Overproduction of polyomavirus middle T antigen in mammalian cells through the use of an adenovirus vector

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Dendritic cells transduced with an adenoviral vector encoding a model tumor-associated antigen for tumor vaccination

Evaluation of the potential role of dendritic cells (DCs) as adjuvants for tumor vaccination has focused primarily on techniques that load DCs with peptide tumor antigens. Our aim has been to optimize the induction of antitumor immunity by enhancing the ability of DCs to present tumor-associated antigens endogenously to the afferent lymphatic system in the appropriate major histocompatibility complex (MHC)-restricted context. We have used replication-defective adenovirus vectors (Ads) to transduce DCs with various genes, including tumor antigen genes. We found that 90% of murine bone marrow derived-DCs could be infected with an Ad vector expressing the beta-galactosidase gene and still retain their physiologic and phenotypic characteristics. Furthermore, we demonstrated that transgene expression was detectable in the spleen for at least 3 days following intravenous injection of Ad-transduced DCs. Using a polyoma middle T (PymT) transgenic murine mammary carcinoma model, we have shown that a single injection of 10(5)-4 x 10(6) DCs transduced with an Ad vector expressing PymT provided complete and specific protection against tumor cell challenge in 100% of vaccinated animals. Immunization against the PymT tumor by injection with the PymT expressing Ad vector alone resulted in varying degrees of effectiveness, was highly dependent upon the route of administration, and led to significant hepatic toxicity that was not seen in mice immunized with DC transduced with the Ad vector. Our results suggest that: (i) DCs can be very efficiently modified by ex vivo Ad transduction to express tumor-specific antigens, (ii) such modified DCs appear nontoxic and stimulate a potent antitumor response.

Generation of recombinant adenovirus vectors with modified fibers for altering viral tropism

To expand the utility of recombinant adenovirus vectors for gene therapy applications, methods to alter native viral tropism to achieve cell-specific transduction would be beneficial. To this end, we are pursuing genetic methods to alter the cell recognition domain of the adenovirus fiber. To incorporate these modified fibers into mature virions, we have developed a method based on homologous DNA recombination between two plasmids. A fiber-deleted, propagation-defective rescue plasmid has been designed for recombination with a shuttle plasmid encoding a variant fiber gene. Recombination between the two plasmids results in the derivation of recombinant viruses containing the variant fiber gene. To establish the utility of this method, we constructed a recombinant adenovirus containing a fiber gene with a silent mutation. In addition, we generated an adenovirus vector containing chimeric fibers composed of the tail and shaft domains of adenovirus serotype 5 and the knob domain of serotype 3. This modification was shown to alter the receptor recognition profile of the virus containing the fiber chimera. Thus, this two-plasmid system allows for the generation of adenovirus vectors containing variant fibers. This method provides a rapid and facile means of generating fiber-modified recombinant adenoviruses. In addition, it should be possible to use this system in the development of adenovirus vectors with modified tropism to allow cell-specific targeting.

A replication-deficient adenovirus enhances liposome-mediated nucleic acid transfer into a stable cell line expressing T7 RNA polymerase

Liposome-mediated transfer of nucleic acids into a cell line expressing bacteriophage T7 RNA polymerase was enhanced by addition of a replication-deficient adenovirus (Ad5-259A) to transfection mixtures. Increasing quantities of Ad5-259A resulted in a dose-related (up to 30-fold) enhancement of reporter gene activity expressed in BT7-H cells transfected with plasmid DNA containing the reporter sequence fused to the internal ribosome entry site of encephalomyocarditis virus. Similarly, Ad5-259A enhanced reporter gene expression 7-fold following transfection of DNA containing the reporter sequence under transcriptional control of the Rous sarcoma virus long terminal repeat. Addition of Ad5-295A to transfection mixtures increased the proportion of cells staining positively for reporter gene activity, from 2 to 25% when the reporter was expressed via the T7 polymerase and from 20 to 50% when the reporter was under the control of a eucaryotic promoter. Thus, Ad5-259A enhanced reporter protein activities expressed by cytoplasmic T7-directed transcription and cap-independent initiation of translation, or nuclear transcription and cap-dependent translation. Transfection enhancement was blocked by neutralizing antibody to Ad5, and is most likely related to the endosome-disrupting activities of the virus. Adenovirus enhancement of liposome-mediated transfection provides a useful method for efficient nucleic acid transfer into eucaryotic cells.

Improved adenovirus vector provides herpes simplex virus ribonucleotide reductase R1 and R2 subunits very efficiently

We have constructed a new adenovirus (Ad) expression vector, pAdBM5, that allows for the production of unprecedented levels of recombinant protein in the human 293 cell line using the Ad expression system. The main feature of this vector is a combination of enhancer sequences that increases the activity of the ectopic major late promoter (MLP) in recombinant Ad. In 293 cells infected with helper-free Ad recombinants generated with the pAdBM5 transfer vector, both herpes simplex virus (HSV) ribonucleotide reductase R1 and R2 subunits represent the most abundant polypeptides, accounting for as much as 15-20% of total cellular proteins. Our data suggest that this level of expression is probably very close to the upper limit of the system. Furthermore, when compared to the widely utilized baculovirus (Bac)/Sf9 expression system, the improved Ad vector showed a better performance for the production and purification of active HSV-2 ribonucleotide reductase R1 and R2 subunits. The R2 subunit was about 5-fold more abundant in recombinant Ad-infected 293 cells than in Bac-infected Sf9 cells while the R1 subunit was produced at roughly similar levels with either system. However, the amount of active soluble R1 obtained from recombinant Ad-infected 293 cells was at least 5 times higher because most of the R1 produced in Sf9 cells was insoluble.

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.

Homologous recombination of adenovirus DNA in mammalian cells: enhanced recombination following UV-irradiation of the virus

We have used adenovirus as a molecular probe to examine the recombination of viral DNA following infection of mammalian cells. The technique gives a quantitative measure of homologous recombination between adenovirus type 2 (Ad2) and Ad5PyMTR3. Ad5PyMTR3 is an insertion mutant of Ad5 containing polyoma virus (Py) DNA inserted into a deleted E1 region of the Ad5 genome. Cells were coinfected with Ad2 and Ad5PyMTR3 and at an appropriate time after infection, viral DNA was extracted from the infected cells, digested with restriction endonuclease and electrophoresed through an agarose gel. Although Ad2 and Ad5 have more than 99% DNA homology, they differ sufficiently in their restriction endonuclease patterns, such that recombinant viral DNA molecules containing the Py insert could be detected and quantified by Southern blotting and hybridization to a radioactive Py DNA probe. Using this method we are able to detect and quantitate recombinant viral DNA molecules containing the Py insert which are present at frequencies down to at least 1 in 100. Recombination was detected in Chinese hamster ovary cells, monkey kidney cells, human HeLa cells, normal human fibroblasts and SV40 transformed human fibroblasts. In experiments using HeLa cells, the frequency of recombination between the Py insert on Ad5PyMTR3 and a number of unique restriction enzyme sites on Ad2 increased with the distance from the Py insert to the restriction site. Also in HeLa cells, recombination increased with increasing amounts of viral DNA synthesis and with increasing UV dose to the virus. UV-irradiation of both coinfecting viruses with 1500 J/m2 resulted in a more than 100-fold reduction in the amount of viral DNA synthesized and about a 3-fold increase in the frequency of recombination.

Simian virus 40 small-t does not transactivate RNA polymerase II promoters in virus infections

Transcriptional stimulatory properties of virus-encoded transactivators appear to be critical for viral gene expression and may be linked to cellular transformation in certain cases. Recently, the simian virus 40 (SV40) 17-kDa small-t antigen was shown to stimulate transcription of polymerase II and III genes in transient transfection assays. In experiments performed in our laboratory, two of the polymerase II promoters of the adenovirus genome, namely, the EII-early and EIII promoters, were transactivation, we examined the transient transfection assays. To further elucidate the mechanism of this transactivation, we examined the ability of small-t to transactivate the adenovirus type 5 EII-early and EIII promoters in CV-1 cells under conditions in which the small-t gene or the reporter genes were introduced into the cells through transfection and other routes. In one approach, we used established CV-1 cell lines which constitutively express the small-t gene, and study of the EII-early promoter was afforded by infection of an EIA-negative adenovirus type 5 variant. For the second approach, a recombinant adenovirus was constructed in which small-t was expressed from a replication origin-negative SV40 early promoter in the EIA region of an adenovirus vector (Ad-SV-t). The effect of small-t on adenovirus EII-early and EIII promoter expression was studied in coinfection or single-infection experiments. In both cases, transcription of the adenovirus early promoters was not stimulated by small-t. These and other results indicate that transactivation of polymerase II promoters by small-t occurs only when the target gene is in a transiently transfected state. Thus, small-t-mediated transactivation of polymerase II promoters is dependent on the type of assay system used and may be mechanistically different from that of the widely studied EIA.

Adenovirus enhancement of transferrin-polylysine-mediated gene delivery

Gene transfer may be accomplished by the receptor-mediated endocytosis pathway using transferrin-polylysine conjugates. For some target cells, however, gene transfer by this vector is extremely limited, despite the presence of the appropriate surface receptors, a phenomenon attributed to lysosomal degradation of endosome-internalized conjugate-DNA complexes. To enhance DNA escape from the cell vesicle system and thus augment gene transfer by this route, we have used the capacity of adenoviruses to disrupt endosomes as part of their entry mechanism. Adenoviral infection augmented levels of gene transfer by transferrin-polylysine conjugates in a dose-dependent manner: levels of gene transfer of greater than 2000-fold above baseline were achieved. Use of the adenovirus in this context allowed enhanced levels of gene transfer in a variety of target cells, including cell lines otherwise refractory to gene transfer by transferrin-polylysine conjugates. This augmentation was based on adenoviral-mediated vesicle disruption, a process independent of viral gene expression. Thus, the development of specific mechanisms to effect release from the endosome in combination with gene transfer by the receptor-mediated endocytosis pathway will increase the utility of this delivery system by allowing high levels of gene expression in target cells.

Evaluation of adenovirus type 4 and type 7 recombinant hepatitis B vaccines in dogs

Recombinant hepatitis B virus vaccines based on adenovirus (Ad) vectors Ad4 and Ad7 have been prepared. However, immunogenicity testing of such vaccines in experimental animals is difficult because these human adenoviruses exhibit a highly restricted host range. In this study, the dog was evaluated as a model for screening Ad4- and Ad7-vectored vaccines. Intratracheal inoculation of dogs with Ad4 and Ad7 induced substantial type-specific humoral immune responses that were significantly higher than responses obtained following pharyngeal or oral inoculations. Inoculation of dogs with recombinant Ad7 and Ad4 vaccines expressing hepatitis B surface antigen (HBsAg) elicited large antibody responses to HBsAg (anti-HBs). Substantial secondary anti-HBs responses were produced upon sequential immunizations with heterotypic Ad7 and Ad4 recombinant vaccines. These data thus indicate that the dog is a useful model for evaluating immune responses to vaccines based on Ad4 and Ad7 vectors.

Evaluation of the transfer and expression in mice of an enzyme-encoding gene using a human adenovirus vector

Mutant mice of the Spf-ash strain have an inherited defect in ornithine transcarbamylase (OTC) protein synthesis, and were used to ascertain the potential of recombinant adenoviruses for introducing and expressing the normal gene lacking in these mice. These OTC mutant mice are characterized by a reduction in the amount of OTC activity, resulting in hyperammonemia, pronounced orotic aciduria, growth retardation, and sparse fur until weaning. A recombinant adenovirus that harbors the rat OTC cDNA under the control of the viral major late promoter (MLP) was constructed and injected into such newborn mice. The effect of the virus was analyzed by monitoring the hepatic OTC enzyme during several months after the injection. An increase in OTC activity was detected and was accompanied by a diminution of orotic acid in the urine. The observation of MLP-OTC mRNA transcripts over 1 year following the injection attests to the relatively long-term presence of the transferred gene. In those mice showing the greatest OTC activity, a normalization of the fur was also observed. The experiments reported here document the feasibility of using adenovirus for the direct delivery in vivo of a gene to restore an impaired metabolism.

The amino terminus of polyomavirus middle T antigen is required for transformation

In polyomavirus-transformed cells, pp60c-src is activated by association with polyomavirus middle T antigen. These complexes have a higher tyrosine kinase activity compared with that of unassociated pp60c-src. Genetic analyses have revealed that the carboxy-terminal 15 amino acids of pp60c-src and the amino-terminal half of middle T antigen are required for this association and consequent activation of the tyrosine kinase. To define in greater detail the borders of the domain in middle T antigen required for activation of pp60c-src, we constructed a set of unidirectional amino-terminal deletion mutants of middle T antigen. Analysis of these mutants revealed that the first six amino acids of middle T antigen are required for it to activate the kinase activity of pp60c-src and to transform Rat-1 fibroblasts. Analysis of a series of insertion and substitution mutants confirmed these observations and further revealed that mutations affecting the first four amino acids of middle T antigen reduced or abolished its capacity to activate the kinase activity of pp60c-src and to transform Rat-1 cells in culture. Our results suggest that the first four amino acids of middle T antigen constitute part of a domain required for activation of the pp60c-src tyrosyl kinase activity and for consequent cellular transformation.

Simultaneous overexpression of avian pp60c-src and polyomavirus middle T antigen in mammalian cells

Recombinant adenoviruses bearing the avian c-src gene and polyomavirus middle-T-antigen gene were isolated and used to simultaneously overexpress both proteins in human 293 cells. Cells overexpressing both proteins had greater middle-T-antigen-associated tyrosine kinase activity than cells overexpressing only middle T antigen. By contrast, the intrinsic pp60c-src tyrosine kinase activity was not greater in cells overexpressing both proteins than in cells overexpressing only pp60c-src. This system of simultaneous overexpression provides a means of obtaining large quantities of pp60c-src, middle T antigen, and the complex between them.

Requirements for species-specific papovavirus DNA replication

Replication of papovavirus DNA requires a functional replication origin, a virus-encoded protein, large T antigen, and species-specific permissive factors. How these components interact to initiate and sustain viral DNA replication is not known. Toward that end, we have attempted to identify the viral target(s) of permissive factors. The functionally defined replication origins of polyomavirus and simian virus 40, two papovaviruses that replicate in different species (mice and monkeys, respectively), are composed of two functionally distinct domains: a core domain and an auxiliary domain. The origin cores of the two viruses are remarkably similar in primary structure and have common binding sites for large T antigen. By contrast, their auxiliary domains share few sequences and serve as binding sites for cellular proteins. It seemed plausible, therefore, that if cellular permissive factors interacted with the replication origin, their targets were likely to be in the auxiliary domain. To test this hypothesis we constructed hybrid origins for DNA replication that were composed of the auxiliary domain of one virus and the origin core of the other and assessed their capacity to replicate in a number of mouse and monkey cell lines, which express the large T antigen of one or the other virus. The results of this analysis showed that the auxiliary domains of the viral replication origins could substitute for one another in DNA replication, provided that the viral origin core and its cognate large T antigen were present in a permissive cellular milieu. Surprisingly, the large T antigens of the viruses could not substitute for one another, regardless of the species of origin of the host cell, even though the two large T antigens bind to the same sequence motif in vitro. These results suggest that species-specific permissive factors do not interact with the origin-auxiliary domains but, rather, with either the origin core or the large T antigen or with both components to effect DNA replication.

Protection of mice against lethal challenge with herpes simplex virus by vaccination with an adenovirus vector expressing HSV glycoprotein B

Increasing attention has been focused on the use of recombinant mammalian viruses as potential vaccines. Recombinant human adenoviruses are one of the more promising vaccine vectors because they can be easily constructed and because live adenovirus vaccines have been administered orally to large numbers of military recruits without adverse reactions. In order to examine the efficacy of human adenoviruses as vaccines we have studied the immunity induced by a recombinant adenovirus vector, AdgB2, which induces high level expression of herpes simplex virus (HSV) glycoprotein B (gB) in human and murine cells. Mice inoculated with AdgB2 produced antibodies specific for gB which neutralized HSV in the presence of complement. Although mice inoculated with AdgB2 showed no ill-effects after AdgB2 inoculation and we were unable to detect replication of human adenoviruses in mice, the mice were protected from a lethal challenge with HSV after a single inoculation with AdgB2.

Expression of biologically active middle T antigen of polyoma virus from recombinant baculoviruses

Two different recombinant baculoviruses have been generated for expressing the middle T antigen (MT) of polyoma virus in insect (Sf9) cells. One (pAcI-PyMT) produces moderate levels of MT and the other (pVL-PyMT) high levels. Indirect immunofluorescence and cellular fractionation studies with pAcI-PyMT infected Sf9 cells give results similar to those observed with wild type polyoma virus infected mouse cells, and show MT to be mainly associated with cytoplasmic membranes in the insect cell. In the latter, a sub-population of MT is phosphorylated in in vitro protein kinase assays. The yields of MT from pVL-PyMT infected cells are high enough to suggest that this protein can now be produced by this method in sufficient amounts for definitive biochemical and crystallographic analyses.

Adenoviruses as vectors for the transfer of genetic information and for the construction of new type vaccines

At present many types of corpuscular nondefective, conditional-defective and helper-dependent expressing adenoviral vectors are available which can be used in constructing gene-engineered live or inactivated viral vaccines. In particular, promising results have been obtained with live recombinant human adenoviruses expressing the S antigen of hepatitis B virus, capsid protein of rotaviruses and gB protein of herpes virus. These recombinants are proper candidates for testing as corresponding vaccine strains, a good alternative to well-known recombinant vaccine virus.

Characterization of polyoma virus early proteins expressed from vaccinia virus recombinants

We previously reported that live recombinant vaccinia viruses (VV) encoding either the large T (LT) or middle T (MT) antigens of polyoma virus (PyV) were able to induce rejection of tumors caused by PyV-transformed cells [Lathe et al., Nature 326 (1987) 878-880]. Here we present evidence that PyV early proteins expressed by the recombinants retain the biochemical characteristics of their authentic counterparts despite the cytopathic effect of VV infection. VV-encoded LT is a nuclear phosphoprotein, with specific DNA binding, ATPase and nucleotide-binding activities. VV-expressed MT associates with cellular kinases, particularly with pp60c-src, by which it is phosphorylated in vitro. Expression levels of LT and MT reached 10(6) molecules per infected cell. The use of VV as a vector is encouraged by the high expression level obtained and because VV infection does not seem to prevent appropriate post-translational processing of proteins encoded by VV recombinants.

Adenovirus vector expressing functional herpes simplex virus ICP0

ICP0, one of the five immediate-early (IE) gene products of herpes simplex virus (HSV), is a potent activator of transcription. To assess the biological activities of ICP0 and to explore its mechanisms of action, two helper-independent recombinant adenoviruses were constructed. In each recombinant, the E1 region was substituted with the ICP0-encoding genomic segment under the control of either the adenovirus major late promoter (MLP-0) or the HSV IE-0 promoter (0PRO-0). Infection of HeLa cells or 293 cells (a human embryo kidney cell line expressing adenovirus 5 E1a and -b functions) with the MLP-0 recombinant results in the synthesis of more IE-0 mRNA and ICP0 protein than did infection with the 0PRO-0 recombinant. Although 293 cells infected with MLP-0 accumulate 5- to 10-fold more IE-0 mRNA late in the infection than cells infected with HSV, the level of the protein product, ICP0, increased only slightly. In 293 cells, both recombinants could replicate, albeit at a slower rate and with lower final yields than wild-type adenovirus. Neither virus replicates its DNA in HeLa cells, and thus ICP0 cannot substitute for adenovirus E1a; however, the level of ICP0 that accumulates in MLP-0-infected HeLa cells was comparable to that of HSV-infected HeLa cells. In a functional test, we demonstrated that the adeno-ICP0 recombinant viruses can transactivate a transfected TK-CAT cassette, indicating that the ICP0 is biologically active.

Expression of bicistronic measles virus P/C mRNA by using hybrid adenoviruses: levels of C protein synthesized in vivo are unaffected by the presence or absence of the upstream P initiator codon

The measles virus (MV) P/C mRNA is functionally bicistronic. Translation is presumed to initiate at both the first and second 5'-proximal AUG codons, leading, respectively, to synthesis of the P and C polypeptides from different overlapping reading frames. To study the function and differential expression of these polypeptides, we have constructed hybrid human adenoviruses capable of expressing high levels of P and C together or of C alone. Cloned cDNA corresponding to the MV P/C gene was coupled to the adenovirus type 2 (Ad2) major late promoter, most of the Ad2 tripartite leader sequence, and the simian virus 40 3'-end processing signal and then used to replace most of the E1a-E1b region of the Ad5 genome in two hybrid adenoviruses: one (Ad5MV/PC13) which contained both 5'-proximal AUG codons of the P/C mRNA and another (Ad5MV/C3) which retained only the second. The sequence context for the P protein initiator AUG codon in Ad5MV/PC13 was made more favorable (GAGAUGG) than the relatively unfavorable context (CCGAUGG) seen in the native MV P/C mRNA. After infection of 293 cells (which provide complementary E1a-E1b functions), both viruses directed equal amounts of P/C-specific mRNA transcription. Ad5MV/PC13 directed the synthesis of both P and C proteins, while Ad5MV/C3 directed the synthesis of C protein alone. Ad5-expressed P protein was phosphorylated, while C was not. C protein had a similar diffuse cytoplasmic localization in both MV and Ad5-infected cells. Ad5MV/C3 and Ad5MV/PC13 directed equal amounts of C protein expression in 293 cells at a level approximately 15 times greater than that seen in MV-infected cells. Thus the level of C protein expression was unaffected by the presence or absence of an out-of-frame upstream AUG codon in a favorable sequence context. This observation cannot be explained by the scanning model for ribosomal initiation and suggests that ribosomes may be binding directly at an internal mRNA site at or near the initiator AUG codon for the C protein.

High-level eucaryotic in vivo expression of biologically active measles virus hemagglutinin by using an adenovirus type 5 helper-free vector system

The entire measles virus (MV) hemagglutinin (HA)-coding region was reconstructed from cloned cDNAs and used as part of a hybrid transcription unit to replace a region of the adenovirus type 5 genome corresponding to the entire E1a transcription unit and most of the E1b transcription unit. The resulting recombinant virus was stable and able to replicate to high titers in 293 cells (which constitutively express the complementary E1a-E1b functions) in the absence of helper virus. During infection of 293 cells, the hybrid virus expressed MV HA protein which was indistinguishable from that expressed in MV-infected cells in terms of immunoreactivity, gel mobility, glycosylation, subcellular localization, and biologic activity. Infection of 293 cells with the hybrid virus led to high-level synthesis of the MV HA protein (equivalent to 65 to 130% of the level seen in MV-infected cells). At late times after high-multiplicity hybrid virus infection of HeLa and Vero cells (which do not express E1 functions), the level of HA protein synthesis was at least 35% of that seen in 293 cells. This MV-adenovirus recombinant will be useful in the study of the biologic properties of the MV HA protein and in assessment of the potential usefulness of hybrid adenoviruses as live-virus vaccine vectors.

Abundant expression of herpes simplex virus glycoprotein gB using an adenovirus vector

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is a major component of infected cell membranes and virion envelopes. Glycoprotein B is known to be essential for entry of viruses into cells and may play important roles in virus-induced cell fusion and other alterations in cell morphology. In order to study the biochemical and immunological properties of gB in isolation from other HSV-1 polypeptides we have constructed human adenovirus vectors capable of expressing high levels of gB. The gB gene was coupled to the SV40 early promoter and inserted into the E3 region of two adenovirus vectors, one in which the E1 region was deleted (AdgB-1) and another which contained E1 sequences (AdgB-2). In AdgB-1 the orientation of the chimeric gB-SV40 gene was right to left, i.e., opposite to the direction of late and E3 mRNA transcription, whereas in AdgB-2 the orientation was left to right. Human 293 cells which express E1 functions supported replication of AdgB-1 and gB was expressed in these cells but not in mouse cells and only at very low levels in human cells other than 293. Replication of AdgB-2 was not limited to 293 cells and the virus was able to induce synthesis of gB at levels equal to or higher than those expressed in HSV-1-infected human or mouse cells. Microscopic examination of AdgB-2-infected cells revealed extensive vacuolization in a manner completely uncharacteristic of adenovirus-infected cells, and fluorescent antibody staining indicated that gB was not only present at the cell surface but also concentrated in the cytoplasmic vacuoles.

A simple technique for the rescue of early region I mutations into infectious human adenovirus type 5

Early region 1 (E1) of the human adenoviruses has many intriguing properties which have prompted numerous mutational studies to help delineate and characterize the domains responsible for these functions. In mutational analyses being done currently, the E1 region is usually cloned into a bacterial plasmid where it is mutated and then the altered E1 sequences are "rescued" back into infectious virus. The most frequently used rescue procedures are somewhat tedious, requiring the purification and fractionation of linear viral DNA or DNA fragments, and often involve the screening of numerous plaque isolates. Several observations we have made recently on the properties of adenovirus DNA in infected cells and on infectious plasmids in transfected cells led us to design a new approach for rescuing E1 mutations into infectious viral genomes. We constructed a plasmid, pJM17, containing the entire Ad5 DNA molecule, with an insert in the E1 region that exceeds the packaging constraints of the adenovirus capsid. Following transfection of pJM17 into 293 cells the plasmid DNA is able to replicate but cannot be packaged into infectious virions. In contrast cotransfection of 293 cells with pJM17 plus an E1-containing plasmid carrying mutated sequences produces recombinant virions at high efficiencies. Neither plasmid needs to be linearized prior to contransfection. The technique eliminates the need to purify and manipulate infectious virion DNA and since no unique restriction sites are needed, both E1A and E1B mutants' as well as foreign gene inserts in the E1 region can be easily rescued into virus.

Analysis of middle tumor antigen and pp60c-src interactions in polyomavirus-transformed rat cells

The relative abundance of pp60c-src molecules associated with polyomavirus (Py) middle tumor antigen (MTAg) and the relative abundance of MTAg associated with pp60c-src in a variety of Py-transformed rat cells was determined by quantitative immunoblot analyses which detect pp60c-src or Py MTAg. The results demonstrate that approximately 5 to 10% of the total immunoprecipitable pp60c-src molecules in Py-transformed rat cells are stably associated with MTAg and have elevated protein kinase activities. In these same cells, it was found that approximately 10 to 15% of the detectable MTAg molecules are stably associated with pp60c-src. Other results presented in this report demonstrate that approximately 50 to 75% of the total MTAg-associated cellular tyrosine kinase activity potentially represents the enzymatic activity of pp60c-src, while the remaining 25 to 50% represents the activity of other cellular tyrosine kinases. Our results also show that most pp60c-src molecules associated with Py MTAg do not possess electrophoretic mobilities that are altered from those of pp60c-src molecules not associated with MTAg or pp60c-src molecules obtained from normal rodent cells.

Stable transfer of a mouse dihydrofolate reductase gene into a deficient cell line using human adenovirus vector

A plasmid containing the mouse dihydrofolate reductase (dhfr) gene was rescued in a human adenovirus in early region 3. Analysis of the insert in the recombinant virus revealed that the dhfr sequences were intact in the viral genome, whereas a part of the ampicillin gene in the plasmid sequences was deleted. The recombinant virus could successfully express this gene in a deficient cell line. A permanent dhfr+ cell line was established by stable transfer of the gene using the recombinant virus.