SECTM1 CAR expression led to fratricide of CD7⁺ cells. (A) Schematic presentation of the MOCK and SECTM1 CAR domains. (B) Representative CAR expression of the T cells was detected by flow cytometric on day 3 after transduction, and the percentage of positive cells is presented in the histogram. (C). The number of T cells was counted on day 3 after transduction. (D) IFNγ secreted into the supernatant of transduced T cell culture medium was measured by ELISA on day 3 after transduction. (E) CD7 expression of NT, MOCK, and SECTM1 CAR T cells was measured by flow cytometry on day 3 after transduction. The percentage of positive cells compared with an isotype control (ISO) is presented in the histogram. Data in panels C and D are presented as the mean ± SD of triplicates.