YTHDF2/m6 A/NF-κB axis controls anti-tumor immunity by regulating intratumoral Tregs.

N6 -methyladenosine (m6 A) in messenger RNA (mRNA) regulates immune cells in homeostasis and in response to infection and inflammation. The function of the m6 A reader YTHDF2 in the tumor microenvironment (TME) in these contexts has not been explored. We discovered that the loss of YTHDF2 in regulatory T (Treg) cells reduces tumor growth in mice. Deletion of Ythdf2 in Tregs does not affect peripheral immune homeostasis but leads to increased apoptosis and impaired suppressive function of Treg cells in the TME. Elevated tumor necrosis factor (TNF) signaling in the TME promotes YTHDF2 expression, which in turn regulates NF-κB signaling by accelerating the degradation of m6 A-modified transcripts that encode NF-κB-negative regulators. This TME-specific regulation of Treg by YTHDF2 points to YTHDF2 as a potential target for anti-cancer immunotherapy, where intratumoral Treg cells can be targeted to enhance anti-tumor immune response while avoiding Treg cells in the periphery to minimize undesired inflammations.

All-trans retinoic acid overcomes solid tumor radioresistance by inducing inflammatory macrophages.

Radiotherapy (RT) is an important anti-cancer treatment modality that activates innate and adaptive immune responses. When all-trans retinoic acid (RA) was administered with radiation, we observed superior antitumor responses compared to ionizing radiation (IR) alone or RA alone. The superior antitumor effects of combination treatment were accompanied by a dramatic increase of TNF-α- and inducible nitric oxide synthase (iNOS)-producing inflammatory macrophages in local and distal non-irradiated (distal) tumors. Inflammatory macrophages are essential for the therapeutic efficacy of combination treatment by inducing effector T cell infiltration and enhancing the effector T cell to regulatory T cell ratio in local and distal tumors. T cells and T cell-derived IFN-γ are crucial for increasing inflammatory macrophage levels in IR and RA treated tumors. Notably, whereas CD8+ T cells are required for the antitumor response to IR, CD4+ T cells are required for the effectiveness of the IR and RA combination. Combination treatment with RA enhanced the abscopal response when radiation and PD-L1 blockade were used together. The synergistic positive feedback loop of inflammatory macrophages and adaptive immunity is required for the antitumor efficacy of IR plus RA combination treatment. Our findings provide a translational and relatively nontoxic strategy for enhancing the local and systemic antitumor effects of IR.

Radiotherapy and immunotherapy converge on elimination of tumor-promoting erythroid progenitor cells through adaptive immunity.

Tumor-induced CD45-Ter119+CD71+ erythroid progenitor cells, termed "Ter cells," promote tumor progression by secreting artemin (ARTN), a neurotrophic peptide that activates REarranged during Transfection (RET) signaling. We demonstrate that both local tumor ionizing radiation (IR) and anti-programmed death ligand 1 (PD-L1) treatment decreased tumor-induced Ter cell abundance in the mouse spleen and ARTN secretion outside the irradiation field in an interferon- and CD8+ T cell-dependent manner. Recombinant erythropoietin promoted resistance to radiotherapy or anti-PD-L1 therapies by restoring Ter cell numbers and serum ARTN concentration. Blockade of ARTN or potential ARTN signaling partners, or depletion of Ter cells augmented the antitumor effects of both IR and anti-PD-L1 therapies in mice. Analysis of samples from patients who received radioimmunotherapy demonstrated that IR-mediated reduction of Ter cells, ARTN, and GFRα3, an ARTN signaling partner, were each associated with tumor regression. Patients with melanoma who received immunotherapy exhibited favorable outcomes associated with decreased expression of GFRα3. These findings demonstrate an out-of-field, or "abscopal," effect mediated by adaptive immunity, which is induced during local tumor irradiation. This effect, in turn, governs the therapeutic effects of radiation and immunotherapy. Therefore, our results identify multiple targets to potentially improve outcomes after radiotherapy and immunotherapy.