CAR T cells after two rounds of tumor stimulation were counted and assessed for cell viability. 1 million cells per condition were stained in cell staining buffer containing cell hashing antibodies for 30 minutes at 4°C. 3ml cell staining buffer was added and centrifuged at 400g for 5 mins. Repeated wash two more times for a total of three washes. Cells were resuspended in 500 μl of cell staining buffer and slowly filtered through a 40 μM cell strainer. Cell concentration and viability were verified and loaded on the 10X Chromium Next GEM Chip K Kit. Libraries were prepared according to manufacturer's protocol (5'V2 kit, 10x Genomics)