Johns Hopkins Medicine researchers reported a biodegradable nanoparticle that delivers mRNA encoding an anti-CD19 chimeric antigen receptor (CAR) directly to T cells in vivo, producing functional CAR T cells and depleting B cells in mice. The approach replaces complex ex vivo manufacturing with targeted lipid/polymer nanoparticles that ‘educate’ circulating T cells to express therapeutic CARs, producing systemic B‑cell depletion in preclinical models. The team published mechanistic and efficacy data in Science Advances, highlighting a simplified delivery vehicle and favorable tolerability in mouse studies. Authors positioned the technology as a pathway to broaden access to CAR T modalities by cutting costs and logistical barriers tied to cell collection, engineering and expansion. Translational questions remain — including dosing, durability of in vivo–generated CAR T cells, off-target expression risks, and manufacturability at clinical scale — but the result is a critical preclinical milestone toward in‑patient CAR T generation.