Gene transfer by viral vectors into blood vessels in a rat model of retinopathy of prematurity

AIMS

To test the feasibility of gene transfer into hyaloid blood vessels and into preretinal neovascularisation in a rat model of retinopathy of prematurity (ROP), using different viral vectors.

METHODS

Newborn rats were exposed to alternating hypoxic and hyperoxic conditions in order to induce ocular neovascularisation (ROP rats). Adenovirus, herpes simplex, vaccinia, and retroviral (MuLV based) vectors, all carrying the beta galactosidase (beta-gal) gene, were injected intravitreally on postnatal day 18 (P18). Two sets of controls were also examined: P18 ROP rats injected with saline and P18 rats that were raised in room air before the viral vectors or saline were injected. Two days after injection, the rats were killed, eyes enucleated, and beta-gal expression was examined by X-gal staining in whole mounts and in histological sections.

RESULTS

Intravitreal injection of the adenovirus and vaccinia vectors yielded marked beta-gal expression in hyaloid blood vessels in the rat ROP model. Retinal expression of beta-gal with these vectors was limited almost exclusively to the vicinity of the injection site. Injection of herpes simplex yielded a punctuate pattern of beta-gal expression in the retina but not in blood vessels. No significant beta-gal expression occurred in rat eyes injected with the retroviral vector.

CONCLUSIONS

Adenovirus is an efficient vector for gene transfer into blood vessels in an animal model of ROP. This may be a first step towards utilising gene transfer as a tool for modulating ocular neovascularisation for experimental and therapeutic purposes.

Alternate adenovirus type-pairs for a possible circumvention of host immune response to recombinant adenovirus vectors

With the help of monoclonal antibodies the existence of at least 18 different earlier not known intertype (IT) specific epitopes were demonstrated in different numbers and combinations on the hexons of different adenovirus serotypes. The IT specific epitopes play an important role in the experimental gene therapy and in the recombinant adenovirus vaccination because of the harmful immune response of the recipient organisms directed against the many different epitopes of the adenovirus vector. For the elimination of harmful effect the authors suggest the use of multiple vectors, each prepared from different adenovirus serotypes showing the loosest antigenic relationship to each other. The vectors would be used sequentially when second or multiple administration is needed. For this purpose the authors determined and described 31 such adenovirus type-pairs, which are probably the best alternates for sequential use in experimental gene therapy.

Characterisation of the fiber gene and partial sequence of the early region 4 of bovine adenovirus 2 (short communication)

The full sequence of the fiber gene and partial sequence of the putative 17 kD protein gene of bovine adenovirus-2 (BAdV-2) were determined. The size of the fiber gene of BAdV-2 proved to be 561 amino acids, of which the amino acids 37 to 385 form a typical shaft domain of 22 repetitive motifs. On the complementary strand, a gene homologous to the 17 kD protein coded in the E4 region of several human adenoviruses was found. The sequence analysis seems to confirm the presence of an intron in the sequenced part of the E4 region.

Porcine adenoviruses: an update on genome analysis and vector development

Although porcine adenoviruses (PAdV) are present in the swine populations worldwide, they usually do not cause any disease, or the infection is only manifested in a mild diarrhoea or respiratory signs. The importance of adenoviruses, however, is constantly growing as there is a possibility of developing them into viral vector vaccines against more significant swine pathogens. A short summary of the well-established facts of porcine adenoviruses is given and recent developments of the genetic analysis of these viruses are discussed in detail. The possibilities of vector development and examples of vector vaccines already reported in the literature are mentioned.

Comparison of the genome of ovine adenovirus types 1 through 5 by restriction enzyme analysis and DNA hybridisation

The DNA of the prototype strains of ovine adenovirus (OAdV) 1 through 5 was analysed by restriction enzyme (RE) digestion. The RE patterns generated by HindIII and PstI enzymes were characteristic of the examined strains. OAdV-2 and 3 resembled each other the most, and their EcoRI and HindIII patterns seemed to be identical. Considering the number of comigrating fragments, serotypes OAdV-2, 3, 4 and 5 looked more closely related to each other than to OAdV-1. This finding was strengthened by Southern blot hybridisations probed with random HindIII clones of OAdV-3. The estimated genome size of the examined OAdV types ranged between 31.9 and 32.8 kilobase pairs. The results supported the new genus classification of OAdVs.

Determination of bovine adenovirus-3 titer based on immunohistochemical detection of DNA binding protein in infected cells

DNA sequence coding for a portion of DNA binding protein (amino acids 3-58) of bovine adenovirus type-3 (BAV-3) was cloned and expressed in Escherichia coli as a fusion protein with Schistosoma japonicum glutathione S-transferase. The fusion protein was affinity purified and used to immunize rabbits. Immunoprecipitation and Western blot analysis showed that the antiserum could specifically recognize a protein of 48 kDa in BAV-3-infected cells, which was produced both in early and late phases of BAV-3 life cycle. Based on the ability of antiserum to recognize DNA binding protein, a novel assay for BAV-3 quantitation was established. The assay is less time consuming and can be performed on a wide variety of bovine cells. In addition, virus titers determined by this assay are comparable to the standard plaque assay.

Four new inverted terminal repeat sequences from bovine adenoviruses reveal striking differences in the length and content of the ITRs

The inverted terminal repeat (ITR) of the genome of four bovine adenovirus (BAdV) types have been sequenced, analysed and compared to the ITRs of other adenoviruses. The length of ITRs of the examined BAdVs ranged between 59 and 368 base pairs, thus the presently known longest adenovirus ITR sequence is from BAdV-10. The conserved motifs and characteristic sequence elements of the ITRs providing different binding sites for replicative proteins of viral and cellular origin seemed to be distributed according to the proposed genus classification of BAdVs. The ITRs of BAdV-10 share similarity with the members of the genus Mastadenovirus, while the ITRs of the other three sequenced serotypes (BAdV-4, 5 and strain Rus) which are candidate members of the genus Atadenovirus are very short and contain NFI and Sp1 binding sites only. The analysis of the new ITRs implied that the nucleotide sequence of the so-called core origin is highly preserved within the mastadenovirus genus only.

The complete nucleotide sequence of porcine adenovirus serotype 5

The complete nucleotide sequence of porcine adenovirus serotype 5 (PAdV-5) has been determined and the putative genomic map was constructed. The size of the genome was found to be 32621 nucleotides. Twenty-eight putative ORFs were identified by their homology to other adenovirus or other virus and eukaryotic genes. Several special protein sequence motifs were identified by their homology to similar protein motifs. The putative promoter regions, polyadenylation and splice sites were predicted and the early and late transcription units were determined. Based on sequence analysis and RNA secondary structure prediction, sequences for virus-associated RNA could not be recognized. Phylogenetic analysis showed that PAdV-5 was more closely related to certain bovine adenoviruses than to other porcine adenoviruses.

Construction and characterization of recombinant porcine adenovirus serotype 5 expressing the transmissible gastroenteritis virus spike gene

Five recombinant porcine adenoviruses of serotype 5 (PAdV-5) carrying the full-length or the 5' 2.2 kb half of the transmissible gastroenteritis virus (TGEV) spike (S) gene were generated by homologous recombination in E. coli strain BJ5183 cells and subsequent transfection of swine testicle cells. The foreign genes were inserted into the E3 region of PAdV-5. One recombinant virus had no deletion in the E3 region, whereas a 1.2 kb fragment was removed from the E3 region in the remainder of the recombinant viruses. One stable construct with a 4.4 kb insertion had a genome size of 109.6% of the wild-type genome, the largest reported for any recombinant adenovirus. Only those viruses that carried the S gene in the left to right orientation expressed the S gene. Three recombinant viruses were tested by oral immunization of pigs and both antibody response and virus shedding were monitored. None of the pigs showed clinical signs and the virus was recovered from rectal swabs until 6-7 days post-infection. Viruses expressing the S gene induced TGEV- and PAdV-5-specific virus-neutralizing antibodies. Moreover, TGEV-specific secretory IgA was detected in the small intestine and in the lungs of the immunized animals.

Adenoviral vector-mediated rescue of the OMP-null phenotype in vivo

The use of gene deletion by homologous recombination to determine gene or protein function has wide application in vertebrate neurobiology. An ideal complement to gene deletion would be subsequent gene replacement to demonstrate re-acquisition of function. Here we used an adenoviral vector to replace the olfactory marker protein (OMP) gene in olfactory receptor neurons of adult OMP-null mice and demonstrated the subsequent re-acquisition of function. Our results show that short-term expression of OMP restores the kinetics of electrophysiological responses of OMP-null mice to those of the control phenotype. This adenoviral-mediated rescue of the OMP-null phenotype is consistent with involvement of OMP in olfactory transduction.

Adenoviral gene transfer of nitric oxide synthase increases cerebral blood flow in rats

OBJECTIVE

Depletion of nitric oxide may play a role in the development of vasospasm after aneurysmal subarachnoid hemorrhage. Replenishment of nitric oxide might be a useful treatment for vasospasm. Using rats, we performed intracisternal injections of replication-defective adenovirus containing the endothelial nitric oxide synthase (eNOS) gene and determined the localization of and effect on cerebral blood flow of transgene expression.

METHODS

Rats underwent baseline measurement of cortical cerebral blood flow using laser Doppler flowmetry. Replication-defective adenovirus containing the Escherichia coli LacZ gene (Ad327beta-Gal, n = 2/time point) or the bovine eNOS gene (AdCD8-NOS, n = 4/time point) or physiological saline solution was injected into the cisterna magna. Cerebral blood flow was measured 1, 2, 4, 7, or 14 days later, and the animals were killed. Expression of beta-galactosidase activity from the LacZ gene was examined by histochemical staining and that of eNOS was examined by polymerase chain reaction assays of messenger ribonucleic acid. Brains were histopathologically examined for inflammation.

RESULTS

Beta-galactosidase activity was observed throughout the leptomeninges and in some cells in the adventitia of small subarachnoid blood vessels in the Ad327beta-Gal-injected rats. Messenger ribonucleic acid for eNOS was detected in the leptomeninges and brainstem 1 and 2 days after injection of AdCD8-NOS. Rats injected with Ad327beta-Gal or physiological saline solution exhibited decreased cerebral blood flow beginning 2 days after virus injection and lasting up to 14 days after injection. Rats injected with AdCD8-NOS developed significant transient increases in cerebral blood flow 2 days after virus injection, followed by slight decreases in blood flow. There was inflammation in the subarachnoid space of all animals; the inflammation was qualitatively worse in animals injected with Ad327beta-Gal, compared with rats injected with AdCD8-NOS or saline solution.

CONCLUSION

Intracisternal injection of replication-defective adenovirus containing the eNOS gene can transiently increase cerebral blood flow.

DNA sequence of frog adenovirus

The genome of frog adenovirus (FrAdV-1) was sequenced and found to be the smallest of all known adenovirus genomes. The sequence obtained was 26163 bp in size and contains a substantial direct repeat near the right terminus, implying that it was derived by recombination from a parental genome of only 25517 bp. The closest relative of FrAdV-1 proved to be turkey adenovirus 3, an avian adenovirus with no previously known near relative. Sequence comparisons showed that the two viruses have equivalent gene complements, including one gene the product of which is related to sialidases. Phylogenetic analyses supported the establishment of a fourth adenovirus genus containing these two viruses, in addition to the established genera Mastadenovirus: and Aviadenovirus: and the proposed genus Atadenovirus: Sixteen genes were identified as being conserved between these four lineages and were presumably inherited from an ancestral adenovirus.

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.

Identification and sequence analysis of the core protein genes of bovine adenovirus 2

The DNA sequence of the genome of bovine adenovirus type 2 (BAdV-2) was determined between map units 42.5 and 50. By sequence analysis and homology search, the genes of five structural proteins were identified within this region: the penton base protein (III; partial sequence), the major core protein precursor (pVII), the minor core protein (V), the mu core protein precursor (pX) and the hexon associated protein precursor (pVI; partial sequence). The putative polypeptides were compared to their known counterparts from other adenoviruses. The existence of protein V and the presence and structure of certain protease cleavage recognition sites confirmed BAdV-2 as a member of the genus Mastadenovirus.

Optimization of bovine coronavirus hemagglutinin-estrase glycoprotein expression in E3 deleted bovine adenovirus-3

Adenoviral vectors expressing foreign genes have many desirable properties in applications such as vaccination. Recently, we have generated replication-competent (E3 deleted) bovine adenovirus-3 (BAV-3) recombinants expressing significant amounts of glycoprotein D (gD) of bovine herpesvirus-1 (a DNA virus). However, attempts to express the RNA virus genes using the same strategy were not successful. In an effort to optimize the expression, we have constructed several BAV-3 recombinants carrying the hemagglutinin esterase (HE) gene of bovine coronavirus (BCV) in the E3 region with or without exogenous transcription control elements. The expression studies suggest that the introduction of a 137 bp chimeric intron upstream of the HE cDNA is able to increase the level of HE gene expression. The introduction of a SV40 early promoter or human cytomegalovirus (HCMV) immediate early (IE) promoter into the expression cassette changed the kinetics of the HE expression. However, the recombinant BAV-3 containing HE under the HCMV IE promoter replicated less efficiently than the wild-type BAV-3. These studies should prove useful in expression of other RNA viral genes in the E3 region of BAV-3 expression system.

Sequencing analysis of the region encoding the DNA polymerase of bovine adenovirus serotypes 2 and 3

Bovine adenoviruses (BAVs) are important pathogens causing significant economic losses to the cattle industry. We have been interested in the differences among serotypes of these viruses, particularly in their pathogenicity and host range. As part of our efforts to better understand these viruses, we have determined the nucleotide sequences for serotype 3 (BAV3) at map coordinates beween 11.7 and 23.7% and for serotype 2 (BAV2) between 13.1 and 24.0%. Analyses of these sequences revealed large open reading frames (ORFs) encoded within the leftward-reading strand of the viral DNA. The coding capacity of the ORF in BAV3 is 1,167 amino acid residues and 1,138 in BAV2. A search in the GenEMBL protein sequence databank for homology to the predicted polypeptide products of these ORFs established their identity as that for the adenovirus (Ad) DNA polymerase (DNA pol). The deduced polypeptide sequences were aligned with each other and with other known Ad DNA pols to reveal regions of homology and similarity. The comparison at the amino acid sequence level not only showed that the bovine Ad DNA pols from the two serotypes are quite distinct from each other, but also revealed that Ad DNA pols contain multiple domains that are highly conserved among human, canine and bovine Ads. These conserved domains are likely important for the multiple functions attributed to Ad DNA pol, which include catalysis of its own initiation complex, elongation of nascent DNA strand, as well as correction of DNA replication errors.

Evaluation of the efficacy of 2',3'-dideoxycytidine against adenovirus infection in a mouse pneumonia model

The antiviral activity of 2',3'-dideoxycytidine (ddC) has been investigated in a mouse pneumonia model. Consolidation of lung, histopathological changes, DNA synthesis as well as levels of TNFalpha were assayed. In this in vivo model, the oral administration of ddC twice daily over 4 days, displayed an inhibitory effect. The drug significantly reduced histopathologic responses. Analysis indicated that under treatment pulmonary lesions were less severe than those of untreated controls. These data confirm the in vitro activity of ddC against adenovirus. Thus, ddC represents a potential therapeutic approach for inhibiting adenovirus infection and may offer promise as an anti-adenovirus agent for immunocompromised patients in whom serious adenovirus infection may prove fatal.

Sequence analysis and deletion of porcine adenovirus serotype 5 E3 region

A 3000 basepair (bp) region corresponding to the E3 region, the flanking pVIII and part of the fiber protein genes, of the two prototype strains (HNF-61 and HNF-70) of porcine adenovirus serotype five (PAdV-5) was sequenced. A potential E3 promoter and poly-A signals were identified. The size of the E3 region was 2039 (strain HNF-61) and 2020 bp (strain HNF-70) the largest E3 so far reported among PAdVs. Three open reading frames (ORF2-4) were identified within the E3 region. Based on the predicted amino acid (aa) sequences ORF2 was similar to other adenovirus E3 ORFs, ORF3 showed some similarity to a bovine adenovirus (BAdV-1) ORF. ORF4 was unique to PAdV-5. E3 mRNA transcripts were detected early in infection by Northern blot analysis. Genomic clones of HNF-70 with a 1505 or 1237 bp deletions in the E3 region were constructed to map non-essential regions. After transfection of the DNA into swine testicle cells, virions were recovered for only the shorter 1237 bp deletion. At least 60% of the E3 region was not essential for virus replication, bringing the theoretical vector capacity of a helper independent PAdV-5 to 2.9 kb.

Sequence analysis of porcine adenovirus type 3 E1 region, pIX and pIVa2 genes, and two novel open reading frames

The porcine adenovirus type 3 (PAd3) genome between map units 0 and 13.7 was sequenced and compared with similar regions of other adenoviruses. This region consists of the left inverted terminal repeat sequences involved in DNA packaging, the entire early region 1 (E1) and the protein IX (pIX) transcription unit. The lower strand contains the C-terminal end of IVa2 of the E2A transcriptional unit and two novel open reading frames (ORFs). The E1 transcription unit consists of ORFs for proteins homologous to the E1A, E1B-17k and E1B-55k of both human adenovirus type 5 (HAd5) and bovine adenovirus type 3 (BAd3). The predicted PAd3 pIX demonstrated homology with the N-terminal portion of the pIXs of HAd5 and BAd3. On the lower strand, immediately after the putative IVa2 ORF, there are two unique ORFs of 208 and 203 amino acid residues that showed homology with Epstein-Barr virus nuclear antigens and other cellular transcription factors.

Circumvention of vector-specific neutralizing antibody response by alternating use of human and non-human adenoviruses: implications in gene therapy

To determine whether non-human adenovirus-specific antibodies are cross-neutralizing, rabbit and mouse anti-human adenovirus type 5 (HAd5), anti-bovine adenovirus type 3 (BAd3), and anti-porcine adenovirus type 3 (PAd3) sera were used in cross-virus neutralization assays. Adenovirus neutralizing antibodies were found to be virus-specific, suggesting that virus neutralizing epitope differs significantly in HAd5, BAd3, and PAd3. To further investigate whether immunity to an HAd5-derived vector could be circumvented by the use of non-human adenoviruses in vivo, mice were first immunized either intranasally or intraperitoneally with HAd5, BAd3, PAd3, or BAd3 + PAd3, and after development of adenovirus-specific antibodies, animals were inoculated with the HAd5 recombinant (AdCA36lacZ) containing the bacterial beta-galactosidase gene under the control of murine cytomegalovirus immediate-early promoter. Virus-inoculated animals developed virus-specific IgG and IgA antibodies. LacZ expression in animals initially primed with HAd5 was significantly reduced (P < 0.05), suggesting that the immune response against the vector could prevent the transgene expression following subsequent inoculation of the same vector, whereas LacZ expression in mice initially primed with BAd3, PAd3, or BAd3 + PAd3 was significantly higher (P > 0.05) than that obtained in HAd5-primed animals. Our results suggest that HAd5-, BAd3-, or PAd3-based vectors may be used sequentially for human gene therapy or vaccine production as a means to avoid immunity to the vector.

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.

Novel human gene transfer vectors: evaluation of wild-type and recombinant animal adenoviruses in human-derived cells

Major disadvantages of human adenovirus (hAd) vectors in gene therapy include preexisting or induced immune responses, and possible coreplication of recombinant hAd in the presence of wild-type hAds. These disadvantages may be overcome by using nonhuman, animal adenoviruses (aAds). We evaluated four different aAds for their potential use as viral vectors. The canine adenovirus type 2 (CAV2) and bovine adenovirus type 3 (BAV3) appeared to be suitable systems, as they infect human cells. CAV2, but not BAV3, caused cytotoxicity, and only limited (CAV2) or no (BAV3) production of infectious virus particles was observed after infection of human cell lines. CAV2 showed higher expression of endogenous genes than did BAV3 in the tested human cells. No interference between hAd and CAV2 or BAV3, such as recombination of DNA or cross-activation of virus replication, was observed in up to five passages in double-infected human cells. Transfection of cloned genomic CAV2 or BAV3 DNA into appropriate permissive cell lines rescued infectious virus. Furthermore, we produced a recombinant E1-deleted BAV3, and showed that it could infect and express a reporter gene in various human cell types. The goal was to construct and evaluate recombinant (E1-deleted) animal adenoviruses (aAds) as new vector systems for human gene therapy. The rationale for developing aAds for human use is the potential higher safety and efficiency, as compared with human adenoviruses (hAds). Coreplication and recombination with preexisting hAds should not be possible owing to lack of homology, and preexisting immunity in the general population should be limited. Of the four aAds we evaluated, BAV3 appeared to be the best candidate. It infects human cells without showing growth or cytotoxic effects, viral gene expression was barely detectable, and no trans-activation of either virus was detected in coinfections with hAd5. Rescue of virus in permissive cells, from plasmids containing the CAV2 or BAV3 genome, confirmed our approach. Furthermore, an E1-deleted recombinant BAV3 was constructed and shown to transduce and express the lacZ reporter gene in human cells.

Replication-defective bovine adenovirus type 3 as an expression vector

Although recombinant human adenovirus (HAV)-based vectors offer several advantages for somatic gene therapy and vaccination over other viral vectors, it would be desirable to develop alternative vectors with prolonged expression and decreased toxicity. Toward this objective, a replication-defective bovine adenovirus type 3 (BAV-3) was developed as an expression vector. Bovine cell lines designated VIDO R2 (HAV-5 E1A/B-transformed fetal bovine retina cell [FBRC] line) and 6.93.9 (Madin-Darby bovine kidney [MDBK] cell line expressing E1 proteins) were developed and found to complement the E1A deletion in BAV-3. Replication-defective BAV-3 with a 1.7-kb deletion removing most of the E1A and E3 regions was constructed. This virus could be grown in VIDO R2 or 6.93.9 cells but not in FBRC or MDBK cells. The results demonstrated that the E1 region of HAV-5 has the capacity to transform bovine retina cells and that the E1A region of HAV-5 can complement that of BAV-3. A replication-defective BAV-3 vector expressing bovine herpesvirus type 1 glycoprotein D from the E1A region was made. A similar replication-defective vector expressing the hemagglutinin-esterase gene of bovine coronavirus from the E3 region was isolated. Although these viruses grew less efficiently than the replication-competent recombinant BAV-3 (E3 deleted), they are suitable for detailed studies with animals to evaluate the safety, duration of foreign gene expression, and ability to induce immune responses. In addition, a replication-competent recombinant BAV-3 expressing green fluorescent protein was constructed and used to evaluate the host range of BAV-3 under cell culture conditions. The development of bovine E1A-complementing cell lines and the generation of replication-defective BAV-3 vectors is a major technical advancement for defining the use of BAV-3 as vector for vaccination against diseases of cattle and somatic gene therapy in humans.

Porcine adenovirus-3 as a helper-dependent expression vector

Porcine adenovirus has been proposed as a potential vector for generating novel and effective vaccines for pigs. As a prerequisite for the generation of helper-dependent porcine adenovirus-3 (PAV-3) vectors, two E1-complementing porcine cell lines expressing E1 proteins of human adenovirus-5 (HAV-5) were made. These cell lines could be efficiently transfected with DNA and allowed the rescue and propagation of a PAV-3 recombinant, PAV201, containing a 0.597 kb E3 deletion and a 0.803 kb E1A deletion. Our data demonstrate that E1A proteins of HAV-5 have the capacity to transform foetal porcine retina cells and complement for the E1A proteins of PAV-3. The green fluorescent protein (GFP) gene placed under the control of a cytomegalovirus immediate early promoter was inserted into the E1A region of the PAV201 genome. Using these cell lines, a helper-dependent PAV-3 recombinant expressing GFP, PAV202, was constructed and characterized. The wild-type PAV-3 and the recombinant PAV202 expressing GFP were used to determine the ability of the virus to enter and replicate in cells of human and animal origin under cell culture conditions. Our results suggest that PAV-3 enters but does not replicate in dog, sheep, bovine and human cells.

The role of the L4 33K gene in adenovirus infection

The late phase of adenovirus infection is characterized not only by the synthesis of late proteins and the assembly of new virions, but also by the inhibition of early gene expression and host cell translation. Previous work has demonstrated that both of these inhibitory effects depend upon expression from the major late transcription unit (MLTU), controlled by the major late promoter (MLP). Furthermore, the repression of early gene expression has been shown to be mediated in trans, suggesting a role for one or more MLTU-encoded soluble factor(s). A possible candidate for such a factor is the L4-encoded 33K gene product, a protein conserved throughout the Mastadenoviridae, but of no known function. To test the role of this protein in viral infection, a stop codon was placed at the 20th position of the 33K ORF. Viable virus with genomes containing the mutation were recovered in an overlap recombination assay. Phenotypic analysis revealed that the mutant virus had a significant deficiency in both kinetics of replication and final yield, as compared to the wild-type virus. Detailed analysis of infected cells showed that there was no detectable change in the regulation of expression of several early genes and the pIX gene. This suggests either that 33K is not involved in this late phase phenomenon or that this function is replaceable by another late protein(s). Late protein synthesis and accumulation were similar to those in wild-type-infected cells. However, the reduced yield of infectious mutant virus could be accounted for by a marked deficiency in the accumulation of intermediate particles and completed capsids, suggesting a role for 33K in the process of assembly. In addition there was a small but reproducible deficiency in the shutoff of host cell translation. These results show that the 33K protein plays an important, although apparently not essential, function in the late phase of virus infection.