CARTs robustly transfect resting NK cells with mRNA. (A) Charge-altering rearrangement and structures of single-lipid and mixed-lipid CARTs. (B) Percentage of transfection of primary resting human NK cells from 3 donors (500 000 cells per well in 100 μL of serum-free RPMI) using L2000, L3000, CART D₁₃:A₁₁, CART O₅:N₆:A₉, or CART BDK-O₇:N₇:A₁₃. CART/mRNA polyplexes were formulated at a 10:1 charge ratio (+/−, assuming all ionizable cationic groups are protonated). NK cells were incubated with the complexes for 6 hours before analysis by flow cytometry. Error bars represent ±standard deviation. **P < .01, ****P < .0001. n.s., not significant via paired Student t test at the 2-sided P = .05 level.