CART transfection of resting NK cells is scalable and selectable. Unless noted, CART/mRNA polyplexes were prepared at a 10:1 (+/−) charge ratio and added to primary resting human NK cells (500 000 cells per well in 100 μL of serum-free RPMI in 96-well plates) and analyzed by flow cytometry after 6 hours. Effect of NK cell density on percentage of GFP⁺ cells (A) and viability (B). (C) Effect of NK cell donor on CART O₅:N₆:A₉–mediated GFP mRNA transfection. (D) Dot plot of GFP expression vs BDK fluorescence when delivering CART BDK-O₇:N₇:A₁₃/GFP mRNA polyplexes to primary resting NK cells. Percentage of NK cells (gated for live cells) that were BDK⁻GFP⁻, BDK⁻GFP⁺, BDK⁺GFP⁻, or BDK⁺GFP⁺. All measurements were run at least in triplicate. Error bars represent ±standard deviation. *P < .05 by unpaired Student t test with Bonferroni’s correction for multiple testing. n.s., not significant at P = .05.