Third-generation CARs improved costimulation by including two co-stimulatory signaling domains (Fig. ) . Incorporating the OX40, ICOS, or CD27 as secondary costimulatory domains increases the expansion and persistence of resting T cells through proinflammatory pathways . In murine models, third-generation CARs mount a more robust antitumor response and contribute to longer-surviving mice . Specifically, ICOS signaling improves CAR-T cell persistence in solid tumors compared to a single costimulatory domain by increasing cytokine release, such as IFN-γ and IL-22 . A clinical study demonstrated third-generation CARs to perform moderately well, with 2 patients achieving complete remission and 1 patient arriving at a partial response . The study observed T cell persistence of up to 12 months with slightly improved antitumor activity, suggesting a benefit from the additional costimulatory domain . Hence, the preclinical and clinical outcomes of third-generation CARs remain promising.