Our single-cell transcriptomic analysis of BM samples identified three samples (at the time of relapse and post second CAR T-cell infusion) with significant numbers of MM cells, evidenced by expression of CD138 and XBP1 (markers of plasma cells), CCND1 (upregulated in this patient with t(11;14)), and lack of RB1 (downregulated in this patient with del13) (Fig. 2C). This evidence concerns the gene SDC1 and Miyoshi myopathy.