CD19⁻ bone marrow PCs resist elimination by CTL019. (A) Bone marrow aspirate from healthy donors were stained and analyzed by flow cytometry. The bottom right panel shows CD19 expression on CD138⁺CD38⁺ PCs (red) and CD20⁺CD19⁺ cells (blue); the green histogram represents CD138⁺CD38⁺ cells with fluorescence-minus-one (CD19) staining. Representative data from 7 donors are shown. The “dump” channel contains stains for viability, CD3, CD14, and CD16. (B) Bone marrow aspirate cells from CHP-11 on day 28 post-CTL019 infusion were analyzed as in panel A. Gating for B cells (top left), PCs (top right) is shown. The bottom left panel shows CD19 expression on CD38⁺CD138⁺ cells (red histogram) and on all singlet events in the forward (FSC) and side scatter (SSC) gate (blue histogram). In both panels A and B, expression of light chains was assessed by intracellular staining. (C) Two hundred thousand cells from the aspirate material shown in panel B were plated in ELISPOT wells, which were stained for total IgG, IgM, and IgA after overnight incubation.