HBx hijacks the miR-19a-3p/BAMBI/TGF-β1 axis to impair the anti-tumour activity of CD4(+) T cells in diffuse large B-cell lymphoma.

BACKGROUND: Hepatitis B virus (HBV) is clinically associated with poor prognosis in diffuse large B-cell lymphoma (DLBCL), while cellular communication in the tumour microenvironment (TME) is recognized as a critical driver of tumour progression. Nevertheless, whether HBV infection mediates DLBCL cell-immune cell crosstalk remains undefined, with the precise mechanisms and associated key molecules remaining elusive. METHODS: SsGSEA, Cox regression (univariate/multivariate), WGCNA, and Kaplan-Meier analyses identified prognostic immune subsets and miRNAs in HBV(+) DLBCL. Dual luciferase assay, qRT-PCR, western blot, ChIP, Co-IP, flow cytometry, enzyme-linked immunosorbent assay, immunohistochemistry, and murine models were employed together to evaluate CD4(+) T cell dysfunction in vitro and in vivo. ScRNA-seq analyses encompassed clustering, pseudotemporal trajectory, and ligand-receptor networks to decode TME dynamics. RESULTS: TME profiling identified diminished CD4⁺ T cell infiltration as an independent predictor of poor survival in HBV⁺ DLBCL. Mechanistically, HBx-mediated down-regulation of miR-19a-3p activated the BAMBI/Wnt signalling pathway, thereby enhancing TGF-β1 secretion and suppressing the anti-tumour activity of CD4(+) T cells. Single-cell analysis revealed that BAMBI(high) DLBCL cells engage CD4(+) T cells via TGFB1-TGFBR2 pair, with TGFBR2 enriched in exhausted subsets of CD4(+) T cells and shaping their dysfunctional fate. Therapeutic restoration of miR-19a-3p or blockade of TGF-β reinforced the CD4⁺ T cell anti-tumour activity and restrained the progression of HBx-overexpressing DLBCL in vivo. CONCLUSIONS: HBx promoted TGF-β1 hypersecretion via miR-19a-3p repression-mediated Wnt/β-catenin activation, directly driving CD4(+) T cell depletion and functional exhaustion in DLBCL. Our work provided important insights into the immune determinants of poor prognosis in HBV(+) DLBCL, highlighting the pivotal role of CD4(+) T cell dysfunction in driving disease progression and adverse clinical outcomes. HIGHLIGHTS: Reduced CD4(+) T cell enrichment in the TME predicted poor survival in HBV(+) DLBCL. Down-regulation of miR-19a-3p by HBx activated the BAMBI-mediated Wnt signalling, amplifying TGF-β1 secretion to suppress anti-tumour activity of CD4⁺ T cells. The TGF-B1/TGFBR2 pair mediated the HBV(+) DLBCL-CD4(+) T cell communication. Targeting TGF-β or miR-19a-3p improved CD4(+) T cell immunity to suppress HBV(+) DLBCL progression.