CTL killing at various effector-target ratios. The cell key is the same as that in Figure 7. These experiments are similar to those discussed in Figure 5 except that here the target cells were incubated with different amounts of effector T cells (giving different effector/target [E/T] ratios). As in Figure 5, these target cells were also preincubated with anti–class 1 antibody (W6/32), anti–class 2 antibody (L243), or no antibody. Shown is a 2-layer panel, and each panel includes the results using 2 MM targets (4 patients total). At the top of each panel are the CTL responses (as percentage of killing with standard deviation) of 3 donors (each experiment performed in quadruplicate) against the MM cells from 2 patients, as indicated. The experimental labels at the bottom of the figure and the target cell key identify these CTL responses, with the E/T ratio indicated at the bottom of each panel. Note that all donors' resultant CTLs effected a level of killing that directly correlated with the E/T ratio, with increasing ratios (increasing addition of CTLs) resulting in increasing target killing. Also note, as in Figure 8, the addition of anti–class 1 antibody-inhibited killing (again, anti–class 2 antibody did not inhibit killing).