Johns Hopkins researchers published Science Advances data showing biodegradable polymeric nanoparticles can deliver mRNA encoding anti‑CD19 CARs directly to T cells in vivo, generating functional CAR‑T cells and depleting B cells in mice. The approach aims to bypass ex vivo manufacturing, potentially reducing cost and complexity for CAR‑T deployment in oncology and autoimmune disease. The team engineered targeted, polymer‑based LNPs that home to T cells and transiently express CAR constructs; treated animals showed durable B cell depletion consistent with CAR‑T activity. Authors highlighted improved scalability, simplified logistics and the prospect of outpatient administration as central advantages. Translational barriers remain—scaling specificity, managing immunogenicity, and defining dosing/long‑term safety—but the platform represents a significant conceptual advance toward off‑the‑shelf cell therapies produced in vivo rather than in manufacturing suites.