Tumor-associated macrophage-derived exosomes modulate the immunotherapeutic sensitivity of SHH-medulloblastoma by targeting m6A-modified FOXD1.
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BACKGROUND: Medulloblastoma (MB) is the most common pediatric malignant brain tumor. Infiltration of tumor-associated macrophages (TAMs) and m6A modification of RNA are correlated with poor prognosis and tumor progression in the Sonic Hedgehog (SHH) subtype (SHH-MB). However, the relationship between TAMs infiltration in SHH-MB and m6A modification status during tumor progression remains unclear. METHODS: Expression of m6A modification-related proteins was assessed in 40 cases of SHH-MB. Genes affected by TAM-derived exosomes were identified with methylated RNA immunoprecipitation sequencing. Mechanisms of m6A modification of FOXD1 were evaluated and combinatorial treatment with AAV2/9-shFOXD1 and PD-1 inhibitors was investigated in the NeuroD2:SmoA1 mouse model. RESULTS: TAMs infiltration led to decreased METTL14 expression, which was mediated by TAM-derived exosomes containing METTL14-specific microRNAs. In turn, this led to lower levels of m6A modifications. Through a screen, FOXD1 was identified as a critical downstream target of TAM-derived exosomes, and its expression level was correlated with poor prognosis in SHH-MBs. Importantly, knockdown of FOXD1 in SHH-MB cells significantly promoted the release of chemokines CXCL10/11, resulting in CD8+ T cell recruitment. Furthermore, treatment with AAV2/9-shFOXD1 significantly enhanced the antitumor effect of the PD-1 inhibitor in transgenic SHH-MB mice. CONCLUSIONS: Our study revealed for the first time that TAM-derived exosomes modulate m6A levels in SHH-MB, which promotes tumor progression via FOXD1. We identified FOXD1 as a novel therapeutic target whose inhibition sensitizes SHH-MB to immune checkpoint blockade.