A central mandate to realize effective gene therapy is the ability to accomplish cell specific delivery. Capitalizing on the in vivo delivery efficacy of adenoviral vectors (Ad), recent studies have highlighted the capacity of targeted Ad to accomplish cell selectivity in this stringent delivery context. Systemic employment of Ad for gene delivery, however, is currently limited by vector particle sequestration in the liver. Recent work in several laboratories, however, has identified the biologic dictates of vector hepatotropism. Based on this understanding, it has now been possible to un-target the liver thereby facilitating strategies designed to achieve cell specific gene delivery in the context of systemic vector administration. Of note, we have recently shown that such liver un-targeting strategies can synergize with described vector targeting methods such as those based upon restricting delivered transgene expression to target cells with a tissue/tumor selective promoter (transcriptional targeting). The dramatic synergistic specificity gains noted with combination of these two approaches logically suggests that further gains may accrue additional targeting methods exploited in combination. In this regard, strategies have been proposed to target Ad based upon re-directing vector binding to target cell specific cell surface markers. Such transductional targeting methods would offer potential synergies with the targeting methods we note above. Such an endeavor has been limited to this point by the inability of current vector engineering to achieve capsid incorporation of antibody targeting species. Herein we seek to address this key limit. First, we have developed a method to replace the native adenovirus fiber with a substitute chimera devoid of the native fiber's knob binding domain. This maneuver eliminates native tropism and allows for the incorporation of a wider range of large/complex candidate targeting ligands. Second, we have demonstrated that the single domain antibody species derived from camelids (sdAb) possess the unique attributes allowing biologic compatibility with adenovirus capsid synthesis and assembly. In the aggregate, these two technologies now allow for the functional incorporation of antibody targeting species into the Ad capsid for the achievement of cell-specific targeting. This additional level of targeting provides for potential synergies with the defined liver un-targeting and transcriptional vector targeting methods we have explored.
The central challenge for any gene therapy intervention is effective gene delivery. In this regard, vectors capable of efficient and selective gene delivery are critical to address this mandate. Our proposal seeks to develop targeted adenoviral vectors and thereby address key proof-of-principle issues of field wide relevance.
| Stephens, Calvin J; Kashentseva, Elena; Everett, William et al. (2018) Targeted in vivo knock-in of human alpha-1-antitrypsin cDNA using adenoviral delivery of CRISPR/Cas9. Gene Ther 25:139-156 |
