<p>T cells and natural killer (NK) cells collaborate to maintain immune homeostasis. Current cancer immunotherapies predominantly rely on the individual application of these cells. Here we use bicistronic vectors to co-express chimeric antigen receptors (CARs) and secreted immune cell engagers (ICEs), leveraging the combined therapeutic potential of both effector cell types. After in vitro validation of immune cell engager secretion and function, various combinatorial approaches are systematically compared in mouse models, identifying a highly effective combination of bispecific killer cell engager (BiKE)-secreting CAR-T cells and NK cells. Beyond a simple combination of conventional CAR-T cells and NK cells, this strategy demonstrates superior efficacy in CD19⁺ B cell leukaemia and lymphoma and EGFR⁺ solid tumour models while reducing the dosage dependence on CAR-T cells. Moreover, CAR-T cells and BiKEs targeting distinct antigens exhibit suppression of tumour cells with heterogeneous antigen expression. These findings indicate that combining BiKE-secreting CAR-T cells and NK cells offers a promising strategy to combat tumour antigen heterogeneity and immune evasion.</p>