Fibroblast-derived PI16 enhances tumor immune-suppressive microenvironment via inducing Tregs differentiation

Area of Science:

• Oncology
• Immunology
• Cancer Biology

Background:

• Esophageal squamous cell carcinoma (ESCC) is aggressive with poor prognosis.
• The tumor microenvironment (TME) critically influences cancer progression and treatment response.
• Fibroblasts within the TME, particularly in lymph nodes, have been implicated in conferring drug resistance to ESCC cells via peptidase inhibitor 16 (PI16).

Purpose of the Study:

• To investigate the role of fibroblast-derived PI16 in the ESCC tumor microenvironment.
• To elucidate the mechanism by which PI16 influences immune cells within the TME.
• To assess the prognostic significance of PI16 expression in ESCC patients.

Main Methods:

• Analysis of public single-cell RNA sequencing data (GSE203115) for ESCC.
• Cell co-culture assays to study regulatory T cell (Treg) differentiation from naïve CD4+ T cells.
• Immunoprecipitation, mass spectrometry, in vitro/in vivo assays, and multiplex fluorescent immunohistochemistry (mfIHC) to determine PI16 function and mechanism involving DOCK2.

Main Results:

• Fibroblasts in ESCC tumors were subcategorized into PI16-expressing (PI16+) and non-expressing (PI16-) populations.
• PI16 was found to induce Treg differentiation from naïve CD4+ T cells via a DOCK2-dependent pathway.
• Inhibition of DOCK2 suppressed PI16-induced Treg differentiation and enhanced effector T cell (Teff) infiltration in vivo.
• Elevated PI16 levels in the tumor stroma correlated with worse long-term survival outcomes in ESCC patients.

Conclusions:

• PI16-producing fibroblasts promote Treg differentiation through DOCK2 interaction, contributing to immune suppression in ESCC.
• High stromal PI16 expression is a negative prognostic marker for ESCC patients.
• Targeting PI16+ fibroblasts represents a potential therapeutic strategy to reverse tumor immune suppression in ESCC.