Exosomes derived from tumor cells play essential role in tumour progression,such as angiogenesis,tumor cells proliferation and immunoregulation,while hypoxia contributes to tumor progression such as angiogenesis and metastasis potentially through exosome secretion.In present study,we cultured several cancer cell lines under hypoxia (1% O2),and found that hypoxia promoted exosome release in the number of exosomes in the medium determined on CD63 immunoblotting.When the exosomes were applied to T cells,we found exosomes from hypoxia cancer cells suppressed T cells proliferation.As TGF-β,iNOS,and PGE2 are important factors mediated T cells suppression,so we used blocking antibodies against the three factors to exosomes,and found that blocking antibody against TGF-β could anneal the immunosuppressive effects of exosomes.These data demonstrated that hypoxia enhances the breast cancer cells secretion of exosome,which contains TGF-β and suppresses T cells proliferation.Our findings has significant implications to understand the underlying mechanisms of immunosuppression in tumor microenvironment,and potentially contribute to cancer therapeutic.