B cells are depleted after melphalan conditioning. Plotted are the average absolute B-cell counts (top), absolute numbers of naive B cells (IgM⁺, CD27⁻; middle), or percentage of B cells with a switched memory phenotype (IgM⁻, CD27⁺; bottom) as a function of time. At most time points, most of the B cells are naive B cells. During the time of maximal B-cell depletion (day 14), switch memory B cells predominate.