High-purity production and precise editing of DNA base editing ribonucleoproteins

Ribonucleoprotein (RNP) complex–mediated base editing is expected to be greatly beneficial because of its reduced off-target effects compared to plasmid- or viral vector–mediated gene editing, especially in therapeutic applications. However, production of recombinant cytosine base editors (CBEs) or adenine base editors (ABEs) with ample yield and high purity in bacterial systems is challenging. Here, we obtained highly purified CBE/ABE proteins from a human cell expression system and showed that CBE/ABE RNPs exhibited different editing patterns (i.e., less conversion ratio of multiple bases to single base) compared to plasmid-encoded CBE/ABE, mainly because of the limited life span of RNPs in cells. Furthermore, we found that off-target effects in both DNA and RNA were greatly reduced for ABE RNPs compared to plasmid-encoded ABE. We ultimately applied NG PAM–targetable ABE RNPs to in vivo gene correction in retinal degeneration 12 (rd12) model mice.