Unravelling the Role of Trophoblastic-Derived Extracellular Vesicles in Regulatory T Cell Differentiation

Regulatory T cells (T_reg) are mandatory elements in the maintenance of human pregnancy, but their de novo differentiation has not been completely exposed. HSPE1 chaperone expressing trophoblast cells may have a role in it. Trophoblast-derived extracellular vesicles (EVs), either at the feto-maternal interface or in circulation, target CD4⁺ T cells. We hypothesized that HSPE1-associated trophoblastic cell line (BeWo)-derived EVs are active mediators of T_reg cell differentiation. We proved at first that recombinant HSPE1 promote human T_reg cell differentiation in vitro. Developing a CRISPR-Cas9 based HSPE1 knockout BeWo cell line we could also demonstrate, that EV-associated HSPE1 induces T_reg development. Next-generation sequencing of miRNA cargo of BeWo-EVs characterized the regulatory processes of T_reg polarization. By the use of single-cell transcriptomics analysis, seven T_reg cell subtypes were distinguished and we demonstrated for the first time that the expression level of HSPE1 was T_reg subtype dependent, and CAPG expression is characteristic to memory phenotype of T cells. Our data indicate that HSPE1 and CAPG may be used as markers for identification of T_reg subtypes. Our results suggest, that trophoblastic-derived iEVs-associated HSPE1 and miRNA cargo have an important role in T_reg cell expansion in vitro and HSPE1 is a useful marker of T_reg subtype characterization.