FYN/LCK kinase balance as a metabolic switch orchestrates progenitor exhausted T Cell differentiation in hepatocellular carcinoma

Background and Aims: 
Immune checkpoint blockade (ICB) shows therapeutic promise in hepatocellular carcinoma (HCC) but is associated with suboptimal responses in patients. Progenitor-exhausted T (Tpex) cells are key responders to ICB, but the regulatory mechanisms governing Tpex maintenance in HCC remain elusive.

Approach and Results:
Through an integrated analysis of HCC single-cell RNA-sequencing datasets, we constructed an exhausted CD8⁺ T-cell atlas and identified the kinase FYN as a marker of Tpex cells in ICB responders. FYN deficiency in CD8⁺ T cells induced LCK hyperactivation, which drove terminal exhaustion under high-affinity antigen stimulation. Mechanistically, LCK hyperactivation disrupted metabolic homeostasis by triggering excessive glycolysis and impairing mitochondrial function in Tpex cells. Conversely, LCK inhibition elevated compensatory FYN activity, restored mitochondrial fitness, and preserved Tpex cell stemness. In preclinical HCC models, transient LCK inhibition during T-cell expansion enhanced adoptive cell therapy efficacy by increasing Tpex cell persistence and stemness. Additionally, preemptive low-dose LCK inhibition before anti–PD-1 therapy expanded the Tpex cell pool, reduced terminal exhaustion, and improved therapeutic outcomes.

Conclusions:
This study establishes the FYN/LCK balance as a critical regulator of the terminal exhaustion of Tpex cells through metabolic reprogramming. These findings suggest that modulating the FYN/LCK kinase balance is a promising strategy to overcome immunotherapy resistance in HCC.