Nature Communications, Published online: 07 September 2026; doi:10.1038/s41467-026-76570-9 T cell proliferative capacity and persistence are key determinants of CAR-T cell therapeutic efficacy. Here, the authors show that CAREp, a microparticle-based platform displaying CAR-targeting antigens and CD28-costimulatory antibodies, selectively and sustainably expands human CD8+ CAR-T cells while maintaining a memory-associated progenitor state and delayed exhaustion.