FADD Activation in Hepatocellular Carcinoma Potentiates CD8+ T-cell Responses and Sensitizes to Immune Checkpoint Inhibitors.

Turning immunologically "cold" tumors "hot" is required for effective immune checkpoint inhibitor (ICI) treatment in hepatocellular carcinoma (HCC). In this study, we identified Fas-associated death domain (FADD) as a key molecule upregulated in HCC with dense tumor-infiltrating CD8+ T cells and better response to ICIs. CRISPR-mediated knockout of Fadd in murine HCC cells led to increased tumor weights in immunocompetent, but not immunodeficient, mice. FADD deficiency also led to decreased intratumoral infiltration of CD8+ T cells and lower production of IFNγ and TNFα. Mechanistically, phosphorylated FADD translocated into the nucleus, in which it interacted with Sam68 to upregulate NF-κB-induced transcription of C-C motif ligand 5, thereby promoting CD8+ T-cell recruitment. Treatment with anti-PD-1 triggered FADD phosphorylation in ICI-sensitive tumors, which was not observed in ICI-resistant tumors. FADD activation through genetic or pharmacologic approaches overcame ICI resistance in orthotopic and spontaneous HCC mouse models in vivo. Together, these findings provide insights into combinatory immunotherapy approaches for patients with HCC. SIGNIFICANCE: FADD signaling in hepatocellular carcinoma cells increases CCL5 production to generate a hot microenvironment that is responsive to immune checkpoint blockade, providing a strategy to improve immunotherapy responses in liver cancer patients.