Superior In Vivo Efficacy for T Cell Engineering via Citronellol‐Tailored mRNA‐tLNPs

Efficient in vivo generation of CAR T cells via mRNA-LNP delivery necessitates high-efficiency T cell engineering, yet current systems remain suboptimal. While lymphoid tropism is essential, it is demonstrated that high tropism alone is insufficient for effective in vivo engineering-some highly tropic LNPs frequently exhibit suboptimal T cell transfection. Crucially, intrinsic T cell transfection potency emerges as an orthogonal and equally critical determinant, consistent with the need for both T cell specificity and transfection efficiency. Through screening a tail-varied ionizable lipid library, H₃T₄ is identified, a citronellol-tailed LNP with enhanced lymphoid tropism and superior intrinsic potency. The CD3-targeted H₃T₄ LNP (αH₃T₄) achieves ~85% in vivo efficacy in T cell engineering, outperforming benchmark LNPs by ∼50% (40% vs. 85%). This proposes a new optimization strategy: effective engineering requires balancing potency and tropism, not maximizing tropism alone. In murine CD19 solid tumor models, αH₃T₄-generated CAR T cells achieved 83% tumor clearance, demonstrating potency-driven efficacy. This work establishes intrinsic transfection potency as a primary tunable parameter for next-generation CAR T platforms.