Approximately five million freshly isolated PBMCs per sample were used for staining. For the first eight patients, we used PE-Labeled Human CD19 (20–291) Protein (Acro Biosystems). Later, anti-FMC63-FITC antibody by Acro Biosystems was used. Comparison of staining with protein CD19 and anti-FMC63 antibody is shown in Supplementary Figure S1 . Besides detection of CAR-T cells the samples were stained with antibodies against antigens CD3, CD4, CD8, CD45RA, CD62L, CD27, CD28, CD57, PD-1, TIM-3, and TIGIT. A second detection panel against antigens CD3, CD4, CD8, CD14, CD16, CD19, CD45, CD56, and TCRgd was used to determine significant leukocyte subsets in the samples. Antibody panels used in this study were used previously (20 (link)) and can be found in Supplementary Tables S1, S2 . All antibodies were titrated before use, and fluorescence-minus-one controls for selected antibodies were measured. Firstly, PBMCs were stained using a fixable blue dead cell stain kit (Thermo Fisher Scientific, United States), washed with FACS buffer, and then stained with antibody mix in Brilliant Stain Buffer (BD) at room temperature for 30 min. The samples were washed with FACS buffer prior to measurement.
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