Objective: This study aimed to elucidate the effects of melanoma-derived exosomes on modulating the differentiation of hematopoietic stem cells (HSCs) towards immunosuppressive myeloid-derived suppressor cells (MDSCs).

Materials and Methods: Exosomes were isolated via ultracentrifugation from conditioned media of the B16F10 murine melanoma cell line after adaptation to exosome-free culture conditions. HSCs were extracted from the bone marrow of adult C57BL/6 mice through density gradient separation and MACS column isolation of CD133+ and CD34+ populations. HSCs were cultured with or without B16F10 exosomes for 24 hours. Flow cytometry analyzed the expression of canonical MDSC surface markers CD11b, Ly6G, and Ly6C. Levels of the immunosuppressive cytokines interleukin-10 (IL-10) and tumor necrosis factor beta (TGF-β) in HSC culture supernatants were quantified by ELISA.

Results: Compared to untreated controls, HSCs treated with B16F10 exosomes displayed significantly increased percentages of CD11b+Ly6G+ granulocytic MDSCs and CD11b+Ly6C+ monocytic MDSCs, with a notable predominance of the Ly6G+ granulocytic subtype. Additionally, exosome-treated HSCs secreted markedly higher levels of the cytokines IL-10 and TGF-β, which are involved in MDSC-mediated immunosuppression.

Conclusions: Our findings demonstrate that melanoma-derived exosomes can orchestrate the differentiation of HSCs into MDSCs with an immunosuppressive phenotype, as evidenced by the upregulation of MDSC surface markers and secreted cytokines. This supports a role for tumor-derived exosomes in driving the systemic expansion and accumulation of immunosuppressive MDSCs through the reprogramming of HSC fate. Elucidating the exosome contents and HSC signaling pathways involved could reveal therapeutic strategies to block this pathway and enhance anti-tumor immunity.