CD34⁺ cell–mediated suppression of CTL responses is prevented by addition of neutralizing anti–TNF-α mAb. A 5-day MLR in which responder cells were stimulated against allogeneic cells from the CD34+ cell donor in the presence (▪) or absence (▨) of CD34⁺ cells was established. Anti–TNF-α mAb was added at the beginning of the culture at a concentration of 5 μg/mL. The CTL activity was determined by the end of 7-day limiting dilution cultures. Data show the average percent responding cultures (± standard deviation) of 3 experiments at cell concentrations of 4 × 10⁴ cells per well. * Indicates statistical significance.