Current advances and future challenges in Adenoviral vector biology and targeting

Abstract

Gene delivery vectors based on Adenoviral (Ad) vectors have enormous potential for the treatment of both hereditary and acquired disease. Detailed structural analysis of the Ad virion, combined with functional studies has broadened our knowledge of the structure/function relationships between Ad vectors and host cells/tissues and substantial achievement has been made towards a thorough understanding of the biology of Ad vectors. The widespread use of Ad vectors for clinical gene therapy is compromised by their inherent immunogenicity. The generation of safer and more effective Ad vectors, targeted to the site of disease, has therefore become a great ambition in the field of Ad vector development. This review provides a synopsis of the structure/function relationships between Ad vectors and host systems and summarizes the many innovative approaches towards achieving Ad vector targeting.

Fig. (1)

(A) CryoEM reconstruction of the Ad5 virion, viewed along the three-fold axis of symmetry at ~21 Å resolution. The flexible fibers are averaged out during the reconstruction and only a small portion can be visualized protruding from each penton base. The central facet of the icosahedron is outlined. (B) Schematic of outer surface of the central facet, indicating the positions of the GON, peripentonal., and adjacent facet hexons as well as the position of the N- and C-terminal domains of protein IX. The four unique hexons of each asymmetric unit are designated by the numeric labels H1, H2, H3, and H4. H1 designates peripentonal hexons, H2 hexons lie along the two-fold axis, H3 hexons surround the three-fold axis and H4 are at the fourth nonequivalent position. Hexons labeled H1’ and H2’ are from the adjacent facet. (C) Schematic of the inner surface of the same facet, indicating the positions of proteins IIIa and VIII. Hexon labeling is the same as in panel (B).

Fig. (2)

Timeline of the Ad5 binding, entry, and trafficking pathway. Initial attachment is mediated through the fiber-CAR interaction. Subsequent binding of the penton base RGD motifs to integrins results in signaling cascades and endocytic uptake. Endosomal acidification is sensed by the incoming virion, resulting in fiber release, vertex disassembly, exposure of protein VI, and lysis of the endosomal membrane. Cytoplasmic virions can then interact with dynein for transport along microtubules to the microtubule organizing center (MTOC). Cellular export factor CRM1 then mediates transfer to the nuclear pore complex (NPC) where the virion binds, disassembles, and releases its genome into the host cell nucleus.

Fig. (3)

General strategies towards redirecting Ad vector transduction to target cells through specific ligand-receptor interactions.