MSCs prevent NK-cell proliferation and activation. (A) NK cells were stimulated with IL-2 (250 U/mL) and cultured with IPS-MSCs or H9-MSCs for 4 days (NK/MSC ratio, 5:1). Results represent a representative experiment in which proliferation of CD56⁺/CD3⁻ NK cells was evaluated using the CFSE dilution method (5μM for 5 minutes at 37°C). (B) Activating receptors expression on activated NK cells cultured with MSCs for 4 days. Gray profiles represent marker expression, whereas open bars represent the negative control. (C) Granzyme B expression was determined by Western blot using anti-granzyme B mAb. GAPDH was used as a loading control. Numbers below each panel represent the intensities of granzyme B adjusted to GAPDH levels. (D) Secretion of IFN-γ in IL-2–activated NK cells after coculture with MSCs for 4 days was evaluated by ELISA assay. Results are representative of 5 independent experiments and are shown as the means ± SD of triplicate samples.