Human adenovirus type 5 recombinants expressing simian immunodeficiency virus macaque strain gag antigens

Regulation of the pyruvate metabolism node by monogene and polygene engineering of HEK-293 cells

HEK-293 cells are increasingly being used in the production of human adenovirus (HAdV) vaccines. However, the production of HAdV vaccine has not met the requirements of industrial production. Recently, we investigated the effects of various regulatory genes of the pyruvate metabolism node on the substance and energy metabolism and adenovirus reproduction in HEK-293 cells. Initially, single regulatory genes, including pkm2, pdhα, pyc2, mpc3, aralar1, ldha and pdk1, were studied. We found that metabolic performance and adenovirus reproduction capacity in HEK-293 cells were improved, and maximum adenovirus titre was increased approximately 15-fold. Next, we co-overexpressed the key genes, including pkm2, pyc2 and aralar1. The PYC2-A-P-L cells that had the appropriate co-overexpression levels of three genes had the most pronounced regulatory effect. The maximum cell density and maximum specific growth rate were increased by 21% compared with that in the control. The ΔLac/ΔGlc and ΔNH₃/ΔGln were decreased by 26% and 27%, respectively. The ATP production rate and the ATP/O₂ ratio were increased by 110% and 20%, respectively. The level of reactive oxygen species (ROS) was reduced by 60%. The adenovirus reproductive ability of the PYC2-A-P-L cells was approximately 30-fold higher than that of the control. The results showed that proper overexpression of the aralar1, pkm2 and pyc2 genes can significantly improve the substance and energy metabolism efficiency in HEK-293 cells, maximize the metabolic balance of pyruvate, and ultimately improve HAdV reproduction. This study provides a method of regulation of pyruvate metabolism and polygenic metabolic engineering in mammalian cells cultured in vitro and suggests an effective method for efficient HAdV production.

HEK-293 cells are increasingly being used in the production of human adenovirus (HAdV) vaccines.

Preventing spontaneous genetic rearrangements in the transgene cassettes of adenovirus vectors

First-generation, E1/E3-deleted adenoviral vectors with diverse transgenes are produced routinely in laboratories worldwide for development of novel prophylactics and therapies for a variety of applications, including candidate vaccines against important infectious diseases, such as HIV/AIDS, tuberculosis, and malaria. Here, we show, for two different transgenes (both encoding malarial antigens) inserted at the E1 locus, that rare viruses containing a transgene-inactivating mutation exhibit a selective growth advantage during propagation in E1-complementing HEK293 cells, such that they rapidly become the major or sole species in the viral population. For one of these transgenes, we demonstrate that viral yield and cytopathic effect are enhanced by repression of transgene expression in the producer cell line, using the tetracycline repressor system. In addition to these transgene-inactivating mutations, one of which occurred during propagation of the pre-viral genomic clone in bacteria, and the other after viral reconstitution in HEK293 cells, we describe two other types of mutation, a small deletion and a gross rearranging duplication, in one of the transgenes studied. These were of uncertain origin, and the effects on transgene expression and viral growth were not fully characterized. We demonstrate that, together with minor protocol modifications, repression of transgene expression in HEK293 cells during viral propagation enables production of a genetically stable chimpanzee adenovirus vector expressing a malarial antigen which had previously been impossible to derive. These results have important implications for basic and pre-clinical studies using adenoviral vectors and for derivation of adenoviral vector products destined for large-scale amplification during biomanufacture.

Development of an Ad7 cosmid system and generation of an Ad7deltaE1deltaE3HIV(MN) env/rev recombinant virus

A strategy to circumvent immune responses to adenovirus (Ad) resulting from natural infection or repeated vector administrations involves sequential use of vectors from different Ad serotypes. To further develop an Ad-HIV recombinant AIDS vaccine approach, a replication-defective recombinant Ad from a non-subgroup C virus was required. Using a cosmid system, we generated an Ad7deltaE1deltaE3HIV(MN) env/rev recombinant virus and compared expression of the inserted HIV genes with a similarly constructed replication-competent Ad7deltaE3HIV(MN)env/rev recombinant. Ad7deltaE1deltaE3HIV(MN)env/rev expressed both HIV env and rev gene products. The envelope protein was correctly processed and functional, mediating syncytia formation of Ad7deltaE1deltaE3HIV(MN) env/rev-infected cells and CD4(+) T lymphocytes. Ad7deltaE1deltaE3HIV(MN)env/rev could be amplified on 293-ORF6 cells, containing the E4 ORF6 gene, shown earlier to support production of an Ad7 vector lacking the E1a gene. The utility of this cell line is now extended to the production of replication-defective Ad7 recombinants lacking E1a, E1b, and protein IX genes. Sequential immunizations with Ad-HIV recombinants based in different Ad serotypes have been shown to effectively elicit both humoral and cellular HIV-specific immune responses. The recombinant Ad7deltaE1deltaE3HIV(MN)env/rev will be useful in such AIDS vaccine strategies. Further, these studies have created new cosmid vectors that can be applied to generation of single- or double-deleted Ad7 recombinants with foreign genes inserted into the E1 and/or E3 regions.

Efficacy of replication-defective adenovirus-vectored vaccines: protection following intramuscular injection is linked to promoter efficiency in muscle representative cells

To investigate the respective role of transduced cells in the induction of immune response following intramuscular inoculation of adenovirus-based vaccines, we generated several replication-defective adenoviruses expressing the glycoprotein D gene of pseudorabies virus under the control of four different promoters: major late promoter of adenovirus type 2, human cytomegalovirus immediate-early promoter/enhancer (CMV), Rous sarcoma virus-long terminal repeat promoter, and human desmin gene 5' regulatory region (DES). All the adenovirus constructs were able to fully protect mice, in the contrary of direct DNA inoculation of plasmids harboring the same transcription units. The far most effective adenovirus constructs, on the criterion of protective doses and specific antibody response induction, were those in which the foreign gene was driven by the DES or CMV promoter. Wide variations in promoter strength in vitro were evidenced in several cell culture types representative of putative target cells following muscular inoculation (myoblasts, myotubes, fibroblasts, macrophages, and endothelial cells). The level of efficacy in vivo, was not correlated with the level of expression in vitro in myotubes, but paralleled the level of expression in endothelial cells and in myoblasts. Together with previously published data, these results suggest that, following adenovirus injection, locally produced cytokines may induce myoblasts to act as local antigen presenting cells.

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.

Human adenovirus type 5 variants with sequence alterations flanking the E2A gene: effects on E2 expression and DNA replication

The human adenovirus type 5 (Ad5) E2 transcription unit is divided into a promoter-proximal region, E2A, and a distal region, E2B, each with its own polyadenylation site. Together these regions encode the three virus-derived proteins necessary for genome replication. Ad5 variants were produced that carried linker insertion mutations immediately 5' and/or 3' to the coding sequence for the E2A gene DNA binding protein (DBP). Two variants carrying solely a 5' lesion showed decreased usage of the adjacent 3' splice site, via which the DBP mRNA is produced, and an increased usage of the alternative downstream splice sites in the E2B region, wherein viral DNA polymerase and terminal protein precursor are encoded; these viruses showed somewhat reduced growth. A variant carrying a 3' lesion showed a marginal increase in DBP expression and slightly accelerated growth. When lesions 5' and 3' to the DBP coding sequence were combined in cis, the resulting virus was severely defective for growth and expressed E2B products to the virtual exclusion of E2A DBP. These data indicate that interactions must occur between the E2A 3' splice site and polyadenylation site before this region can be treated as an exon by the RNA processing machinery, and that a sequence alteration at the polyadenylation site that alone has only minor effects on the pattern of RNA processing can drastically affect terminal exon usage when placed in cis with a mutation that reduces splicing efficiency at the upstream 3' splice site. The data further indicate that, in vivo, Ad5 DNA replication is limited by prevailing DBP levels rather than by levels of polymerase or terminal protein precursor.

Human immunodeficiency virus type 1 Rev-dependent effects on the late gene expression of recombinant human adenovirus

Both human adenovirus type 5 (Ad5) and human immunodeficiency virus (HIV-1) encode functions (E1b 55K/E4 orf6 and Rev respectively) which are needed for the efficient cytoplasmic accumulation of late viral mRNAs and which act post-transcriptionally. The similarity between these two regulatory systems was explored by constructing recombinant Ad5 carrying either one or both of the two components of the HIV-1 system (Rev and its RNA target sequence, RRE) and analysing the effects on Ad5 gene expression. In the presence of a functional Ad5 regulatory system, the HIV-1 system had no detectable effect on Ad5 gene expression. When the Ad5 system was rendered inoperative by mutation, the HIV-1 Rev/RRE system brought about a modest increase in the cytoplasmic accumulation of RRE-containing mRNAs. This was not sufficient to complement effectively the defect due to the Ad5 mutation. These data suggest that HIV-1 Rev acts on a similar pool of nuclear RNA to that targeted by Ad5 E1b 55K/E4 orf6 but functions inefficiently in the situation studied here. Effects were also observed on the accumulation of certain Ad5 mRNAs from which the RRE had been removed by splicing. No change was observed in the balance of production of differentially spliced mRNAs from the RRE-containing primary transcript when Rev was present. These observations are therefore more consistent with a mode of action for Rev that involves commitment of nuclear RNAs to transport than with models in which Rev acts as an inhibitor of splicing.

Constitutive episomal expression of polypeptide IX (pIX) in a 293-based cell line complements the deficiency of pIX mutant adenovirus type 5

The human adenovirus type 5 capsid is composed of a number of distinct polypeptides. It has been shown previously that one of these, polypeptide IX (pIX), is not absolutely required for the production of viable virus. However, viruses lacking this polypeptide have a significantly reduced packaging limit and, in the one case studied, also show a thermolabile virion phenotype. This report describes the use of eukaryotic episomal vectors based on the Epstein-Barr virus replicon to generate cells which stably express pIX. These cells provide pIX that is efficiently incorporated into virions that are genetically pIX-; such enhanced thermostability. These cells have also been used to isolate a genetically pIX- virus having a genome of length some 2.3 kbp in excess of the previously defined packaging limit for pIX- virus; the resulting virions have wild-type thermostability. These cells expand the theoretical capacity of adenovirus vectors for foreign DNA to around 9.2 kbp and may therefore be useful in gene therapy applications in which vector capacity is limiting.

Adenovirus vectors as recombinant viral vaccines

Adenoviruses can efficiently induce immunity in the lung following single enteric delivery. These viruses can also be engineered to express a number of heterologous proteins in vitro. In the past 10 years, recombinant adenoviruses expressing a variety of antigens have been constructed and tested. This article reviews the main properties of adenoviruses which render them attractive for vaccine development, as well as the results of the immunization studies performed to date. Some disadvantages of this technology and the desired characteristics of second generation adenoviral vectors are discussed.