Site-Specific Gene Addition for Gene Therapy: Promising Method for Safe and Efficacious Targeting

Strategic Insights -

Researchers have made significant progress in developing site-specific gene addition for gene therapy, a method that can allow stable transgene expression without the need for promiscuously integrating vectors. This approach holds promise for safe and efficacious targeting, particularly in cases where on-target and off-target effects are a concern. In a recent study, investigators demonstrated the effectiveness of recombinant adeno-associated virus (rAAV)-mediated promoterless gene targeting without nucleases in treating haemophilia B in mice.

Key Takeaways:

  • Site-specific gene addition can allow stable transgene expression for gene therapy, preferred over the use of promiscuously integrating vectors that are associated with clonal expansion and oncogenesis.
  • Site-specific endonucleases can induce high rates of targeted genome editing, but safety concerns persist, including endonuclease-associated adverse effects and oncogene activation caused by promoter integration.
  • Researchers have developed a method of recombinant adeno-associated virus (rAAV)-mediated promoterless gene targeting without nucleases, demonstrating the potential for safe and efficacious targeting.
  • The method involves targeting a promoterless human coagulation factor IX (F9) gene to the liver-expressed mouse albumin (Alb) locus, where F9 expression is linked to robust hepatic albumin expression without disrupting it.
  • The study achieved on-target integration into approximately 0.5% of the albumin alleles in hepatocytes, resulting in stable F9 plasma levels at 7-20% of normal in treated F9-deficient mice.
  • The method may allow for safe and efficacious gene targeting in both infants and adults by greatly diminishing off-target effects while still providing therapeutic levels of expression from integration.
  • The study concluded that transgene integration as a 2A-fusion to a highly expressed endogenous gene may obviate the requirement for nucleases and/or vector-borne promoters.

Statistics:

  • Approximately 0.5% of the albumin alleles in hepatocytes were integrated with the F9 gene.
  • Stable F9 plasma levels were achieved at 7-20% of normal in treated F9-deficient mice.
  • The study demonstrated a significant reduction in off-target effects compared to traditional methods.
  • The method may allow for safe and efficacious gene targeting in both infants and adults.

Sources:

  • Promoter less gene targeting without nucleases ameliorates haemophilia B in mice. Nature, 2015;517(7534):360-476.
  • University of California, Dept. of Med, San Francisco, CA 94143, United States (A. Barzel, et al.)
  • Science (additional authors: N.K. Paulk, Y. Shi, Y. Huang, K. Chu, F. Zhang, P.N. Valdmanis, L.P. Spector, M.H. Porteus, K.M. Gaensler and M.A. Kay)
  • Nature Publishing Group (www.nature.com/)
  • NewsRx LLC (2015)