Esophageal cancer derived exosomes imbalance circulating Tfh/Tfr via EXO-PDL1 to promote immunosuppression

Abstract

Abstract Background: Esophageal cancer (EC) is a deadly malignancy. Exosomal programmed death ligand 1 (EXO-PDL1) induces immune escape to promote tumor progression. Furthermore, the imbalance between circulating follicular helper T cells (Tfh) and circulating follicular regulatory T cells (Tfr) is related to the progression of many malignant tumors. However, the role of the EC derived EXO-PDL1 in circulating Tfh/Tfr is unknown. Methods: Circulating Tfh and circulating Tfr cells were determined using flow cytometry. Exosomes were isolated using differential centrifugation and PDL1 expression on exosomes was tested using ELISA. Exosomes were cultured in vitro for Tfh and Tfr cells expansion assays. Naïve CD4+ T cells were isolated, stimulated, and cultured in vitro with exosomes to evaluate the frequencies, phenotypes, and functions of Tfh and Tfr cells.. Results: For EC patients, the proportion of circulating Tfh cells was lower than that in HD whereas the proportion of circulating Tfr cells was higher. EC patients showed a significantly lower circulating Tfh/Tfr and a higher level of EXO-PDL1 than HD, and a negative correlation was noted between EXO-PDL1 and circulating Tfh/Tfr. EXO-PDL1 inhibited the expansion of Tfh cells and enhanced the percentage of CTLA4+Tfh cells. Additionally, the levels of IL-21 and IFN-γ decreased, whereas IL-10 level was increased. EXO-PDL1 promoted the expansion and suppressive functions of circulating Tfr cells, the increased percentages of CTLA4+ Tfr cells and ICOS+ Tfr cells were accompanied with higher levels of IL-10, IFN-γ, and IL-21. Conclusions: Our results suggest a novel mechanism of EXO-PDL1 mediated immunosuppression in EC. Thus, inhibiting EXO-PDL1 to restore circulating Tfh/Tfr balance may provide new therapeutic approaches in EC treatment.