CD19 CAR T cells were transduced via lentivirus and the CD19 CAR expression can be quantified by the co‐expressed GFP (525 nm) signal; IFN‐γ DPA reaction was detected at the same 630 nm channel; CD3 signals were detected at 690 nm which is critical to determine if the cell in the droplet is T‐cell or other cell types such as cancer cells; Lastly, CD8 fluorescence signal at 780 nm was used to further stratify the CD3+ T‐cells to CD8+ or CD8− cells which are assumed to be CD4+ T‐cells. Here, CD4 is linked to cancer.