Patient 10 entered a stringent complete remission. (A) Before treatment, patient 10’s bone marrow was stained for BCMA by IHC. BCMA expression was uniform but dim on the MM cells (500×). (B) Flow cytometry of patient 10’s bone marrow showed dim but uniform BCMA expression on the CD19-negative malignant plasma cells (red), whereas BCMA expression was absent on CD19⁺ B lymphocytes (black). The plot shows a combination of the plasma cell gate (CD38^bright, CD138⁺, CD45^dim-negative) and the mature B-cell gate (CD45⁺, CD19⁺ lymphocytes). (C) Four hours after CAR-BCMA infusion, patient 10 became febrile. He was febrile for 7 days. The plot shows the maximum temperature for each day. The CRP was elevated. (D) Before initiation of protocol treatment, patient 10 had a hypercellular bone marrow (hematoxylin and eosin). Bone marrow cells were ≥90% plasma cells as shown by CD138 staining. BCMA expression was dim but present. (E) Four weeks after CAR T-cell infusion, the bone marrow was hypocellular, and bone marrow plasma cells were completely absent as shown by the negative CD138 and BCMA staining. (F) Eight weeks after CAR T-cell infusion, the bone marrow was recovering with an overall cellularity of 25%, and plasma cells remained absent. Magnification for D-F was 40×. (G) Immediately before CAR-BCMA infusion, the patient had a serum IgA level of 2633 mg/dL. After CAR T-cell infusion on day 0, serum IgA decreased until reaching undetectable levels. (H) IHC staining of patient 10’s bone marrow showed an infiltrate of CD3⁺ T cells 4 weeks after CAR T-cell infusion. (I) Flow cytometry with a PE-BCMA-Fc reagent showed that 31% of bone marrow T cells were CAR-BCMA T cells 4 weeks after CAR T-cell infusion. The plot is gated on CD45⁺ and CD3⁺ lymphocytes.