生物工程学报  2024, Vol. 40 Issue (2): 458-472
http://dx.doi.org/10.13345/j.cjb.230468
中国科学院微生物研究所、中国微生物学会主办
0

文章信息

郭雨洁, 段海潇, 程奕宁, 杨斌丰, 胡翰, 刘滨磊, 汪洋
GUO Yujie, DUAN Haixiao, CHENG Yining, YANG Binfeng, HU Han, LIU Binlei, WANG Yang
稳定表达CD19-FLUC-GFP的CT26细胞系的构建及鉴定
Construction and identification of a stable CT26 cell line expressing CD19-FLUC-GFP
生物工程学报, 2024, 40(2): 458-472
Chinese Journal of Biotechnology, 2024, 40(2): 458-472
10.13345/j.cjb.230468

文章历史

Received: June 27, 2023
Accepted: September 8, 2023
Published: September 25, 2023
稳定表达CD19-FLUC-GFP的CT26细胞系的构建及鉴定
郭雨洁1 , 段海潇1 , 程奕宁1 , 杨斌丰2 , 胡翰1 , 刘滨磊1 , 汪洋1     
1. 湖北工业大学生物工程与食品学院, 湖北 武汉 430068;
2. 武汉滨会生物科技股份有限公司, 湖北 鄂州 436000
摘要:实体瘤缺乏明确的嵌合抗原受体T细胞(chimeric antigen receptor T-cell, CAR-T)治疗靶点。因此,通过慢病毒将已经明确的靶点分子CD19带入实体瘤细胞系,研究CD19 CAR-T细胞对其的杀伤,能够为CAR-T细胞针对实体瘤的治疗提供潜在的支撑。本研究利用三质粒慢病毒系统构建了稳定表达CD19、萤火虫荧光素酶(firefly luciferase, FLUC)和绿色荧光蛋白(green fluorescent protein, GFP)的结肠癌CT26细胞系CT26-CD19-FLUC-GFP。该细胞系与CT26细胞系的生长活性一致。通过流式细胞术检测不同代次CT26-CD19-FLUC-GFP细胞,证实了CT26-CD19-FLUC-GFP细胞连续传代至第5、10、22代后CD19及GFP的稳定表达。进一步证实,连续传代至第22代的CT26-CD19-FLUC-GFP细胞中的CD19 mRNA及FLUC表达水平显著高于对照组CT26细胞。与T细胞相比,CD19 CAR-T细胞能够显著杀伤CT26-CD19-FLUC-GFP细胞及MC38-CD19细胞。CT26-CD19-FLUC-GFP细胞腹腔植入小鼠体内1周后,通过活体成像仪可以检测到腹腔区域的FLUC表达。上述结果表明,成功构建了稳定表达CD19-FLUC-GFP的CT26细胞系,且该细胞系能够被CD19 CAR-T细胞特异性杀伤。
关键词CD19    萤火虫荧光素酶    CT26细胞    嵌合抗原受体T细胞(CAR-T)    慢病毒    
Construction and identification of a stable CT26 cell line expressing CD19-FLUC-GFP
GUO Yujie1 , DUAN Haixiao1 , CHENG Yining1 , YANG Binfeng2 , HU Han1 , LIU Binlei1 , WANG Yang1     
1. School of Biological Engineering and Food, Hubei University of Technology, Wuhan 430068, Hubei, China;
2. Wuhan Binhui Biopharmaceutical Co., Ltd., Ezhou 436000, Hubei, China
Abstract: Solid tumors lack well-defined targets for chimeric antigen receptor T-cell (CAR-T) therapy. Therefore, introducing a known target molecule, CD19, into solid tumor cell lines via lentiviral transduction to investigate the cytotoxicity of CD19 CAR-T cells can potentially support CAR-T cell therapy against solid tumors. In this study, a stable colon cancer CT26 cell line, CT26-CD19-FLUC-GFP, expressing CD19, firefly luciferase (FLUC), and green fluorescent protein (GFP), was constructed using a triple-plasmid lentiviral system. The growth characteristics of this cell line were consistent with those of the CT26 cell line. Subsequent flow cytometry analysis confirmed stable expression of CD19 and GFP in CT26-CD19-FLUC-GFP cells after serial passaging up to the 5th, 10th, and 22nd generations. Further validation revealed significantly higher levels of CD19 mRNA and FLUC expression in CT26-CD19-FLUC-GFP cells continuously passaged up to the 22nd generation compared to the control CT26 cells. In comparison to T cells, CD19 CAR-T cells demonstrated substantial cytotoxicity against CT26-CD19-FLUC-GFP cells and MC38-CD19 cells. One week after intraperitoneal implantation of CT26-CD19-FLUC-GFP cells into mice, FLUC expression in the peritoneal region could be detected. These results indicate the successful establishment of a stable CT26 cell line expressing CD19-FLUC-GFP, which can be specifically targeted by CD19 CAR-T cells.
Keywords: CD19    firefly luciferase (FLUC)    CT26 cells    chimeric antigen receptor T-cell (CAR-T)    lentivirus    

结肠癌是一种常见的恶性肿瘤,在我国,患结肠癌后5年生存率仅有57.6%,远低于亚洲其他一些国家[1],需要尽快制定新的策略以治疗结直肠癌[2]。结肠癌的主要治疗手段为手术治疗、放疗和化疗[3],但是其恶性程度高且术后易复发转移[4]。探索结肠癌的免疫疗法成为重要治疗方向,近年来也兴起了一些靶向免疫疗法,可以精准靶向癌细胞的某个靶点,杀伤癌细胞并对正常细胞伤害较小,而且可以避免放化疗副作用的产生,如PD-1/PD-L1靶向免疫治疗[5]、CD19 CAR-T靶向细胞治疗[6]

CD19分子在B细胞成熟和分化过程中具有重要作用[7-14]。CD19 CAR-T细胞治疗在血液系统肿瘤治疗上取得了显著的效果。由于实体瘤缺乏明确靶点,因此CAR-T细胞治疗在实体瘤的治疗上存在着挑战。

实验动物模型是恶性肿瘤研究的基础,小鼠繁殖周期短、实验成本低且操作较为简易[15],因此,小鼠模型仍然是药物发现和新兴疗法的临床前评估重要手段[16-17]。目前随着先进的成像模式、多种细胞系和转基因建模方法的发展,慢病毒载体已被用于多种疾病的基因治疗,慢病毒可以将目的外源基因整合进靶细胞基因组,实现靶细胞长期稳定地表达目的基因[18-19]。如体外治疗的造血干细胞[20-25]或T细胞[26-27]的转导、体内治疗向神经系统[28]和视网膜[29]输送基因。生物发光成像技术实现了对荷瘤小鼠实时、连续及非侵入性观察,能够动态监控小鼠体内肿瘤细胞的生长和转移情况[30-33]。本研究采用三质粒慢病毒系统构建稳定表达CD19、萤火虫荧光素酶基因(firefly luciferase, FLUC)和绿色荧光蛋白基因(green fluorescent protein, GFP)的结肠癌细胞系,对该细胞系及CT26细胞系进行生长特性、功能特性研究,并对其体内成瘤及荧光素酶表达进行研究。包括结肠癌在内的实体瘤缺乏特异性标记物,使得CAR-T细胞难以识别和攻击肿瘤细胞,特别是与血液肿瘤相比,缺乏CD19或B细胞成熟抗原(B cell maturation antigen, BCMA)等明确的可以作为CAR-T细胞治疗靶点的表面标记物。本研究构建的稳定表达CD19-FLUC-GFP的CT26细胞系,在CT26细胞上加上CD19 CAR-T细胞靶点,为CD19 CAR-T细胞治疗结肠癌提供体外、体内药效学评价模型。

1 材料与方法 1.1 材料

pCDH-CMV-MSLN-P2A-FLUC-EF1α-GFP载体质粒、辅助包装质粒pMD2.G和pSPAX2购自武汉淼灵生物科技有限公司;HEK293T细胞、小鼠结肠癌细胞(CT26)、小鼠结肠癌细胞(MC38)购自美国典型培养物保藏中心(American Typical Culture Collection, ATCC),pBDP-CD19质粒、鼠源CD19 CAR-T细胞、MC38-CD19细胞和大肠杆菌(Escherichia coli) DH5α感受态均由本实验室提供;限制性内切酶(Xba Ⅰ和EcoR Ⅰ)购自NEB公司;高保真酶(2×Phanta Flash Master Mix)、ClonExpress Ⅱ One Step Cloning Kit (Exnase Ⅱ、5×CE Buffer)、质粒小提试剂盒和反转录试剂盒均购自南京诺唯赞生物科技有限公司;RNA提取试剂盒和琼脂糖凝胶DNA回收试剂盒购自天根生化科技(北京)有限公司;LipofectamineTM 8000转染试剂和嘌呤霉素(puromycin dihydrochloride)购自碧云天生物技术有限公司;慢病毒浓缩液购自TaKaRa生物技术公司;Anti-human PE CD19抗体购自Biolegend;实时定量PCR试剂SYBR® Green Realtime PCR Master Mix购自ToYoBo;引物合成和测序均由擎科生物科技有限公司完成。6−8周龄BALB/c雌性小鼠,购自湖北食品药品安全评价中心,饲养于湖北工业大学无特定病原体(specific pathogen free, SPF)级动物房。所有动物实验均遵守湖北工业大学科研伦理与科技安全委员会的相关规定(批准号:HBUT20200021)。

1.2 方法 1.2.1 慢病毒载体的构建

CD19片段从pBDP-CD19质粒上进行PCR扩增,正向引物为5′-TGACCTCCATAGAAGATTCTAGAATGCCCCCCCCCAGGCT-3′,反向引物为5′-TCTTCCATGGTGGCGAATTCCGGTCCAGGATTCTCTTCGACATCTCCGGCTTGTTTCAG-3′。鉴定并回收PCR产物。将载体pCDH-CMV-MSLN-P2A-FLUC-EF1α-GFP经过双酶切后进行胶回收,并与CD19扩增产物通过重组酶Exnase Ⅱ进行重组。将重组产物转化E. coli DH5α感受态细菌,涂布于含氨苄青霉素(100 µg/mL)的LB平板培养基上,放置37 ℃培养箱过夜培养。挑取单克隆菌落,进行菌落PCR鉴定,选取阳性克隆进行摇菌培养、质粒提取、酶切鉴定和测序比对,并将菌液保存。

1.2.2 慢病毒包装与滴度检测

抽提pCDH-CMV-CD19-P2A-FLUC-EF1α-GFP载体质粒与辅助包装质粒pMD2.G、pSPAX2。将HEK293T细胞以1×106个/mL的密度接种入10 cm的培养皿中。24 h后,细胞汇合度达到80%左右进行质粒共转染。转染后48 h和72 h收集细胞上清[34];1 000×g离心10 min,将离心后的上清液转移到新的50 mL离心管中,经0.45 μm滤膜除杂,加入1/3病毒上清液体积的慢病毒浓缩液混匀后孵育过夜。次日1 500×g、4 ℃离心45 min,弃上清,加入200 μL PBS重悬,获得浓缩后的病毒,分装后保存在−80 ℃。病毒转导前一天将HEK293T细胞接种于96孔板,6×104个/孔。转导前将孔板中培养基换成含有终浓度6 μg/mL聚凝胺(polybrene)的完全培养基,37 ℃培养箱孵育30 min。通过流式细胞术检测慢病毒滴度[35],将慢病毒进行10倍梯度稀释至1 000倍稀释。将每管稀释后的病毒分别加入HEK293T细胞中,每个梯度重复3孔,阴性对照重复3孔。37 ℃培养箱培养,48 h后通过流式细胞仪检测表达GFP的细胞比例。经流式软件处理完数据后,计算慢病毒滴度:转导单位(transducing unit, TU)/mL=细胞数×GFP表达率×稀释倍数/病毒接种体积(mL)。

1.2.3 CT26-CD19-FLUC-GFP稳转细胞系的筛选

将CT26细胞接种于24孔板,每孔细胞数4×105个,于37 ℃、5% CO2浓度的细胞培养箱培养,避光加入5、10、15、20、25、30、35、40、45、50 μg/mL梯度的嘌呤霉素。连续4 d观察细胞存活率,第4天细胞完全死亡对应的最低浓度为最低致死浓度。在96孔板中接种CT26细胞2×104个,24 h后细胞长至80%融合度时,更换为含有6 μg/mL polybrene的新鲜培养基,放置在CO2培养箱孵育30 min,取10 μL浓缩后的慢病毒转导至CT26细胞[36]。48 h后,扩培至24孔板,更换为含有30 μg/mL嘌呤霉素的10% FBS DMEM/F12继续培养3 d,弃掉含有嘌呤霉素的培养基,让剩余细胞长到合适的细胞密度。在倒置荧光显微镜下观察到细胞表达绿色荧光,采用有限稀释法将其密度稀释至500个/mL,按照100 μL/孔接种入96孔板中,培养期间观察单克隆生长情况,后依次扩培至6孔板,得到6株稳定表达CD19-FLUC-GFP基因的CT26细胞系,通过流式细胞术和Western blotting筛选出CD19表达量最高的单克隆细胞系。

1.2.4 实时无标记细胞分析法检测CT26-CD19-FLUC-GFP稳转细胞系生长活性

Agilent xCELLigence RTCA S16实时无标记细胞分析仪内设对照组和实验组,将CT26细胞和CT26-CD19-FLUC-GFP细胞每孔各接种2×104个。使用Agilent xCELLigence RTCA S16实时无标记细胞分析仪观察CT26-CD19-FLUC-GFP与CT26细胞的生长活性。

1.2.5 流式检测CT26-CD19-FLUC-GFP稳转细胞系中CD19及GFP的表达

检测连续传代至第5、10、22代以及冻存1年后复苏并连续传10代的CT26-CD19-FLUC-GFP细胞的CD19及GFP的表达。收集6孔板内的CT26细胞(阴性对照)和CT26-CD19-FLUC-GFP细胞至1.5 mL EP管,500×g离心5 min,弃上清,使用100 μL PBS重悬CT26和CT26-CD19-FLUC-GFP细胞,其中CT26-CD19-FLUC-GFP细胞加入5 μL anti-human PE-CD19抗体,4 ℃避光孵育30 min后,加500 μL PBS洗涤,500×g离心5 min,弃上清,加500 μL PBS重悬后流式细胞仪检测。

1.2.6 Real-time qPCR检测CT26-CD19-FLUC-GFP稳转细胞系CD19 mRNA水平

提取CT26细胞和连续传至22代的CT26-CD19-FLUC-GFP细胞的RNA,反转录成cDNA,进行real-time qPCR检测。50 μL反应体系:SYBR® Green Realtime PCR Master Mix 25 μL,上下游引物(10 μmol/L)各2 μL,模板cDNA 5 μL,蒸馏水16 μL。反应条件:95 ℃ 15 s,60 ℃ 15 s,72 ℃ 45 s,40个循环;hCD19正向引物5′-CTACCTGATCTTCTGCCT-3′,反向引物5′-ATCCTCTTCCTCTTCCTC-3′;内参mGAPDH正向引物5′-AGGTCGGTGTGAACGGATTTG-3′,反向引物5′-TGTAGACCATGTAGTTGAGGTCA-3′。

1.2.7 多功能酶标仪检测CT26-CD19-FLUC-GFP稳转细胞系中FLUC的表达

将CT26细胞(阴性对照)和连续传至22代的CT26-CD19-FLUC-GFP细胞接种于96孔板,4.5×104个/孔,重复3孔。每孔加入100 μL的d-荧光素钾盐,放入37 ℃培养箱孵育10 min,多功能酶标仪检测FLUC的相对表达量。

1.2.8 CD19 CAR-T细胞对CT26-CD19-FLUC-GFP及MC38-CD19细胞杀伤试验

将鼠源T细胞和鼠源CAR-T细胞分别按照效靶比=2:1加入CT26-CD19-FLUC-GFP细胞和MC38-CD19细胞,使用Agilent xCELLigence RTCA S16实时无标记细胞分析仪分析鼠源T细胞和鼠源CAR-T细胞对CT26-CD19-FLUC-GFP及MC38-CD19的杀伤。

1.2.9 CT26-CD19-FLUC-GFP稳转细胞系体内表达FLUC

对BALB/c雌性小鼠分别腹腔植瘤CT26细胞和连续传代至22代的CT26-CD19-FLUC-GFP细胞。植瘤细胞密度为1×107个/mL,每只小鼠腹腔注射100 μL。植瘤1周后,观察肿瘤生长情况,荷瘤小鼠每只腹腔注射100 μL d-荧光素钾盐,10 min后于小动物活体成像仪下观察FLUC的表达。

1.2.10 统计分析

用GraphPad Prism 7.0软件对数据进行统计分析。结果以x±s表示。两组间比较用t检验,P < 0.05表示具有统计学意义。

2 结果与分析 2.1 重组慢病毒载体pCDH-CMV-CD19-P2A-FLUC-EF1α-GFP的构建

对CD19进行PCR扩增,扩增结果如图 1A所示,条带大小与预期一致(1 668 bp)。将CD19 PCR扩增产物回收并与载体质粒pCDH-CMV-MSLN-P2A-FLUC-EF1α-GFP进行重组,重组产物转化E. coli DH5α感受态细胞,接种于含氨苄青霉素(100 µg/mL)的LB平板培养基中,37 ℃培养箱过夜培养。挑取单克隆菌落,进行菌落PCR鉴定(图 1B)。对阳性克隆提取质粒,进行双酶切鉴定(图 1C)。对质粒进行测序分析,结果显示质粒构建正确。构建成功的慢病毒载体pCDH-CMV-CD19-P2A-FLUC-EF1α-GFP如图 1D所示。

图 1 慢病毒质粒构建 Fig. 1 Construction of lentivirus plasmid. A:PCR鉴定. M:2 000 bp DNA marker;1:CD19片段;2:CD19-P2A片段. B:菌落PCR. M:5000 bp DNA marker;1−9:单克隆菌落;10:阴性对照. C:双酶切鉴定. M:15000 bp DNA marker;1:双酶切片段(Xba Ⅰ和EcoR Ⅰ). D:质粒构建示意图 A: PCR identification. Lane M: 2 000 bp DNA marker; Lane 1: CD19 fragments; Lane 2: CD19-P2A fragments. B: Colony PCR. Lane M: 5000 bp DNA marker; Lane 1−9: Monoclonal colonies; Lane 10: Negative control. C: Double enzyme digestion identification. Lane M: 15000 bp DNA marker; 1: Double enzyme-digested fragments (Xba Ⅰ and EcoR Ⅰ). D: Schematic diagram of plasmid construction.
2.2 过表达CD19-FLUC-GFP的慢病毒包装及滴度测定

将慢病毒载体pCDH-CMV-CD19-P2A-FLUC-EF1α-GFP与辅助质粒pMD2.G、pSPAX2共转染HEK293T细胞包装病毒,转染后24、48和72 h在倒置荧光显微镜下观察到GFP表达(图 2A)。流式细胞仪检测转染72 h后HEK293T的GFP和CD19的表达,经Flowjo软件处理得到GFP和CD19的双阳性率均高于90% (图 2B),根据GFP表达率计算慢病毒滴度(TU/mL)= 6×104×6.82%×100/0.01=4.1×107 TU/mL (图 2C)。

图 2 慢病毒包装及滴度检测 Fig. 2 Packaging and titer detection of lentivirus. A:在转染后的24、48和72 h,使用荧光显微镜(10倍放大)检测293T细胞中GFP表达. B:通过流式细胞术检测293T细胞上的CD19和GFP表达. 1:对照组293T细胞;2:转染后72 h的293T细胞. C:通过流式细胞术检测不同稀释梯度下的慢病毒的GFP表达. 1:293T细胞;2−4:浓缩前分别稀释了10、100和1 000倍的病毒GFP表达;5−7:浓缩后分别稀释了10、100和1 000倍的病毒GFP表达 A: Detecting GFP expression on 293T cells using a fluorescence microscope (10×) at 24 h, 48 h, and 72 h post transfection. B: Detecting CD19 and GFP expression on 293T cells by flow cytometry. 1: Control 293T cells; 2: 293T cells at 72 h post transfection. C: GFP expression detection of lentivirus under different dilution gradients by flow cytometry. 1: 293T cells; 2−4: GFP expression of virus before concentration, which diluted 10×, 100×, 1 000×; 5−7: GFP expression of virus after concentration, which diluted 10×, 100×, 1 000×.
2.3 CT26-CD19-FLUC-GFP稳转细胞系的筛选

CT26细胞在嘌呤霉素处理的第4天,30 μg/mL的剂量下观察到细胞全部死亡,因此后续筛选的嘌呤霉素浓度确定为30 μg/mL (图 3A)。过表达CD19-FLUC-GFP的慢病毒转导CT26细胞48 h后,于倒置荧光显微镜下可以观察到GFP的表达,证明慢病毒转导成功。经过嘌呤霉素筛选出的细胞培养1周后,得到6株稳定表达GFP及CD19的单克隆细胞,其中,B10、D7、G7单克隆细胞的GFP及CD19双阳性细胞的比例高于95%。其中G7单克隆细胞的GFP及CD19双阳性细胞比例最高,达到99.6% (图 3B)。针对筛选到的6株单克隆细胞的Western blotting检测如图 3C所示,6株单克隆细胞均能够检测到CD19的表达(95 kDa),其中,G7单克隆细胞的CD19相对表达量最高。挑选G7为后续实验的单克隆细胞系,并于倒置荧光显微镜下观察G7单克隆细胞系的GFP表达(图 3D)。

图 3 单克隆细胞系的筛选 Fig. 3 Screening of monoclonal cell lines. A:CT26细胞对于嘌呤霉素的敏感曲线. B:用流式细胞仪检测筛选出的单克隆细胞系中CD19和GFP的表达. C:用免疫印迹法检测筛选出的单克隆细胞系中CD19的表达. D:使用显微镜在白光下(100倍放大)观察筛选出的单克隆细胞系G7. E:用荧光显微镜(100倍放大)检测筛选出的单克隆细胞系G7中GFP的表达 A: The sensitivity curve of CT26 cells to puromycin. B: Flow cytometry to detect the expression of CD19 and GFP in the screened monoclonal cell lines. C: Western blotting to detect the expression of CD19 in the screened monoclonal cell lines. D: Screened monoclonal cell line G7 observed by microscope with white light (100×). E: Expression of GFP in the screened monoclonal cell line G7 by fluorescence microscope (100×).
2.4 CT26-CD19-FLUC-GFP稳转细胞系与CT26细胞系的生长活性监测

经Agilent xCELLigence RTCA S16实时无标记细胞分析仪实时监测观察,已筛选的稳定表达CD19-FLUC-GFP的CT26细胞与CT26细胞生长活性趋于一致(图 4)。

图 4 CT26-CD19-FLUC-GFP与CT26细胞生长活性比较 Fig. 4 Comparison of the growth activity of CT26-CD19-FLUC-GFP and CT26 cells.
2.5 检测不同代次CT26-CD19-FLUC-GFP细胞CD19及GFP的表达

通过流式细胞术检测不同代次的CT26-CD19-FLUC-GFP细胞GFP及CD19的表达。结果显示CT26-CD19-FLUC-GFP细胞GFP和CD19在连续传代至第5代(图 5A)、10代(图 5B)、22代(图 5C)中均有稳定表达。将CT26-CD19-FLUC-GFP细胞冻存1年后,复苏细胞,连续传10代,其CD19及GFP稳定表达(图 5D)。

图 5 不同代次CT26-CD19-FLUC-GFP细胞的CD19及GFP表达   Fig. 5 The expression of CD19 in CT26-CD19-FLUC-GFP cells of different generation. 在连续传代5代(A)、10代(B)和22代(C)后检测CT26-CD19-FLUC-GFP细胞中CD19和GFP的表达. D:细胞冷冻保存一年后, CT26-CD19-FLUC-GFP细胞连续传代10代,检测GFP和CD19的表达 Detection of CD19 and GFP expression in CT26-CD19-FLUC-GFP cell after continuous passage for 5 generations (A), 10 generations (B), and 22 generations (C). D: After one year of cell cryopreservation, CT26-CD19-FLUC-GFP cell was continuous passaged for 10 generations, the expression of GFP and CD19 was detected.
2.6 CD19 mRNA在CT26-CD19-FLUC-GFP稳转细胞系中高表达

分别提取连续传代至第22代的CT26-CD19-FLUC-GFP细胞与CT26细胞mRNA,反转录成cDNA。使用Real-time PCR对CD19 mRNA进行检测。结果表明CD19 mRNA在CT26-CD19-FLUC-GFP细胞中高表达(图 6)。

图 6 CT26-CD19-FLUC-GFP细胞中CD19 mRNA的表达   Fig. 6 Detection of CD19 mRNA in CT26-CD19-FLUC-GFP monoclonal cell line. 与CT26细胞系相比,CT26-CD19-FLUC-GFP细胞系中CD19 mRNA显著上调表达(***:P < 0.001,t-检验) CD19 mRNA was significantly upregulated in CT26-CD19-FLUC-GFP cell line compared with CT26 cell line (***: P < 0.001, t-test).
2.7 FLUC在CT26-CD19-FLUC-GFP稳转细胞系中高表达

将CT26细胞、连续传代至第22代的CT26-CD19-FLUC-GFP细胞接种至96孔板,每孔加入100 μL的d-荧光素钾盐,使用多功能酶标仪检测FLUC的表达,证实CT26-CD19-FLUC-GFP细胞大量表达FLUC,相较于对照细胞CT26有40 000多倍的上调表达(图 7)。

图 7 检测CT26-CD19-FLUC-GFP细胞的FLUC表达   Fig. 7 Detection of FLUC expression in CT26-CD19-FLUC-GFP monoclonal cell line. 与CT26细胞系相比,CT26-CD19-FLUC-GFP细胞系中FLUC的表达显著上调(****:P < 0.000 1,t-检验) FLUC expression was significantly upregulated in CT26-CD19-FLUC-GFP cell line compared with CT26 cell line (****: P < 0.000 1, t-test).
2.8 CT26-CD19-FLUC-GFP细胞被CD19 CAR-T细胞特异性识别

将鼠源T细胞、鼠源CAR-T细胞分别与CT26-CD19-FLUC-GFP细胞和MC38-CD19细胞按照效靶比=2:1共孵育,使用Agilent xCELLigence RTCA S16实时无标记细胞分析仪分析鼠源T细胞及鼠源CAR-T细胞对CT26-CD19-FLUC-GFP细胞和MC38-CD19细胞的杀伤。结果表明,鼠源CAR-T细胞对CT26-CD19-FLUC-GFP细胞和MC38-CD19细胞的杀伤显著高于鼠源T细胞对其的杀伤(图 8),这表明CD19 CAR-T细胞能够特异性识别CT26-CD19-FLUC-GFP细胞以及MC38-CD19细胞。

图 8 CD19-CAR-T细胞对其靶细胞的杀伤 Fig. 8 Killing of target cells by CD19 CAR-T cells. CD19 CAR-T细胞对CT26-CD19-FLUC-GFP细胞(A)和MC38-CD19细胞(B)的杀伤作用 Killing of CT26-CD19-FLUC-GFP cells (A) and MC38-CD19 cells (B) by CD19 CAR-T cells.
2.9 CT26-CD19-FLUC-GFP稳转细胞系体内功能鉴定

将CT26细胞和连续传代至第22代的CT26-CD19-FLUC-GFP细胞腹腔植瘤1周后,在腹腔注射d-荧光素钾盐,通过小动物活体成像仪可以观察到CT26-CD19-FLUC-GFP植瘤组小鼠腹腔有大量FLUC的表达(图 9)。

图 9 CT26-CD19-FLUC-GFP稳转细胞系体内成瘤和FLUC的表达   Fig. 9 In vivo tumor formation and FLUC expression. A:对照组小鼠腹腔内植入CT26细胞. B:实验组小鼠腹腔内植入CT26-CD19-FLUC-GFP细胞. C:CT26-CD19-FLUC-GFP组小鼠与CT26组相比,FLUC的表达显著上调(****:P < 0.000 1,t-检验) A: Control group mouse with intraperitoneal implanted CT26 cells. B: Experimental group mouse with intraperitoneal implanted CT26-CD19-FLUC-GFP cells. C: Compared to the CT26 group, the expression of FLUC is significantly upregulated in the mouse of CT26-CD19-FLUC-GFP group (****: P < 0.000 1, t-test).
3 讨论与结论

CAR-T细胞治疗作为一种革命性的免疫疗法,在治疗血液肿瘤方面取得了显著的成功。然而,CAR-T细胞治疗在实体瘤治疗中面临着一个挑战,即缺乏明确的靶点。相比之下,血液肿瘤通常具有表面标记物,如CD19、CD20或BCMA,可作为CAR-T细胞治疗的靶点。但是,实体瘤的异质性和缺乏特异性标记物使得寻找合适的靶点变得困难。CD19抗原对B细胞的发育和成熟有着重要作用[37-39]。CD19分子是一种稳定的靶点,在大多数B细胞相关恶性肿瘤中广泛表达,不易发生突变或下调。这使得CD19分子成为一个可靠的治疗靶点,能够持续有效地识别和攻击癌细胞,减少肿瘤耐药和复发风险。CD19靶向免疫疗法,如CD19 CAR-T细胞免疫疗法,在B细胞相关血液肿瘤以及其他类型的CD19阳性的恶性肿瘤(包括某些非霍奇金淋巴瘤、慢性淋巴细胞性白血病等)中取得了良好的治疗效果[40-41]。在实体瘤缺乏明确CAR-T治疗靶点的情况下,通过慢病毒将已经明确的靶点分子CD19带入实体瘤细胞系,研究CD19 CAR-T细胞对其的杀伤,能够为CAR-T细胞针对实体瘤的治疗提供潜在的支撑。本研究构建的稳定表达CD19-FLUC-GFP的CT26细胞系能够为CD19 CAR-T细胞治疗提供明确靶点,GFP的表达为针对该细胞系的体外杀伤提供荧光标记信号,该细胞系在荷瘤小鼠体内FLUC的表达为针对该细胞系的体内杀伤提供检测基础。该细胞系为CD19 CAR-T细胞治疗结肠癌提供体外、体内的药效评价模型。为探索治疗结肠癌的免疫疗法、结肠癌发生进展机制和候选药物的评估方面提供支持,为肿瘤转移机制、新抗癌药物的发现等提供可靠有效的模型。

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