It relates to immune cells (e.g., T cells such as CAR-T cells, NK cells such as CAR-NK cells) modified to have no or reduced expression and/or function of one or more target proteins selected from the group consisting of: Signal Peptide Peptidase Like 3 (SPPL3), FADD, FAS, CASP8, ARID1A, BAK1, BID, ETS1, IKZF2, and HIST1H1B (such as SPPL3), uses thereof, and methods for generating thereof. Also provided are uses of the one or more target proteins (e.g., SPPL3) as a biomarker.