What if immune cells could be reprogrammed to fight cancer directly inside the body, instead of in a lab? A new @NatureBiotech study from MIT used lipid nanoparticles to deliver CAR mRNA directly to natural killer (NK) cells. Up to 80% of NK cells were reprogrammed in mice using an NKG2D-targeted particle. Targeting NKG2A, an inhibitory checkpoint, both delivered the mRNA and relieved an inhibitory brake, leading to complete tumor regression in most treated mice in a melanoma model, with no recurrence through day 100. CAR expression was temporary, and repeat dosing may be needed. Still preclinical. But a cell therapy delivered from a vial instead of manufactured in a lab could transform access to cancer treatment.