Background: Insufficient infiltration of CD8+ T cells in the tumor microenvironment (TME) critically restricts antitumor immunity and cancer immunotherapy efficacy. The purpose of this study was to identify novel tumor cell-intrinsic regulators of T-cell infiltration and to elucidate their mechanisms of action.
Methods: We performed a genome-wide Sleeping Beauty transposon mutagenesis screen in murine breast cancer models. Protein-protein interactions were identified by mass spectrometry and validated by co-immunoprecipitation. Gene and protein expression levels were assessed by reverse transcription and quantitative PCR and western blotting. T-cell infiltration and function were evaluated using flow cytomet... More
Background: Insufficient infiltration of CD8+ T cells in the tumor microenvironment (TME) critically restricts antitumor immunity and cancer immunotherapy efficacy. The purpose of this study was to identify novel tumor cell-intrinsic regulators of T-cell infiltration and to elucidate their mechanisms of action.
Methods: We performed a genome-wide Sleeping Beauty transposon mutagenesis screen in murine breast cancer models. Protein-protein interactions were identified by mass spectrometry and validated by co-immunoprecipitation. Gene and protein expression levels were assessed by reverse transcription and quantitative PCR and western blotting. T-cell infiltration and function were evaluated using flow cytometry, immunohistochemistry (IHC), multiplex IHC, and by analyzing bulk and single-cell RNA sequencing data complemented by bioinformatic analysis. The specific dephosphorylation sites on LGALS1 were confirmed through phosphomimetic mutant experiments. T-cell infiltration was further validated using an in vitro T-cell transendothelial migration assay and in vivo mouse models.
Results: Our screening identified 39 candidate genes, with tumor cell-intrinsic dual-specificity phosphatase 22 (DUSP22) expression correlating with enhanced CD8+ T-cell accumulation and suppressed tumor progression. Overexpression of DUSP22 resulted in increased CD8+ T-cell infiltration and enhanced T-cell function. Mechanistically, DUSP22 binds to LGALS1 and dephosphorylates it at the Ser8 and Thr58 residues, leading to LGALS1 degradation and subsequent alleviation of LGALS1-mediated immunosuppression. In human breast cancer samples, LGALS1 expression was negatively correlated with both DUSP22 levels and CD8+ T-cell infiltration. Therapeutic targeting of the DUSP22-LGALS1 axis significantly enhanced CD8+ T-cell infiltration and synergized with anti-programmed cell death protein-1 therapy to boost antitumor responses.
Conclusions: Our findings unveil a novel phosphorylation-dependent DUSP22-LGALS1 axis that reprograms the immunosuppressive TME. This work thus proposes a promising therapeutic strategy to overcome immune checkpoint blockade resistance in breast cancer.
