hMSCs-derived exosomal MIR17HG promotes follicular helper T cell differentiation and osteosarcoma progression via the...

Osteosarcoma (OS) is a life-threatening malignancy in children and adolescents, with limited treatment options for resistant or metastatic disease. Exosomes derived from hMSCs regulate tumor immunity by transporting molecules such as long non-coding RNA (lncRNA). The lncRNA MIR17HG is known to promote OS progression, yet its role in regulating T follicular helper (Tfh) cell differentiation in OS is unclear. This study is the first to systematically explore how MIR17HG influences Tfh cell differentiation, activation, and OS cell proliferation via the miR-372-3p/BCL6 signaling cascade.

Exosomes were extracted from hMSCs using differential centrifugation. Characterization of hMSCs-derived exosomes was conducted by TEM, NTA and western blotting. The expression of MIR17HG, BCL6 and PD-1 was determined by qRT‒PCR or western blotting. The differentiation and activation of Tfh cells, as well as OS apoptosis, were assessed through flow cytometry. OS cell viability was determined by a CCK-8 assay. The effect of hMSCs-Exo-MIR17HG on tumors was assessed in an MG63-derived xenograft mouse model. The expression of Ki67 was examined via IHC. RNA immunoprecipitation was performed to validate the interaction between MIR17HG and miR-372-3p. A dual-luciferase reporter assay was performed to explore the correlation between miR-372-3p and BCL6.

The lncRNA MIR17HG was expressed in hMSCs-derived exosomes and upregulated by overexpression. hMSCs-Exo or hMSCs-Exo-MIR17HG promoted the differentiation and activation of Tfh cells, accompanied by increased PD-1 and BCL6 expression in CD4⁺ T cells, which enhanced OS cell proliferation. Furthermore, hMSCs-Exo-MIR17HG exerted a tumor-promoting effect in a CDX mouse model. Mechanistically, the effects driven by MIR17HG were abolished by miR-372-3p overexpression, and BCL6 was identified as a direct functional target of miR-372-3p.

These findings demonstrate that exosomal MIR17HG derived from hMSCs drives the differentiation of follicular helper T cells and the progression of OS via the miR-372-3p/BCL6 axis.