Tumor spheroid–infiltrating CTLs exhibit a diminished ability for cytokine production, and oxamic acid is able to prevent this suppression. (A) MCTSs were generated in the presence or absence of oxamic acid from exponentially growing MelIm tumor cells. After 4 to 5 days, medium was replaced by a suspension containing 0.4 × 106/mL CTLs. Infiltrating CTLs were visualized in 5-μm paraffin sections by staining for the T-cell marker CD3 (bar = 100 μm). (B) Day-4 to day-11 MCTSs were generated in the presence or absence of 60 mM oxamic acid (OA) and supernatants analyzed for lactate content. Horizontal bars represent the mean values. (C) Reduction of IFN-γ–positive CTLs relative to control cells without MCTSs against the lactate content of the MCTS coculture. (D) After 24 hours of coculture, day-5 MCTSs were disintegrated, and cells were stained intracellularly for IL-2 and IFN-γ. CTLs cultured in medium without MCTSs were used as control. Shown are representative data of 3 independent experiments.
