柏倉 裕志

Staphylococcus aureus Cas9 (SaCas9) is smaller than the widely used Streptococcus pyogenes Cas9 (SpCas9) and has been harnessed for gene therapy using an adeno-associated virus vector. However, SaCas9 requires a longer NNGRRT (where N is any nucleotide and R is A or G) protospacer adjacent motif (PAM) for target DNA recognition, thereby restricting the targeting range. Although PAM-relaxed Cas9 variants have been developed, expanded targeting is often accompanied by compromised target specificity. Here, we report the rational engineering of eSaCas9-NNG, a SaCas9 variant that recognizes relaxed NNG PAMs while maintaining high target fidelity, thereby overcoming a fundamental trade-off in Cas9-based genome editing. eSaCas9-NNG efficiently induces indels and base conversions at endogenous sites bearing NNG PAMs in human cells and mice, with editing efficiencies comparable to those of other PAM-relaxed nucleases, including SpRY, SpG, and iGeoCas9, but with reduced off-target activity. We further determine the cryo-electron microscopy structures of eSaCas9-NNG in five distinct functional states, revealing the structural basis for its relaxed PAM recognition, improved target specificity, and nuclease activation. Overall, our findings demonstrate that eSaCas9-NNG could be used as a versatile genome editing tool for in vivo gene therapy, and improve our mechanistic understanding of the diverse CRISPR-Cas9 nucleases.

The major challenges of gene therapy for hemophilia A using adeno-associated virus (AAV) vectors are reducing vector doses and the long-term maintenance of stable factor VIII (FVIII). In this study, we developed engineered human B-domain-deleted FVIIIs (FVIIISQ) with enhanced secretion and coagulation potential. Intracellular accumulation was markedly reduced in some engineered FVIIISQ, resulting in reduced unfolded protein responses. The administration of AAV vectors carrying engineered FVIIISQ to hemophilia A mice resulted in ∼8-fold higher FVIII activity and 4-fold higher FVIII antigen levels compared with wild-type FVIIISQ administration. The specific FVIII activity of the engineered FVIIISQ was 3.6 times higher than that of the wild-type FVIIISQ, and its binding to activated coagulation factor IX was significantly enhanced, which is supported by the structural analysis. In macaques, the administration of AAV5 vector carrying the engineered FVIIISQ without CpG sequences resulted in a supraphysiological increase in plasma FVIII activity at a dose one-thirtieth that of valoctocogene roxaparvovec (2 × 1012 vector genome per kg). The engineered FVIIISQ may thus provide stable, long-term therapeutic efficacy in AAV-mediated hemophilia A gene therapy even at low doses.