Esophageal cancer-derived exosomes imbalance Tfh/Tfr cell ratio in the tumor immune microenvironment via EXO-PDL1 to promote immunosuppression

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 follicular helper T cells (Tfh) and follicular regulatory T cells (Tfr) numbers is related to the progression of many malignant tumors. However, the role of the EC-derived EXO-PDL1 in Tfh/Tfr ratio is unknown. Methods : Tfh and Tfr numbers in samples obtained from 45 patients with EC and 33 healthy donors (HD) were determined using flow cytometry. Exosomes were isolated using differential centrifugation from patients’ plasma and PDL1 expression on exosomes was tested using ELISA. Exosomes were cultured in vitro for Tfh and Tfr cells expansion assays. CD4 + T cells were isolated, stimulated, and cultured in vitro with exosomes to evaluate the levels, phenotypes, and functions of Tfh and Tfr cells. Results : In patients with EC, the proportion of Tfh cells was lower than that in HD (P<0.001) whereas the proportion of Tfr cells was higher than that in HD (P<0.001). Patients with EC also showed a significantly lower ratio of Tfh/Tfr cells and a higher level of EXO-PDL1 than HD did (P<0.001). Additionally, a negative correlation was noted between EXO-PDL1 and Tfh/Tfr (R=-0.74, P<0.05). EC cell derived EXO-PDL1 inhibited the expansion of Tfh cells and enhanced the percentage of CTLA4 + Tfh cells. Moreover, the levels of IL-21 and IFN-γ decreased, whereas IL-10 level was increased in response to EC cell derived EXO-PDL1. EXO-PDL1 promoted the expansion and suppressive functions of 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. Finally, EC derived exosomes promoted the imbalance of Tfh/Tfr ratio via the EXO-PDL1. Conclusions : Patients with EC have imbalanced Tfh/Tfr ratio, which is attributed to EC-derived EXO-PDL1. Our results suggest a novel mechanism of EXO-PDL1-mediated immunosuppression in EC. Thus, inhibiting EXO-PDL1 to restore Tfh/Tfr cell balance may provide new therapeutic approaches in EC treatment.