András Piffkó

Metastatic progression is a major cause of radiotherapy (RT) failure, yet the mechanisms linking RT to immune suppression and metastasis remain unclear. Here, we identify YTHDF2 as a radiation-induced immune checkpoint in dendritic cells (DCs). By analyzing patient biopsies from a clinical trial (NCT03223155), we discover that increased YTHDF2 expression in DCs after RT correlates with treatment failure after RT. Mechanistically, ionizing radiation induces SPI1, which drives transcription of Ythdf2 in DCs. Upregulated YTHDF2 promotes m6A-mediated degradation of Notch pathway regulators (Mfng, Aph1b, Aph1c), impairing MHC-I cross-presentation and CD8+ T cell activation, thereby facilitating tumor immune evasion and metastatic spread. Crucially, targeting YTHDF2 restores DC immunogenicity, enhances RT-induced tumor control, and improves DC-based cancer vaccines when combined with RT, providing a clinically actionable strategy to overcome RT resistance and metastasis.

Metastasis-directed therapies such as stereotactic body radiotherapy (SBRT) are increasingly used in patients with metastatic cancer with limited disease burden. Although effective for local control, emerging evidence suggests that SBRT may have unintended systemic effects that reshape the tumor-immune landscape. A recent study identifies amphiregulin (AREG), an EGFR ligand, as a key mediator of radiation-induced changes in metastatic behavior. In clinical cohorts and murine models, SBRT led to marked AREG upregulation. Rather than promoting tumor cell proliferation directly, AREG acted through the myeloid compartment, inducing monocyte differentiation into immunosuppressive macrophages and enabling immune escape. Elevated AREG—either at baseline or following SBRT—was associated with increased metastatic progression and inferior survival. Mechanistically, AREG signaling induced CD47 expression on tumor cells, further impairing macrophage-mediated clearance. Therapeutically, AREG blockade, especially combined with anti-CD47 antibodies, synergized with radiotherapy to suppress both local and distant diseases in preclinical models. These findings reveal both challenges and opportunities: whereas radiation effectively suppresses new metastatic seeding, it may reorganize the biological ecosystem in ways that unmask dormant disease. Understanding these dual effects offers therapeutic opportunities through combination approaches targeting radiation-induced pathways. AREG emerges as both a biomarker and therapeutic target. Integrating biomarker-informed strategies with metastasis-directed therapies may be essential for achieving durable disease control and optimizing outcomes in metastatic cancer.

Cancer-associated fibroblasts (CAFs) have a pivotal cancer-supportive role, yet CAF-targeted therapies are lacking^1,2. Here, using spatial transcriptomics and single-cell RNA sequencing, we investigate the role of nicotinamide N-methyltransferase (NNMT) in high-grade serous ovarian cancer. Mechanistically, NNMT-induced H3K27me3 hypomethylation drives complement secretion from CAFs, attracting immunosuppressive myeloid-derived suppressor cells (MDSCs) to the tumour. Nnmt knockout in immunocompetent mice impairs tumour growth in syngeneic ovarian, breast and colon tumour models through enhanced CD8⁺ T cell activation. Using high-throughput screening, we develop a potent and specific NNMT inhibitor that reduces the tumour burden and metastasis in multiple mouse cancer models and restores immune checkpoint blockade efficacy by decreasing CAF-mediated recruitment of MDSCs and reinvigorating CD8⁺ T cell activation. Our findings establish NNMT as a central CAF regulator and a promising therapeutic target to mitigate immunosuppression in the tumour microenvironment.

The anti-tumour effect of radiotherapy beyond the treatment field—the abscopal effect—has garnered much interest¹. However, the potentially deleterious effect of radiation in promoting metastasis is less well studied. Here we show that radiotherapy induces the expression of the EGFR ligand amphiregulin in tumour cells, which reprogrammes EGFR-expressing myeloid cells toward an immunosuppressive phenotype and reduces phagocytosis. This stimulates distant metastasis growth in human patients and in pre-clinical mouse tumour models. The inhibition of these tumour-promoting factors induced by radiotherapy may represent a novel therapeutic strategy to improve patient outcomes.

The RNA N ⁶ -methyladenosine (m ⁶ A) reader YTHDF1 is implicated in cancer etiology and progression. We discovered that radiotherapy (RT) increased YTHDF1 expression in dendritic cells (DCs) of PBMCs from patients with cancer, but not in other immune cells tested. Elevated YTHDF1 expression in DCs was associated with poor outcomes for patients receiving RT. We found that loss of Ythdf1 in DCs enhanced the antitumor effects of ionizing radiation (IR) by increasing the cross-priming capacity of DCs across multiple murine cancer models. Mechanistically, IR upregulated YTHDF1 expression in DCs through stimulator of IFN genes/type I IFN (STING/IFN-I) signaling. YTHDF1 in turn triggered STING degradation by increasing lysosomal cathepsins, thereby reducing IFN-I production. We created a YTHDF1 deletion/inhibition prototype DC vaccine that significantly improved the therapeutic effect of RT and radioimmunotherapy in a murine melanoma model. Our findings reveal a layer of regulation between YTHDF1/m ⁶ A and STING in response to IR, which opens new paths for the development of YTHDF1-targeting therapies.

Supplementary Figure S3. Changes in MC38 tumor cDC populations after local RT.

Purpose:Radiation-mediated immune suppression limits efficacy and is a barrier in cancer therapy. Radiation induces negative regulators of tumor immunity including regulatory T cells (Treg). Mechanisms underlying Treg infiltration after radiotherapy (RT) are poorly defined. Given that conventional dendritic cells (cDC) maintain Treg, we sought to identify and target cDC signaling to block Treg infiltration after radiation.Experimental Design:Transcriptomics and high dimensional flow cytometry revealed changes in murine tumor cDC that not only mediate Treg infiltration after RT but also associate with worse survival in human cancer datasets. Antibodies perturbing a cDC-CCL22-Treg axis were tested in syngeneic murine tumors. A prototype interferon–anti-epidermal growth factor receptor fusion protein (αEGFR-IFNα) was examined to block Treg infiltration and promote a CD8+ T cell response after RT.Results:Radiation expands a population of mature cDC1 enriched in immunoregulatory markers that mediates Treg infiltration via the Treg-recruiting chemokine CCL22. Blocking CCL22 or Treg depletion both enhanced RT efficacy. αEGFR-IFNα blocked cDC1 CCL22 production while simultaneously inducing an antitumor CD8+ T cell response to enhance RT efficacy in multiple EGFR-expressing murine tumor models, including following systemic administration.Conclusions:We identify a previously unappreciated cDC mechanism mediating Treg tumor infiltration after RT. Our findings suggest blocking the cDC1-CCL22-Treg axis augments RT efficacy. αEGFR-IFNα added to RT provided robust antitumor responses better than systemic free interferon administration and may overcome clinical limitations to interferon therapy. Our findings highlight the complex behavior of cDC after RT and provide novel therapeutic strategies for overcoming RT-driven immunosuppression to improve RT efficacy.See related commentary by Kalinski et al., p. 4260

Supplementary Figure S2. Flow cytometric characterization of tumor cDC after local radiation