Rituximab-resistant splenic B cells are CD27⁺ IgG⁺. The B-cell content was analyzed at the time of splenectomy, 3 months after 4 cycles of rituximab (patient RTX6, Table 2). (A) CD19 and CD27 staining of blood PBMCs. (B) Staining of the splenic MNCs. From left to right: 7-AAD staining; CD19 and CD27 staining gated on 7-AAD–negative cells; IgG and isotype control staining of CD19⁺ 7-AAD–negative cells. Eighty percent of the splenic CD19⁺ B cells were of the IgG⁺CD27⁺ memory phenotype.