An Ovine Adenovirus Vector Lacks Transforming Ability in Cells That Are Transformed by AD5 E1A/B Sequences

Abstract

Adenoviruses of the Mastadenovirus and Aviadenovirus genera are able to transform certain cell types and induce tumor formation in susceptible animals. For the mastadenoviruses the E1A/B sequences are largely responsible for these properties but E4 sequences may also be involved. The transforming sequences of the aviadenoviruses, which lack E1A/B and E4 homologues, have not yet been fully identified. The recent proposal for a third genus of adenoviruses, which apparently lack an E1A homologue and have weak E1B homology, prompted an examination of the transforming properties of ovine adenovirus OAV287 (OAV), the prototype member of the new group. When OAV and human adenovirus type 5 (Ad5) were used to infect primary rat embryo cells, transformed foci developed in Ad5- but not in OAV-infected cultures. Similarly, after plasmid transfection, baby rat kidney cells were transformed by Ad5 E1A/B but not by OAV sequences. When CSL503 cells, an ovine cell line that is permissive for OAV, were transfected with Ad5 E1A/B sequences, transformed foci again appeared. However, plasmids or fragments containing complete or partial OAV genome sequences did not detectably transform CSL503 cells under the same conditions. When Ad5 E1A/B sequences were incorporated into the complete OAV genome and transfected, transformed clones were again obtained, showing that the gene dosage and transfection conditions were not limiting for transformation. The provision of Ad5 E1A and OAV sequences in combination marginally increased the number of morphologically altered foci in baby rat kidney cells but failed to induce multilayered focus formation. The data suggest that OAV lacks transforming functions in the cell types examined. Additional information suggesting that OAV may have a fundamentally distinct strategy for replication compared with other Ads is discussed.

Biology of Ovine Adenovirus Infection of Nonpermissive Cells

“…On the other hand, we conclude that even in the presence of viral DNA replication and synthesis of early and late gene products, OAdV replication remains blocked in nonovine cells. Together with the lack of transforming ability of OAdV (60) and the lack of transcomplementation of OAdV by Ad5 (30), our data have important positive implications for the biosafety of OAdV vectors.…”

Gene therapy for prostate cancer delivered by ovine adenovirus and mediated by purine nucleoside phosphorylase and fludarabine in mouse models

“…This is the subject of continuing studies, but so far it has been shown that OAdV does not replicate in a variety of cell human lines, 39 nor does it transform rodent cells that are transformed by human AdV5. 46 In addition, intravenous administration of approximately 10 11 virus particles into SCID or BALB/c mice did not cause overt toxicity. 37 Tumors based on the RM1 cell line grown in C57BL/6 mice grow far more aggressively than does prostate cancer in man.…”

Preclinical evaluation of a prostate-targeted gene-directed enzyme prodrug therapy delivered by ovine atadenovirus

“…17 As previously mentioned, the vectors have a favorable biosafety profile in human cells with respect to replication, transformation and complementation. [9][10][11][12] In addition, the legitimacy of the overall PNP-GDEPT strategy has been well documented. 17,20,21 In this study where vector was delivered intratumorally, there was no histological evidence of treatment toxicity in liver, spleen, kidney, lung or gut.…”

“…This virus is the prototype of a new genus that is distinct from the mastadenoviruses that contains all human adenoviruses. OAdV vectors escape pre-existing antibodies in sera that neutralize human adenoviruses 8 and have a favorable biosafety profile: they are replication abortive in human cells, 9 lack transforming activity 10 and are not complemented in coinfected cells by replicating human adenoviruses. 11,12 OAdV can also infect cells in human prostate biopsies maintained in organ culture.…”