Myeloma patient CD4⁺ T-cell numbers are unchanged during therapy, but their ability to secrete IL-2 is impaired. (A) Twenty-five MM patient PBMC CD4⁺ T-cell frequency (left panel) and absolute number per milliliter was calculated (right panel). (B) To assess whether NK cell dysfunction at cycle 6 of treatment correlated with reduced IL-2 production, PBMCs from 11 MM patients were collected at baseline and cycle 6, and IL-2 secretion was assessed by cytokine bead array on culture supernatant (left panel). To assess the ability of MM patient PBMCs to respond to stimulation, the cells were stimulated with OKT-3 and anti-CD28/49d before assessing IL-2 production (right panel).