4. Conclusion

Currently, various approaches including both viral and nonviral vector-based delivery methods are studied for safe and efficient human gene therapy. They have their own properties, such as duration of gene expression, size of transgene to load, possible organs and their expected volumes in single procedure, and repeatability. Conditions to treat are also diverse. Congenital disease such as hemophilia possibly requires long-term transgene expression for decades. For in vivo gene editing based on CRISPR/Cas9, short-term transgene expression may be preferred, to prevent off-target effect. Therefore, the transient gene expression mediated by the nonviral vector-based delivery may have great advantages when it comes to gene editing. Among the methods, as described above, HGD may be a promising delivery approach as it is simpler and more efficient. Currently, we are modifying the original HGD method used in small animals in order to apply it into large animals to test its efficacy and safety. Metabolic and genetic diseases, which show lower level of normal functional protein, are so far good candidates for this type of procedure. Although there is evidence showing transgene expression and that the procedure was safely performed in pigs [54–57], dogs [58, 59], and baboons [60, 61], further preclinical studies are necessary prior to human therapy application.
