CTSL loss leads to anti-PD-1 immunotherapy resistance in lung cancer by suppressing the anti-tumor function of peripheral CD8+ T cells.

Non-small cell lung cancer (NSCLC) has a high incidence rate, and most patients develop resistance to anti-PD-1 immunotherapy, resulting in shortened survival. Current evidence suggests that peripheral T cells, particularly CD8+ T cells, play a key role in the response to anti-PD-1 immunotherapy. However, the key molecules that impair peripheral CD8+ T cell function and thereby drive resistance to anti-PD-1 immunotherapy remain unclear. This study aims to demonstrate that loss of cathepsin L (CTSL) expression in peripheral CD8+ T cells is a critical factor driving resistance to anti-PD-1 therapy in NSCLC. Using flow cytometry, we tracked the dynamic expression patterns of CTSL in peripheral CD8+ T cells from NSCLC patients receiving anti-PD-1 therapy, as well as its longitudinal distribution across different T cell subsets. We then investigated the association between CTSL expression levels in peripheral CD8+ T cells and the expression of anti-tumor effector molecules. Finally, through bioinformatics analysis, flow cytometry, ELISA, and pharmacological interventions, we explored the functional relationship between CTSL and NLRP3 inflammasome activation in mediating the anti-tumor function of CD8+ T cells. CTSL expression in peripheral CD8+ T cells was demonstrated as a predictor of improved clinical response to anti-PD-1 immunotherapy in NSCLC (p < 0.01). Subset analysis revealed that in anti-PD-1-resistant patients, CTSL expression was significantly reduced in effector memory CD8+ T cells and terminally differentiated effector memory CD8+ T cells. Mechanistically, CTSL upregulation enhanced the expression of functional molecules in CD8+ T cells, including perforin, granzyme, IFN-γ, and Ki67. Functional exploration experiments further showed not only a positive correlation between CTSL and NLRP3 expression in peripheral CD8+ T cells, but also that activation of NLRP3 reversed the anti-tumor dysfunction of CD8+ T cells induced by CTSL inhibition. Loss of CTSL expression in peripheral CD8+ T cells is a key factor driving resistance to anti-PD-1 immunotherapy in NSCLC. CTSL loss may impair the anti-tumor function of CD8+ T cells by inhibiting NLRP3 inflammasome activation. This study not only provides a potential circulating biomarker for predicting response to anti-PD-1 therapy, but also offers new perspectives for understanding the mechanisms of resistance.