Fig. 7

Adenosine generated by CeCa-MSCs strongly inhibits cytotoxic CTL activity. CTLs specific for the antigenic peptide YMLDLQPETT from the HPV-16 E7 protein were cultured for 3 h in the presence of synthetic 500 μM Ado (a) or supernatants (Sup) obtained from NCx-MSC or CeCa-MSC cultures, (b) and (c) respectively, and subsequently challenged against T2 cells loaded with the antigenic peptide YMLDLQPETT at 10:1, 5:1 and 2.5:1 ratios of effector:target cells. Some cells were cultured in the presence of 300 μM caffeine (CAF), a nonselective antagonist of Ado receptors, or 1 µM ZM241385 (ZM), a selective antagonist of A2A receptor. CTLs cultured for 3 h in the presence of 500 μM synthetic Ado were used as positive controls to analyze the inhibitory effect of Ado on CTL cytotoxic activity. The antagonists CAF and ZM were added to some culture media to block the inhibitory effect of Ado. The cytotoxic activity of CTLs was determined by a cell viability method through a CFSE and 7AAD labeling as indicated in “Methods” section. Significant differences *(P < 0.05) and **(P < 0.01) were obtained compared with the cytotoxic activity of CTLs cultured in absence of Ado. Data are representative of three independent experiments, and the mean ± SEM are shown