library_construction_protocol: MM1S-Luc cells were intravenously (i.v.) injected to 6-10-week old NSG mice via tail vein (2x106 cells/mouse). After 5 days, tumor xenografts were confirmed by bioluminescence imaging. Mice were injected intravenously with dosed 2.5 × 105BCMA-CAR T cells followed by treatment with TAK-981 (7.5 mg/kg, intraperitoneally (i.p.) twice per week, BIW) or Vehicle (Veh) for 2 weeks. Bone marrow mononuclear cells were isolated and stained with human CD45 antibody. Total human T cells were sorted by gating GFP-/DAPI-/human CD45+. About 1000 cells were captured per sample on a 10xGenomics Chromium controller using a 10X V3.1 Single Cell 3' Solution kit (10xGenomics, Chromium Next GEM Single Cell 3' Regent kits V3.1, Cat. PN-1000268). All protocols were performed following the manufacture's instruction. Final sequencing libraries were analyzed on a High Sensitivity DNA Chip (Agilent, Cat 5067-4626) to determine the library size. The library concentration was determined with a Qubit high Sensitivity DNA assay Kit (Thermo, Cat. Q32854). The libraries were sequenced with the paired end setting of 28 cycles of read1, 101 cycles of R2, 8 cycles of index i7 and 8 cycles of index i5 read on Illumina NovaSeq 6000 platform with S4 Reagent kit v1.5 (Illumina, Cat 20028313) at TGEN with a depth of 100K - 135K reads per cell.