as a potential regulator of T-cell function and inflammatory responses. MTHFD2 is upregulated in whole blood cells across various autoimmune diseases, including RA.15 This enzyme supports de novo nucleotide synthesis and regulates DNA methylation and histone modifications in effector T cells, particularly Th17 cells. Preclinical studies have demonstrated that targeting MTHFD2 reduces disease severity in multiple sclerosis disease models by promoting regulatory T-cell differentiation.15 MTX remains the cornerstone treatment for autoimmune arthritis, such as RA, and acts as a folate antagonist primarily through the inhibition of dihydrofolate reductase (DHFR) and other folate-dependent enzymes, ultimately interfering nonspecifically with one-carbon metabolism.16–18 Beyond DHFR, MTX also targets many more enzymes, such as ATIC and TYMS, contributing to the accumulation of adenosine and suppression of immune cell function. However, its broad disease unspecific mechanism of action affects healthy proliferating cells,19,20 contributing to systemic toxicity, and a considerable subset of patients develops inadequate responses or intolerance, necessitating treatment escalation.21 These challenges call for precise approaches to Signal T (...truncated)