Figure 5.

Soluble CD137 in the supernatant of hypoxia-treated CT26 cells blocks CD137L-mediated T-cell costimulation. Cultures of CD8⁺-purified OT1 WT or OT1 CD137^−/− T cells were stimulated with anti-CD3 mAb for 48h prior to seeding in co-cultures with 293T transfected or not with CD137L as indicated. T cells were pre-loaded with Violet 450 fluorescent dye and dilution of the fluorescent dye was used as a surrogate marker of T-cell proliferation. Cultures were conditioned with cell culture supernatants (1/16 diluted) of normoxia- or hypoxia-treated CT26 cells. (A) Representative flow cytometry histograms showing the extent of inhibition of proliferation by the sCD137-containing supernatants at 72h of coculture. (B) Pooled data of two independent experiments identically performed. MFI: mean fluorescence intensity; SN: supernatant.