Bovine Adenovirus-3 Tropism for Bovine Leukocyte Sub-Populations

A number of characteristics including lack of virulence and the ability to grow to high titers, have made bovine adenovirus-3 (BAdV-3) a vector of choice for further development as a vaccine-delivery vehicle for cattle. Despite the importance of blood leukocytes, including dendritic cells (DC), in the induction of protective immune responses, little is known about the interaction between BAdV-3 and bovine blood leukocytes. Here, we demonstrate that compared to other leukocytes, bovine blood monocytes and neutrophils are significantly transduced by BAdV404a (BAdV-3, expressing enhanced yellow green fluorescent protein [EYFP]) at a MOI of 1-5 without a significant difference in the mean fluorescence of EYFP expression. Moreover, though expression of some BAdV-3-specific proteins was observed, no progeny virions were detected in the transduced monocytes or neutrophils. Interestingly, addition of the "RGD" motif at the C-terminus of BAdV-3 minor capsid protein pIX (BAV888) enhanced the ability of the virus to enter the monocytes without altering the tropism of BAdV-3. The increased uptake of BAV888 by monocytes was associated with a significant increase in viral genome copies and the abundance of EYFP and BAdV-3 19K transcripts compared to BAdV404a-transduced monocytes. Our results suggest that BAdV-3 efficiently transduces monocytes and neutrophils in the absence of viral replication. Moreover, RGD-modified capsid significantly increases vector uptake without affecting the initial interaction with monocytes.

Effects of tumor necrosis factor on viral replication and pulmonary inflammation during acute mouse adenovirus type 1 respiratory infection

CD8 T cells contribute to effective clearance of mouse adenovirus type 1 (MAV-1) and to virus-induced pulmonary inflammation. We characterized effects of a CD8 T cell effector, TNF, on MAV-1 pathogenesis. TNF inhibited MAV-1 replication in vitro. TNF deficiency or immunoneutralization had no effect on lung viral loads or viral gene expression in mice infected intranasally with MAV-1. Absence of TNF delayed virus-induced weight loss and reduced histological evidence of pulmonary inflammation, although concentrations of proinflammatory cytokines and chemokines in bronchoalveolar lavage fluid (BALF) were not significantly affected. BALF concentrations of IL-10 were greater in TNF-deficient mice compared to controls. Our data indicate that TNF is not essential for control of viral replication in vivo, but virus-induced TNF contributes to some aspects of immunopathology and disease. Redundant CD8 T cell effectors and other aspects of immune function are sufficient for antiviral and pro-inflammatory responses to acute MAV-1 respiratory infection.

Evasion of host immune responses by tumours and viruses

Viruses and tumours use various mechanisms to avoid immune surveillance. Oncogenic viruses have achieved a balance with the immune system through evolutionary time to ensure long-term persistence. Mutations that promote escape mechanisms favouring tumour growth to the detriment of host survival through reproductive age offer no selective advantage and will not generally be maintained in the viral genome that persists in nature. Conventional (non-oncogenic) and tumour viruses interact with various immune mediators and T cells in different ways. Oncogenic viruses cannot operate solely in the context of a lytic cycle, though this may be characteristic of the initial phase of infection that is limited by the acute immune response. Some oncogenic viruses interact with normal cellular growth control and signalling mechanisms. Synthesis of key viral proteins may be tightly controlled in replicating cells that are subject to T cell surveillance, such as basal epithelia, while productive infection occurs in non-proliferating progeny that are lost under normal physiological conditions, such as desquamating epithelia. Tumorigenesis may be an aberrant consequence of the molecular mechanisms needed to maintain this pattern of viral growth regulation in the context of the cell cycle. Vaccines designed to limit the acute phase of infection with cell-free oncogenic viruses should be as effective as those for conventional viruses.

E1A promoter of bovine adenovirus type 3

Conserved motifs of eukaryotic gene promoters, such as TATA box and CAAT box sequences, of E1A of human adenoviruses (e.g human adenovirus 5) lie between the left inverted terminal repeat (ITR) and the ATG of E1A. However, analysis of the left end of the bovine adenovirus 3 (BAdV-3) genome revealed that the conserved sequences of the E1A promoter are present only in the ITR. As such, the promoter activity of ITR was tested in the context of a BAdV-3 vector or a plasmid-based system. Different regions of the left end of the BAdV-3 genome initiated transcription of the red fluorescent protein gene in a plasmid-based system. Moreover, BAdV-3 mutants in which the open reading frame of E1A was placed immediately downstream of the ITR produced E1A transcript and could be propagated in non-E1A-complementing Madin-Darby bovine kidney cells. These results suggest that the left ITR contains the sole BAdV-3 E1A promoter.

[Molecular biology of adenoviral vectors]

Gene therapy is based on the use of DNA as a therapeutic material as an alternative therapeutic tool for treatment of human diseases. All proteins are codified into the DNA and several diseases result from the absence or aberrant expression of one or related genes, absence of expression of functional proteins, and alterations for regulation process in transport and degradation mechanisms. In this regard, several diseases could be potentially treated through the expression of the normal form of the involved protein. However, the main objective is to achieve a successful genetic material delivery into the target site and avoid the destruction of DNA or the selected vehicle before arrival at the final destination. Several efficient viral gene transfer systems have been developed. Viral-mediated gene delivery for experimental models has been designed from herpes virus (HV), adenovirus (adenovirous), adeno-associated virus (AAV) and retroviruses (lentiviral vectors). In this review we will discuss the specific biological and cloning properties of adenoviral vectors as a gene transfer tool and potential medical implications for gene therapy.

293T cells expressing simian virus 40 T antigen are semi-permissive to bovine adenovirus type 3 infection

Human cells do not normally support productive bovine adenovirus type 3 (BAdV-3) infection. Here, the outcome of BAdV-3 infection of both 293 cells and 293 cells modified to constitutively express the simian virus 40 (SV-40) T antigen (293T cells) was studied. Whereas BAdV-3 could efficiently infect 293 cells, there was a block in virus DNA replication, late-gene expression and virus production. In contrast, replication and efficient virus production could be detected in 293T cells infected with BAdV-3 or transfected with a replication-competent genomic BAdV-3 clone (pFBAV304). Early-phase gene expression was detected readily in both BAdV-3-infected 293 and 293T cells. However, the progression to efficient viral DNA synthesis and late-phase protein synthesis occurred only in 293T cells. Electron microscopy and virus growth kinetics demonstrated the formation of progeny virus in 293T cells. The SV-40 T antigens act to overcome a barrier in BAdV-3 DNA replication in 293 cells.

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.

The coiled-coil domain of the adenovirus type 5 protein IX is dispensable for capsid incorporation and thermostability

The 14.4-kDa hexon-associated protein IX (pIX) acts as a cement in the capsids of primate adenoviruses and confers a thermostable phenotype. Here we show that deletion of amino acids 100 to 114 of adenovirus type 5 pIX, which eliminates the conserved coiled-coil domain, impairs its capacity to self-associate. However, pIXDelta100-114 is efficiently incorporated into the viral capsid, and the resulting virions are thermostable. Deletion of the central alanine-rich domain, as in pIXDelta60-72, does not impair self-association, incorporation into the capsid, or the thermostable phenotype. These data demonstrate, first, that the self-association of pIX is dispensable for its incorporation into the capsid and generation of the thermostability phenotype and, second, that the increased thermostability results from pIX monomers binding to different hexon capsomers rather than capsid stabilization by pIX multimers.

Role of Bovine Adenovirus-3 33K protein in viral replication

The L6 region of bovine adenovirus type (BAdV)-3 encodes a nonstructural protein named 33K. To identify and characterize the 33K protein, rabbit polyclonal antiserum was raised against a 33K-GST fusion protein expressed in bacteria. Anti-33K serum immunoprecipitated a protein of 42 kDa in in vitro translated and transcribed mRNA of 33K. However, three proteins of 42, 38, and 33 kDa were detected in BAdV-3 infected cells. To determine the role of this protein in virus replication, a recombinant BAV-33S1 containing insertional inactivation of 33K (a stop codon created at the seventh amino acid of 33K ORF) was constructed. Although BAV-33S1 could be isolated, the mutant showed a severe defect in the production of progeny virus. Inactivation of the 33K gene showed no effect on early and late viral gene expression in cells infected with BAV-33S1. However, formation of mature virions was significantly reduced in cells infected with BAV-33S1. Surprisingly, insertional inactivation of 33K at amino acid 97 (pFBAV-33.KS2) proved lethal for virus production. Although expression of early or late genes was not affected, no capsid formation could be observed in mutant DNA-transfected cells. These results suggest that 33K is required for capsid assembly and efficient DNA capsid interaction.

Altered tropism of recombinant bovine adenovirus type-3 expressing chimeric fiber

Recombinant bovine adenovirus-3 (BAV-3) has been used as a gene delivery vector for vaccination of calves. However, its usefulness as a vector for non-bovine species is limited due to poor transduction efficiency. To develop BAV-3 based vector for non-bovine species, we determined the feasibility of making targeted BAV-3 vector by modifying its natural tropism. We constructed a chimeric virus, BAV600, in which the knob region of the BAV-3 fiber protein was replaced with that from human adenovirus type 5 (HAV-5). Unmodified BAV-3 vector (BAV304) was able to transduce and direct the expression of green fluorescent protein (GFP) in non-bovine cells, with low efficiency. In contrast, the transduction efficiency of BAV600 in these cells was increased by 3-67-fold. Although, expression of early and late genes was detected in non-human cells, no progeny virus (BAV600) was detected in these cells. Our results suggest that it is possible to develop BAV-3 vectors with tropism for non-bovine species.

Identification of cis-acting sequences required for selective packaging of bovine adenovirus type 3 DNA

The assembly of adenovirus particles is a multistep process, in which viral genomic DNA is selected and subsequently inserted into preformed empty capsids. The selective encapsidation of the adenovirus genome is directed by cis-acting packaging motifs, termed A repeats due to their AT-rich character in DNA sequence. A repeats are usually located at the left end of the viral genome. In this report, the construction and analysis of bovine adenovirus type 3 (BAdV-3) mutants containing deletion mutations introduced into the AT-rich regions are described. The main cis-acting packaging domains of BAdV-3 were localized between nt 224 and 540 relative to the left end of the viral genome. They displayed a functional redundancy and followed a hierarchy of importance. In addition, the results demonstrated that not all of the AT-rich units functioned as cis-acting packaging motifs.

Adenovirus with insertion-mutated E1A selectively propagates in liver cancer cells and destroys tumors in vivo

The adenovirus E1A proteins are involved in the transcriptional activation of viral and cellular genes needed for controlling cell cycle and virus replication. Undifferentiated embryonic carcinoma cells have the ability to produce an E1A-like activity that can induce the expression of E1A-targeted adenoviral and cellular genes in the absence of the E1A products. Differentiated embryonic carcinoma cells lose the ability to produce the E1A-like activity. In this study, we investigated the E1A-like activity in cancer cells with an adenovirus having a mutated E1a gene. The mutation is generated by the insertion of a large DNA fragment in the E1a gene and interrupts the COOH-terminal region of both the E1A 12S and 13S proteins. The E1a-mutated virus can efficiently replicate in HepG2 and Hep3B liver cancer cells and produce high titers of virus. Replication of the E1a-mutated virus inhibits tumor formation and destroys tumors in vivo. The results obtained in this study imply that cancer cells may produce an E1A-like activity to support the selective replication of mutated virus in cancer cells. In addition, we found that although the E1a-mutated virus could not replicate in Huh1.cl2 liver cells, the viral DNA could amplify in the cells. This result suggests that replication of adenoviral DNA is necessary, but not sufficient, for generating infectious viral progeny and destroying tumor cells.

Apoptosis in calf pneumonia induced by endobronchial inoculation with bovine adenovirus type 3 (BAV-3)

Three calves aged 1 week (group 1), three aged 6 weeks (group 2) and three aged 6 weeks (having been pretreated with dexamethasone) (group 3) were infected endobronchially with bovine adenovirus type 3 (BAV-3). All calves had received colostrum. The histopathological, immunohistochemical, ultrastructural and TUNEL features were examined on post-inoculation day (PID) 3, 5 and 7. Viral replication and intranuclear inclusions were frequently observed in groups 1 and 3, but not in group 2. The lesions became progressively severe on PID 5 and 7 in group 1. In group 3, however, the cellular injury caused by BAV-3 was of short duration and the lesions began to resolve at PID 7. Numerous apoptotic cells were seen in the PID 3 calves of all three groups, and in the PID 7 calves of groups 2 and 3; however, the PID 5 and 7 calves of group 1 showed only a few apoptotic cells in the alveolar septa. The results indicated that (1) the durability of BAV-3 infection in the lung was closely related to apoptosis, and (2) the host defence mechanism that induced apoptosis in infected cells was age-related.

Development and characterization of bovine x human hybrid cell lines that efficiently support the replication of both wild-type bovine and human adenoviruses and those with E1 deleted

The 293 cell line that was generated by transforming human embryonic kidney cells with human adenovirus type 5 (HAV5) early region 1 (E1) sequences is an excellent host for generating and growing HAV5 recombinants with E1 deleted, but it does not support the replication of bovine adenovirus type 3 (BAV3). Madin-Darby bovine kidney (MDBK), an established bovine cell line, is an excellent host for growing and plaquing BAV3. For the purpose of combining the unique characteristics of these two cell lines (293 and MDBK), we generated a number of bovine x human hybrid (BHH) cell lines. Comparison of three BHH hybrid clones-BHH3, BHH8, and BHH2C-with 293-Puro (puromycin-resistant 293 cells) and MDBK-Neo (G418-resistant MDBK cells) cell lines for total cellular DNA content, species-specific surface markers, isoenzyme analysis, and karyotyping indicate that they are hybrid in nature. BHH clones constitutively expressed the E1 proteins (E1A, E1B-21kDa, and E1B-55kDa) of HAV5 and efficiently supported the replication of both wild-type and replication-incompetent bovine or human adenoviruses. Transient gene expression experiments with a plasmid encoding the bacterial beta-galactosidase gene demonstrated that BHH cell hybrids seem to have better transfection efficiencies than either of the parental cell lines. These cell lines will be useful for isolating and growing replication-competent human or bovine adenovirus recombinants with E1 deleted and for the study of cellular or viral factors important for viral replication. The development of somatic cell hybrids appears to be a simple way of combining some of the desirable characteristics present separately in two parental cell lines.

A 72-bp internal deletion in the left inverted terminal repeat of the bovine adenovirus type 3 genome does not affect virus replication

The genome of bovine adenovirus type 3 (BAV3) is flanked by 195-base pair (bp) inverted terminal repeats (ITR). We isolated a BAV3 mutant (BAV3c29) having an internal deletion within the left ITR. The deletion eliminated 72 bp between nucleotides (nt) 89 and 162, including most of the GC-rich sequences located close to the end of the ITR sequences. This deletion did not seem to have any affect on the virus plaque size or morphology and the kinetics of viral replication compared to wild-type (wt) BAV3. The nt sequence of the right ITR of BAV3c29 remained identical to the right or left ITR of wt BAV3. These results indicate that the cis-acting sequences present within the 72 bp between nt 89 and 162 of the left ITR are not essential for BAV3 DNA replication in cultured cells.

Mutational analysis of early region 4 of bovine adenovirus type 3

The primary objective of characterizing bovine adenovirus type 3 (BAV3) in greater detail is to develop it as a vector for gene therapy and vaccination of humans and animals. A series of BAV3 early region 4 (E4) deletion-mutant viruses, containing deletions in individual E4 open reading frames (Orf) or combinations of Orfs, were generated by transfecting primary fetal bovine retinal cells with E4-modified genomic DNA. Each of these mutants was further analyzed for growth kinetics, viral DNA accumulation, and early-late protein synthesis. Mutant viruses carrying deletions in Orf1, Orf2, Orf3, or Orf4 showed growth characteristics similar to those of the E3-deleted BAV3 (BAV302). DNA accumulation and early/late protein synthesis were also indistinguishable from those of BAV302. However, mutant viruses carrying a deletion in Orf5, Orfs 1-3 (BAV429), or Orfs 3-5 (BAV430) were modestly compromised in their ability to grow in bovine cells and express early/late proteins. E4 mutants containing larger deletions, Orfs 1-3 (BAV429) and Orfs 3-5 (BAV430), were further tested in a cotton rat model. Both mutants replicated as efficiently as BAV3 or BAV302 in the lungs of cotton rats. BAV3-specific IgA and IgG responses were detected in serum and at the mucosal surfaces in cotton rats inoculated with mutant viruses. In vitro and in vivo characterization of these E4 mutants suggests that none of the individual E4 Orfs are essential for viral replication. Moreover, successful deletion of a 1.5-kb fragment in the BAV3 E4 region increased the available insertion capacity of replication-competent BAV3 vector (E3-E4 deleted) to approximately 4.5 kb and that of replication-defective BAV3 vector (E1a-E3-E4 deleted) to approximately 5.0 kb. This is extremely useful for the construction of BAV3 vectors that express multiple genes and/or regulatory elements for gene therapy and vaccination.

Cancer gene therapy: fringe or cutting edge?

Direct targeting of cancer cells with gene therapy has the potential to treat cancer on the basis of its molecular characteristics. But although laboratory results have been extremely encouraging, many practical obstacles need to be overcome before gene therapy can fulfil its goals in the clinic. These issues are not trivial, but seem less formidable than the challenge of killing cancers selectively and rationally--a challenge that has been successfully addressed.

Bovine adenovirus type 3 E1B(small) protein is essential for growth in bovine fibroblast cells

In order to study the function of bovine adenovirus type 3 (BAV-3) E1A and E1B(small) proteins, we constructed two mutants: (a) BAV102A carries an in-frame deletion in the coding region for the E1A protein (nt 831-1080); (b) BAV102B carries an insertion of triple stop codons in the E1B region (nt 1654, 178 bp downstream of the E1B(small) start codon), which stops the translation of the E1B(small) gene. BAV102A virus could grow to the wild-type BAV-3 titer in transformed cell line VIDO R2 (HAV-5 E1 transformed) cells, but no progeny virus could be found in fetal bovine retina cells (FBRC). RT-PCR and Western blot analysis showed that neither mRNA transcripts nor protein expression of early genes [E1B(small) and DNA binding protein (DBP)] could be detected in BAV102A infected FBRC. The BAV102B grew 1.5 log less than wild-type BAV-3 in FBRC; however, no BAV102B progeny virus could be observed in bovine fibroblast (BFB) cells. No appreciable difference was observed in DBP transcript synthesis between wild-type BAV-3- or BAV102B-infected FBRC. However, compared to wild-type BAV-3, BAV102B viral DNA synthesis and fiber gene expression were found to be slightly reduced in FBRC. In contrast, compared to wild-type BAV-3, DBP transcripts and viral DNA synthesis were drastically reduced in BAV102B-infected BFB cells. In addition, no fiber gene expression could be detected in BAV102B-infected BFB cells. These results suggest that BAV-3 E1A is essential for virus replication and is required for activating the transcription of other BAV-3 early genes. However, the requirement for E1B(small) protein for BAV-3 replication appears to be cell type-dependent.

Characterization of a new adenovirus isolated from black-tailed deer in California

An adenovirus associated with systemic and localized vascular damage was demonstrated by transmission electron microscopy and immunohistochemistry in a newly recognized epizootic hemorrhagic disease in California black-tailed deer. In this study, we describe the cultural, physicochemical and serological characteristics of a virus isolated from lung using neonatal white-tail deer lung and turbinate cell cultures. The virus had the cultural, morphological and physicochemical characteristics of members of the Adenoviridae family. The virus would not replicate in low passage fetal bovine, caprine or ovine cells. Antiserum to the deer adenovirus, strain D94-2569, neutralized bovine adenovirus type-6 (BAdV-6), BAdV-7, and caprine adenovirus type-1 (GAdV-1). Antiserum to BAdV-6 did not neutralize the deer adenovirus but antiserum to BAdV-7 and GAdV-1 neutralized the deer adenovirus. Cross-neutralization with the other bovine, caprine and ovine adenovirus species was not observed. Restriction endonuclease patterns generated for the deer adenovirus were unique compared to those for the currently recognized bovine, caprine and ovine adenovirus types. Amino acid sequence alignments of the hexon gene from the deer adenovirus strain D94-2569 indicate that it is a member of the proposed new genus (Atadenovirus) of the Adenoviridae family. While closely related antigenically to BAdV-7 and GAdV-1, the deer adenovirus appears sufficiently distinct culturally and molecularly to justify consideration as a new adenovirus type.

Blood clearance rates of adenovirus type 5 in mice

Persistence of adenovirus type 5 in blood has implications for the pathogenicity of the virus infection and for the use of this virus in oncolysis and gene therapy. In this study, the kinetics of adenovirus clearance from blood in mice has been evaluated. After a single inoculation of concentrated virus into the vena cava, virus half-life was less than 2 min. Depletion of Kupffer cells (KC) resulted in increased viraemia. After tail-vein injection, virus and latex beads co-localized within KC. An important factor in clearance by KC is the negative charge of particles. Deletion of the hexon hypervariable region 1 acidic stretch decreased the negative charge of the virion but it did not increase blood persistence. Coating with PEG ('PEGylation') reduced the clearance rate but also reduced infectivity.

Mouse adenovirus type 1 replication in vitro is resistant to interferon

The effects of mouse interferon (IFN)-alpha/beta and recombinant IFN-gamma on mouse adenovirus type 1 (MAV-1) replication were investigated in single-cycle infectious virus yield reduction assays on mouse L929 cells. Viral yields at 3 days postinfection indicated that wt MAV-1 and pmE314, an early region 3 null mutant, were relatively insensitive to both IFN-alpha/beta and IFN-gamma, whereas early region 1A (E1A) mutants pmE109 (null), dlE105 (conserved region 1 deletion, CR1 Delta), dlE102 (CR2 Delta), and dlE106 (CR3 Delta) were sensitive. MAV-1 E1A that was inducibly expressed in mouse fibroblast 37.1 cells rescued vesicular stomatitis virus from the antiviral effect of IFN-alpha/beta but not from the antiviral effect of IFN-gamma. Interferon-inducible gene expression was reduced in 37.1 cells as compared to the parental 3T6 cell line. Steady-state levels of IFN-inducible gene mRNAs were also reduced in 3T6 cells infected with the wild-type virus and pmE314 but not in cells infected with pmE109. These results suggest that the MAV-1 E1A gene product is capable of interfering with the signaling pathways of both types of IFN, although modulation of IFN-alpha/beta antiviral activity was more pronounced.

Normal development, wound healing, and adenovirus susceptibility in beta5-deficient mice

Integrins have been shown to play important roles in embryonic development, wound healing, metastasis, and other biological processes. alphavbeta5 is a receptor for RGD-containing extracellular matrix proteins that has been suggested to be important in cutaneous wound healing and adenovirus infection. To examine the in vivo function of this receptor, we have generated mice lacking beta5 expression, using homologous recombination in embryonic stem cells. Mice homozygous for a null mutation of the beta5 subunit gene develop, grow, and reproduce normally. Keratinocytes harvested from beta5(-/-) mice demonstrate impaired migration on and adhesion to the alphavbeta5 ligand, vitronectin. However, the rate of healing of cutaneous wounds is not different in beta5(-/-) and beta5(+/+) mice. Furthermore, keratinocytes and airway epithelial cells obtained from null mice show adenovirus infection efficiency equal to that from wild-type mice. These data suggest that alphavbeta5 is not essential for normal development, reproduction, adenovirus infection, or the healing of cutaneous wounds.

The distribution and kinetics of polyomavirus in lungs of intranasally infected newborn mice

The primary cell types that sustain polyomavirus (Py) replication following intranasal infection as well as the nature of the host cellular response to Py were unknown. As this is an essential and specific site for virus entry, it seems likely that viral gene function must be adapted to these mucosal tissues. Using immunohistochemistry and in situ hybridization, we determined the cell types in the lung that support Py gene expression and replication following intranasal inoculation of newborn mice within 24 h of birth. Lungs were collected daily from days 1 to 10 postinfection for Py DNA and early T antigen analysis and for histological examination by H&E staining, using methods that preserve the delicate newborn lung architecture. Viral DNA was present in increasing quantities from 2 to 6 dpi in a subset of the Clara cells lining the inner lumen of the bronchi and bronchioles, while T antigen expression was present in a majority of the cells in the bronchi and bronchiole lumen. A distinct and transient pattern of hyperplasia was observed among the cells expressing T antigen and was present from 3 through 6 dpi. Py DNA-containing cells exfoliated into the bronchiole lumen and alveolar ducts, but Py T antigen was not detected in these cells. Py DNA was first detected at 2 dpi, increased through 6 dpi, and abruptly declined through 9 dpi at which time there was no sign of viral DNA in the lungs by in situ hybridization. An unusual infiltration of neutrophils began before the presence of exfoliated cells or Py replication and continued for 2-3 days and was followed by a lymphocytic infiltration at 8-10 dpi lasting 2-3 days. Neither the hyperplasia nor the neutrophil infiltration occurred following infection with the MOP1033 MT-Ag or RB1 LT-Ag mutants of Py. In addition, both the neutrophil infiltration and the transient hyperplasia are in stark contrast to the heavy macrophage infiltration that follows infection of lungs with mouse adenovirus. Thus it appears that Py elicits a distinct host response pattern not seen with other DNA viral infections.

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.

Group D adenoviruses infect primary central nervous system cells more efficiently than those from group C

Group C adenovirus-mediated gene transfer to central nervous system cells is inefficient. We found that wild-type group D viruses, or recombinant adenovirus type 2 (Ad2) (group C) modified to contain Ad17 (group D) fiber, were more efficient in infecting primary cultures of neurons. Together with studies on primary vascular endothelial cells and tissue culture cell lines, our results indicate that there is not a universally applicable adenovirus serotype for use as a gene transfer vector.

Mouse adenovirus type 1 early region 1A is dispensable for growth in cultured fibroblasts

Mouse adenovirus type 1 (MAV-1) mutants with deletions of conserved regions of early region 1A (E1A) or with point mutations that eliminate translation of E1A were used to determine the role of E1A in MAV-1 replication. MAV-1 E1A mutants expressing no E1A protein grew to titers comparable to wild-type MAV-1 titers on mouse fibroblasts (3T6 fibroblasts and fibroblasts derived from Rb+/+, Rb+/-, and Rb-/- transgenic embryos). To test the hypothesis that E1A could induce a quiescent cell to reenter the cell cycle, fibroblasts were serum starved to stop DNA replication and cellular replication and then infected with the E1A mutant and wild-type viruses. All grew to equivalent titers. Steady-state levels of MAV-1 early mRNAs (E1A, E1B, E2, E3, and E4) from 3T6 cells infected with wild-type or E1A mutant virus were examined by Northern analysis. Steady-state levels of mRNAs from the mutant-infected cells were comparable to or greater than the levels found in wild-type virus infections for most of the early regions and for two late genes. The E2 mRNA levels were slightly reduced in all mutant infections relative to wild-type infections. E1A mRNA was not detected from infections with the MAV-1 E1A null mutant, pmE109, or from infections with similar MAV-1 E1A null mutants, pmE112 and pmE113. The implications for the lack of a requirement of E1A in cell culture are discussed.

Mouse adenovirus type-1 replication is restricted to vascular endothelium in the CNS of susceptible strains of mice

Previous studies have shown that mouse adenovirus type-1 (MAV-1) caused a fatal hemorrhagic encephalitis in certain strains of mice. C57BI/6 mice exhibited 100% mortality when given as little 10(3) plaque-forming units (PFU) of MAV, in contrast to BALB/c mice which were resistant to as many as 10(6) PFU. Susceptible animals died with a flaccid paralysis on the 3rd or 4th day after inoculation. The brains and spinal cords of these animals displayed numerous petechial hemorrhages that were found in virtually all areas of the brain, but were more numerous in white matter. In this paper, immunohistochemistry and electron microscopy were used to identify the viral target of replication within the CNS of susceptible mice. These studies showed that the CNS vascular endothelial cell was the primary site of viral replication within the CNS of mice infected with MAV-1. Characterization of cytokine mRNA levels and disease course in immunodeficient mice revealed that the host immune response played little, if any, role in the pathogenesis of MAV-1 disease in susceptible mice and was not responsible for the resistance of BALB/c mice. These results support the conclusion that disease course and outcome in susceptible and resistant strains of mice were determined primarily by the ability of the virus to replicate within the CNS vascular endothelium.

Sequence, transcriptional analysis, and deletion of the bovine adenovirus type 1 E3 region

The early 3 (E3) transcriptional unit of human adenoviruses (HAV) encodes proteins that modulate host antiviral immune defenses. HAV E3 sequences are highly variable; different HAV groups encode phylogenetically unrelated proteins. The role of the E3 region of many human and animal adenoviruses is unknown because the sequences are unrelated to previously characterized viruses and the functions of proteins encoded by these regions have not been studied. We sequenced a portion of the bovine adenovirus serotype 1 (BAV-1) genome corresponding to the putative E3 region. This sequence was substantially different from other adenoviral E3 sequences, including those of two other bovine adenoviruses. However, two regions of putative sequence conservation were identified. BAV-1 E3 sequences were identified in early and late transcripts, but, unlike HAV, introns were not detected in the E3 region transcripts. Like HAV E3, a majority of the BAV-1 E3 region was not essential for growth in cell culture, as demonstrated by the construction of a recombinant BAV-1 lacking 60% of the putative E3 region.

Dissociative expression of adenoviral-mediated E. coli LacZ gene between ischemic and reperfused rat brains

A replication-defective adenoviral vector containing the E. coli lacZ gene was directly injected into the ischemic or reperfused cerebral cortex of rats. An administration of adenoviral vector showed a slight to moderate expression of the lacZ gene in the cerebral cortex of the middle cerebral artery (MCA) region until 2 days after the MCA occlusion. In contrast, expression of the lacZ gene was not observed, or only minimally so, in the reperfused brain until 2 days after a 90 min of transient MCA occlusion. However, the lacZ expression dramatically increased at 7 days after the reperfusion, then diminished by 21 days. The majority of brain cells that expressed the lacZ gene were neurons and a fraction (5-10%) were astroglial cells. The present study showed that an exogenous gene was transferred and expressed in neural cells of ischemic and reperfused brains in vivo, but the temporal profile of the expression is dissociative.

Mechanisms of unusually high antioxidant activity of RSV-SR-transformed cells and of its suppression by activated p21ras

We have previously demonstrated that hamster embryo fibroblasts (HEFs) transformed by Rous Sarcoma virus, Schmidt-Ruppin strain (RSV-SR) are highly resistant to damage by H202 (H2O2R), (in contrast to HEFs transformed spontaneously, or by bovine adenovirus and SV40), while N-ras transfection of RSV-SR transformants leads to suppression of pp6Ov-scr and of H2O2R. In this study we have examined (1) mechanisms of antioxidant activity (AOA) of HEFs transformed by these agents and (2) the possible role of the v-src gene in unusually high AOA of RSV-SR transformants and of activated ras oncogenes in its suppression. All transformants exhibit increased catalase and glutathione peroxidase (GP) activities, while SOD, glutathione and glutathione reductase (GR) were reduced. As compared with other transformants, the significantly higher catalase and the low SOD activities were characteristic of RSV-SR-transformants, while an increase in GP was observed in all types of transformants. Correspondingly, RSV-SR-transformants showed an extremely high H202-catabolizing activity (H2O2CA) and no lipid peroxidation chain reaction (LPCR). N-ras-induced suppression of pp60v-scr of RSV-SR-transformed HEFs coincided with the suppression of catalase, GP, H202 and H202CA. However, suppression of catalase and GP was also observed in N-ras- and Ha-ras-transfected, spontaneously transformed HEFs. Thus, extremely high catalase activity and suppression of LPCR are apparently the main mechanisms of the unusually high H202R of RSV-SR transformants, while its suppression by activated ras oncogenes may also take place in some transformants, free of v-src activity.

A p53 mutation in exon 5 associated with adenovirus transformation

The adenovirus type 5 (Ad5) 55-kDa E1B oncoprotein has been shown to form complexes with the p53 tumor suppressor protein. These complexes are thought to interfere with normal p53 activity and may be responsible for the paucity of p53 mutations in cells transformed by these viruses. This report describes an example of a p53 mutation in exon 5 in an Ad5-transformed cell line that exhibited less expression of E1B 55-kDa protein and a longer tumor-latency phenotype than another Ad5-transformed cell line expressing wild-type p53. The finding of a p53 mutation in an Ad5-transformed cell line is unusual, especially considering the current theory that p53-E1B interactions play an important role in adenovirus transformation. This mutation could represent an alternative method of inactivating p53 function in the absence of sufficient levels of E1B 55-kDa oncoprotein.