PLD1 and PLD2 promote an immunosuppressive tumor microenvironment via CCL19-dependent macrophage polarization and...

Tumor cells shape the immunosuppressive tumor microenvironment (TME) through coordinated interactions with tumor-associated macrophages (TAMs), regulatory T cells (T_regs), 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 T_reg 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.