Expression of hepatitis B surface antigen with a recombinant adenovirus

The tripartite leader sequence is required for ectopic expression of HAdV-B and HAdV-E E3 CR1 genes

The unique repertoire of genes that characterizes the early region 3 (E3) of the different species of human adenovirus (HAdV) likely contributes to their distinct pathogenic traits. The function of many E3 CR1 proteins remains unknown possibly due to unidentified intrinsic properties that make them difficult to express ectopically. This study shows that the species HAdV-B- and HAdV-E-specific E3 CR1 genes can be expressed from vectors carrying the HAdV tripartite leader (TPL) sequence but not from traditional mammalian expression vectors. Insertion of the TPL sequence upstream of the HAdV-B and HAdV-E E3 CR1 open reading frames was sufficient to rescue protein expression from pCI-neo constructs in transfected 293T cells. The detection of higher levels of HAdV-B and HAdV-E E3 CR1 transcripts suggests that the TPL sequence may enhance gene expression at both the transcriptional and translational levels. Our findings will facilitate the characterization of additional AdV E3 proteins.

Oral adenoviral-based vaccines: historical perspective and future opportunity

Adenoviral vaccines delivered orally have been used for decades to prevent respiratory illness, but are now being seriously explored again as a platform technology to make vaccines against a variety of pathogens. Years of use in military populations as a preventative measure for adenoviral infection have demonstrated the safety of oral administration of adenovirus. The advantages of using this approach as a platform technology for vaccines include rapid development and distribution, as well as ease of administration. Recent discoveries may allow this platform approach to reach the clinic within a few years.

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.

Neutralizing antibodies elicited by immunization of monkeys with DNA plasmids and recombinant adenoviral vectors expressing human immunodeficiency virus type 1 proteins

Immunization with recombinant serotype 5 adenoviral (rAd5) vectors or a combination of DNA plasmid priming and rAd5 boosting is known to elicit potent immune responses. However, little data exist regarding these immunization strategies and the development of anti-human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies. We used DNA plasmids and rAd5 vectors encoding the HIV-1 89.6P or chimeric HxB2/BaL envelope glycoprotein to immunize macaque monkeys. A single rAd5 immunization elicited anti-Env antibody responses, but there was little boosting with subsequent rAd5 immunizations. In contrast, rAd5 boosting of DNA-primed monkeys resulted in a rapid rise in antibody titers, including the development of anti-HIV-1 neutralizing antibodies. The potency and breadth of neutralization were evaluated by testing plasma against a panel of 14 clade B primary isolates. Moderate levels of plasma neutralizing activity were detected against about one-third of the viruses tested, and immunoglobulin G fractionation demonstrated that virus neutralization was antibody mediated. After a challenge with a chimeric simian-human immunodeficiency virus (SHIV89.6P), an anamnestic neutralizing antibody response was observed, although the breadth of the response was limited to the subset of viruses that were neutralized after the primary immunization. These data are the first detailed description of the anti-HIV-1 neutralizing antibody response in nonhuman primates elicited by DNA and rAd5 immunization. In addition to the well-established ability of DNA priming and rAd5 boosting to elicit potent anti-HIV-1 cellular immune responses, this immunization strategy elicits anti-HIV-1 neutralizing antibodies and therefore can be used to study novel Env immunogens designed to elicit more potent neutralizing antibodies.

The Gordon Wilson Lecture: viruses and human disease

In many ways, Ebola virus infection provides a model for understanding the toxicity of viruses and their causal role in human disease. The highly aggressive course of Ebola virus infection provides a model for understanding the molecular mechanisms of viral cytotoxicity. In addition, the use of animal models and definition of immune correlates, which lead to protection, may provide lessons that are applicable to other viral infections. Perhaps the greatest challenge facing biomedical science today is the containment of the human immunodeficiency virus, the causative agent of AIDS. In many ways the critical obstacles to the development of a vaccine for HIV are similar to those observed with Ebola virus infection. Because the reservoir of infection is not known and human-to-human spread has been documented, vaccines may provide the best opportunity to contain and limit the spread of infection worldwide. Similar to Ebola virus, there are few convincing examples of immune resistance of HIV infection. In addition, it has been difficult to identify broadly neutralizing antibodies that can prevent infection in vitro or in vivo. In defining immune correlates, relevant animal models, and mechanisms of cytotoxicity, it is hoped that similar efforts may lead to effective vaccines for other infectious diseases. In this way, Ebola virus infection provides a useful paradigm for understanding the genetic determinants of viral disease and in facilitating the development of treatments and prevention of viral infections.

Development of a preventive vaccine for Ebola virus infection in primates

Outbreaks of haemorrhagic fever caused by the Ebola virus are associated with high mortality rates that are a distinguishing feature of this human pathogen. The highest lethality is associated with the Zaire subtype, one of four strains identified to date. Its rapid progression allows little opportunity to develop natural immunity, and there is currently no effective anti-viral therapy. Therefore, vaccination offers a promising intervention to prevent infection and limit spread. Here we describe a highly effective vaccine strategy for Ebola virus infection in non-human primates. A combination of DNA immunization and boosting with adenoviral vectors that encode viral proteins generated cellular and humoral immunity in cynomolgus macaques. Challenge with a lethal dose of the highly pathogenic, wild-type, 1976 Mayinga strain of Ebola Zaire virus resulted in uniform infection in controls, who progressed to a moribund state and death in less than one week. In contrast, all vaccinated animals were asymptomatic for more than six months, with no detectable virus after the initial challenge. These findings demonstrate that it is possible to develop a preventive vaccine against Ebola virus infection in primates.

A recombinant measles virus expressing hepatitis B virus surface antigen induces humoral immune responses in genetically modified mice

It has been shown previously that measles virus (MV) can be successfully used to express foreign proteins (M. Singh and M. A. Billeter, J. Gen. Virol. 80:101-106, 1998). To develop an inexpensive MV-based vaccine, we generated recombinant MVs that produce structural proteins of hepatitis B virus (HBV). A recombinant virus that expressed the HBV small surface antigen (HBsAg) was analyzed in terms of its replication characteristics, its genetic stability in cell culture, and its immunogenic potential in genetically modified mice. Although this virus showed a progression of replication slightly slower than that of the parental MV, it appeared to stably maintain the added genetic information; it uniformly expressed the appropriately glycosylated HBsAg after 10 serial passages. Genetically modified mice inoculated with this recombinant MV produced humoral immune responses against both HBsAg and MV proteins.

Recombinant viruses as vectors for mucosal immunity

The development and characterization of viral based vaccine vectors is extremely active research field. Much of this work has been facilitated by developments in molecular biology that allow work with large plasmid-based vectors, as well as the use of PCR. Several different vector systems are now available using RNA viruses and DNA viruses. Each vector system has its own strengths and weaknesses. Due to the differences and diversity between the viruses used as vectors, it is doubtful that a single system will be useful for all desired vaccines. However, the further development of existing, as well as potentially new systems, will provide a repertoire for vaccinologists to design the recombinant vaccine which will generate an optimal humoral and immune response for protection against infection or disease caused by pathogens that infect via mucosal surfaces.

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

A major obstacle to the success of gene therapy strategies that directly target cancer cells is the poor vector distribution within solid tumors. To address this problem, we developed an E1b 55 kDa attenuated, replication-competent adenovirus (Ad.TKRC) which expresses the herpes simplex-1 thymidine kinase (HSVtk) gene to sensitize tumors to ganciclovir (GCV). Efficacy of this combined strategy was tested in nude mice with subcutaneous human A375 melanoma and ME180 cervical carcinomas. Intratumoral injection of a replication-defective adenoviral vector expressing HSVtk (Ad.TK) followed by GCV treatment resulted in doubling of the survival time of mice bearing A375 tumors and 20% long-term survival of mice with ME180 tumors. Treatment of tumors with Ad.TKRC without GCV resulted in a similar antitumor effect, confirming that the replicating vector has an oncolytic effect. When GCV was initiated 3 days after Ad.TKRC injection, survival of mice with each tumor type was greatly prolonged, with 60% of animals with ME180 tumors surviving for over 160 days. These results confirm that both the oncolysis caused by a replicating virus and suicide/prodrug gene therapy with HSVtk/GCV have potent antitumor effects. When combined, these two approaches are complementary resulting in a significantly improved treatment outcome.

An adenovirus-simian immunodeficiency virus env vaccine elicits humoral, cellular, and mucosal immune responses in rhesus macaques and decreases viral burden following vaginal challenge

Six female rhesus macaques were immunized orally and intranasally at 0 weeks and intratracheally at 12 weeks with an adenovirus type 5 host range mutant (Ad5hr)-simian immunodeficiency virus SIVsm env recombinant and at 24 and 36 weeks with native SIVmac251 gp120 in Syntex adjuvant. Four macaques received the Ad5hr vector and adjuvant alone; two additional controls were naive. In vivo replication of the Ad5hr wild-type and recombinant vectors occurred with detection of Ad5 DNA in stool samples and/or nasal secretions in all macaques and increases in Ad5 neutralizing antibody in 9 of 10 macaques following Ad administrations. SIV-specific neutralizing antibodies appeared after the second recombinant immunization and rose to titers > 10,000 following the second subunit boost. Immunoglobulin G (IgG) and IgA antibodies able to bind gp120 developed in nasal and rectal secretions, and SIV-specific IgGs were also observed in vaginal secretions and saliva. T-cell proliferative responses to SIV gp140 and T-helper epitopes were sporadically detected in all immunized macaques. Following vaginal challenge with SIVmac251, transient or persistent infection resulted in both immunized and control monkeys. The mean viral burden in persistently infected immunized macaques was significantly decreased in the primary infection period compared to that of control macaques. These results establish in vivo use of the Ad5hr vector, which overcomes the host range restriction of human Ads for rhesus macaques, thereby providing a new model for evaluation of Ad-based vaccines. In addition, they show that a vaccine regimen using the Ad5hr-SIV env recombinant and gp120 subunit induces strong humoral, cellular, and mucosal immunity in rhesus macaques. The reduced viral burden achieved solely with an env-based vaccine supports further development of Ad-based vaccines comprising additional viral components for immune therapy and AIDS vaccine development.

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.

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.

Coexpression of the simian immunodeficiency virus Env and Rev proteins by a recombinant human adenovirus host range mutant

Recombinant human adenoviruses (Ads) that replicate in the intestinal tract offer a novel, yet practical, means of immunoprophylaxis against a wide variety of viral and bacterial pathogens. For some infectious agents such as human immunodeficiency virus (HIV), the potential for residual infectious material in vaccine preparations must be eliminated. Therefore, recombinant human Ads that express noninfectious HIV or other microbial proteins are attractive vaccine candidates. To test such an approach for HIV, we chose an experimental model of AIDS based on simian immunodeficiency virus (SIV) infection of macaques. Our data demonstrate that the SIV Env gene products are expressed in cultured cells after infection with a recombinant Ad containing both SIV env and rev genes. An E3 deletion vector derived from a mutant of human Ad serotype 5 that efficiently replicates in both human and monkey cells was used to bypass the usual host range restriction of Ad infection. In addition, we show that the SIV rev gene is properly spliced from a single SIV subgenomic DNA fragment and that the Rev protein is expressed in recombinant Ad-SIV-infected human as well as monkey cells. The expression of SIV gene products in suitable live Ad vectors provides an excellent system for studying the regulation of SIV gene expression in cultured cells and evaluating the immunogenicity and protective efficacy of SIV proteins in macaques.

Adenovirus-human immunodeficiency virus (HIV) envelope recombinant vaccines elicit high-titered HIV-neutralizing antibodies in the dog model

Recombinant human adenoviruses (Ads) (types 4, 5, and 7) expressing the HIV-1 envelope membrane glycoprotein (gp160) were tested for immunogenicity in the dog. Administration of recombinant Ad7-env by intratracheal inoculation resulted in a low serum antibody response to gp160, which developed over several weeks. A strong neutralizing antibody response to the Ad7 vector developed within 1 week of infection. A subsequent booster inoculation 12 weeks later with the heterotypic Ad4-env recombinant virus resulted in significantly enhanced humoral responses directed at the envelope antigen, as measured by both ELISA and Western blot analysis as well as high-titer type-specific neutralizing antibodies, with some animals achieving neutralization titers approaching 1000. Recombinant HIV envelope glycoprotein derived from Ad-HIV-infected cell cultures was used as a subunit booster injection for dogs that had previously received sequential immunizations with heterotypic recombinant Ads. Significant immune responses against the envelope developed as measured by ELISA, Western blot analysis, and neutralization assays. These data indicate that live recombinant Ad-HIV vaccines are capable of inducing high-titer type-specific neutralizing antibodies to gp160 in vivo. Recombinant HIV envelope glycoprotein subunit vaccines, prepared from Ad-env-infected cells, are capable of boosting these responses.

Co-expression of hepatitis B virus antigens by a non-defective adenovirus vaccine vector

Adenovirus type 7 vaccine strain was engineered to express foreign antigens from both the E3 early promoter in the E3 region and the major late promoter inserted between the E4 region and the right inverted terminal repeat. This multiple expression vector was used to express hepatitis B core antigen (HBcAg), hepatitis B e antigen (HBeAg), and hepatitis B surface antigen (HBsAg). The gene inserted in the E3 region was derived from the core gene of the hepatitis B virus genome. When the precore region was present, an immunoreactive group of proteins with molecular weights ranging from 15,000 to 19,000 was secreted into the media. Velocity sedimentation centrifugation of media and lysates from cells infected with recombinants containing the core gene with the precore region resulted in peaks of HBeAg at the top of the gradient where authentic HBeAg should be found. In addition to the core gene in the E3 region, the surface antigen gene of hepatitis B virus was inserted behind the major late promoter in the E4 region resulting in an adeno-hepatitis recombinant virus capable of expressing both the core gene and the HBsAg cells. Cells infected with the adeno-hepatitis recombinants could also be stained with peroxidase-conjugates after reacting to antibody against HBcAg. Inoculation of dogs with the recombinant viruses which contained the core gene, with and without the precore sequence, resulted in a significant antibody response to HBcAg/HBeAg. The dogs also produced a significant antibody response to HBsAg as well as neutralizing antibody to adenovirus.

Establishment of a foreign antigen secretion system in mycobacteria

In order to develop recombinant Mycobacterium bovis BCG into a useful multivaccine vehicle, we established a foreign antigen secretion system in mycobacteria in which an extracellular alpha antigen of Mycobacterium kansasii was utilized as a carrier. By using this system, a B-cell epitope (Glu-12-Leu-Asp-Arg-Trp-Glu-Lys-Ile-19) of human immunodeficiency virus type 1 p17gag, which was identified by a fusion protein-based method, has been successfully obtained from BCG along with the alpha antigen. This is the first report of expression and secretion of a foreign viral antigen from BCG. It is possible that the system can become a universal vaccination vehicle applicable to protection against various infectious diseases.

Development of new cell lines for animal cell biotechnology

Mammalian cell culture has been an important technique in laboratory-scale experimentation for many decades. Developments in large-scale culture have been due to the need to grow large numbers of cells to support the growth of viruses for vaccine production, and more recently, for growing hybridoma cells as a source of monoclonal antibody. Increasingly, however, pharmaceutical products such as hormones, enzymes, growth factors, and clotting factors are being produced from cell lines which have been manipulated by recombinant DNA techniques. It is clear, therefore, that the high cost of growing mammalian cells on a large scale does not necessarily prohibit their use for biotechnology, and indeed there is considerable evidence to suggest that animal cell biotechnology will continue to be a major growth area in the future.

Immunogenicity and efficacy testing in chimpanzees of an oral hepatitis B vaccine based on live recombinant adenovirus

As a major cause of acute and chronic liver disease as well as hepatocellular carcinoma, hepatitis B virus (HBV) continues to pose significant health problems world-wide. Recombinant hepatitis B vaccines based on adenovirus vectors have been developed to address global needs for effective control of hepatitis B infection. Although considerable progress has been made in the construction of recombinant adenoviruses that express large amounts of HBV gene products, preclinical immunogenicity and efficacy testing of candidate vaccines has remained difficult due to the lack of a suitable animal model. We demonstrate here that chimpanzees are susceptible to enteric infection by human adenoviruses type 7 (Ad7) and type 4 (Ad4) following oral administration of live virus. Moreover, after sequential oral immunization with Ad7- and Ad4-vectored vaccines containing the hepatitis B surface antigen (HBsAg) gene, significant antibody responses to HBsAg (anti-HBs) were induced in two chimpanzees. After challenge with heterologous HBV, one chimpanzee was protected from acute hepatitis and the other chimpanzee experienced modified HBV-induced disease. These data demonstrate the feasibility of using orally administered recombinant adenoviruses as a general approach to vaccination.

Expression and characterization of hepatitis B virus surface antigen polypeptides in insect cells with a baculovirus expression system

The baculovirus Autographa californica nuclear polyhedrosis virus was used as an expression vector to produce hepatitis B virus surface antigen with and without the pre-S domain. The S gene product was expressed as both fusion and nonfusion polypeptides. No difference was observed in the posttranslational modification of the fusion and nonfusion polypeptides. The S proteins were not secreted into the medium but were inserted into the endoplasmic reticulum, glycosylated, and partially extruded into the lumen of the endoplasmic reticulum as 22-nm lipoprotein particles. The oligosaccharide chains on the insect cell-derived S protein were of the N-linked high-mannose form, in contrast to the complex-type oligosaccharides detected on plasma-derived hepatitis B virus surface antigen. The pre-S-S polypeptides were inserted into the endoplasmic reticulum, glycosylated, and modified by fatty acid acylation with myristic acid. A procedure was developed to purify the S protein from cellular membranes by using detergent extraction and immunoaffinity chromatography. The purified S protein was in the form of protein-detergent micelles and was highly antigenic and immunogenic.

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.

Successful vaccination with a polyvalent live vector despite existing immunity to an expressed antigen

A global vaccination strategy must take into account production and delivery costs as well as efficacy and safety. A heat-stable, polyvalent vaccine that requires only one inoculation and induces a high level of humoral and cellular immunity against several diseases is therefore desirable. A new approach is to use live microorganisms such as mycobacteria, enteric bacteria, adenoviruses, herpesviruses and poxviruses as vaccine vectors. A potential limitation of live polyvalent vaccines, however, is existing immunity within the target population not only to the vector, but to any of the expressed antigens. This could restrict replication of the vector, curtail expression of antigens, and reduce the total immune response to the vaccine. Recently acquired immunity to vaccinia virus can severely limit the efficacy of a live recombinant vaccinia-based vaccine, so a strategy involving closely spaced inoculations with the same vector expressing different antigens may present difficulties. We have constructed a recombinant vaccinia virus that expresses surface proteins from two diverse pathogens, influenza A virus haemagglutinin and herpes simplex virus type 1 (HSV-1) glycoprotein D. Mice that had recently recovered from infection with either HSV-1 or influenza A virus could still be effectively immunized with the double recombinant.

A new hamster model for adenoviral vaccination

Both adult and baby hamsters infected intranasally with human adenovirus type 5 exhibited virologic, serologic, and histologic evidence of infection. When 8-day old hamsters were infected with 4 x 10(6) pfu, concentrations of virus up to 2 x 10(6) pfu/animal were detected in the lung, peaking on day 2. The minimum infectious dose was 1 x 10(3) pfu/animal. This model may be useful in studies of conventional and recombinant adenoviral vaccines for humans.

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.

Development and testing of AIDS vaccines

Recent advances in delineating the molecular biology of human immunodeficiency virus type 1 (HIV-1) have led to innovative approaches to development of a vaccine for acquired immunodeficiency syndrome (AIDS). However, the lack of understanding of mechanisms of protective immunity against HIV-1, the magnitude of genetic variation of the virus, and the lack of effective animal models for HIV-1 infection and AIDS have impeded progress. The testing of AIDS vaccines also presents challenges. These include liability concerns over vaccine-related injuries; identification of suitable populations for phase 3 efficacy studies; balancing the ethical obligation to counsel research subjects to avoid high-risk behavior with the necessity to obtain vaccine efficacy data; and the effect of vaccine-induced seroconversion on the recruiting and welfare of trial volunteers. Several candidate AIDS vaccines are nevertheless currently under development, and some are undergoing phase 1 clinical trials. Rapid progress will depend on continued scientific advancement in conjunction with maximum use of resources, open information and reagent exchange, and a spirit of international collaboration.

Efficient transcription, not translation, is dependent on adenovirus tripartite leader sequences at late times of infection

To determine whether the tripartite leader is required for efficient translation in adenovirus-infected cells at late times of infection, we constructed recombinant adenoviruses containing the influenza virus nucleocapsid protein (NP) gene expressed under the control of the adenovirus major late promoter (MLP). We chose the NP gene because previous results showed that the influenza virus NP mRNA was an extremely effective initiator of translation in cells which were superinfected with influenza virus at late times of adenovirus infection (M. G. Katze, B. M. Detjen, B. Safer, and R. M. Krug, Mol. Cell. Biol. 6:1741-1750, 1986). The NP gene in the adenovirus recombinants was inserted downstream of an MLP that replaced part of the early (E1A) region. The resulting NP mRNAs either lacked any tripartite leader sequences or contained at their 5' ends various portions of the tripartite leader: 33, 172, or all 200 nucleotides of the leader. The relative amounts of the NP protein synthesized by the recombinants were directly proportional to the amounts of the NP mRNA made, indicating that the presence of 5' tripartite leader sequences did not enhance the translation of NP mRNA. In addition, the sizes of the polysomes containing NP mRNA were not increased by the presence of tripartite leader sequences, indicating that the initiation of translation was not enhanced by these sequences. On the other hand, the presence of tripartite leader sequences immediately downstream of the MLP did enhance the transcription of the inserted NP gene, as shown by Northern (RNA) analysis of in vivo NP mRNA levels and by in vitro runoff assays with isolated nuclei. Our results indicate that more than 33 nucleotides of the first leader segment of the tripartite leader are required for optimal transcription from the MLP.

The adenovirus tripartite leader sequence can alter nuclear and cytoplasmic metabolism of a non-adenovirus mRNA within infected cells

All mRNAs encoded by the adenovirus major late transcription unit share a common 5' noncoding region, 200 nucleotides in length, termed the tripartite leader sequence. To assess function of the tripartite leader, recombinant viruses were prepared which carried either a bona fide herpes simplex virus thymidine kinase gene or a modified thymidine kinase gene whose normal 5' noncoding domain was replaced with the adenovirus leader sequence. The tripartite leader simultaneously decreased the nuclear half-life and increased the cytoplasmic half-life of the thymidine kinase-specific mRNA. The tripartite leader stabilized the non-adenovirus mRNA only within the environment of an adenovirus-infected cell during the late phase of the infectious cycle.

Distinctive properties of the hepatitis B virus envelope proteins

Using recombinant adenoviral vectors, we expressed and characterized the large, middle, and major envelope proteins of hepatitis B virus (HBV). Cells infected with the recombinant adenovirus which contained the large envelope gene (HS1.HP) expressed predominantly large envelope and small but detectable quantities of middle (4%) and major (6%) envelope proteins in the cell lysate. No HBV envelope proteins were detected in the culture medium from HS1.HP-infected cells. Cells infected with recombinant adenovirus which contained the middle envelope gene (HS2.HP) expressed and secreted the middle and major envelope proteins in a molar ratio of 3:1. Cells infected with the recombinant adenovirus which contained the major envelope gene (HS.HP) expressed and secreted major envelope proteins. The HBV envelope proteins secreted by cells infected with either HS2.HP or HS.HP were assembled in 22-nm particles, as shown by velocity sedimentation rate determination, buoyant densities, and electron microscopy. Cells coinfected with a recombinant adenovirus which contained the large envelope gene and with either HS2.HP or HS.HP expressed similar quantities of the large, middle, and major envelope proteins in the cell lysates. Secretion of the major and middle envelope proteins was inhibited more than 95% by the presence of the large envelope proteins. These results suggest that differential biosynthesis, transport, and processing of the envelope proteins occur during HBV infection, allowing efficient assembly and secretion of virions and hepatitis B surface antigen particles.

Expression of the F and HN glycoproteins of human parainfluenza virus type 3 by recombinant vaccinia viruses: contributions of the individual proteins to host immunity

cDNA clones containing the complete coding sequences for the human parainfluenza virus type 3 (PIV3) fusion (F) and hemagglutinin-neuraminidase (HN) glycoprotein genes were inserted into the thymidine kinase gene of vaccinia virus (WR strain) under the control of the P7.5 early-late vaccinia virus promotor. The recombinant vaccinia viruses, designated vaccinia-F and vaccinia-HN, expressed glycoproteins in cell culture that appeared to be authentic with respect to glycosylation, disulfide linkage, electrophoretic mobility, cell surface expression, and, in the case of the HN protein, biological activity. Cotton rats inoculated intradermally with vaccinia-HN developed serum neutralizing antibody titers equal to that induced by respiratory tract infection with PIV3, whereas animals receiving vaccinia-F had threefold lower neutralizing antibody titers. A single immunization with either recombinant vaccinia virus induced nearly complete resistance in the lower respiratory tract of these animals. With regard to protection in the upper respiratory tract, animals immunized with vaccinia-HN or vaccinia-F exhibited reductions in PIV3 replication of greater than 3,000-fold and 6-fold, respectively. This large difference (greater than 500-fold) in reduction of PIV3 replication in the upper respiratory tract was in contrast to the relatively modest difference (3-fold) in serum neutralizing antibody titers induced by vaccinia-HN versus vaccinia-F. This dissociation between the level of neutralizing antibodies and protection suggested that immunity to PIV3 is complex, and that immune mechanisms other than serum neutralizing antibodies make important contributions to resistance to infection. Overall, under these experimental conditions, vaccinia-HN induced a substantially more protective immune response than did vaccinia-F.

Recombinant adenovirus induces antibody response to hepatitis B virus surface antigen in hamsters

Recombinant adenoviruses carrying the hepatitis B virus surface antigen coding sequence in the adenovirus E3 region were constructed using DNA from either adenovirus type 5 or an adenovirus type 5 E3-region deletion mutant. Both of these recombinant adenoviruses replicated as efficiently as wild-type adenovirus in all human cells tested, including the human diploid cell strain WI-38. This indicates that insertion of the hepatitis B virus surface antigen gene into the E3 region does not significantly affect viral replication. Human cells infected with these recombinant adenoviruses secreted immunoreactive hepatitis B virus surface antigen. Since a practical small animal model for human adenoviruses was lacking, a hamster model was developed to evaluate the immunogenic potential of these recombinant adenoviruses. Upon intranasal inoculation, both wild-type adenovirus and the adenovirus E3-region deletion mutant replicated in the lungs of these animals and induced an antibody response against adenovirus. Hamsters similarly immunized with the live recombinant adenoviruses produced antibody against both adenovirus and hepatitis B virus surface antigen.

Expression of hepatitis B virus surface and core antigens: influences of pre-S and precore sequences

Amphotropic retroviral expression systems were used to synthesize hepatitis B virus surface antigen (HBsAg) and core antigen. The vectors permitted establishment of cell lines which expressed antigen from either the retroviral long terminal repeat or the mouse metallothionein-I promoter. HBsAgs were synthesized containing no pre-S sequences, pre-S(2) sequences alone, or pre-S(1) plus pre-S(2) sequences. Inclusion of pre-S(2) sequences did not affect the secretion or density of HBsAg particles but did reduce their mass by approximately 30%. Addition of pre-S(1) sequences almost completely abolished secretion of HBsAg and resulted in its localization in an aqueous-nonextractable pre- or early-Golgi cellular compartment. HBsAg was localized to the cytoplasm of the cell. This localization was unaffected by the presence of pre-S sequences in the antigen. Cell lines synthesizing hepatitis B antigens from core DNA fragments, containing or not containing precore sequences, secreted hepatitis B e antigen. However, the absence of precore DNA sequences resulted in additional synthesis of hepatitis core antigen, which was predominantly nuclear in localization.

In vivo identification of sequence elements required for normal function of the adenovirus major late transcriptional control region

A series of adenovirus type 5 variants were constructed to identify the sequence elements which comprise the major late transcriptional control region in the context of the viral chromosome. The variant chromosomes carried a second copy of DNA sequence derived from the region surrounding the major late mRNA cap site. The reiterated segments replaced the normal transcriptional control region of the E1A gene. By monitoring the rate of E1A transcription subsequent to infection with the variants, it was possible to evaluate the capabilities of the substituted major late elements. A segment derived from -55 to +33 (relative to the major late cap site at +1) functioned for early transcription, in the presence of the E1A enhancer domain, but failed to direct enhanced levels of activity late after infection. A segment from -122 to +33 directed both early and enhanced late transcription. The rate of late E1A transcription directed by this element was about 40% of that displayed by the major late control region at its normal position. Inclusion of additional upstream sequences (to -565) did not increase late transcription rates. Thus, function of the adenovirus major late control region.