靶基因调控的脐血干/祖细胞体外长期扩增与调控

背景:脐血干细胞是基因治疗最理想的靶细胞之一,但基因转移率低下是目前面临的主要障碍.酪氨酸激酶JAK2在造血干/祖细胞自我更新中扮演着重要的作用,为了克服脐血基因转移率低下的障碍,根据基因调控表达技术原理,是否可开发一个可以靶向扩增JAK2基因修饰的脐血CD34 细胞体系.目的:探讨转基因JAK2介导的脐血干祖细胞长期扩增调控的可行性和安全性. 单位:卫生部北京医院血液科.材料:实验于2003-06/2006-04在卫生部北京医院血液科实验室完成.脐血取自健康、足月、自然分娩后立即断脐的脐血.脐血由北京医院妇产科提供,产妇及家属均知情同意,实验经医学伦理委员会批准.MiniMACS磁性分离仪、免疫磁珠吸附CD34单抗购自德国Miltenyi Biotec公司, 流式细胞仪购自美国FACScalibur,人重组干细胞因子、Flt3配体、人白介素-6、粒细胞-巨噬细胞集落刺激因子、粒细胞集落刺激因子、血小板生成素为PeproTec产品,SPF级裸鼠购自北京医科大学动物中心.方法:构建逆转录病毒载体MGI-F2JAK2,内含有JAK2基因的功能催化区和两个与小分子靶向基因合成药物(AP20187)结合的位点蛋白(2xF36v,F2)组成.AP20187可与F36v特异结合引起JAK2二聚化而激活细胞内信号传导.该载体同时含有绿色荧光蛋白报告基因,用作检测细胞增殖的标记.应用MiniMACS免疫磁珠分选系统纯化分离脐血CD34 细胞,用含JAK2的逆转录病毒上清转染脐血CD34 细胞.转导后的CD34 细胞在集落刺激因子、Flt3配体、血小板生成素、白介素-6细胞因子的联合培养条件下,以不加或加入AP20187分别作为对照组和实验组.主要观察指标:①应用流式细胞仪测定两组CD34 细胞中所含绿色荧光蛋白细胞的百分率,确定基因转移率.②扩增后的脐血祖细胞集落培养结果.③取培养10周的脐血CD34 细胞于裸鼠的胁部皮下注射,30 d后观察成瘤情况.结果:①实验组与对照组均可获得CD34 细胞大量扩增.随着培养时间的延长,实验组扩增的CD34 细胞GFP阳性率由基线水平逐渐上升于第11周时达到95%以上,而对照组绿色荧光蛋白报告基因阳性率逐渐下降到基线水平以下并逐渐消失.②实验组转基因CD34 细胞于12周后仍可产生造血祖细胞集落红系祖细胞、粒单系祖细胞、脐血多向造血祖细胞,所形成的造血祖细胞集落以粒单系祖细胞为主.③裸鼠实验无致瘤特性.结论:转染JAK2 基因的人脐血CD34 细胞协同其他细胞因子可以体外长期扩增脐血干祖细胞,对今后开展干细胞治疗某些遗传性血液病有潜在的应用价值.

Targeted expansion and regulation of genetically modified cord blood stem/progenitor cells in vitro

BACKGROUND: Cord blood stem cells are one of ideal target cells for gene therapy, but low gene transferring rate is the main difficulty at recent. Janus kinase tyrosine 2 (JAK2) plays an important role in self-renewing of cord blood stem/progenitor cell12s. Therefore, cord blood CD34+ cell line modified by target-amplified JAK2 genes has been developed yet by using gene regulating expression technique in order to overcome low transferring rate of cord blood genes.OBJECTIVE: To investigate the feasibility and reliability of a long-term amplified regulation for cord blood stem/progenitor cells mediated by transgene JAK2. SETTING: Department of Hematology, Beijing Hospital, Ministry of Health.MATERIALS: The experiment was carried out in the Laboratory of Hematological Department, Beijing Hospital, Ministry of Health from June 2003 to April 2006. Cord blood was derived from umbilical cord which was immediately cut from healthy, full-term and natural-parturition infants and was provided by Department of Obstetrics & Gynecology, Beijing Hospital. The experiment was approved by the local ethical committee, and informed consent was obtained from expectant mothers and their relatives for the use of cord blood cells. MiniMACS magnetic separation apparatus and immunomagnetic beads adsorbing CD34 single antibody were provided by Miltenyi Biotec Company, Germany; flow cytometer by FACScalibur, USA; recombinant human stem cell factor (rhSCF), Flt3 ligand (FL), human interleukin-6 (hIL-6), granulocyte macrophage colony stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF) and thrombopoeitin (TPO) by PeproTec Company; nude mice of the SPF level by Animal Center of Beijing Medical University.METHODS: Retroviral vector MGI-F2JAK2, which was composed of functional catalytic domain of JAK2 genes and two site proteins (2xF36v, F2) combined with synthetic drug (AP20187) of target gene of small molecules, was constructed. AP20187 might specially combine with F36v to cause dimerization of JAK2 so as to activate signal conduction in cells. In addition, the vector included green fluorescence protein reporter gene, which was regarded as a label to detect proliferation. MiniMACS magnetic separation apparatus was used to purify and separate cord blood CD34+ cells. While, retrovirus supernatant including JAK2 was used to transfer cord blood CD34+ cells. After transduction, CD34+ cells were cultured with stem cell factor (SCF), Flt3 ligand, TPO and IL-6 and divided into control group (not adding AP20187) and experimental group (AP20187).MAIN OUTCOME MEASURES: ① Flow cytometer was used to detect percentage of green fluorescence protein reporter gene in the CD34+ cells and to determine gene transferring rate. ② Colony culture results of cord blood stem/progenitor cells after amplification. ③ Nude mice were given subcutaneous injection of ten-week cultured cord blood CD34+ cells at costa and neoplasia was observed after 30 days. RESULTS: ① Plentiful amplification of CD34+ cells was observed in both experimental group and control group. With the culture time passing by, positive rate of gel-filtered platelet of amplified CD34+ cells in the experimental group was gradually increased based on the basic level and more than 95% in the 11th week; however, positive rate of green fluorescence protein reporter gene in the control group was gradually decreased below the basic level and disappeared finally. ② Transgenic CD34+ cells in the experimental group still could generate brust forming unit-erythroid (BFU-E), colony-forming units granulocute/monocyte (CFU-GM) and multipotential hematopoietic progenitors (CFU-Mix); especially, CFU-GM was the main cell in hemopoietic progenitor cell (HPC). ③ Nude mice did not have neoplasia. CONCLUSION: Human cord blood CD34+ cells of transferring JAK2 genes may cooperate with other cytokines to amplify cord blood stem/progenitor cells in vitro for long. Therefore, this is potentially valuable for stem cells to treat some hereditary hematologic disease.