HDAC inhibitors interfere barely with T-lymphocyte or NK cell activity. (A) NK cells were pretreated for 4 hours with ITF2357 (50 nM), SAHA (0.5 μM), TSA (1 μM), HC-toxin (1 μM), or tubacin (10 μM) and coincubated with ⁵¹Cr-labeled K562 cells for 4 hours at a different effector-target (E/T) ratio, in the presence of the same HDAC inhibitors. Results are expressed as percentage of cytotoxicity as described. (B) NK cells treated for 4 hours with ITF2357 (50 nM), SAHA (0.5 μM), TSA (1 μM), HC-toxin (1 μM), or tubacin (10 μM) were fixed, permeabilized, and stained with anti-tubulin-α (not shown) or anti-acetyl-tubulin-α and analyzed by cytofluorimetry. The different cultures stained equally with anti-tubulin-α (not shown). Data are expressed as mean fluorescence intensity (mean FI) of cells stained for acetyl-tubulin-α. (C) Allospecific T cells from 7-day MLR (10⁵) were pretreated for 4 hours with ITF2357 (50 nM), SAHA (0.5 μM), TSA (1 μM), HC-toxin (1 μM), or tubacin (10 μM) and coincubated with 10⁴ allogeneic DCs for 18 hours in the presence of the same HDAC inhibitors and of 1 μCi (0.037 MBq) of [³H]thymidine per well. Cells were harvested and counted in a beta counter. Tests were conducted in triplicate, and results are expressed as mean cpm ± SD. For each panel, one representative experiment of at least 3 performed is shown.