Transcription units of E1a, E1b and pIX regions of bovine adenovirus type 3.

The major mRNA species in the E1 region of the genome of bovine adenovirus type 3 (BAV3) have been defined by using a combination of PCR, 5' RACE, Northern analysis and DNA sequencing. Independent transcription initiation sites were identified for each of the E1a, E1b and protein IX (pIX) transcription units, but all mRNA species terminated at the same poly(A) addition site immediately downstream of the pIX open reading frame. Thus, the BAV3 E1 region, which consists of the E1a and E1b genes together with that for pIX, functions as a nested overlapping transcription unit. One major mRNA species encoding the E1a protein was found and two mRNAs encoding E1b species, the smaller of which encodes the E1b 17K protein alone and the larger encodes both 17K and 47K E1b proteins, were identified. One mRNA species encodes pIX. The E1a transcript, encoding the predicted 214 residue E1a protein, has four exons. The smaller E1b mRNA has two exons, the second of which corresponds to the last exon of E1a. No introns were detected in the larger E1b mRNA that encodes both the E1b 17K and 47K proteins nor in the mRNA encoding pIX. The relative times of appearance of the mRNAs from the E1-pIX gene region following infection of bovine cells with BAV3 was determined.

Development and use of a 293 cell line expressing lac repressor for the rescue of recombinant adenoviruses expressing high levels of rabies virus glycoprotein.

An expression cassette designed for high-level production of rabies virus glycoprotein (RG) could not be rescued into a replication-defective, adenovirus-based vector using standard procedures. To overcome this difficulty, a 293-based cell line, designated 293LAP13, was constructed that contained and expressed a derivative of the lac repressor protein. The lac operator sequence, to which the repressor binds, was incorporated into an expression cassette, containing a promoter and intron, designed for high-level production of RG. Insertion of a single operator sequence immediately downstream of the transcription start site and the use of the 293LAP13 cell line allowed recombinant viruses that could not be isolated with 293 cells to be rescued efficiently. The operator-containing virus reached higher titres in 293LAP13 than in parental 293 cells and also produced plaques more efficiently in 293LAP13 cells. Moreover, in non-complementing human and canine cell lines, adenovirus vectors with a promoter-intron expression cassette expressed RG at much higher levels than vectors lacking the intron. These observations, together with the demonstration that expression of RG by operator-containing vectors was repressed markedly in 293LAP13 cells and that this inhibition was relieved at least partly by IPTG, suggest that the 293LAP13 cell line may be useful for the rescue and propagation of many vectors in which high expression of the desired protein prevents vector rescue in 293 cells.

Human adenovirus type 5 vectors expressing rabies glycoprotein.

The prevalence of wildlife rabies throughout the world and the continued spread of this disease in North America highlights the need for oral vaccines which may be used safely and effectively to vaccinate a number of species that are reservoirs or vectors of rabies. We have previously shown that AdRG1, a replication competent recombinant human adenovirus type 5 (Ad5) expressing a rabies glycoprotein (RG), can induce immunity to rabies in rodent, canine, and skunk model systems. To improve the Ad5 vector system as a potential oral vaccine, we have constructed additional Ad5 recombinant vectors and compared RG expression in cell culture and immunogenicity in animals. Two new replication competent vectors are compared. AdRG1.3, which carries RG with accompanying SV40 poly A addition sequences within an E3 deletion, and AdRG4, which has RG in the E3 deletion but under the control of an exogenous Ad2 major late promoter, both express higher levels of RG in permissive cell culture than did AdRG1 and both elicit high levels of serum anti-rabies antibodies by parenteral or oral routes in animals. AdRG1.3 may be a more effective vaccine vector in species which are non-permissive for the replication of human Ad5.

Pathology and immunogenicity in the cotton rat (Sigmodon hispidus) model after infection with a bovine adenovirus type 3 recombinant virus expressing the firefly luciferase gene.

The histopathology of adenovirus pneumonia in cotton rats (Sigmodon hispidus) due to bovine adenovirus type 3-luciferase recombinant virus (BAd3-Luc), which has a 0.7 kb deletion from the early region 3 (E3) replaced with the firefly luciferase gene, was compared with that produced by the parental wild-type (wt) bovine adenovirus type 3 (BAd3). After intranasal inoculation of cotton rats with 3 x 10(7) p.f.u. of BAd3-Luc, the infectious virus titres in the lungs at various times post-infection were similar to those of animals infected with the parental virus. Quantitative analysis of histopathological changes and immunohistochemical staining showed that the character and severity of the lesions were indistinguishable in the two infections. Luciferase activity was detected in the lungs of BAd3-Luc-inoculated animals until 4 days post-infection (p.i.). Antibodies to both BAd3 and luciferase were detected in sera collected from BAd3-Luc-infected animals until at least 6 weeks p.i. These results show that Bad3-Luc produces pulmonary lesions in cotton rats similar to those of wt BAd3 and suggest that BAd3-based vectors may be suitable for the development of live recombinant virus vaccines.

Characterization of a human adenovirus 5: rabies glycoprotein recombinant vaccine reisolated from orally vaccinated skunks.

An infectious recombinant human adenovirus which carries the rabies glycoprotein gene and accompanying SV40 control elements can be given orally to skunks to immunize them against rabies. We have looked for adenovirus in the feces and oral fluids of animals that have been given this recombinant and have obtained 111 virus positive samples from 16 test animals. DNA from these virus isolates was examined for possible mutations. One possible insertion mutation was detected by SmaI restriction endonuclease analysis of genomic DNA. Further analysis by HaeIII restriction and nucleotide sequencing of polymerase chain reaction products encompassing the whole SV40-rabies insert revealed that this isolate contained an insert of the 72 base pair sequence found in the SV40 promoter region. A second mutation, in which 54 base pairs were deleted from within the rabies glycoprotein gene, was also detected in two independent isolates from one skunk.

Induction of antibodies protecting against transmissible gastroenteritis coronavirus (TGEV) by recombinant adenovirus expressing TGEV spike protein.

Ten recombinant adenoviruses expressing either fragments of 1135, 1587, or 3329 nt or the full-length spike gene of transmissible gastroenteritis coronavirus (TGEV) have been constructed. These recombinants produce S polypeptides with apparent molecular masses of 68, 86, 135, and 200 kDa, respectively. Expression of the recombinant antigen driven by Ad5 promoters was inhibited by the insertion of an exogenous SV-40 promoter. Most of the recombinant antigens remain intracytoplasmic in infected cells. All the recombinant-directed expression products contain functional antigenic sites C and B (Gebauer et al., 1991, Virology 183, 225-238). The recombinant antigen of 135 kDa and that of 200 kDa, which represents the whole spike protein, also contain antigenic sites D and A, which have previously been shown to be the major inducers of TGEV-neutralizing antibodies. Interestingly, here we show that recombinant S protein fragments expressing only sites C and B also induced TGEV-neutralizing antibodies. The chimeric Ad5-TGEV recombinants elicited lactogenic immunity in hamsters, including the production of TGEV-neutralizing antibodies. The antisera induced in swine by the Ad5 recombinants expressing the amino-terminal 26% of the spike protein (containing sites C and B) or the full-length spike protein, when mixed with a lethal dose of virus prior to administration to susceptible piglets, delayed or completely prevented the induction of symptoms of disease, respectively.

Investigation of promoter function in human and animal cells infected with human recombinant adenovirus expressing rotavirus antigen VP7sc.

Human adenovirus (Ad) vectors are being used increasingly for a variety of applications in vaccination and gene therapy. The ability of vectors to enter cells and the efficiency of promoters expressing the therapeutic gene or vaccine antigen are critical to the outcome of such experiments. To identify promoters which might be suitable for use under a variety of conditions we have investigated the expression of a rotavirus antigen, VP7sc, employing several commonly used promoters carried in E1-substituted Ad vectors both in cell types which support virus replication and in cells which do not. Although not all gene constructions were identical, wide variations in promoter function were evident even in human 293 cells which support virus replication. The simian virus type 40 (SV40) early and beta-actin promoters expressed poorly; the SV40 late promoter was somewhat better. The human IE94 cytomegalovirus (CMV) promoter and a modified Ad major late promoter were best, functioning equally well but with different kinetics. In other human cell lines the CMV promoter was more versatile, generally providing sustained expression at a significant level, in one case for at least 6 days. In addition, as mouse, rabbit and pig models of rotavirus infection are under investigation and VP7sc is a vaccine antigen, we also investigated the ability of the recombinant adenovirus to infect cells from these and other sources. VP7sc expression was detected in several heterologous cell types, illustrating the ubiquity of the human Ad receptor and the versatility of human Ad as vectors when suitable promoters are used.

Foreign gene expression by human adenovirus type 5-based vectors studied using firefly luciferase and bacterial beta-galactosidase genes as reporters.

Adenovirus (Ad) vectors have been used extensively to obtain high-level expression of foreign genes in mammalian cells and are currently being studied for use as live viral-vectored vaccines and as gene transfer vectors for gene therapy. Many Ad recombinants have been generated that express foreign genes inserted in early region 3 (E3); however, little has been done to study the importance for gene expression of regulatory sequences flanking the gene. We have generated a series of Ad5 helper-independent vectors that contain the firefly luciferase gene or the bacterial beta-galactosidase gene (LacZ) with or without simian virus 40 (SV40) regulatory sequences, combined with E3 deletions of 1.88 or 2.69 kb. The greatest levels of luciferase expression were obtained with a vector containing the luciferase gene under the control of the SV40 promoter and polyadenylation signal inserted in a 1.88-kb E3 deletion. In contrast, LacZ expression was highest with a vector containing the LacZ gene with just the SV40 polyadenylation sequence combined with a 1.88-kb E3 deletion. It was also observed that regardless of the SV40 sequences flanking the reporter gene or the E3 deletion used, expression from the luciferase recombinants was dependent on viral DNA replication, whereas expression from the LacZ recombinants was only partially reduced when DNA replication was blocked. Analyses of RNA by dot blot hybridizations revealed that the levels of reporter gene-specific mRNA for various vectors in each series did not vary significantly. These results indicate that the kinetics and efficiency of expression of genes inserted into the E3 region, in nonconditional helper-independent vectors, may be more strongly dependent on the sequences in the foreign gene insert itself than on flanking regulatory sequences such as those used here, derived from SV40.

Methods for construction of adenovirus vectors.

Adenoviruses are attracting increasing attention as general purpose mammalian cell expression vectors, as recombinant vaccines, and potentially as vectors for gene therapy. Not only is the adenovirus genome relatively easy to manipulate by recombinant DNA techniques, but adenovirus vectors are relatively stable, grow to high titers, and can transduce a variety of cell types in cell culture and in vivo. Vectors can be designed that are either replication competent or replication defective and, in the latter case, are highly efficient at delivering and expressing genes in mammalian cells without resulting in cell killing. Methods are described for growing, titrating, and purifying adenoviruses, for extracting viral DNA from purified virions and from infected cells, for rescuing inserts of foreign DNA into the viral genome, and for assessing expression of inserted genes in adenovirus vectors.

Development of a bovine adenovirus type 3-based expression vector.

We constructed a non-defective bovine adenovirus type 3 recombinant (BAd3-Luc) containing the firefly luciferase gene inserted in the early region 3 (E3) of the BAd3 genome. Deletion of a 696 bp XhoI-NcoI E3 segment and insertion of the luciferase gene in E3 was confirmed by Southern blot analyses. Luciferase was expressed in Madin-Darby bovine kidney cells infected with BAd3-Luc as measured by enzymic assays and Western blotting. Analyses of luciferase expression in the presence or absence of 1-beta-D-arabinofuranosylcytosine indicated that approximately 70-75% of luciferase expression was dependent on viral DNA replication, suggesting that transcription of the gene was at least partially under the control of a late promoter. Although yields of infectious virus for BAd3-Luc were approximately 10-fold lower than for wild-type virus, replication of the vector was still relatively efficient. In a Western blot experiment, anti-luciferase antibody reacted with a 62 kDa protein which is of the same molecular mass as the purified firefly luciferase polypeptide. Luciferase was also expressed in the 293 cell line infected with BAd3-Luc for at least 6 days post-infection as monitored by luciferase assays. Based on these observations we suggest that BAd-based expression vectors should have excellent potential for the development of recombinant vaccines for cattle and may also be suitable as vectors for gene transfer into human cells.

The relationship of Piry virus to other vesiculoviruses: a re-evaluation based on the glycoprotein gene sequence.

By sequencing the 3 half of the Piry virus genome, we show that Piry virus, like the other vesiculoviruses, contains the genes for nucleoprotein N, phosphoprotein P, matrix protein M, glycoprotein G and polymerase protein L, in that order. Our analysis of the Piry G protein sequence suggests that Piry and Chandipura are related to each other as closely as the Indiana and New Jersey vesicular stomatitis virus serotypes are to each other. A re-examination of amino acid sequences in the nucleocapsid protein shows that this relationship is also true of the more conserved central region of this protein and that the greatest divergence between Piry and Chandipura has occurred in two other regions of the nucleocapsid protein.

An efficient and flexible system for construction of adenovirus vectors with insertions or deletions in early regions 1 and 3.

Human adenoviruses (Ads) are attracting considerable attention because of their potential utility for gene transfer and gene therapy, for development of live viral vectored vaccines, and for protein expression in mammalian cells. Engineering Ad vectors for these applications requires a variety of reagents in the form of Ads and bacterial plasmids containing viral DNA sequences and requires different strategies for construction of vectors for different purposes. To simplify Ad vector construction and develop a procedure with maximum flexibility, efficiency, and cloning capacity, we have developed a vector system based on use of Ad5 DNA sequences cloned in bacterial plasmids. Expanded deletions in early region 1 (3180 bp) and early region 3 (2690 or 3132 bp) can be combined in a single vector that should have a capacity for inserts of up to 8.3 kb, enough to accommodate the majority of cDNAs encoding proteins with regulatory elements. Genes can be inserted into either early region 1 or 3 or both and mutations or deletions can be readily introduced elsewhere in the viral genome. To illustrate the flexibility of the system, we have introduced a wild-type early region 3 into the vectors, and to illustrate the high capacity for inserts, we have isolated a vector with two genes totaling 7.8 kb.

The E1 sequence of bovine adenovirus type 3 and complementation of human adenovirus type 5 E1A function in bovine cells.

The bovine adenovirus type 3 (BAV3) genome was sequenced from the left end to the HindIII site at 11%. This region comprises the entire E1 transcription unit including the open reading frames (ORF) for proteins homologous to the E1A, E1B proteins and protein IX of human adenovirus type 5 (Ad5). A portion of the BAV3 E1A protein showed significant homology with conserved region 3 (CR3), the principal transactivation region of Ad5 E1A. The BAV3 E1A protein also contains a consensus sequence known to be important for interaction with the cellular Rb protein but lacks most of the sequence corresponding to the second exon of Ad5 E1A. Promoter sequences for BAV3 E1B were not defined though the relevant region contains a 35-base pair repeat sequence. Two ORFs define the BAV3 E1B coding unit; one with regions homologous to sequences within the Ad5 E1B 19k protein, and an overlapping ORF with significant homology to the Ad5 E1B 55k protein. The encoded BAV3 E1B proteins of 157 and 420 amino acid residues (R) have predicted unmodified molecular weights of 17,393 and 46,734 respectively. Immediately following the E1B coding region there is a transcription unit containing an SP1 binding site and TATA box followed by an ORF which encodes a protein of 125R and predicted molecular weight of 13,706 with homology to protein IX of Ad5. Five concensus poly A addition sites are located in the 350 base pairs immediately following the protein IX coding region. The homology of sequences in the Ad5 E1A CR3 region and the corresponding BAV3 protein suggested that the BAV3 protein could transactivate certain Ad5 genes normally transactivated by the Ad5 E1A product. Evidence for this hypothesis was obtained in studies in which bovine cells in culture were coinfected with BAV3 and a human adenovirus type 5 (Ad5) recombinant viral vector lacking the E1A region and having a lacZ reporter gene within the E3 region dependent on E1A for its expression. Coinfection resulted in the induction of beta-galactosidase activity and the increased expression of other Ad5 early (E2A 72k) and late (hexon) proteins.

Mouse hepatitis virus spike and nucleocapsid proteins expressed by adenovirus vectors protect mice against a lethal infection.

Infection with the mouse hepatitis coronavirus (MHV) provides an excellent model for the study of viral diseases of the central nervous system and the gastrointestinal tract. With the ultimate aim of studying mucosal immunity to MHV we have cloned the genes encoding the structural proteins of MHV strain A59 (MHV-A59) into the E3 region of a human adenovirus type 5 vector. Infection of HeLa cells with the resulting recombinant adenoviruses AdMHVS, AdMHVN and AdMHVM revealed the correct expression of the spike (S), nucleocapsid (N) and membrane (M) proteins, respectively. Intraperitoneal inoculation of BALB/c mice with the recombinant viruses elicited serum antibodies which specifically recognized the respective MHV proteins in an immunoprecipitation assay. Only antibodies to the S protein neutralized MHV-A59 in vitro but titres were low. When analysed by ELISA or by immunofluorescence only the antibody response to the N protein was significant; weak responses or no detectable response at all were found for S and M, respectively. Upon intracerebral challenge with a lethal dose of MHV-A59 we found that a significant fraction of animals vaccinated with adenovirus vectors expressing either the S protein or N protein were protected. This protective effect was significantly stronger when the animals were given a booster immunization with the same vector prior to challenge. No protection was induced by AdMHVM. Interestingly, enhanced protection resulted when AdMHVS and AdMHVN were applied in combination as compared to survival after single immunizations. The results indicate that both the N and S proteins generate a protective immune response and suggest that this response is enhanced by combined expression of the two proteins.

Packaging capacity and stability of human adenovirus type 5 vectors.

Adenovirus vectors are extensively used for high-level expression of proteins in mammalian cells and are receiving increasing attention for their potential use as live recombinant vaccines and as transducing viruses for use in gene therapy. Although it is commonly argued that one of the chief advantages of adenovirus vectors is their relative stability, this has not been thoroughly investigated. To examine the genetic stability of adenovirus type 5 vectors and in particular to examine the relationship between genetic stability and genome size, adenovirus vectors were constructed with inserts of 4.88 (herpes simplex virus type 1 gB), 4.10 (herpes simplex virus type 1 gB), or 3.82 (LacZ) kb combined with a 1.88-kb E3 deletion or with a newly generated 2.69-kb E3 deletion. The net excess of DNA over the wild-type (wt) genome size ranged from 1.13 to 3.00 kb or 3.1 to 8.3%. Analysis of these vectors during serial passage in tissue culture revealed that when the size exceeded 105% of the wt genome length by approximately 1.2 kb (4.88-kb insert combined with a 1.88-kb deletion), the resulting vector grew very poorly and underwent rapid rearrangement, resulting in loss of the insert after only a few passages. In contrast, vectors with inserts resulting in viral DNA close to or less than a net genome size of 105% of that of the wt grew well and were relatively stable. In general, viruses with genomes only slightly above 105% of that of the wt were unstable and the rapidity with which rearrangement occurred correlated with the size of the insert. These findings suggest that there is a relatively tight constraint on the amount of DNA which can be packaged into virions and that exceeding the limit results in a sharply decreased rate of virus growth. The resultant strong selection for variants which have undergone rearrangement, generating smaller genomes, is manifested as genetic instability of the virus population.

Immunogenicity in mice of tandem repeats of an epitope from herpes simplex gD protein when expressed by recombinant adenovirus vectors.

The antigenic and immunogenic potential was examined of human adenovirus type 5 (Ad) recombinants carrying and expressing from one to four tandem repeats of a linear neutralizing epitope from the gD protein of herpes simplex virus type 1 (HSV-1) as a fusion with the beta-galactosidase protein. The fusion proteins produced by these Ad vectors in infected cell culture reacted with a herpes simplex virus (HSV) epitope-specific monoclonal antibody to a degree dependent on the number of epitope repeats in the protein. Mice immunized by intraperitoneal injection of the Ad vectors developed an anti-HSV immune response as measured by ELISA and by HSV-1 neutralization assays. The mean antibody titre induced by a single injection of the Ad vector increased with the number of epitope repeats expressed by the recombinant. Any animal that had developed a serum-neutralizing titre of at least 1:80 survived challenge with a normally lethal dose of HSV-2 administered by the intraperitoneal route. Recombinant vectors expressing four repeats of the HSV epitope were as effective in antibody induction and protection as an adenovirus vector carrying and expressing the entire HSV gD protein. These results suggest that the expression of tandem repeats of appropriate epitopic sequences by adenovirus vectors may provide a safe and effective method of immunizing against HSV infection.

Protective immunity to rotavirus-induced diarrhoea is passively transferred to newborn mice from naive dams vaccinated with a single dose of a recombinant adenovirus expressing rotavirus VP7sc.

VP7sc is a novel rotavirus antigen engineered for presentation at the cell surface. Several recombinant viruses were constructed in which VP7sc was inserted into the E3 region of the human type 5 adenovirus (Ad5) genome and expression and transport of the antigen was monitored in cultured 293 cells. The recombinant virus showing the greatest level of expression (Ad5/7.4) was then used to determine whether antibodies to VP7sc could be induced in a nonhuman host. BALB/c and CBA/H mice were inoculated with Ad5/7.4 by iv, ip, oral and intranasal routes and serum antibody levels were assayed by ELISA. All vaccinated animals seroconverted but, depending on the route of vaccination, not all animals showed a significant secondary response following re-inoculation. The ability of Ad5/7.4 to induce protective immunity in mice was also examined using several vaccination regimes. A single dose of Ad5/7.4 given intranasally to dams not previously exposed to rotavirus was sufficient to induce immunity which could be passively transferred to protect suckling neonates. Recombinant adenoviruses expressing protective antigens therefore may provide an alternative to the use of attenuated rotaviruses in the development of a vaccine against gastroenteritis.

Monitoring foreign gene expression by a human adenovirus-based vector using the firefly luciferase gene as a reporter.

We have constructed a helper-independent adenovirus type 5-luciferase recombinant (Ad5-Luc 3) containing the firefly luciferase gene flanked by simian virus 40 (SV40) regulatory sequences inserted in the early region 3 (E3) of the Ad5 genome. Expression of luciferase in cells infected with Ad5-Luc3 was relatively efficient. In HeLa cells approximately 20 micrograms luciferase per 10(6) cells was made by 36 h post-infection and a 62 kilo-Dalton (kDa) luciferase band was clearly visible in a [35S]methionine-labeled Ad5-Luc 3-infected cell extract analyzed directly by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results of experiments in which cultured cells were infected with Ad5-Luc 3 in the presence or absence of 1-beta-D-arabinofuranosyl cytosine (AraC) showed that the majority of luciferase expression was dependent on viral DNA replication. This suggested that the enzyme was probably translated primarily from mRNA derived from transcripts expressed from the major late promoter of Ad5. An anti-luciferase antibody was raised in a rabbit and used to further characterize the luciferase expressed in HeLa cells infected with Ad5-Luc 3 by immunoprecipitations and Western blot analyses. The half-life of luciferase expressed in HeLa cells infected with Ad5-Luc 3 was calculated to be approximately 6-8 h by pulse chase analysis. Luciferase is likely to be a useful marker for monitoring virus dissemination and gene expression in experimental animals because assays for enzymatic activity are extremely sensitive and backgrounds are low in all tissues. In mice inoculated intraperitoneally (i.p.) with Ad5-Luc 3, luciferase activity was detected in the liver, spleen, kidney, and lung. A single i.p. inoculation of mice with Ad5-Luc 3 was sufficient to raise anti-luciferase antibody and Ad5 neutralizing antibody which persisted for at least 8 weeks. Even in the presence of circulating anti-luciferase and Ad5 neutralizing antibodies, luciferase activity could be detected in the livers, spleens, and kidneys of mice inoculated i.p. a second time with Ad5-Luc 3.

Sequence analysis of bovine adenovirus type 3 early region 3 and fibre protein genes.

The DNA sequences of the early region 3 (E3) and fibre protein genes of bovine adenovirus type 3 (BAd3) have been determined and the amino acid sequences predicted to be encoded by their open reading frames (ORFs) compared to those of the fibre and E3 proteins from other Ads. One of the BAd3-E3 proteins contains a region homologous to the 14.7K E3 protein of human Ad5 (HAd5). The putative BAd3 fibre protein contains a number of regions homologous to the HAd2 fibre protein sequence, but is predicted to be 244 amino acids longer owing to an increase in the number of repeating structural motifs of hydrophobic amino acid residues in the shaft region. Sequences to the left of the BAd3-E3 gene region contained the 3' end of another ORF with extensive identity with the hexon-associated protein precursor (pVIII) of HAd2. Like mouse Ad1 and canine Ad1, the BAd3 E3 gene is approximately 1.5 kb, about half the size of the E3 region of HAd2 and HAd5.