Defining CAR as a cellular receptor for the avian adenovirus CELO using a genetic analysis of the two viral fibre proteins

Abstract

The coxsackievirus and adenovirus receptor (CAR) is a high affinity receptor used by adenoviruses, including adenovirus type 5 (Ad5). The adenovirus fibre molecule bears the high affinity cell binding domain of Ad5, allowing virions to attach to CAR. The avian adenovirus CELO displays two fibre molecules on its capsid and it was logical to expect that the cell binding functions of CELO might also reside in one or both of these fibres. We had previously shown that the cell binding properties of CELO resemble Ad5, suggesting that the two viruses use similar receptors. Experiments with CAR-deficient CHO cells and CHO cells modified to express CAR demonstrated that CELO has CAR-dependent transduction behaviour like Ad5. Mutations were introduced into the CELO genome to disrupt either the long fibre 1 or the short fibre 2. A CELO genome with fibre 2 disrupted did not generate virus, demonstrating that fibre 2 is essential for some stage in virus growth, assembly or spread. However, a CELO genome with disrupted fibre 1 gene produced virus (CELOdF1) that was capable of entering chicken cells, but had lost both the ability to efficiently transduce human cells and the CAR-specific transduction displayed by wild-type CELO. The ability of CELOdF1 to transduce chicken cells suggests that CELOdF1 may still bind, probably via fibre 2, to a receptor expressed on avian but not mammalian cells. CELOdF1 replication was dramatically impaired in chicken embryos, demonstrating that fibre 1 is important for the in vivo biology of CELO.

Restoration of p53 tumor-suppressor activity in human tumor cells in vitro and in their xenografts in vivo by recombinant avian adenovirus CELO-p53

“…[16][17][18][19] Avian Ad CELO (FAV-1) seems to be a promising candidate for the development of alternative Ad vectors that are able to transfer genes into different human cells, with the efficiencies comparable to those of Ad5 vectors. [17][18][19][20] There are three features of the CELO virus that distinguish it from human Ads and provide additional advantages for gene therapy applications. First, there is no pre-existing immune response to this virus in human population.…”

“…Indeed, unlike other Ads, the CELO virus is characterized by two different-length fibers at each vertex of a virion. 20 The CELO long fiber is responsible for the recognition of the coxsackie-Ad receptor (CAR), [20][21][22][23][24] and, unlike the short CELO fiber, it is dispensable for both virus assembly and its penetration into permissive cells. 20 Thus, it seems that the directed modifications within the long fiber can alter virus specificity to definite cell types without significant change of its natural tropism.…”

Chick embryo lethal orphan virus can be polymer-coated and retargeted to infect mammalian cells

“…However, while Coxsackie-adenovirus receptor (CAR) is the primary receptor for initial cell attachment for most human adenovirus serotypes, 1 it has also been demonstrated to act as a CELO virus fibre 1 receptor, permitting attachment to cells lacking the avian cell surface receptor. 38 Following staining with an antihCAR antibody, flow cytometry revealed that high levels of surface CAR expression in DU-145 and PNT-2 cells ( Figure 2, Table 1) correlated with greater CELOluc transduction ( Figure 1) and likewise low CAR expression on PC-3 and PNT1a cells correlated with poor levels of CELOluc transduction.…”

“…4,5 To avoid pre-existing humoral immunity in patients, several groups have investigated adenovirus serotypes from alternative species such as cows, [6][7][8][9][10][11][12][13][14] sheep, [15][16][17][18][19][20][21][22][23][24][25] chimpanzees, [26][27][28] dogs [29][30][31][32][33][34][35][36] and chickens. [37][38][39][40] Chicken embryo lethal orphan virus (CELO; fowl adenovirus type 1), characterized as an infectious agent in 1957, 41 is attractive as a gene delivery vector since it is simple and cheap to produce in bulk in chicken embryos and has a good safety profile being completely replication defective in human cells, even in the presence of wild-type human adenovirus. 42 CELO is structurally similar to mammalian adenoviruses possessing an icosahedral capsid of 70-80 nm composed of hexon and penton proteins.…”

“…Fibre 1 is 42.5 nm in length and contains a sharp kink, while fibre 2 is 8.5 nm in length and straight. [42][43][44][45] Although recombinant CELO has been demonstrated to transduce a range of mammalian cell lines and primary cells, [37][38][39][40] in general, the level of transgene expression falls below that of adenovirus type 5 (Ad5) vectors when delivered at comparable multiplicity of infection.…”