J. Freire, S. Pang, J. E. McGee, M. J. Heinrich, J. Xie, E. Hammarlund, D. Shaw, Y. Zhou, Y. K. Wang, C. Porter, L. Dang, E. San Antonio, Z. Yu, K. Li, S. Stone, H. Lidov, J. Farrell, E. K. Osterweil, W. Wong, M. Grinstaff, X. Han
Facile, non-genomic integrating gene delivery technologies are lacking for rapid onset and prolonged protein expression in the brain. Here we report the protein expression and cell type tropism for an advanced messenger ribonucleic acid (mRNA) technology, modified 5-hydroxymethylcytidine (hm5C) self-amplifying ribonucleic acid (saRNA), when injected into the mouse brain or applied to ex vivo human cortical brain slices. saRNA, encoding fluorescent proteins, encapsulated in an LNP formulation comprising ALC-0315 (present in Comirnaty(R)) efficiently mediates long-lasting protein expression in mouse brain cells beyond five weeks, with detectable expression in some neurons at three months. hm5C saRNA substantially outperforms N1m{Psi} mRNA. In addition to transfecting astrocytes and neurons at the injection site, hm5C saRNA-LNPs label neurons retrogradely. Excitingly, hm5C saRNA-LNPs afford protein expression in human cortical brain slices, with expression emerging within 24 hours and lasting beyond 76 days. Modified saRNA provides new opportunities for mechanistic neuroscience research and therapeutic development.