Human APOBEC3G incorporation into murine leukemia virus particles

The human APOBEC3G protein exhibits broad antiretroviral activity against a variety of retroviruses. It is packaged into viral particles and executes its antiviral function in the target cell. The packaging of APOBEC3G into different viral particles requires a mechanism that confers this promiscuity. Here, APOBEC3G incorporation into murine leukemia virus (MLV) was studied using retroviral vectors. APOBEC3G uptake did not require either its cytidine deaminase activity or the presence of a retroviral vector genome. Results from immunoprecipitation and co-localization studies of APOBEC3G with a MLV Gag-CFP (cyan fluorescent protein) fusion protein imply an interaction between both proteins. RNase A treatment did not inhibit the co-precipitation of Gag-CFP and APOBEC3G, suggesting that the interaction is RNA independent. Like human immunodeficiency virus (HIV) Gag, the MLV Gag precursor protein appears to interact with APOBEC3G, indicating that Gag contains conserved structures which are used to encapsidate APOBEC3G into different retroviral particles.     

肝细胞移植临床前研究：大鼠肝细胞分离,培养和逆转录病毒转导

目的建立完善的肝细胞培养系统，研究逆转录病毒载体转移并表达于大鼠原代肝细胞。方法采用表皮生长因子（ＥＧＦ）刺激大鼠原代肝细胞增殖，以表达β－半乳糖苷酶的双顺反子逆转录病毒载体（ｐＧＣＥＮ／β－ｇａｌ）感染肝细胞。Ｘ－ｇａｌ原位染色方法检测肝细胞内ＬａｃＺ的表达，采用ＰＣＲ方法扩增ＮｅｏＲ基因，从ＤＮＡ水平证实逆转录病毒载体整合入肝细胞。结果ＥＧＦ在体外可刺激肝细胞增殖并维持肝细胞功能，肝细胞表达β－半乳糖苷酶基因，肝细胞中可扩增出ＮｅｏＲ基因片断。结论双顺反子逆转录病毒载体可有效介导β－ｇａｌ和ＮｅｏＲ基因表达于大鼠肝细胞，提示可用于标记原代大鼠肝细胞，有利于研究肝细胞移植后移植之肝细胞在体内的寿命、分布及功能。     

Fetal gene therapy

Fetal gene therapy has the potential to treat inherited genetic diseases in utero before significant organ damage has occurred. Rapidly expanding stem cell populations may be targeted and the introduction of transgenes to the fetus during development of the immune system could result in immune tolerance and facilitate repeat treatment postnatally. Genetic diseases such as cystic fibrosis, which are life-threatening and for which there are no currently acceptable treatments available, are suggested targets for this therapy.

Ultrasound may be a safe method of delivering a therapeutic gene into the fetus, although most studies have used more invasive techniques, even in large animal models. Viral vectors currently offer the most potential. Adenovirus-based vectors are stable, independent of host cell replication, efficient at tissue infection and have been used as a 'pathfinder' to test routes of administration. Unfortunately, they are also highly immunogenic and other systems based on retrovirus or adeno-associated virus may offer advantages because of their lower immunogenicity and potential for permanent transgene expression.

Our group is developing the fetal sheep model for the investigation of ultrasound-guided gene therapy in utero. This model is suitable since the sheep fetus is tolerant to manipulations, has a consistent gestation period and shows many similarities with human pregnancy. We have demonstrated significant transfection of the fetal liver and adrenal cortex after ultrasound-guided percutaneous injection of the umbilical vein with adenoviral vectors in the late gestation sheep. We are investigating and here discuss alternative routes of administration to target the fetus in early gestation via ultrasound-guided minimally invasive techniques.     

Efficient retroviral transduction of human B-lymphoid and myeloid progenitors: marked inhibition of their growth by the <Emphasis Type="Italic">Pax5</Emphasis> transgene

We applied a coculture system for the genetic manipulation of human B-lymphoid and myeloid progenitor cells using murine bone marrow stromal cell support, and investigated the effects of forced Pax5 expression in both cell types. Cytokine-stimulated cord blood CD34⁺ cells could be transduced at 85% efficiency and 95% cell viability by a single 24-h infection with RD114-pseudotyped retroviral vectors, produced by the packaging cell line Plat-F and bicistronic vector plasmids pMXs-Ig, pMYs-Ig, or pMCs-Ig, encoding EGFP. Infected CD34⁺ cells were seeded onto HESS-5 cells in the presence of stem cell factor and granulocyte colony-stimulating factor, allowing the extensive production of B progenitors and granulocytic cells. We examined the cell number and CD34, CD33, CD19, and CD20 lambda and kappa expressions by flow cytometry. Ectopic expression of Pax5 in CD34⁺ cells resulted in small myeloid progenitors coexpressing CD33 and CD19 and inhibited myeloid differentiation. After 6 weeks, the number of Pax5-transduced CD19⁺ cells was 40-fold lower than that of control cells. However, the expression of CD20 and the κ/λ chain on Pax5-transduced CD19⁺ cells suggests that the Pax5 transgene may not interfere with their differentiation. This report is the first to describe the effects of forced Pax5 expression in human hematopoietic progenitors.     

系统性红斑狼疮肿瘤坏死因子受体Ⅱ196位点基因多态性及重组反转录病毒载体的构建

目的调查南方地区中国人肿瘤坏死因子受体Ⅱ(TNFRⅡ)196位基因多态性与系统性红斑狼疮(SLE)的关系并构建野生和突变的反转录病毒载体以研究其功能差异。方法利用聚合酶链反应-限制性片段长度多态性(PCR-RFLP)方法检测了106例SLE和119名健康人TNFRⅡ196位的基因型。将扩增TNFRⅡ196McDNA克隆到PMD18-T载体上,定点突变为TNFRⅡ196R,然后亚克隆到反转录病毒载体PLXSN上(PLXSN-TNFRⅡ196M和PLXSN-TNFRⅡ196R)并分别转染大鼠系膜细胞,以四甲基偶氮唑(MTT)法观察对系膜细胞增生的影响。结果①SLE组TNFRⅡ196R等位基因型明显高于正常组(35.2%vs14.3%,P<0.05);②成功构建野生型和突变型重组反转录病毒载体;③rhTNF-α刺激后196R型转染系膜细胞的增生明显高于196M型(P<0.05)。结论TNFRⅡ196R与中国南方地区SLE相关,其可以高效传导TNF-α的信号,可能参与SLE的发病。     

Boundary sequences stabilize transgene expression from subtle position effects in retroviral vectors

Transgene expression shut-down, attenuation and/or variability from integrated retroviral vectors pose a major obstacle to gene therapy trials involving hematopoietic cells. We have undertaken a systematic assessment of the behavior of different configurations containing IFN-β SAR and/or 5′HS4 β-globin insulator sequences within a gammaretroviral vector optimized for high-level expression, focusing on the long-term achievement of stable, homogeneous transgene expression in the successfully transduced cells. Introduction of these cis regulatory elements did not perturb virus production and stability. Conversely, the SAR/5′HS4 insulator combination appeared to increase the homogeneity of EGFP expression in mass cultures. Furthermore, a clonal analysis of the dispersion of EGFP expression revealed that the IFN-SAR/5′HS4 insulator dyad was particularly effective in reducing the variability of transgene expression when both sequences were placed in opposite orientations within the retroviral backbone. These results may prove useful for the design of more stable retroviral expression cassettes able to counteract chromosomal position effects.     

靶向表达的逆转录病毒载体LN.ALBTRS.TK的构建

目的:构建出在肝细胞中具靶向表达潜能的逆转录 TK 基因载体。方法:用 p2335A-1中的一段2.0Kb的人白蛋白组织特异性转录调节序列(ALBTRS)取代 pSTK 中的 SV40启动子,所构建的载体命名为 LN.ALB-TRS.TK。结果:载体 LN.ALBTRS.TK 的结构中,含有 ALBTRS 启动子,具有在肝细胞中特异表达白蛋白的潜能,载体经酶切鉴定表明结构符合要求。结论:成功地构建出具靶向表达潜能的逆转录载体 LN.ALBTRS.TK。