Treatment rapidly reduces circulating CLL cell levels in responding patients, while nonresponders show more gradual depletion. The figure shows the absolute peripheral blood CLL cell count on a logarithmic scale (top panel) and the percentage of CLL cells in the bone marrow (bottom panel) in nonresponding (▦, n = 27) and responding patients (□, n = 16). The schema for alemtuzumab therapy is indicated by the gray arrows at the top of the graph. PRE indicates pretreatment. The line at the top of each box denotes the 75th percentile; the line at the bottom of each box, the 25th percentile; the line in the middle of each box, the 50th percentile or median; the upper bar, the 95th percentile; and the lower bar, the 5th percentile.