Similarly, 4-1BBζ signaling in CARs has been shown to trigger T cell apoptosis, thereby hampering their antitumor activity.39 Further investigations assert that CD19-CD28ζ showcases better efficacy compared with CD19-4-1BBζ in counteracting low antigen tumors.40 Nevertheless, only partial tumor remission was achieved with FCRL5-CD28ζ CAR-T-cell administration. This evidence concerns the gene CD19 and neoplasm.