Relationship between maximum trough concentrations of alemtuzumab and clinical response: intravenous study. The highest trough concentration of alemtuzumab (which generally occurred following the penultimate or last dose) is plotted against the clinical response at the end of intravenous treatment as determined by NCI criteria. PD indicates progressive disease; SD, stable disease; PR, partial remission; CR, complete remission. A better clinical outcome was significantly associated with higher alemtuzumab concentrations (P = .006, Kruskal-Wallis test). There was an even stronger correlation between high trough concentrations (> 8 μg/mL) and good responses measured by less than 0.1% CLL cells in the bone marrow (•; P < .0001). Three patients who died before the end of the planned treatment course are not included in this figure. Of those patients, 2 had low alemtuzumab concentrations (≤ 1.1 μg/mL) and progressive disease at the time of death. The third had a high antibody concentration (18.3 μg/mL) and low levels of residual disease (0.21%). Each symbol represents a single patient; • indicates a patient with no detectable MRD; ○, a patient with detectable MRD.