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.     

一种辅助病毒依赖型腺病毒载体的构建及其在小鼠体内的应用

腺病毒载体具有在离体细胞和动物体内高效转移和表达外源基因的优点,但由于第一代腺病毒载体能在靶细胞内表达病毒结构蛋白,并诱导机体的细胞和体液免疫反应,影响了目的基因在体内的稳定表达。为了克服这一缺点,构建了一种辅助病毒依赖型腺病毒载体ＨＡｄＩ－ｈＦＶＩＩ。该载体去除了病毒基因组的ｌ３、Ｌ１、Ｌ２、ＶＡＩ－ＶＡＩ、ｐＴＰ等基因序列。在第一代重组病毒ＡｄＩ－ｈＦＶＩＩ辅助下,能在２９３细胞包装和扩增。经氯化铯梯度超速离心后,能与辅助病毒有效分离。小鼠体内研究表明,该载体能在体内高效转移和表达ｈＦＶＩＩ基因。与笫一代腺病毒载体比较,外源基因表达稳定性明显提高,提示该载体在体内具有较低的免疫原性。     

Preparation of isotopically labelled recombinant β-defensin for NMR studies

Apoptosis is a major problem in animal cell cultures during production of biopharmaceuticals, such as recombinant proteins or viral vectors. A 293 cell line constitutively expressing vMIA (viral mitochondria-localized inhibitor of apoptosis) was constructed and examined on production of a model recombinant protein, green fluorescent protein (GFP) in the adenovirus-293 expression system, and on production of a model infectious adenoviral vector. vMIA-293 cells were more resistant than the parental 293 cells to apoptosis induced by either oxidative stress, or by adenovirus infection. The yield of GFP produced in vMIA-293 cell cultures was consistently higher (140%) compared to that in the parental cells. vMIA reduced production of adenovirus infectious particles, which was not due to a decline of adenovirus replication, since adenoviral DNA replication rate in vMIA-293 cells was higher than that in the parental cells.In conclusion, introduction of the vMIA gene into the 293 cell line is a promising strategy to improve recombinant protein production in the adenovirus-293 expression system.     

Role for the adenovirus IVa2 protein in packaging of viral DNA

Although it has been demonstrated that the adenovirus IVa2 protein binds to the packaging domains on the viral chromosome and interacts with the viral L1 52/55-kDa protein, which is required for viral DNA packaging, there has been no direct evidence demonstrating that the IVa2 protein is involved in DNA packaging. To understand in greater detail the DNA packaging mechanisms of adenovirus, we have asked whether DNA packaging is serotype or subgroup specific. We found that Ad7 (subgroup B), Ad12 (subgroup A), and Ad17 (subgroup D) cannot complement the defect of an Ad5 (subgroup C) mutant, pm8001, which does not package its DNA due to a mutation in the L1 52/55-kDa gene. This indicates that the DNA packaging systems of different serotypes cannot interact productively with Ad5 DNA. Based on this, a chimeric virus containing the Ad7 genome except for the inverted terminal repeats and packaging sequence from Ad5 was constructed. This chimeric virus replicates its DNA and synthesizes Ad7 proteins, but it cannot package its DNA in 293 cells or 293 cells expressing the Ad5 L1 52/55-kDa protein. However, this chimeric virus packages its DNA in 293 cells expressing the Ad5 IVa2 protein. These results indicate that the IVa2 protein plays a role in viral DNA packaging and that its function is serotype specific. Since this chimeric virus cannot package its own DNA, but produces all the components for packaging Ad7 DNA, it may be a more suitable helper virus for the growth of Ad7 gutted vectors for gene transfer.     

表达丙型肝炎病毒NS3抗原的重组腺病毒构建及体外表达

为探索研制丙型肝炎疫苗的新途径,以期获得防治丙型肝炎的重组腺病毒减毒活疫苗,我们构建了表达丙型肝炎病毒(Hepatitis C virus ,HCV)非结构蛋白3(non structural protein 3,NS3)抗原的重组腺病毒RAd NS3,并检测其在体外表达。应用PCR从真核表达质粒pRC/NS3 中扩增编码HCV NS3 蛋白(329-935aa)的基因片段,定向克隆到重组腺病毒AdEasy-1系统的穿梭质粒pAdTrack CMV上,采用细菌内同源重组"两步转化法"构建携带HCV NS3基因的重组腺病毒基因组质粒pAd HCV NS3,转染293 细胞,成功包装出重组腺病毒RAd NS3,利用它有效地感染人肝癌细胞株HepG2,经RT PCR及免疫印迹等不同方法检测表明,被感染细胞能表达HCVNS3蛋白,为后续进行重组腺病毒在动物体内诱导抗HCV免疫应答能力的研究奠定了基础。     

Requirement of the adenovirus IVa2 protein for virus assembly

The adenovirus L1 52/55-kDa protein is required for viral DNA packaging and interacts with the viral IVa2 protein, which binds to the viral packaging sequence. Previous reports suggest that the IVa2 protein plays a role in viral DNA packaging and that this function of the IVa2 protein is serotype specific. To further examine the function of the IVa2 protein in viral DNA packaging, a mutant virus that does not express the IVa2 protein was constructed by introducing two stop codons at the beginning of the IVa2 open reading frame in a full-length bacterial clone of adenovirus type 5. The mutant virus, pm8002, was defective for growth in 293 cells, although it replicated its DNA and produced early and late viral proteins. Electron microscopic and gradient analyses revealed that the mutant virus did not assemble any viral particles in 293 cells. In 293-IVa2 cells, which express the IVa2 protein, infectious viruses were produced, although the titer of the mutant virus was lower than that of the wild-type virus, indicating that these cells may not fully complement the mutation. The mutant viral particles produced in 293-IVa2 cells were heterogeneous in size and shape, less stable, and did not traffic efficiently to the nucleus. Marker rescue experiments with a wild-type IVa2 DNA fragment confirmed that the only mutations present in pm8002 were in the IVa2 gene. The results indicate that the IVa2 protein is required for adenovirus assembly and suggest that virus particles may be assembled around the DNA rather than DNA being packaged into preformed capsids.     

复制缺陷型腺病毒载体介导hVEGF cDNA在C2C12和NIH3T3细胞中的表达

 为提高hVEGFcDNA在心肌中的表达 ,降低在其它组织中表达可能产生的不良反应 ,用PCR法得到人磷酸肌酸激酶 (MCK)增强子和CMV核心启动子 .利用克隆技术构建了含双拷贝MCK增强子 (m)和人巨细胞病毒 (CMV)核心启动子 (c)的嵌合启动子 (mmc) ,构建真核表达质粒pK3 mmcLacZ ,制备受mmc嵌合启动子调控的重组腺病毒Ad mmcVEGF .经X gal染色、β 半乳糖苷酶定量分析、RT PCR、hVEGFELISA定量分析、VEGF活性测定等研究表明 ,mmc启动VEGF基因在小鼠肌细胞C2C12和NIH3T3细胞中能有效表达且具有一定的肌细胞特异表达功能