Normal and malignant B-lineage cells were eliminated from the blood and BM of patient 3. (A) Before treatment, the blood of patient 3 contained an elevated number of B cells, 96% of which were leukemia cells. After treatment, the blood B-cell count has remained below normal and patient 3 has been in complete remission for 67 weeks. B cells were quantitated by flow cytometry staining of CD19⁺ cells. (B) CD19 IHC staining of the BM of patient 3 is shown before treatment and 13 weeks after treatment. The BM contained large numbers of CD19⁺ cells before treatment. Thirteen weeks after treatment, CD19⁺ cells were nearly absent. (C) CD20 IHC staining of the BM of patient 3 is shown before treatment and 13 weeks after treatment. The BM contained large numbers of CD20⁺ cells before treatment. Thirteen weeks after treatment, CD20⁺ cells were nearly absent. (D) Flow cytometric results of a BM aspirate from patient 3 are shown. Plots are gated on lymphoid cells by forward and side scatter. A monoclonal population of B cells expressing the characteristic CD19⁺ and CD5⁺ phenotype of CLL (circled) was present before treatment but not 13 weeks after treatment.