Macrophage DHX34 as a negative regulator of the CX3CL1-CX3CR1 axis and CD8+ T-cell infiltration in hepatocellular carcinoma.

BACKGROUND

Tumor-associated macrophages (TAMs) are the dominant myeloid population in hepatocellular carcinoma (HCC) and critically shape the chemokine milieu that governs CD8+ T-cell entry. However, how macrophage-intrinsic regulators of chemokine expression influence antitumor immunity and response to immunotherapy remains unclear. We postulated that the macrophage RNA helicase DEAH-box helicase 34 (DHX34) suppresses production of the chemokine fractalkine (CX3CL1), thereby limiting chemotaxis of CX3CR1+ CD8+ T cells and diminishing the therapeutic efficacy of programmed cell death protein-1 (PD-1) blockade. We therefore examined the impact of macrophage DHX34 on T-cell trafficking and tumor control.

METHODS

We profiled DHX34 expression and subcellular distribution across human single-cell RNA-sequencing datasets and confirmed its pattern in murine TAMs. To investigate its function, we implemented myeloid-restricted Dhx34 deletion and evaluated tumor growth, intratumoral CD8+ T-cell abundance, and the efficacy of PD-1 blockade. Mechanistic experiments were performed using bone marrow-derived macrophages treated with tumor culture supernatant. CX3CL1 expression was measured by qPCR, ELISA, and immunoblotting, and CD8+ T-cell migration was assayed using Transwell assays.

RESULTS

DHX34 was enriched in TAMs, and higher DHX34 abundance correlated with lower CD8+ T-cell numbers and faster tumor growth. Myeloid-restricted Dhx34 deletion increased CX3CL1 expression and release in TAMs, thereby augmenting the influx of CX3CR1+ CD8+ T cells without altering their proliferation or viability. Consequently, DHX34 deficiency elevated intratumoral CD8+ T cell levels, slowed tumor expansion, and increased susceptibility to PD-1 blockade.

CONCLUSIONS

Within tumor-associated macrophages, DHX34 suppressed CX3CL1 output, limiting the tumor entry of CX3CR1-positive CD8+ T cells and, in turn, impairing control of HCC and reducing responsiveness to checkpoint therapy. Targeting DHX34 may potentiate PD-1 blockade in HCC.