Characterisation of Australian ovine adenovirus isolates

Molecular characterization of a bovine adenovirus type 7 (Bovine Atadenovirus F) strain isolated from a systemically infected calf in Germany

Bovine adenovirus 7 (BAdV-7) is an unclassified member of the genus Atadenovirus with a worldwide distribution and has been reported to induce clinical disease of varying severity in infected cattle, ranging from asymptomatic infections to severe enteric or respiratory disease. In this study, we used next-generation sequencing to obtain the first complete genome sequence of a European strain of BadV-7, from pooled spleen and liver tissue obtained from a deceased newborn Limousin calf. Histopathological analysis and electron microscopy showing systemic lesions in multiple organs with intranuclear amphophilic inclusions observed in endothelial cells in multiple peripheral tissues. Virus isolation was readily achieved from tissue homogenate using bovine esophagus cells (KOP-R), a strategy which should facilitate future in vitro or in vivo BAdV-7 studies. Phylogenetic analysis of available genome sequences of BAdV-7 showed that the newly identified strain groups most closely with a recent BAdV-7 strain, SD18-74, from the USA, confirming that this newly identified strain is a member of the Atadenovirus genus. The fiber gene was found to be highly conserved within BAdV-7 strains but was highly divergent in comparison to Ovine adenovirus 7 (OAdV-7) (39.56% aa sequence identity). Furthermore, we report a variable region of multiple tandem repeats between the coding regions of E4.1 and RH5 genes. In summary, the presented pathological and molecular characterization of this case suggests that further research into the worldwide molecular epidemiology and disease burden of BAdV-7 is warranted.

Identification and genetic characterization of an isolate of bovine adenovirus 7 from the United States, a putative member of a new species in the genus Atadenovirus

The bovine adenovirus 7 (BAdV-7) isolate SD18-74 was recovered from lung tissue of calves in South Dakota. The 30,043-nucleotide (nt) genome has the typical organization of Atadenovirus genus members. The sequence shares over 99% nt sequence identity with two Japanese BAdV-7 sequences, followed by 74.9% nt sequence identity with the ovine adenovirus 7 strain OAV287, a member of the species Ovine atadenovirus D. SD18-74 was amplified in both bovine and ovine primary nasal turbinate cells, demonstrating greater fitness in bovine cells. The genomic and biological characteristics of BAdV-7 SD18-74 support the inclusion of the members of the BAdV-7 group in a new species in the genus Atadenovirus.

Isolation and complete genome sequence analysis of a novel ovine adenovirus type representing a possible new mastadenovirus species

Pathological examination of a suckling male lamb showed severe viral pneumonia with suspected bacterial superinfection. Adenovirus was detected by immunohistochemical examination of the affected lung samples. Detection of the suspected adenovirus by PCR and subsequent isolation of the virus were successful. Using next-generation sequencing, the full genome of this ovine adenovirus was sequenced and analysed. A genome sequence comparison showed that it was a novel mastadenovirus type (named "ovine adenovirus 8") that did not belong to any of the established adenovirus species. The genome is 36,206 bp long, containing 93-bp inverted terminal repeats and 29 predicted genes, including the two genus-specific genes (encoding proteins V and IX). Ovine adenovirus 8 shows the closest relationship to ovine adenovirus 6. These two viruses seem to merit the establishment of a novel ovine mastadenovirus species for them, for which we proposed the name "Ovine mastadenovirus C".

Comparative analysis of ovine adenovirus 287 and human adenovirus 2 and 5 based on their codon usage

Ovine adenovirus 287 (OAdV287) emerges as one of the most promising gene vectors resulting from its unique biological characteristics. To obtain a more detailed knowledge about the codon usage of OAdV287, a comparative study based on the codon usage of OAdV287 and the prototypes of human adenovirus serotypes 2 and 5 (HAdV2/5) was carried out. Some commonly used indices measuring the codon usage patterns, including effective number of codons, relative synonymous codon usage, and statistical methods, were adopted. Overall, OAdV287 had a more biased and conservative codon usage pattern than that of HAdV2/5. Both mutation pressure and natural selection played important roles in shaping the codon usage patterns of these three adenoviruses. All the preference codons of OAdV287 had A/U ends and were totally different from those of sheep and humans; however, the preference codons of HAdV2/5 mostly had G/C ends and were mostly coincident with those of sheep and humans. The codon usage analysis in this study supplies some clues for further comprehending the unique biological characteristics of OAdV287 as gene vectors.

Induction of both cellular and humoral immunity following a rational prime-boost immunization regimen that incorporates recombinant ovine atadenovirus and fowlpox virus

Recombinant fowlpox viruses (rFPV) and ovine atadenoviruses (rOAdV) are being developed as safe, nonpathogenic, prophylactic and therapeutic vaccine vectors. There is scope, however, to improve the limited immune responses elicited by each of these vaccine vectors. Using previously determined and optimized routes of administration and viral doses, we characterized the primary adaptive immune responses elicited by recombinant variants of each virus. We demonstrate the contrasting nature of the response elicited by each recombinant virus. Whereas rFPV generates predominately cell-mediated immunity to our nominal target antigen, ovalbumin (OVA), rOAdV drives strong humoral responses. By defining the time taken to achieve maximal cytotoxic T cell responses and by studying the different patterns and kinetics of major histocompatibility complex class I-restricted OVA antigen expression postimmunization, we proposed a heterologous prime-boost regimen of immunization with rOAdV followed by rFPV. The subsequent experimental results showed that this approach produced robust cell-mediated and humoral immune responses against OVA that, importantly, were accompanied by weak anti-viral vector antibody responses. These results, therefore, represent a novel and potentially clinically applicable way to achieve broadly based and effective immunity to the antigens encoded by vectored vaccines.

Serologic and hexon phylogenetic analysis of ruminant adenoviruses

The objectives of this study were to determine the antigenic relationship among ruminant adenoviruses and determine their phylogenetic relationship based on the deduced hexon gene amino acid sequence. Results of reciprocal cross-neutralization tests demonstrated antigenic relationships in either one or both directions among bovine adenovirus type 6 (BAdV-6), BAdV-7, ovine adenovirus type 7 (OAdV-7), caprine adenovirus type 1 (GAdV-1), and deer adenovirus (Odocoileus adenovirus 1, OdAdV-1). No antigenic cross-reactivity was observed among BAdV-1 through -5, and -8 and the other putative ruminant adenoviruses. Two PCR primer sets, one for mastadenovirus and atadenovirus that amplified an approximately 2,700-bp region in the hexon genes were used for comparative studies. Phylogenetic analysis of the deduced hexon amino acid sequences clustered the ruminant adenoviruses on the Mastadenovirus and Atadenovirus genus branches of the Adenoviridae tree. The recent classification of BAdV-6, and -7 as members of the genus Atadenovirus was supported by phylogenetic distance matrix analysis of their deduced hexon amino acid sequences. Further, we propose that BAdV-6 and -7 be recognized as members of new Atadenovirus species, Bovine adenovirus E and Bovine adenovirus F, respectively. Phylogenetic analysis of OdAdV-1 places this virus in the genus Atadenovirus with a proposed new species Odocoileus adenovirus A. OAdV-6 and GAdV-2 are proposed as members of new Mastadenovirus species Ovine adenovirus C and Goat adenovirus A, respectively.

An adenovirus serotype 5 vector with fibers derived from ovine atadenovirus demonstrates CAR-independent tropism and unique biodistribution in mice

Many clinically important tissues are refractory to adenovirus (Ad) infection due to negligible levels of the primary Ad5 receptor the coxsackie and adenovirus receptor CAR. Thus, development of novel CAR-independent Ad vectors should lead to therapeutic gain. Ovine atadenovirus type 7, the prototype member of genus Atadenovirus, efficiently transduces CAR-deficient human cells in vitro, and systemic administration of OAdV is not associated with liver sequestration in mice. The penton base of OAdV7 does not contain an RGD motif, implicating the long-shafted fiber molecule as a major structural dictate of OAdV tropism. We hypothesized that replacement of the Ad5 fiber with the OAdV7 fiber would result in an Ad5 vector with CAR-independent tropism in vitro and liver "detargeting" in vivo. An Ad5 vector displaying the OAdV7 fiber was constructed (Ad5Luc1-OvF) and displayed CAR-independent, enhanced transduction of CAR-deficient human cells. When administered systemically to C57BL/6 mice, Ad5Luc1-OvF reporter gene expression was reduced by 80% in the liver compared to Ad5 and exhibited 50-fold higher gene expression in the kidney than the control vector. To our knowledge, this is the first report of a fiber-pseudotyped Ad vector that simultaneously displays decreased liver uptake and a distinct organ tropism in vivo. This vector may have future utility in murine models of renal disease.

LH3, a “homologue” of the mastadenoviral E1B 55-kDa protein is a structural protein of atadenoviruses

Ovine adenovirus serotype 7 (OAdV), the prototype atadenovirus, has gene homologues for most mastadenovirus structural proteins but lacks proteins V and IX. Instead, OAdV has structural proteins of 32 and 42 kDa although the gene encoding the latter had not previously been identified. The presently reported studies of OAdV virions have now identified a minor structural polypeptide of approximately 40 kDa as the product of the L1 52/55-kDa gene and, more surprisingly, shown that the 42-kDa protein is encoded by LH3. This gene product was previously thought to be a homologue of mastadenovirus E1B 55 kDa, which is a multi-functional, non-structural protein that cooperates with E1A in cell transformation. The lack of transforming activity previously demonstrated for OAdV combined with a structural role for the LH3 product indicates that the protein has a different function in atadenoviruses. We discuss the abundance and likely core location of LH3 in the virion and the possible derivation of the E1B 55-kDa gene from the LH3 gene.

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

Gene-directed enzyme prodrug therapy (GDEPT) based on the Escherichia coli enzyme, purine nucleoside phosphorylase (PNP), provides a novel strategy for treating slowly growing tumors like prostate cancer (CaP). PNP converts systemically administered prodrug, fludarabine phosphate, to a toxic metabolite, 2-fluoroadenine, that kills PNP-expressing and nearby cells by inhibiting DNA, RNA and protein synthesis. Reporter gene expression directed by a hybrid prostate-directed promoter and enhancer, PSMEPb, was assayed after plasmid transfection or viral transduction of prostate and non-CaP cell lines. Androgen-sensitive (AS) LNCaP-LN3 and androgen-independent (AI) PC3 human CaP xenografts in nude mice were injected intratumorally with an ovine atadenovirus vector, OAdV623, that carries the PNP gene under PSMEPb, formulated with cationic lipid for enhanced infectivity. Fludarabine phosphate was then given intraperitoneally for 5 days at 75 mg/m2/day. PNP expression was evaluated by enzymic conversion of its substrate using reverse phase HPLC. OAdV623 showed excellent in vitro transcriptional specificity for CaP cells. In vivo, expression of PNP persisted for > 6 days after OAdV623 injection and a single treatment provided 100% increase in tumor doubling time and > 50% inhibition of tumor growth for both LNCaP-LN3 and PC3 lines, with increased tumor necrosis and apoptosis and decreased tumor cell proliferation. OAdV623 significantly suppressed the growth of AS and AI human CaP xenografts in mice.

Ovine atadenovirus: a review of its biology, biosafety profile and application as a gene delivery vector

The ovine adenovirus isolate OAdV287 is the prototype of the newly recognized genus of atadenoviruses. Although not as well studied as human mastadenoviruses, a substantial amount of work has now been carried out with this virus and an understanding of its interesting and unique properties is beginning to emerge. In this article the biology and biosafety profile of the virus is reviewed. This knowledge underpins the exploitation of the virus as a gene delivery vector. Its potential as a vaccine vector and its application to the treatment of prostate cancer is summarized and discussed.

Identification of an ovine atadenovirus gene whose product activates the viral E2 promoter: possible involvement of E2F-1

Activation of the adenoviral E2 promoter is an early step in adenovirus gene expression. For members of the mast- and aviadenoviruses, this requires induction of the cellular transcription factor E2F by virally encoded gene products such as E1A, E4orf6/7 and orf22/GAM-1. The newly recognized genus atadenovirus, of which the ovine isolate OAdV is the prototype, lacks any sequence homology to those genes. To find a possible link between E2 promoter activation and OAdV gene expression, we utilized a screening method to search for genes within the OAdV genome that were capable of stimulating the viral E2 promoter. One such gene, E43, was identified within the proposed E4 region toward the right-hand end of the OAdV genome. The E43 gene product was also found to be capable of stimulating E2F-1-dependent gene expression. A closer inspection of the E2 promoter revealed the presence of a non-palindromic E2F binding site within the OAdV E2 promoter. Mutation of this site markedly reduced both E2F-1- and E43-dependent promoter activation. Moreover, a direct protein-protein interaction of the E43 gene product with E2F, but not with the retinoblastoma protein pRb, suggested a possible cooperation between these two proteins in activating the E2 promoter. The importance of the E43 gene product for virus replication is also underlined by the finding that an OAdV recombinant with a functionally inactivated E43 gene showed severely inhibited virus growth.

Construction, rescue, and characterization of vectors derived from ovine atadenovirus

Gene transfer vectors derived from ovine atadenovirus type 7 (OAdV) can efficiently infect a variety of mammalian cells in vitro and in vivo to deliver and express transgenes. However, early OAdV vectors were designed on human mastadenovirus principles prior to the complete characterization of OAdV genes and transcripts. The distinctive arrangement of the OAdV genome has suggested ways to improve OAdV vector design and utility. We therefore developed a cosmid-based approach that allows efficient construction of recombinant ovine atadenovirus genomes in which the transgene is inserted at one of three sites. Viruses were rescued by transfection of viral DNA into a new ovine fetal skin fibroblast producer cell line, HVO156. The suitability of the three insertion sites was compared with respect to virus rescue efficiency, gene expression levels, and genetic stability of the vectors. We found that one vector with a transgene inserted at site 1, between the pVIII and fiber genes, was unstable. Only one vector that carried a transgene at site 2, near the right end of the genome, together with a nearby deletion was rescued. In contrast, several vectors with different transgenes inserted in site 3, between the E4 and RH transcription units, were repeatedly rescued, and these vectors were stable over at least four passages. Transgene orientation in site 3 had only little effect on expression. Finally, a vector carrying a human factor IX cDNA at site 3, when administered intravenously, produced nearly physiological levels of human factor IX in mice. The availability of an efficient method for vector construction and the identification of a new insertion site for virus rescue and gene expression substantially enhance the utility of the OAdV vector system.

Molecular evolution of adenoviruses

New advances in the field of genetic characterization of adenoviruses originating from different animal species are summarized. Variations seen in the host range and specificity, pathogenicity, genomic arrangement or gene complement are much wider than expected based on previous studies of human adenoviruses. Several exceptional adenoviruses from the two traditional conventional genera are now removed, and proposed to form at least two new genera. The eventual host origin of the new genera, however, is not clarified. Novel results from the genomic and phylogenetic analyses of adenoviruses originating from lower vertebrate species (including reptiles, amphibians and fish) seem to imply that probably five major clusters of adenoviruses exist corresponding to the five major classes of Vertebrata. Adenoviruses, which are now suspected to have common origin with enterobacterium phages from the family Tectiviridae, are perhaps very ancient indeed, and may have undergone a co-evolution with vertebrate hosts.

Identification of a unique family of F-box proteins in atadenoviruses

Ovine adenovirus isolate 287 (OAdV-7) is the prototype of the atadenoviruses, a genus whose strategy for infection and replication is still being elucidated. A transcription unit at the right end of the genome contains four related genes (ORFs RH1, 2, 4, and 6), at least three of which are nonessential for replication in vitro. Related genes are also present in the genomes of bovine and avian atadenoviruses. To investigate how these apparently redundant genes are decoded, a more detailed transcription map of the right end of the OAdV-7 genome has been deduced. Eight transcripts that were derived from a promoter in the terminal repeat sequence were identified. Five were potentially bicistronic. The transcripts could encode all the potential proteins of the region subject to efficient reinitiation of translation. However, the most interesting and surprising finding in this work was that the related RH proteins carry an F-box motif. This was first identified in OAdV-7 RH1 and subsequently found in RH2, 4, and 6 proteins and the related reading frames from the bovine and avian atadenoviruses. Although very rare among viral proteins, several hundred cellular proteins contain F-box motifs. F-box proteins facilitate the degradation of a variety of important regulatory proteins via SCF ubiquitin ligase complexes. Thus, it appears that atadenoviruses have adopted a strategy to regulate a key cellular pathway(s) that distinguishes them from the other adenovirus genera and from most viruses in general.

Biology of ovine adenovirus infection of nonpermissive cells

Nonhuman adenoviruses, including those of the genus Atadenovirus, have the potential to serve as vectors for vaccine and gene therapy applications in humans, since they are resistant to preexisting immunity induced by human adenoviruses in the majority of the population. In this study, we elucidate the outcome of infection by ovine adenovirus type 7 isolate 287 (OAdV) of several nonovine cell types. We show here that OAdV infects a wide range of nonovine cells but is unable to complete its replication cycle in any of them. In nonovine, nonfibroblast cells, viral replication is blocked at an early stage before the onset of, or early in, DNA replication. Some fibroblasts, on the other hand, allow viral DNA replication but block virus production at a later stage during or after the translation of late viral proteins. Late viral proteins are expressed in cells where viral DNA replication takes place, albeit at a reduced level. Significantly, late proteins are not properly processed, and their cellular distribution differs from that observed in infected ovine cells. Thus, our results clearly show that OAdV infection of all nonovine cells tested is abortive even if significant viral DNA replication occurs. These findings have significant positive implications with respect to the safety of the vector system and its future use in humans.

Genomic and phylogenetic analyses of an adenovirus isolated from a corn snake (Elaphe guttata) imply a common origin with members of the proposed new genus Atadenovirus

Approximately 60% of the genome of an adenovirus isolated from a corn snake (Elaphe guttata) was cloned and sequenced. The results of homology searches showed that the genes of the corn snake adenovirus (SnAdV-1) were closest to their counterparts in members of the recently proposed new genus ATADENOVIRUS: In phylogenetic analyses of the complete hexon and protease genes, SnAdV-1 indeed clustered together with the atadenoviruses. The characteristic features in the genome organization of SnAdV-1 included the presence of a gene homologous to that for protein p32K, the lack of structural proteins V and IX and the absence of homologues of the E1A and E3 regions. These characteristics are in accordance with the genus-defining markers of atadenoviruses. Comparison of the cleavage sites of the viral protease in core protein pVII also confirmed SnAdV-1 as a candidate member of the genus ATADENOVIRUS: Thus, the hypothesis on the possible reptilian origin of atadenoviruses (Harrach, Acta Veterinaria Hungarica 48, 484-490, 2000) seems to be supported. However, the base composition of DNA sequence (>18 kb) determined from the SnAdV-1 genome showed an equilibrated GC content of 51%, which is unusual for an atadenovirus.

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

A gene-directed enzyme pro-drug therapy (GDEPT) based on purine nucleoside phosphorylase (PNP), that converts the prodrug, fludarabine to 2-fluoroadenine, has been described, but studies are limited compared with other GDEPTs. We investigated the in vitro and in vivo efficacies of PNP-GDEPT for treating androgen-independent (AI) prostate cancer. The PNP gene controlled by Rous sarcoma virus (RSV) constitutive promoter was delivered using a recombinant ovine adenovirus vector (OAdV220) that uses a different receptor from human adenovirus type 5. In vitro, OAdV220 provided increased transgene expression over a comparable human Ad5 vector in infected AI, murine RM1 prostate cancer cells. Subsequent in vivo testing was therefore confined to OAdV220. Transduction of RM1 cells with OAdV220 before implantation in immunocompetent mice dramatically inhibited subcutaneous (s.c.) tumor growth when fludarabine phosphate was administered systemically and increased mouse survival in a dose-dependent manner. In tumor-bearing C57BL/6 mice, a single intratumoral injection of OAdV220 produced detectable PNP activity for at least 6 days and with prodrug, retarded the growth of aggressive RM1 s.c. tumors by 35% at day 14. There was a consistent trend to reduction of pre-established intraprostatic RM1 tumors. A similar regimen induced significant therapeutic efficacy in human PC3 xenografts. Thus, ovine adenovirus-mediated GDEPT using the PNP system was effective in vivo against AI prostate cancers, the aggressive murine RM1, and the human PC3 lines. Methods that improve viral dissemination and stimulate the immune system in vivo may further improve efficacy.

Complementation of a defective human adenovirus by an otherwise incompatible ovine adenovirus recombinant carrying a functional E1A gene

All known human adenoviruses are classified as mastadenoviruses, while the ovine adenovirus (OAdV) serotype 7 is the prototype of the atadenoviruses, a proposed new genus. OAdV replicates abortively in human cell types and has potential as a gene transfer vector. However, the function of OAdV nonstructural genes is poorly understood and it is unclear whether OAdV replication might be complemented by a replicating human AdV in coinfected cells. To investigate possible interactions three human cell lines were singly infected with OAdV or human AdV5 or doubly infected. The development of a cytopathic effect and genome replication was monitored over three passages in each cell type. No significant OAdV replication occurred in any of the cell types examined either in the presence or in the absence of replicating AdV5. No aberrant AdV5 genome products were detected in coinfected cells. In contrast, in coinfected cells an OAdV recombinant that expressed the AdV5 E1A gene was able to promote the replication of an AdV5 E1A-deficient mutant, demonstrating trans-complementation between appropriate viruses. These findings have implications for the biosafety of OAdV vectors and their possible utility for enhancing gene delivery.

Ovine adenovirus serotype 7-associated mortality in lambs in the United States

Adenoviral infections were diagnosed in three neonatal lambs that died spontaneously, and no other etiologic agents were identified. Clinical signs were anorexia, weakness, abdominal distention, and sudden death. Microscopic lesions consisted of multifocal necrotizing hepatitis, multifocal subacute interstitial nephritis, and loss of enterocytes from intestinal villi. Adenovirus inclusions were identified by light microscopy in the kidneys only. Adenoviral antigen, however, was identified in the liver, kidney, and intestine of the lambs by immunohistochemical techniques. An ovine adenovirus serotype 7, not previously isolated from sheep in the United States, was characterized from these lambs.

Ovine adenovirus vectors mediate efficient gene transfer to skeletal muscle

Ovine adenovirus (OAV) vectors represent a promising tool for human gene therapy since these vectors overcome the problem of pre-existing immunity against human adenovirus vectors. In this report we investigated the in vivo characteristics of this novel vector system with respect to its potential for gene transfer into skeletal muscle. We found that moderate doses of an OAV-derived vector expressing the human alpha1-antitrypsin gene (OAVhaat) infected skeletal muscle in mice very efficiently resulting in high serum hAAT levels. The infection was restricted to skeletal muscle, but gene expression was transient and vector DNA was rapidly cleared. Vector clearance was also observed with a vector that lacked the transgene. The loss of vector DNA was accompanied by a cellular immune response in the infected muscle but was not connected with detectable expression of early or late genes of the viral backbone as analyzed by RT-PCR. A very low dose of OAVhaat (3x 10(7) infectious particles) was sufficient to produce reasonable amounts (>100 ng/ml) of serum hAAT, and this was accompanied by a weak immune response to the vector. Under these conditions, a second intramuscular injection of the same recombinant OAV vector was successful. Our study expands the known tissue tropism of OAV-derived vectors in vivo and points to the possible utility of the vector for muscle gene transfer and vaccination.

An ovine adenovirus vector lacks transforming ability in cells that are transformed by AD5 E1A/B sequences

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.

DNA sequencing and phylogenetic analysis of the protease gene of ovine adenovirus 3 suggest that adenoviruses of sheep belong to two different genera

Until now, the only published ovine adenovirus DNA sequence was the complete genome of ovine adenovirus isolate 287 (OAV287) which, compared to other mammalian adenoviruses, possesses strikingly unique genomic organisation and should properly be classified into a new adenovirus genus. The protease gene sequence of ovine adenovirus type 3 (OAdV-3) was determined and analysed. The results of phylogenetic analysis of the 205 residue long protein demonstrated that OAdV-3 belongs to the genus Mastadenovirus, and is surprisingly closely related to bovine adenovirus type 2. In spite of the common host origin, the evolutionary distance between OAdV-3 and OAV287 proved to be great suggesting that sheep, similarly to cattle and fowl, might be infected by distantly related adenoviruses belonging to different genera.

Ovine adenovirus vectors overcome preexisting humoral immunity against human adenoviruses in vivo

Recombinant human adenoviruses (hAd) have become widely used as tools to achieve efficient gene transfer. However, successful application of hAd-derived vectors in clinical trials is limited due to immunological and potential safety problems inherent in their human origin. In this study, we describe a recombinant ovine adenovirus (OAV) as an alternative vector for gene transfer in vivo. In contrast to an hAd vector, the OAV vector was not neutralized by human sera. An OAV vector which contained the cDNA of the human alpha1-antitrypsin (hAAT) gene linked to the Rous sarcoma virus promoter was generated and administered systemically to mice. The level and duration of hAAT gene expression was similar to that achieved with an hAd counterpart in both immunocompetent and immunodeficient mice. However, the tissue distribution of the OAV vector differed from that observed for hAd vectors in that the liver was not the dominant target. Significantly, we demonstrated efficient gene transfer with the OAV vector into mice immunized with hAd vectors and vice versa. We also confirm that the immune response to a transgene product can prevent its functional expression following sequential application of a vector. Our results suggest a possible solution to endemic humoral immunity against currently used hAd vectors and should therefore have an impact on the design of improved gene therapy protocols utilizing adenovirus vectors.

Altered tropism of an ovine adenovirus carrying the fiber protein cell binding domain of human adenovirus type 5

Ovine adenovirus OAV287 (OAV) is phylogenetically and serotypically distinct from human Ad5. OAV grows productively in CSL503 foetal ovine lung cells and abortively infects several human cell lines. OAV has a unique fiber and a penton protein that lacks a recognisable integrin-binding motif. It is not known whether a secondary receptor is required for infection. A hybrid virus was constructed in which the cell binding domain on the OAV fiber protein was exchanged for the equivalent region from human adenovirus type 5. The hybrid OAV grew to titres that were 1 to 2 log10 lower than wild-type OAV in permissive ovine cells. Human Ad5 also infected CSL503 cells but failed to compete with OAV for receptor binding sites on those cells. However, the hybrid virus did compete with Ad5, consistent with its use of the Ad primary receptor. The hybrid virus was also neutralised by Ad5 antiserum whereas OAV was not. Human 293 kidney and LNCaP prostate cell lines that were not detectably infected by OAV were infected by the hybrid virus and other human prostate and breast cancer cell lines showed greatly enhanced infectivity. Thus, modification of the fiber cell binding domain was sufficient to profoundly alter the tropism of OAV, suggesting that the interaction between the primary receptor and the virus particle is the major factor controlling virus entry during infection.

Identification of transcripts and promoter regions of ovine adenovirus OAV287

The ovine adenovirus isolated OAV287 represents a new group of adenoviruses that are distinct from the Mast- and Aviadenoviruses by several criteria, including genome arrangement. The OAV major late promoter and some late transcripts were previously mapped. To better define the probable coding sequences and to identify the approximate location of early promoters a partial transcription map of the genome was elucidated using a PCR-based approach. This was possible because the complete nucleotide sequence of the genome was known. The strategy permitted the identification of transcription start sites and RNA splice junctions and allowed the approximate location of promoters in the lefthand end, IVa2, E2, P32K, and E4 regions to be deduced. The data showed that lefthand end and E4 regions are controlled by three and two temporally distinct promoters, respectively. The E2 region is controlled by a single promoter, in contrast to Mastadenoviruses, where E2 expression is controlled by the E2A and E2B promoters. The p32kDa structural protein at the lefthand end and the IVa2 protein are also expressed from their own promoters. These data contribute to the first overview of transcription from a non-Mastadenovirus genome.

Sequencing and phylogenetic analysis of the protease gene, and genetic mapping of bovine adenovirus type 10 define its relatedness to other bovine adenoviruses

The complete genome of a bovine adenovirus (BAV) type 10 isolate was molecularly cloned and partially sequenced. The encoded proteins were predicted by computer analysis of the DNA sequences of the ends or the entire length of the cloned viral fragments, and thus a rough genetic map was constructed. The protease gene of BAV-10 was completely sequenced and used in phylogenetic analysis. Based on the results of the phylogenetic analysis, and the location and presence of certain genes thought to be specifically characteristic of subgroup 1 or subgroup 2 BAVs, it could be concluded that, in spite of the striking similarity in certain biological properties, BAV-10 is not related to subgroup 2 BAVs as originally described. It does not however fit clearly into subgroup 1 either, the members of which show closer relationship with human adenoviruses. BAV-10 therefore should best be considered as the first member of a third subgroup of BAVs.

Gene expression by atypical recombinant ovine adenovirus vectors during abortive infection of human and animal cells in vitro

An bovine adenovirus, which is phylogenetically distinct from the Mastadeno- and Aviadenoviruses, was used to construct recombinants in which reporter genes were expressed from the OAV major late, or human cytomegalovirus promoters. It was demonstrated by transgene expression that OAV could infect bovine nasal turbinate and rabbit kidney cells as well as a range of human cell types, including lung and foreskin fibroblasts as well as liver, prostate, breast, colon, and retinal lines. Some human lines, e.g., 293 and LNCaP were not detectably infected. Infection occurred even though OAV has a fiber protein with a unique cell binding domain and a penton protein that lacks the integrin-binding Arg-Gly-Asp motif which facilitates entry by human adenoviruses. Most cell lines showed little or no ill effect for several days after infection but a prominent cytopathic effect appeared in fibroblasts after 3-4 days. However, no viral DNA synthesis was detected and replication was abortive. Viral promoter activity during infection of nonpermissive cell types was assayed by RT-PCR. Early promoter activity was detectable in some, but not all cell types. In a liver and a colon carcinoma cell line, none of the promoters examined was significantly active, even when a higher multiplicity of infection was used. Major late promoter activity was not detectable in any cell type. The lack of DNA replication and MLP function suggests that a critical transition from early to late gene expression does not occur during abortive infection by OAV.

Construction of ovine adenovirus recombinants by gene insertion or deletion of related terminal region sequences

An ovine adenovirus which may be the prototype for a new group of adenoviruses has been engineered as a gene transfer vector. One recombinant containing a 0.95-kb insertion expressed a sheep parasite antigen from the ovine adenovirus major late promoter and tripartite leader sequences. It was shown that insertions of at least 4.3 kb were tolerated at either one of two sites in the genome without the introduction of a compensating deletion. The unique structure of this viral genome was further emphasized by the discovery that four open reading frames at the right hand end show significant identity to each other but not to other sequences in the databases. Two other unrelated open reading frames were also present. RT-PCR analysis identified two transcripts in this region which were derived from a promoter which was located very close to, or within the ITR sequence. Splicing removed all but the first and last of the ORFs from these RNAs, suggesting that some sequences might be nonessential for replication in vitro. A approximately 2-kb deletion, which removed or truncated the internal reading frames was introduced into the region without affecting virus viability. The carrying capacity of OAV recombinants should therefore be at least 6.3 kb. The relative packaging capacity of OAV (114%) therefore exceeds that of Ad5 (105%), although a comparison of virus particle sizes by electron microscopy showed that OAV was smaller than Ad5. These studies improve the potential utility of OAV as a gene transfer vector.

Close phylogenetic relationship between egg drop syndrome virus, bovine adenovirus serotype 7, and ovine adenovirus strain 287

A cloned egg drop syndrome (EDS) virus genomic DNA fragment containing the protease gene has been identified and the complete nucleotide sequence of the protease and partial nucleotide sequence of the hexon genes has been determined. Phylogenetic analysis of the protease gene has revealed EDS virus to be genetically more closely related to bovine adenovirus type 7 (BAV-7) and ovine adenovirus isolate 287 (OAV287) than either of these two viruses are to other members of the genus Mastadenovirus or EDS virus is to an other member of the Aviadenovirus genus. The three viruses share further similarities in that they have a high percentage AT content in their genome and are characterized by having more compact genomes than other adenoviruses. The protease gene from all three viruses contained the active site residues (H55-D72-C122 triad) and C104 (providing a disulfide bond to cofactor pVIc). However, P137, found in all other members of the Mastadenovirus genus, and thought to be involved in trafficking, was missing from the protease of the EDS virus, BAV-7, and OAV287. These results suggest that EDS virus should be classified along with BAV-7 and OAV287 in a separate taxon.

Nucleotide sequence of ovine adenovirus tripartite leader sequence and homologues of the IVa2, DNA polymerase and terminal proteins

Ovine adenovirus OAV287 was previously isolated from sheep in Western Australia. Here we describe a portion of its genome between map units 10.3 and 31.7 which includes major ORFs for homologues of the IVa2 polypeptide and the DNA replication proteins, Terminal protein and DNA polymerase, as well as the N-terminal portion of the 52/55-kDa polypeptide. In addition, as a prelude to possible adaptation of this virus as a vector we have mapped the elements which make up the tripartite leader sequence of late mRNAs, thereby defining the probable location of the OAV major late promoter. In other human and animal adenovirus genomes, one or two VA RNA genes are encoded between the ORFs for Terminal protein and 52/55-kDa polypeptides. In OAV, these ORFs overlap, suggesting that if VA RNA genes are present, they may lie elsewhere in the OAV genome.