Ifnγ/pd-l1 signaling improves the responsiveness of anti-pd-1 therapy in colorectal cancer: An in vitro study

Abstract

Introduction: Programmed cell death 1 ligand 1 (PD-L1) can be upregulated in cancer cells via interferon gamma (IFNγ) in the tumor microenvironment. IFNγ/PD-L1 signaling is associated with the response to immune checkpoint blockade in melanoma patients. Our previous investigation indicated that the microsatellite instability-high (MSI-H) cell line might exhibit selective hyperresponsiveness to IFNγ treatment, which contributes to increased PD-L1 expression and may be a mechanism of response to anti-PD-1 therapy in colorectal cancer. Methods: The present study evaluated the expression of PD-L1 in a set of MSI and microsatellite stability (MSS) cell lines with IFNγ treatment. The differential signaling molecules associated with signal transducer and activator of transcription (STAT) contribut-ing to hyperresponsiveness to IFNγ exposure were also investigated. Furthermore, we established a coculture assay containing CT26 cells with higher expression of PD-L1 and peripheral blood mononuclear cells (PBMCs) in vitro. Changes in cancer cell viability as well as apoptosis status in response to anti-PD-1 therapy were demonstrated. We further observed changes in the percentage of CD4+ and CD8+ lymphocytes after PD-1 immunother-apy in the coculture assay. Finally, the average extent of inflammation and adaptive immunity factors in the assay was also investigated. Results: This in vitro study revealed that the MSI cell line might exhibit hyperresponsive-ness to IFNγ exposure, and IFNγ induced upregulation of PD-L1 mainly through increased STAT1 and decreased STAT3 signaling. IFNγ/PD-L1 signaling participated in the response to anti-PD-1 therapy mainly through the CTL profile. Discussion: Our findings reinforce previous knowledge of the fact that the response to immune checkpoint blockade occurs mainly in patients with a preexisting intratumoral IFNγ/ PD-L1 signal, thus suggesting potential therapeutic strategies to enhance responsiveness to PD-1 blockade immunotherapy in most patients with colorectal cancer.