Researchers reported an mRNA delivery system designed to generate functional CAR T cells inside the body, removing the need for external immune stimulation or antibody targeting. Using polymer–lipid nanoparticles, the approach preferentially delivers genetic cargo to T cells in the spleen after systemic administration while simultaneously activating those T cells. The study, published in Nature Materials, positions the platform as a path toward in situ CAR T manufacturing. If replicated in translational models, the technology could reduce manufacturing complexity and supply bottlenecks that have constrained CAR T scale-up.