Hypoxia Potentiates Glioma Immunosuppression inhibitions was further potentiated by hypoxia as previous shown but could be reversed with WP1066 to the greater degree than WP744. B. The supernatant culture mediums from the gCSCs induces an increase in the number of FoxP3+ regulatory T cells among the gated CD4+ T cells that is further enhanced under conditions of hypoxia as previously shown. This was reversed with WP744 to a greater degree than with WP1066. The controls were T cells cultured in respective neurosphere medium of normoxia and hypoxic conditions. * P,0.05 versus untreated gCSCs exposed to normoxia or hypoxia C. Both WP1066 and WP744 reversed the inhibition of phagocytosis in monocytes by hypoxia exposed gCSCs in all 4 gCSCs. Shown are representative high-power fluorescent microscope images (40X) of monocytes cultured with (i) hypoxia-exposed gCSC supernatant, (ii) WP1066-treated, hypoxia-exposed gCSC supernatant, and (iii) WP744-treated, hypoxia-exposed gCSC supernatant. * P,0.05 versus untreated hypoxia-exposed gCSCs. doi:10.1371/journal.pone.0016195.g006 Conclusion This study demonstrates that hypoxia increases the ability of gliomas to induce immunosuppressive cells such as Tregs and M2 macrophages and thus plays a key role in both tumor-mediated innate and adaptive immune suppression. These findings also help to reconcile the disparate findings that immune therapeutic approaches can be used successfully in preclinical model systems but have yet to achieve successful responses in the vast majority of patients by demonstrating the importance of the tumor hypoxic environment in markedly inducing the immune suppressive properties of the GBM. 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