Immunosuppression of breast cancer cells mediated by transforming growth factor-β in exosomes from cancer cells

Exosomes derived from tumor cells are essential for processes involved in tumor progression, including angiogenesis, tumor cell proliferation and immunoregulation. In addition, exosome secretion may contribute to the mechanisms of hypoxia-induced angiogenesis and metastasis of tumors. In the present study, as it is one of the most common cancers in females, breast cancer, cell lines were cultured under hypoxic (1% O-2) and normoxic conditions to evaluate the effects of hypoxia on exosome production. Under hypoxic conditions an increase in the number of exosomes in the medium, determined by CD63 immunoblotting, was observed. Application of these exosomes to T cells revealed that they were able to suppress T cell proliferation. As transforming growth factor-beta (TGF-beta), interleukin-10, and prostaglandin E2 are important factors in the mediation of T cell suppression, the exosomes were subsequently treated with antibodies against these three factors. The results revealed that anti-TGF-beta was capable of ameliorating the immunosuppressive effects of exosomes. These data demonstrate that hypoxia enhances the secretion of exosomes by breast cancer cells, which acts to suppress T cell proliferation via TGF-beta. The findings have significant implications for understanding the underlying mechanisms of immunosuppression in tumor microenvironments, and for the potential development of cancer therapies.