IRF1 Inhibits Antitumor Immunity through the Upregulation of PD-L1 in the Tumor Cell

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• The transcription factor Interferon Regulatory Factor 1 (IRF1) has been predominantly linked to tumor suppression in prior research.
• Its precise role in tumor cell-intrinsic functions and cancer progression remains incompletely understood.

Purpose of the Study:

• To investigate the role of IRF1 in tumor cell-intrinsic functions and its impact on tumor growth and anti-tumor immunity.
• To elucidate the mechanisms by which IRF1 influences the tumor microenvironment and immune cell interactions.

Main Methods:

• Utilized mouse models of colon carcinoma (MC38, CT26) and melanoma (B16) with IRF1-deficient tumor cells.
• Conducted detailed profiling of tumor-infiltrating leukocytes and assessed CD8+ T cell cytotoxicity.
• Analyzed Programmed Death-Ligand 1 (PD-L1) expression in tumor cells in vitro and in vivo.

Main Results:

• IRF1-deficient tumors exhibited reduced growth in mouse models, dependent on host CD8+ T cells.
• CD8+ T cells infiltrating IRF1-deficient tumors showed enhanced cytotoxicity.
• IRF1-deficient tumor cells displayed impaired PD-L1 upregulation, increasing susceptibility to T cell-mediated killing.
• Restoration of PD-L1 expression in IRF1-deficient cells re-established tumor growth.

Conclusions:

• IRF1 possesses a tumor cell-intrinsic function that promotes tumor growth, contrary to its established tumor-suppressive roles.
• IRF1 deficiency enhances anti-tumor immunity by increasing CD8+ T cell cytotoxicity and sensitivity to T cell-mediated killing, partly via PD-L1 regulation.
• These findings highlight IRF1's complex role in tumor immune escape and suggest its potential as a therapeutic target.