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

Four decades of adenovirus gene transfer vectors: History and current use

Replication-deficient adenovirus-based gene therapy vectors were the first vectors demonstrated to mediate effective, robust in vivo gene transfer. The ease of genome engineering, large carrying capacity, and methods for large-scale vector production made adenoviral vectors a primary focus in the early days of gene therapy. Many vector modifications such as capsid engineering and regulated and cell-specific transgene expression were first demonstrated in adenovirus (Ad) vectors. However, early human studies proved disappointing, with safety and efficacy issues arising from anti-vector innate and acquired immune responses. While many gene therapy researchers moved to other vectors, others recognized that the immune response and limited duration of transgene expression were useful in the correct context. The striking example of this was the use of several effective adenovirus vectors engineered as COVID-19 vaccines estimated to have been administered to 2 billion people. In addition to vaccines, current applications of Ad vectors relate to anti-cancer therapies, tissue remodeling, and gene editing.

Generation of a thermostable, oral Zika vaccine that protects against virus challenge in non-human primates

Here we report the development of a thermally stable, orally administered, candidate Zika vaccine using human serotype 5 adenovirus (AdHu5). We engineered AdHu5 to express the genes for the envelope and NS1 proteins of Zika virus. AdHu5 was formulated using a proprietary platform, OraPro, comprising a mix of sugars and modified amino acids that can overcome elevated temperatures (37 C), and an enteric coated capsule that protects the integrity of the AdHu5 from the acid in the stomach. This enables the delivery AdHu5 to the immune system of the small intestine. We show that oral delivery of AdHu5 elicited antigen-specific serum IgG immune responses in a mouse model and in a non-human primate model. Importantly, these immune responses were able reduce viral counts in mice and to prevent detectable viraemia in the non-human primates on challenge with live Zika virus. This candidate vaccine has significant advantages over many current vaccines that are maintained in a cold or ultra-cold chain and require parenteral administration.

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Adenoviromics: Mining the Human Adenovirus Species D Genome

Human adenovirus (HAdV) infections cause disease world-wide. Whole genome sequencing has now distinguished 90 distinct genotypes in 7 species (A-G). Over half of these 90 HAdVs fall within species D, with essentially all of the HAdV-D whole genome sequences generated in the last decade. Herein, we describe recent new findings made possible by mining of this expanded genome database, and propose future directions to elucidate new functional elements and new functions for previously known viral components.

Flagellin FljB as an adjuvant to the recombinant adenovirus rabies glycoprotein vaccine increases immune responses against rabies in mice

Rabies virus (RABV) causes an acute progressive viral encephalitis. Although currently licensed vaccines have an excellent safety and efficacy record, the development of a safer and more cost-effective vaccine is still being sought. An E1-deleted, replication-defective human adenovirus type 5 (HAd5) vector expressing RABV glycoprotein (HAd5-G) is thought to be a promising candidate vaccine for immune prophylaxis against rabies. Salmonella enterica serovar Typhimurium (S. Typhimurium) flagellin is a well-known immune adjuvant. In this work, we have researched the adjuvant effect of flagellins (FljB and FliC) for HAd5 in mice for the first time. We found that the recombinant HAd5 expressing RABV glycoprotein and FljB (HAd5-GB), if administered intramuscularly, but not orally, could induce stronger immune responses and provide better protection against rabies than HAd5-G or the recombinant HAd5 expressing glycoprotein and FliC (HAd5-GC). These results suggest that the recombinant HAd5-GB has potential for development as a promising rabies vaccine.

Homologous recombination in E3 genes of human adenovirus species D

Genes within the E3 transcription unit of human adenoviruses modulate host immune responses to infection. A comprehensive genomics and bioinformatics analysis of the E3 transcription unit for 38 viruses within human adenovirus species D (HAdV-D) revealed distinct and surprising patterns of homologous recombination. Homologous recombination was identified in open reading frames for E3 CR1α, CR1β, and CR1γ, similar to that previously observed with genes encoding the three major structural capsid proteins, the penton base, hexon, and fiber.

Advances and future challenges in recombinant adenoviral vectored H5N1 influenza vaccines

The emergence of a highly pathogenic avian influenza virus H5N1 has increased the potential for a new pandemic to occur. This event highlights the necessity for developing a new generation of influenza vaccines to counteract influenza disease. These vaccines must be manufactured for mass immunization of humans in a timely manner. Poultry should be included in this policy, since persistent infected flocks are the major source of avian influenza for human infections. Recombinant adenoviral vectored H5N1 vaccines are an attractive alternative to the currently licensed influenza vaccines. This class of vaccines induces a broadly protective immunity against antigenically distinct H5N1, can be manufactured rapidly, and may allow mass immunization of human and poultry. Recombinant adenoviral vectors derived from both human and non-human adenoviruses are currently being investigated and appear promising both in nonclinical and clinical studies. This review will highlight the current status of various adenoviral vectored H5N1 vaccines and will outline novel approaches for the future.

Sublingual immunization with recombinant adenovirus encoding SARS-CoV spike protein induces systemic and mucosal immunity without redirection of the virus to the brain

Background

Sublingual (s.l.) administration of soluble protein antigens, inactivated viruses, or virus-like particles has been shown to induce broad immune responses in mucosal and extra-mucosal tissues. Recombinant replication-defective adenovirus vectors (rADVs) infect mucosa surface and therefore can serve as a mucosal antigen delivery vehicle. In this study we examined whether s.l. immunization with rADV encoding spike protein (S) (rADV-S) of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) induces protective immunity against SARS-CoV and could serve as a safe mucosal route for delivery of rADV.

Results

Here, we show that s.l. administration of rADV-S induced serum SARS-CoV neutralizing and airway IgA antibodies in mice. These antibody responses are comparable to those induced by intranasal (i.n.) administration. In addition, s.l. immunization induced antigen-specific CD8⁺ T cell responses in the lungs that are superior to those induced by intramuscular immunization. Importantly, unlike i.n. administration, s.l. immunization with rADV did not redirect the rADV vector to the olfactory bulb.

Conclusion

Our study indicates that s.l. immunization with rADV-S is safe and effective in induction of a broad spectrum of immune responses and presumably protection against infection with SARS-CoV.

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.

Immune response by nasal delivery of hepatitis B surface antigen and codelivery of a CpG ODN in alginate coated chitosan nanoparticles

Alginate coated chitosan nanoparticles were previously developed with the aim of protecting the antigen, adsorbed on the surface of those chitosan nanoparticles, from enzymatic degradation at mucosal surfaces. In this work, this new delivery system was loaded with the recombinant hepatitis B surface antigen (HBsAg) and applied to mice by the intranasal route. Adjuvant effect of the delivery system was studied by measuring anti-HBsAg IgG in serum, anti-HBsAg sIgA in faeces extracts or nasal and vaginal secretions and interferon-gamma production in supernatants of the spleen cells. The mice were primed with 10 microg of the vaccine associated or not with nanoparticles and associated or not with 10 microg CpG oligodeoxynucleotide (ODN) followed by two sequential boosts at three week intervals. The association of HBsAg with the alginate coated chitosan nanoparticles, administered intranasally to the mice, gave rise to the humoral mucosal immune response. Humoral systemic immune response was not induced by the HBsAg loaded nanoparticles alone. The generation of Th1-biased antigen-specific systemic antibodies, however, was observed when HBsAg loaded nanoparticles were applied together with a second adjuvant, the immunopotentiator, CpG ODN. Moreover, all intranasally vaccinated groups showed higher interferon-gamma production when compared to naïve mice.

Therapeutic potential of adenovirus as a vaccine vector for chronic virus infections

Therapeutic vaccines for chronic infections and cancer are needed. Challenges faced by therapeutic vaccines differ from those of preventative vaccines. Whereas the latter target a naive immune system, the former have to readjust an antigen-experienced immune system that is subverted due to sustained exposure to antigen. E1-deleted adenoviral vectors have succeeded preclinically as preventative vaccines and are now in clinical trials. Their potential as therapeutic vaccines for diseases caused by chronic virus infections or virus-associated malignancies remains to be explored in more depth and may require modifications to circumvent negative immunoregulatory pathways that develop following chronic infections or during tumour progression.

Functions and mechanisms of action of the adenovirus E3 proteins

In the evolutionary battle between viruses and their hosts, viruses have armed themselves with weapons to defeat the host's attacks on infected cells. Various proteins encoded in the adenovirus (Ad) E3 transcription unit protect cells from killing mediated by cytotoxic T cells and death-inducing cytokines such as tumor necrosis factor (TNF), Fas ligand, and TNF-related apoptosis-inducing ligand (TRAIL). The viral protein E3-gp19 K blocks MHC class-I-restricted antigen presentation, which diminishes killing by cytotoxic T cells. The receptor internalization and degradation (RID) complex (formerly E3-10.4 K/14.5 K) stimulates the clearance from the cell surface and subsequent degradation of the receptors for Fas ligand and TRAIL, thereby preventing the action of these important immune mediators. RID also downmodulates the epidermal growth factor receptor (EGFR), although what role, if any, this function has in immune regulation is uncertain. In addition, RID antagonizes TNF-mediated apoptosis and inflammation through a mechanism that does not primarily involve receptor downregulation. E3-6.7 K functions together with RID in downregulating some TRAIL receptors and may block apoptosis independently of other E3 proteins. Furthermore, E3-14.7 K functions as a general inhibitor of TNF-mediated apoptosis and blocks TRAIL-induced apoptosis. Finally, after expending great effort to maintain cell viability during the early part of the virus replication cycle, Ads lyse the cell to allow efficient virus release and dissemination. To perform this task subgroup C Ads synthesize a protein late in infection named ADP (formerly E3-11.6 K) that is required for efficient virus release. This review focuses on recent experiments aimed at discovering the mechanism of action of these critically important viral proteins.

Adenovirus and adeno-associated virus vectors

Recombinant adenovirus (rAd) and recombinant adeno-associated virus (rAAV) are among the most extensively used vectors in gene therapy studies to date. These two vectors share some similar features such as a broad host range and ability to infect both proliferating and quiescent cells. However, they also possess their own unique set of properties that render them particularly attractive for gene therapy applications. rAd vectors can accommodate larger inserts, mediate transient but high levels of protein expression, and can be easily produced at high titers. Development of gutted rAd vectors has further increased the cloning capacity of these vectors. The gaining popularity of rAAV use in gene therapy can be attributed to its lack of pathogenicity and added safety due to its replication defectiveness, and its ability to mediate long-term expression in a variety of tissues. Site-specific integration, as occurs with wild-type AAV, will be a unique and valuable feature if incorporated into rAAV vectors, further improving their safety. This paper describes these properties of rAd and rAAV vectors, and discusses further development and vector improvements that continue to extend the utility of these vectors, such as cell retargeting by capsid modification, differential transduction by use of serotypes, and extension of the cloning capacity of rAAV vectors by dual vector heterodimerization.

Recombinant adenovirus vectors expressing interleukin-5 and -6 specifically enhance mucosal immunoglobulin A responses in the lung

In this study, we have examined the in vivo effects of interleukin-5 (IL-5) and IL-6 over-expression on systemic and mucosal immune responses using recombinant human type 5 adenoviruses capable of expressing these cytokines upon infection. A recombinant adenovirus containing the murine IL-5 gene within the E3 region was constructed and found to express high levels of IL-5 protein both in vitro and in vivo. Intranasal inoculation of mice with this vector or a vector expressing murine IL-6 increased adenovirus-specific immunoglobulin A (IgA) titres in lung lavage fluid threefold compared with those elicited by control virus. The simultaneous expression of both cytokines by co-inoculation altered the kinetics of the mucosal anti-adenovirus IgA response and resulted in a more than additive increase in antibody titres. The co-expression effect on IgA synthesis was not due to an increase in numbers of antigen-specific resident lung tissue lymphocytes. When mucosal IgG responses were examined, IL-6 expression had the largest impact on anti-adenovirus levels, whereas co-expression produced an intermediate response. Systemic immune responses were also affected by IL-6 expression as a twofold increase in serum IgG anti-adenovirus titres was observed after a secondary challenge with wild-type adenovirus. These results demonstrate a relevant role for IL-5 and IL-6 in the development of mucosal immune responses in vivo and suggest that the incorporation of either IL-5 and/or IL-6 into recombinant adenovirus vectors may be a useful tool in the development of mucosal vaccines.

Adenoviruses as vectors for delivering vaccines to mucosal surfaces

Immunization of mucosal surfaces has become an attractive route of vaccine delivery because of its ability to induce mucosal immunity. Although various methods of inducing mucosal immunity are being developed, our laboratory has focused on developing adenoviruses as replication-competent and replication-incompetent vectors. The present report will summarize our progress in sequencing the entire bovine adenovirus-3 genome and identifying regions which can be deleted and subsequently used as insertion sites for foreign genes in developing recombinant viral vaccines. Using these recombinant viruses, we demonstrated the 'proof-of-principle' in developing mucosal immunity and, more importantly, inducing protection against bovine herpes virus in a natural host-cattle. Finally, we demonstrated that immunity and protection occurred even in animals that had pre-existing antibodies to the vector.

Induction of humoral and cellular immune responses against the nucleocapsid of bovine viral diarrhea virus by an adenovirus vector with an inducible promoter

A new recombinant adenovirus was constructed that expressed the nucleocapsid (C protein or p14) of the bovine viral diarrhea virus (BVDV) under the control of a tetracycline-regulatable promoter. Mice covaccinated with this recombinant adenovirus, accompanied by another recombinant adenovirus expressing the trans-activator protein, induced a strong humoral immune response to the BVDV/C protein as detected by ELISA. Splenocytes from mice immunized with the recombinant adenovirus showed a specific proliferation response to both genotypes (type 1 and 2) of BVDV. High levels of IFN-gamma were detected in the supernatant of murine mononuclear cells of mice immunized by the recombinant adenovirus when stimulated in vitro by both genotypes of BVDV. These results indicate that this recombinant adenovirus is highly immunogenic and stimulates both cellular and humoral immune responses against the nucleocapsid of BVDV.

Construction and characterization of E3-deleted bovine adenovirus type 3 expressing full-length and truncated form of bovine herpesvirus type 1 glycoprotein gD

Using the homologous recombination machinery of E. coli, a 1.245-kb deletion was introduced in the E3 region of bovine adenovirus 3 (BAV3) genomic DNA cloned in a plasmid. Transfection of the restriction enzyme-excised, linear E3-deleted BAV3 genomic DNA into primary fetal bovine retina cells produced infectious virus (BAV3. E3d), suggesting that all the E3-specific open reading frames are nonessential for virus replication in vitro. Using a similar approach, we constructed replication-competent (BAV3.E3gD and BAV3. E3gDt) BAV3 recombinant expressing full-length (gD) or truncated (gDt) glycoprotein of bovine herpes virus 1. Recombinant gD and gDt proteins expressed by BAV3.E3gD and BAV3.E3gDt, respectively, were recognized by gD-specific monoclonal antibodies directed against conformational epitopes, suggesting that antigenicity of recombinant gD and gDt was similar to that of the native gD expressed in bovine herpes virus 1-infected cells. Intranasal immunization of cotton rats induced strong gD- and BAV3-specific IgA and IgG immune responses. These results suggest that replication-competent bovine adenovirus 3-based vectors have potential for the delivery of vaccine antigens to the mucosal surfaces of animals.

Induction of immunity in the respiratory tract and protection from bovine herpesvirus type 1 infection by different routes of immunization with recombinant adenovirus

To investigate the capability of different routes of immunization with replication-competent recombinant adenovirus to induce antigen-specific antibody responses, we immunized cotton rats with a human adenovirus type 5 (HAd5) vector expressing the glycoprotein D (gD) of bovine herpesvirus type 1 (BHV-1) (gD-dE3). Different routes of mucosal and systemic immunization (intraduodenal-oral, intraduodenal, intranasal and intradermal) with gD-dE3 stimulated similar levels of gD-specific IgG in the serum of cotton rats. However, intranasal (i.n.) immunization stimulated higher levels of gD-specific IgA in the lung and nasal washes, and higher frequency of gD-specific antibody secreting cells in the lung than did the intradermal immunization. Higher levels of antibody in the respiratory tract following i.n. immunization correlated with better protection of the lungs against i.n. BHV-1 challenge. Intraduodenal-oral immunization induced more gD-specific antibodies in the respiratory tract than intraduodenal immunization alone. Adenovirus dissemination to most organs tested was evident following each route of immunization, which is important to consider when studying the mechanism of induction of immunity by recombinant adenoviruses.

Recombinant viral vector vaccines for the veterinary use

Recently, genetically engineering using recombinant DNA techniques has been applied to design new viral vaccines in order to reduce some problems which present viral vaccines have. Up to now, many viruses have been investigated for development of recombinant attenuated vaccines or live viral vectors for delivery of foreign immunogenic antigens. In this review, we introduced three kind of viruses; herpesviruses, vaccinia viruses, and adenoviruses, which have best widely been studied as recombinant vaccines or delivery vaccines for the veterinary use.

Construction of ovine adenovirus recombinants by gene insertion or deletion of related terminal region sequences

An ovine adenovirus which may be the prototype for a new group of adenoviruses has been engineered as a gene transfer vector. One recombinant containing a 0.95-kb insertion expressed a sheep parasite antigen from the ovine adenovirus major late promoter and tripartite leader sequences. It was shown that insertions of at least 4.3 kb were tolerated at either one of two sites in the genome without the introduction of a compensating deletion. The unique structure of this viral genome was further emphasized by the discovery that four open reading frames at the right hand end show significant identity to each other but not to other sequences in the databases. Two other unrelated open reading frames were also present. RT-PCR analysis identified two transcripts in this region which were derived from a promoter which was located very close to, or within the ITR sequence. Splicing removed all but the first and last of the ORFs from these RNAs, suggesting that some sequences might be nonessential for replication in vitro. A approximately 2-kb deletion, which removed or truncated the internal reading frames was introduced into the region without affecting virus viability. The carrying capacity of OAV recombinants should therefore be at least 6.3 kb. The relative packaging capacity of OAV (114%) therefore exceeds that of Ad5 (105%), although a comparison of virus particle sizes by electron microscopy showed that OAV was smaller than Ad5. These studies improve the potential utility of OAV as a gene transfer vector.

Generation of antiserum to specific epitopes

The ability to prevent disease by immunization with subunit vaccines that incorporate specific epitopes was demonstrated by DiMarchi et al. (1), who used a synthetic peptide to protect cattle against foot-and-mouth disease. However, generation of antibody to peptide antigens is often difficult owing to the small molecular mass and limited chemical complexity. We tested the hypothesis that recombinant DNA and synthetic peptide techniques would make it possible to stimulate vigorous immune responses to specific epitopes of an outer membrane protein of Neisseria gonorrhoeae. The MtrC AP1 sequence from the invariant MtrC gonococcal lipoprotein was genetically fused to maltose binding protein. The resultant fusion protein was used as the primary immunogen to stimulate MtrC AP1-specific antiserum. To enhance antibody production specific to MtrC AP1, boosting immunizations were performed with synthetic MtrC AP1 sequence contained in a multiple antigenic peptide system immunogen. The MtrC AP1-specific antiserum strongly recognized the MtrC protein on Western blots and appeared to bind native MtrC protein in situ. The generation of antibody in this fashion provides the technology to produce antibody to defined epitopes of any protein, including those found in the gonococcal outer membrane. The ability of those antibodies to inhibit bacterial growth or to activate complement protein can then be tested.

Costimulatory protein B7-1 enhances the cytotoxic T cell response and antibody response to hepatitis B surface antigen

There is a need for more effective therapy for chronic virus infections. A principle natural mechanism for elimination of virus-infected host cells is activation of viral antigen-specific cytotoxic T lymphocytes (CTL). In an effort to develop methods of inducing virus-specific CTL responses that might be utilized in therapy of virus infections, we have investigated the effect of B7, a costimulatory factor for T-cell activation. In this study we show that delivery of genes encoding human B7-1 and a viral antigen in the same recombinant viral vector to cells of mice induces a greater viral antigen-specific CTL response than does similar delivery of the viral antigen gene alone. Two recombinant adenovirus vectors were constructed with the foreign genes inserted in the early region 3. One of them (Ad1312) directed expression of the surface antigen gene of hepatitis B virus (HBS); the other (Ad1310) directed coexpression of HBS and human B7-1 (CD80) by means of an internal ribosomal entry site placed between the two coding sequences. When inoculated into BALB/c mice, both vectors induced a viral surface antigen-specific CTL response. The response induced by Ad1310 was stronger than that by Adl312 as measured by a chromium release assay for CTL activity and limiting dilution analysis for CTL precursor frequency, indicating that the B7-1 gene co-delivered with the HBS gene had an enhancing effect on the CTL response against surface antigen. Ad1310 also induced a higher titer of antibody against surface antigen than did Ad1312. This result suggests that expression of a costimulatory protein and a viral antigen in the same cells in vivo induces stronger immune responses than expression of the antigen alone. This could be a novel strategy for development of both preventive and therapeutic vaccines against infectious agents.

Induction of mucosal immunity in cotton rats to haemagglutinin-esterase glycoprotein of bovine coronavirus by recombinant adenovirus

An effective vaccine against enteric bovine coronavirus (BCV) must be able to induce mucosal immunity. We recently described the construction of recombinant human adenovirus type 5 (hAd5) carrying the BCV haemagglutinin-esterase (HE) gene in the early transcription region 3 of the adenovirus genome. In this study, we examined the induction of systemic and mucosal immune responses to the hAd5 vector carrying the BCV HE gene (AdBcHE) following intranasal or enteric immunization of cotton rats. Regardless of the route of administration, mucosal immunization with AdBcHE induced significant levels of anti-HE IgG antibodies in serum. In addition, following intranasal immunization with AdBcHE, significant levels of anti-HE IgA antibodies were found in lung washes of immunized cotton rats. Furthermore, the specific anti-HE antibodies in sera and mucosal secretions efficiently neutralized BCV infectivity in vitro. T-cell proliferation and cell-mediated cytotoxic responses against the BCV HE were elicited in the spleen of intranasally immunized animals. The results demonstrate that mucosal immunization with AdBcHE is capable of inducing both systemic and mucosal immunity to the BCV HE. These immune responses may be important in protecting animals from BCV infection.

Immunogenicity of recombinant adenovirus-human immunodeficiency virus vaccines in chimpanzees following intranasal administration

Recombinant adenovirus (Ad)-human immunodeficiency virus (HIV) vaccines expressing HIVIIIB Env and Gag proteins were evaluated for immunogenicity in chimpanzees following intranasal administration. When Ad7-, Ad4-, and Ad5-vectored vaccines were administered sequentially at 0, 24, and 52 weeks, respectively, to three chimpanzees, the inoculations resulted in limited virus replication in the nasopharynx, but extensive Ad-HIV replication occurred in the intestine. High-titered IgG serum antibody responses to Env and Gag that were nonneutralizing were induced following booster administration of Ad4-HIV recombinant viruses. Following the Ad5-HIV booster, low levels of neutralizing antibodies as well as V3 loop antibodies were induced in all three chimpanzees that persisted for several months. Administration of a gp160 subunit vaccine (baculovirus derived) in SAF-m 24 weeks later boosted broadly neutralizing serum antibodies that peaked within 1 month of the injection. Two additional subunit boosters 19 and 37 weeks later were progressively less effective at stimulating serum neutralizing antibody responses. Substantial local immune responses were induced in nasal, vaginal, and salivary secretions following the third Ad-HIV intranasal immunization. These responses were further boosted with the gp160 subunit vaccine, which also stimulated production of rectal antibodies. The predominant responses in all secretions tested were of the IgG isotype, although some IgA responses were also detected. Strong blastogenic responses to HIV recombinant Env and Gag proteins were induced after each immunization.

Protection against lethal lymphocytic choriomeningitis virus (LCMV) infection by immunization of mice with an influenza virus containing an LCMV epitope recognized by cytotoxic T lymphocytes

The reverse genetics system has made it possible to modify the influenza virus genome. By this method, we were able to assess influenza virus as a vaccine vector for protecting BALB/c mice against otherwise lethal lymphocytic choriomeningitis virus (LCMV) infection. A single dose of influenza virus [A/WSN/33 (H1N1)] bearing a cytotoxic T-lymphocyte-specific epitope of the LCMV nucleoprotein (residues 116 to 127) in the neuraminidase stalk protected mice against LCMV challenge for at least 4 months. The immunity was mediated by cytotoxic T lymphocytes and was haplotype specific, indicating that the observed protective response was solely a consequence of prior priming with the H-2d LCMV nucleoprotein epitope expressed in the recombinant influenza virus. We also found that as many as 58 amino acids could be inserted into the neuraminidase stalk without loss of viral function. These findings demonstrate the potential of influenza virus as a vaccine vector, with the neuraminidase stalk as a repository for foreign epitopes.

Packaging capacity and stability of human adenovirus type 5 vectors

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

Deletion mutation analysis of the adenovirus type 2 E3-gp19K protein: identification of sequences within the endoplasmic reticulum lumenal domain that are required for class I antigen binding and protection from adenovirus-specific cytotoxic T lymphocytes

Adenovirus E3-gp19K is a transmembrane glycoprotein, localized in the endoplasmic reticulum (ER), which forms a complex with major histocompatibility complex (MHC) class I antigens and retains them in the ER, thereby preventing cytolysis by cytotoxic T lymphocytes (CTL). The ER lumenal domain of gp19K, residues 1 to 107, is known to be sufficient for binding to class I antigens; the transmembrane and cytoplasmic ER retention domains are located at residues ca. 108 to 127 and 128 to 142, respectively. To identify more precisely which gp19K regions are involved in binding to class I antigens, we constructed 13 in-frame virus deletion mutants (4 to 12 amino acids deleted) in the ER lumenal domain of gp19K, and we analyzed the ability of the mutant proteins to form a complex with class I antigens, retain them in the ER, and prevent cytolysis by adenovirus-specific CTL. All mutant proteins except one (residues 102 to 107 deleted) were defective for these properties, indicating that the ability of gp19K to bind to class I antigens is highly sensitive to mutation. All mutant proteins were stable and were retained in the ER. Sequence comparisons among adenovirus serotypes reveal that the ER lumenal domain of gp19K consists of a variable region (residues 1 to 76) and a conserved region (residues 77 to 98). We show, using the mutant proteins, that the gp19K-specific monoclonal antibody Tw1.3 recognizes a noncontiguous epitope in the variable region and that disruption of the variable region by deletion destroys the epitope. The monoclonal antibody and class I antigen binding results, together with the serotype sequence comparisons, are consistent with the idea that the ER lumenal domain of gp19K has three subdomains that we have termed the ER lumenal variable domain (residues 1 to ca. 77 to 83), the ER lumenal conserved domain (residues ca. 84 to 98), and the ER lumenal spacer domain (residues 99 to 107). We suggest that the ER lumenal variable domain of gp19K has a specific tertiary structure that is important for binding to the polymorphic alpha 1 and alpha 2 domains of class I heavy (alpha) chains. We suggest that the ER lumenal conserved domain of gp19K may interact with some conserved protein, perhaps the highly conserved alpha 3 domain of class I heavy chains. Finally, the ER lumenal spacer domain may allow the ER lumenal variable and conserved domains to extend out from the ER membrane so that they can interact with class I heavy chains.

Immunogenicity of recombinant human adenovirus-human immunodeficiency virus vaccines in chimpanzees

Recombinant human adenovirus (Ad) type 4-, 5-, and 7-vectored vaccines expressing either the HIV env or gag-protease genes were tested for immunogenicity in three chimpanzees. The first phase of the vaccination protocol consisted of a primary and two booster immunizations with Ad-HIVs by the oral route of administration, followed by a single booster immunization with Gag and/or Env subunit vaccines. The second phase of the vaccination protocol consisted of intranasal administration of Ad-HIVs previously administered by the oral route. Following the first phase adenovirus was shed into stools for only 1-7 days and modest type-specific anti-adenovirus neutralizing antibody titers were induced. Strong anti-Env binding antibody responses were detected in all three animals following the second oral booster immunization. One chimpanzee responded with a low-titered type-specific neutralizing antibody response to HIV. Cell-mediated immune responses to Env were not detected after the primary vaccination, but were detected following all booster immunizations. Administration of the Gag subunit vaccine boosted both humoral and cell-mediated immune responses to Gag antigens. In contrast, the Env subunit vaccine boosted cellular but not humoral immune responses. In the second phase of the vaccination protocol, both virus shedding and anti-adenovirus responses were enhanced. All three chimpanzees responded to the intranasal administration of Ad7-HIVs with boosted anti-HIV serum responses, including low-titered type-specific neutralizing antibodies, elicited anti-HIV antibodies at secretory sites, and stimulated cell-mediated immune responses to both Gag and Env antigens.

Characterization of mutants within the gene for the adenovirus E3 14.7-kilodalton protein which prevents cytolysis by tumor necrosis factor

The 14,700-Da protein (14.7K protein) encoded by the E3 region of adenovirus has previously been shown to protect mouse cells from cytolysis by tumor necrosis factor (TNF). Delineating the sequences in the 14.7K protein that are required for this activity may provide insight into the mechanism of protection from TNF by 14.7K as well as the mechanism of TNF cytolysis. In the present study, we examined the ability of 14.7K mutants to protect cells from lysis by TNF. In-frame deletions as well as Cys-to-Ser mutations in the 14.7K gene were generated by site-directed mutagenesis and then built into the genome of a modified adenovirus type 5 (dl7001) that lacks all E3 genes. dl7001, which replicates to the same titers as does adenovirus type 5 in cultured cells, has the largest E3 deletion analyzed to date. 51Cr release was used to assay TNF cytolysis. Our results indicate that most mutations in the 14.7K gene result in a loss of function, suggesting that nearly the entire protein rather than a specific domain functions to prevent TNF cytolysis.

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.

Transient expression assay in a baculovirus system using firefly luciferase gene as a reporter

Transient gene expression assays were developed to assess the function of the regulatory sequences of baculoviruses Bombyx mori nuclear polyhedrosis virus (BmNPV) and Autographa californica nuclear polyhedrosis virus (AcNPV) in insect cells of Bombyx mori and Spodoptera frugiperda, respectively. DNA sequences encoding luciferase (luc) of the firefly Photinus pyralis was successfully employed in the expression assay as a reporter gene. Recombinant plasmids were constructed containing the luc gene under control of baculovirus-specific or heterologous promoters. Cotransfection of Bombyx mori and Spodoptera frugiperda cells with recombinant plasmids carrying virus-specific promoter sequences and BmNPV and AcNPV DNA, respectively, gave rise to efficient synthesis of luciferase (Luc), while heterologous promoters induced a low level of luc expression. We found that flanking sequences of the AcNPV DNA in the transfer plasmid contained an unknown promoter conferring an efficient luc expression. The activity of this promoter was modulated by the polh promoter sequences. The assay allows one to conduct highly sensitive monitoring of the transient expression of foreign genes from the transfecting plasmids prior to construction of recombinant viruses.

Expression of the OSU rotavirus outer capsid protein VP4 by an adenovirus recombinant

Full-length cDNA of the VP4 gene of porcine rotavirus strain OSU was cloned into adenovirus type 5 (Ad5) downstream of the E3 promoter. The plaque-purified recombinant (Ad5-OSU VP4) expressed apparently authentic VP4 rotavirus outer capsid protein. The protein had the same molecular size (85 kDa) and electrophoretic mobility as did native OSU VP4 and was immunoprecipitated by a polyclonal antiserum raised to OSU VP4. Cotton rats that possessed prechallenge rotavirus antibodies that may have been acquired either passively or actively developed neutralizing antibodies against the OSU strain following intranasal administration of the live Ad5-OSU VP4 recombinant. The neutralizing activity was enhanced by a parenteral booster injection with baculovirus-expressed OSU VP4 antigen. In addition, a high titer of neutralizing antibodies was induced by parenteral administration of the latter antigen and subsequent intranasal administration of the Ad5-OSU VP4 recombinant. These observations indicate that the VP4 outer capsid protein of a rotavirus strain can be expressed by a recombinant adenovirus vector. This approach warrants further exploration for immunization against rotavirus disease.

Adenovirus infection and specific secretory IgA responses in the intestine of infants

We investigated adenovirus (Ad) infection of the intestine and Ad group-specific fecal IgA antibody responses in seven infants who were followed up from birth to 16 months to seven years of age. We isolated in tissue culture from fecal samples not only enteric Ad type 41 but also other Ads (types 2, 3, 5, 6, and 12). We also detected Ad antigens in the feces by ELISA at the times of infection with even non-enteric Ads, suggesting that a large amount of antigens were produced in the intestine. We found that repeated Ad infections with different serotypes were occurring and there were good fecal IgA antibody responses at each time. The infection seemed usually mild or asymptomatic: only one out of 23 occasions of the detected infections required hospitalization.

Studies on the stability of a human adenovirus-rabies recombinant vaccine

Human adenovirus type 5 containing the rabies virus glycoprotein gene (rHAd-RG1) has potential for the oral vaccination of animals. The stability of this recombinant was tested indoors and outdoors by measuring the loss in virus infectivity. Under indoor conditions the stability of the recombinant virus was studied in an egg yolk-containing commercial stabilizer and a simple buffered salt solution (EBSS; Earle's balanced salt solution) at 4 degrees C and room temperature (24-25 degrees C). Over 16 days, there was a more rapid loss in virus titer at room temperature than at 4 degrees C in both suspending media; however, these differences were slight and may be significant when the overall stability of the vaccine is considered. When the virus was mixed with either 10% (w/v) fox or skunk feces or EBSS, placed on stainless steel disks and the disks kept under ambient conditions (air temperature 24-25 degrees C; relative humidity 45-50%), there was a more rapid decline in virus titer in the fecal suspensions (3% remained after 72 h) than in EBSS (26% remained after 72 h). When bait-coated blister packs of the vaccine were placed in an outdoor location in the fall (October) season, there was a larger drop in the virus titer for vaccines placed in the sun (54% over 32 days) than for those in the shade (40% over 32 days). Incorporating proteinaceous stabilizers in the vaccine samples for outdoor study showed virus stability was not enhanced in their presence.(ABSTRACT TRUNCATED AT 250 WORDS)

Transduction of the CHO aprt gene into mouse L cells using an adeno-5/APRT recombinant virus

An adenovirus-5 recombinant virus Adapt1 carrying the Chinese hamster ovary (CHO) adenine phosphoribosyltransferase (aprt) gene was constructed by insertion of a 2.5-kb fragment containing the complete CHO aprt structural gene linked to a Moloney murine sarcoma virus (MSV) promoter into the E3 region of adenovirus-5. The CHO aprt gene was in the opposite orientation to the adenovirus E3 promoter. Mouse Lapt- tk- (LAT) cells expressed the CHO aprt gene when infected with the virus, even at low MOI (O.1). APRT activity was detectable from approximately 20 h postinfection. At a low frequency, LAT cells were transformed to aprt+, and four stable transductants were selected in adenine, azaserine (AA) medium. Such cells expressed APRT at approximately 50% wild-type activity and the enzyme was shown to be CHO APRT by starch gel electrophoresis. DNA was isolated from the transductants and probed with CHO aprt-specific DNA and with viral DNA probes. The results indicated that the CHO aprt gene was integrated into the LAT cells at a site other than mouse aprt. Although neighboring viral sequences were integrated and maintained in the transductants, viral sequences further upstream and downstream of the aprt gene were absent.

The 10,400- and 14,500-dalton proteins encoded by region E3 of adenovirus form a complex and function together to down-regulate the epidermal growth factor receptor

In adenovirus-infected cells, the epidermal growth factor receptor (EGF-R) is internalized from the cell surface via endosomes and is degraded, and the E3 10,400-dalton protein (10.4K protein) is required for this effect (C. R. Carlin, A. E. Tollefson, H. A. Brady, B. L. Hoffman, and W. S. M. Wold, Cell 57:135-144, 1989). We now report that both the E3 10.4K and E3 14.5K proteins are required for this down-regulation of EGF-R in adenovirus-infected cells. Down-regulation of cell surface EGF-R was demonstrated by results from several methods, namely the absence of EGF-R autophosphorylation in an immune complex kinase assay, the inability to iodinate EGF-R on the cell surface, the formation of endosomes containing EGF-R as detected by immunofluorescence, and the degradation of the metabolically [35S]Met-labeled fully processed 170K species of EGF-R. No effect on the initial synthesis of EGF-R was observed. This down-regulation was ascribed to the 10.4K and 14.5K proteins through the analysis of cells infected with rec700 (wild-type), dl748 (10.4K-, 14.5K+), or dl764 (10.4K+, 14.5K-) or coinfected with dl748 plus dl764. Further evidence that the 10.4K and 14.5K proteins function in concert was obtained by demonstrating that the 10.4K protein was coimmunoprecipitated with the 14.5K protein by using three different antisera to the 14.5K protein, strongly implying that the 10.4K and 14.5K proteins exist as a complex. Together, these results indicate that the 10.4K and 14.5K proteins function as a complex to stimulate endosome-mediated internalization and degradation of EGF-R in adenovirus-infected cells.

Adenovirus precipitating antibodies in the sera of brush-tailed possums in New Zealand

Sera collected from the Australian brush-tailed possum Trichosurus vulpecula in New Zealand in 1975 and 1989 were tested for the presence of antibodies to adenovirus. Of the 231 sera tested in an agar gel diffusion test, eight (3.5%) had precipitating antibodies to the group specific antigen of mammalian adenoviruses. Available data allowed 99/231 sera to be classified as being obtained from either adult (total 62) or sexually immature (total 37) possums. From the adult animals, 4/62 (6.5%) sera were positive, while no reactive sera were detected among the 37 immature animals. The results provide evidence that natural infection by an adenovirus occurs in possums in New Zealand. Further work needs to be carried out to isolate this adenovirus to enable detailed serological and epidemiological studies to be performed. A species-specific possum adenovirus could have potential in the biological control of this species.

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.

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.