Lck-IN-5 (example C10) is a potent and selective inhibitor of lymphocyte-specific protein tyrosine kinase (LCK). It specifically disrupts the interaction between the SH3 domain of LCK and the RK motif of CD3ε, inhibiting LCK recruitment to the T-cell receptor. Lck-IN-5 modulates the activity of CD3ε-containing CAR-T and TRuC-T cells, reduces cytokine secretion, and promotes a central memory-like phenotype associated with enhanced persistence. This compound is applicable in research on autoimmune diseases and graft-versus-host disease.