Association of TGF-β and lactate in the induction of regulatory T cells by mesenchymal-CRC organoids

Abstract

Regulatory T cells (Treg cells) are a specialized subset of CD4+ T cells with an important role in immune regulation and disease pathogenesis. Treg cells can have an unfavorable effect in the context of cancer by suppressing anti-tumor immune responses. In CRC tumors, Treg cell enrichment correlates with tumor progression and metastasis, immunotherapy failure, and poor prognosis. In this study, we established cell-cell contact co-cultures with murine mesenchymal-CRC organoid lines and CD4+ T cells from Foxp3EGFP mice to explore the mechanisms underlying Treg cell enrichment in mesenchymal CRC. We analyzed the effect of two mesenchymal-CRC organoid lines on CD4+ T cell activation and Treg cell induction by flow cytometry. Our findings showed that mesenchymal-CRC organoid lines induce Treg cells in a transforming growth factor β (TGF-β)-dependent manner when co-cultured with CD4+ T cells. Furthermore, we studied the effect of TGF-β and lactate on the induction of Treg cells by culturing CD4+ T cells in low and high concentrations of TGF-β with or without lactate. We demonstrated that lactate enhanced CD4+ T cell activation but not Treg cell induction in conditions with low and high TGF-β concentrations. Overall, we developed an in vitro model with mesenchymal-CRC organoid lines and CD4+ T cells in which Treg cells are induced in a TGF-β-dependent manner. This Treg cell induction mimics to some extent the Treg cell enrichment in mesenchymal-CRC tumors described in literature. Thus, this co-culture model may help us study Treg cells in the context of mesenchymal CRC.