PLD1 and PLD2 promote an immunosuppressive tumor microenvironment via CCL19-dependent macrophage polarization and PD-L1 induction

www.nature.com/emm ARTICLE OPEN PLD1 and PLD2 promote an immunosuppressive tumor microenvironment via CCL19-dependent macrophage polarization and PD-L1 induction Hyesung Lee 1 , Seong Hun Lim 1 , Won Chan Hwang2, Tae Hyun Kim1, Kyeongseok Bae1, Jinu Lee1 and Do Sik Min1 ✉ 1234567890();,: © The Author(s) 2026 Tumor cells shape the immunosuppressive tumor microenvironment (TME) through coordinated interactions with tumor-associated macrophages (TAMs), regulatory T cells (Tregs), immune checkpoint pathways and suppressive cytokines, thereby limiting the efficacy of immunotherapy across diverse cancer types. Phospholipase D (PLD) enzymes, particularly the PLD1 and PLD2 isoforms, have been implicated in oncogenic signaling and tumor progression; however, their tumor-intrinsic roles in modulating the immune landscape remain largely undefined. Here we demonstrated that both genetic ablation and pharmacological inhibition of PLD1 and PLD2 reprogram the TME and enhance antitumor immunity in a syngeneic melanoma model. Elevated PLD expression is associated with increased infiltration of M2-like TAMs, decreased ‘eat me’ signals and enhanced ‘don’t eat me’ signals. Conversely, loss or inhibition of PLD1 and PLD2 reduced Treg recruitment and enhanced infiltration of Th1, Th17 and cytotoxic CD8⁺ T cells, accompanied by downregulation of immune checkpoint molecules and restoration of T cell effector function. Depletion studies revealed that PLD-driven TAM polarization critically impairs CD8⁺ T cell-mediated antitumor responses. Mechanistically, PLD1 and PLD2 enhance CCL19 secretion, promote macrophage polarization toward an immunosuppressive phenotype and induce programmed death-ligand 1 (PD-L1) expression by activating the PI3K–Akt–NF-κB signaling axis, thereby promoting tumor immune evasion. Notably, PLD inhibition reduced CCL19 production, abrogated IFN-γ- or CCL19-induced PD-L1 expression, decreased TAM infiltration and increased CD8⁺ T cell infiltration, collectively shifting the TME toward an immune-activated state. These findings suggest that tumor-intrinsic PLD1 and PLD2 function as modulators of immune suppression and that PLD inhibition represents a promising strategy to overcome resistance to cancer immunotherapy. Experimental & Molecular Medicine; https://doi.org/10.1038/s12276-026-01742-y INTRODUCTION Cancer develops through interactions between malignant cells and the surrounding tumor microenvironment (TME), which comprises diverse stromal components, including multiple immune cell subsets, fibroblasts and endothelial cells1–3. Accumulating evidence indicates that the immunosuppressive TME drives tumor initiation, progression and therapeutic resistance1. Consequently, targeting the TME has emerged as a key strategy to reverse immunosuppression and enhance antitumor immune responses. Among immune populations within the TME, tumorassociated macrophages (TAMs) are vital in establishing an immunosuppressive milieu by promoting tumor growth, angiogenesis and immune evasion through continuous crosstalk with cancer cells2–4. TAMs exhibit substantial phenotypic plasticity, transitioning between pro-inflammatory and tumoricidal M1-like states, as well as anti-inflammatory and tumor-promoting M2-like states, in response to local microenvironmental cues5. The M1-like and M2-like nomenclature is used to denote dominant functional polarization states within the TME, rather than rigid or mutually exclusive macrophage subsets. M2-like TAMs function as major drivers of tumor progression and potent suppressors of adaptive immunity. Consequently, reprogramming TAMs from an M2-like immunosuppressive phenotype to a pro-inflammatory M1-like state is a promising strategy to enhance T cell-mediated immunity and overcome immune resistance6. Notably, tumor-PD-L1 and TAMs engage in a bidirectional regulatory loop in which PD-L1 modulates TAM polarization while TAM-derived cytokines promote PD-L1 expression in cancer cells, collectively amplifying immune evasion7. Melanoma, the most aggressive form of skin cancer, accounts for most skin cancer-related deaths worldwide8. Although immune checkpoint blockade (ICB) has produced substantial clinical responses in advanced melanoma by restoring cytotoxic T cell activity, most patients exhibit primary resistance or develop secondary resistance during therapy9–11. Addressing this limitation requires a deeper understanding of the molecular and cellular mechanisms driving immune suppression within the melanoma TME. PD-L1 is expressed in tumor cells and regulates immune responses through dual mechanisms. Through interaction with PD1 in T cells, PD-L1 induces T cell exhaustion or apoptosis and attenuates antitumor activity12,13. Beyond this direct inhibition, 1 College of Pharmacy, Yonsei University, Incheon, Republic of Korea. 2Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea. ✉email: Received: 31 December 2025 Revised: 5 March 2026 Accepted: 22 March 2026 H. Lee et al. 2 PD-L1 shapes the broader TME by promoting immunosuppressive populations such as TAMs and myeloid-derived suppressor cells (MDSCs), thereby reinforcing immune escape14,15. Tumor-derived cytokines and chemokines influence macrophage polarization and immune checkpoint expression, driving metastasis, angiogenesis and therapeutic resistance. Accordingly, identifying tumorintrinsic regulators that control cytokine secretion, macrophage polarization and PD-L1 induction is critical to overcoming immune suppression in cancer16,17. Recent findings have indicated that tumor-intrinsic lipid signaling pathways serve as key modulators of cytokine secretion and immune cell recruitment. Among these, phospholipase D (PLD) and its enzymatic product phosphatidic acid (PA) function as central mediators of oncogenic signaling, vesicular trafficking and membrane dynamics18. Although the canonical roles of PLD1 and PLD2 (PLD1/2) in promoting tumor proliferation, invasion and metastasis are well established18,19, their contributions to immunosuppressive TME remodeling remain poorly understood. Evidence suggests that PLD isoforms exert context-dependent immunomodulatory effects. Inhibition of PLD1 induces immunogenic cell death and enhances the efficacy of cancer immunotherapy in colorectal cancer19, whereas PLD2 regulates cytokine production in macrophages and modulates T cell responses20. These findings suggest that PLD isoforms influence antitumor immunity by regulating cytokine secretion and immune cell recruitment. However, the mechanisms by which tumor-intrinsic PLD1/2 coordinate macrophage polarization and immune checkpoint regulation in the melanoma TME remain unknown. Here, we aimed to elucidate the mechanisms by which tumor-intrinsic PLD1/2 regulate CCL19-dependent TAM polarization and PD-L1 induction and to determine the broader importance of PLD1/2 activity in establishing an immunosuppressive TME. MATERIALS AND METHODS Human skin cancer (...truncated)