Targeted delivery of mRNA to immune cells for in vivo cell therapy.

Messenger RNA (mRNA) therapeutics have revolutionized biomedicine by enabling direct in vivo programming of immune cells. This strategy bypasses the complex manufacturing and high costs associated with ex vivo cell therapies. However, efficient and specific systemic delivery of mRNA to target immune cell subsets remains a major translational hurdle. This review systematically examines engineering strategies that address this challenge. We first outline the key biological barriers to mRNA delivery, such as serum instability, nonspecific biodistribution, cellular uptake heterogeneity, and inefficient endosomal escape. Next, we comprehensively review advances in lipid nanoparticle (LNP) engineering, including discovering novel lipids, modulating compositions, conjugating targeting ligands, and incorporating stimuli-responsive elements, to enable enhanced tropism toward specific immune cells. Representative applications in oncology, protein replacement, autoimmune disease, and tissue regeneration are highlighted. Finally, we address translational challenges in safety, scalable manufacturing, and regulatory issues. The integration of rational material design, high-throughput screening, artificial intelligence, and interdisciplinary collaboration will be essential to advance next-generation targeted in vivo mRNA cell therapies toward clinical translation.