1.研(yan)究背景(jing)
基(ji)因(yin)治療是(shi)一種(zhong)新型的(de)(de)(de)(de)(de)治療手段(duan),它(ta)可(ke)以(yi)治療多種(zhong)疾(ji)(ji)(ji)病(bing)(bing)(bing),包括癌癥、遺傳性(xing)疾(ji)(ji)(ji)病(bing)(bing)(bing)、神經(jing)性(xing)疾(ji)(ji)(ji)病(bing)(bing)(bing)、感染性(xing)疾(ji)(ji)(ji)病(bing)(bing)(bing)、心血管疾(ji)(ji)(ji)病(bing)(bing)(bing)和自身免疫性(xing)疾(ji)(ji)(ji)病(bing)(bing)(bing)等,它(ta)針(zhen)對的(de)(de)(de)(de)(de)是(shi)疾(ji)(ji)(ji)病(bing)(bing)(bing)的(de)(de)(de)(de)(de)根(gen)源(yuan)而不僅(jin)僅(jin)是(shi)疾(ji)(ji)(ji)病(bing)(bing)(bing)的(de)(de)(de)(de)(de)癥狀。如此有效(xiao)的(de)(de)(de)(de)(de)治療方法有什么(me)特(te)殊性(xing)呢(ni)?其實很簡(jian)單,它(ta)就是(shi)將外源(yuan)正常基(ji)因(yin)借助一定的(de)(de)(de)(de)(de)技術(shu)或(huo)者載體導入(ru)靶細胞,從而糾正或(huo)補償缺陷和異常基(ji)因(yin)引(yin)起的(de)(de)(de)(de)(de)疾(ji)(ji)(ji)病(bing)(bing)(bing),以(yi)達(da)到治療疾(ji)(ji)(ji)病(bing)(bing)(bing)的(de)(de)(de)(de)(de)目的(de)(de)(de)(de)(de)(圖1)。
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圖1:基因治療的(de)示意圖(來源于://www.fda.gov/)
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圖2:3款獲批上市的基于AAV載體的基因藥物的時間表
(Lugin, M. L., et al. (2020). ACS Nano 14(11): 14262-14283.)
上述取得的成就,再加上美國臨床試驗數據庫(ClinicalTrials.gov)中的一系列臨床前和臨床研究均證實了AAV載體的安全性和有效性。但是野生型AAV畢竟不是為了遞送疾病治療基因而進化的。而且,體內預存的中和抗體和AAV載體的承載能力進一步限制了AAV載體的廣泛應用。目前,科學家們研究的重點主要集中在工程化AAV載體,用于提高其安全性、靶向性和轉導效率。工程化AAV載體的構建方法多種多樣,本篇我們將重點(dian)跟大(da)家分享衣殼修飾的工程(cheng)化AAV載體(ti)(圖3)。
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圖3:工程化AAV載體的示意圖
2.AAV基因組(zu)結構(gou)
了解AAV基因組結構是構建工程化AAV的基礎。野生型(xing)AAV含有約4.7kb的(de)單鏈線性DNA基(ji)因(yin)(yin)組,三個基(ji)因(yin)(yin)Rep, Cap和X的(de)兩端(duan)各由145bp的(de)ITR組成,可形成T型(xing)的(de)發夾結構(圖4)。Rep基(ji)因(yin)(yin)編碼(ma)病毒(du)轉錄調(diao)控(kong)、復(fu)制(zhi)和包裝必需的(de)四個調(diao)控(kong)蛋白:Rep78, Rep68, Rep52 和Rep40。Cap基(ji)因(yin)(yin)編碼(ma)三個重疊的(de)結構蛋白(VP1, VP2, VP3,其(qi)表達比例(li)為1:1:10)和VPs入核必需的(de)裝配激活蛋白AAP(assembly-activating protein)。X基(ji)因(yin)(yin)編碼(ma)基(ji)因(yin)(yin)組復(fu)制(zhi)中具(ju)有支持功能(neng)的(de)蛋白質。
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圖4:AAV2載體的基因組結構
(Buning, H. and A. Srivastava (2019). Mol Ther Methods Clin Dev 12: 248-265.)
3.AAV衣殼(ke)結構
AAV衣殼結構的解析有助于理解AAV如何感染細胞和確定工程化AAV衣殼修飾的位置。腺相關病毒的衣殼呈T=1二十面體(二十面體是由20個三角形圍成的凸多面體,每5個三角形圍出一個五倍頂,通過每一對相對著的五倍頂有一個五倍旋轉軸;通過每一對相對著的三角形中心有1個三倍旋轉軸;通過每一對相對著的棱的中點有1個二倍旋轉軸)。它由60個VP單體通過這些旋轉軸的相互作用裝配而成,這些VP單體可以全部為VP3,也可以由VP1、VP2、VP3共同構成。
AAV衣(yi)殼(ke)表面(mian)的(de)顯著(zhu)特(te)征是(shi)(shi)二(er)倍(bei)(bei)凹地(di)(di),三(san)倍(bei)(bei)凸(tu)起(qi)(qi)和五倍(bei)(bei)通(tong)道(圖(tu)5)。圓柱(zhu)形通(tong)道連通(tong)衣(yi)殼(ke)內外,是(shi)(shi)AAV DNA進入衣(yi)殼(ke)的(de)地(di)(di)方,它參(can)與 Rep 蛋白結合、衣(yi)殼(ke)蛋白裝配、VP1 N 末端(duan)外露(lu)、AAV病(bing)毒(du)感染等多個過程(cheng);二(er)倍(bei)(bei)凹地(di)(di)是(shi)(shi)病(bing)毒(du)衣(yi)殼(ke)最薄的(de)地(di)(di)方;三(san)倍(bei)(bei)凸(tu)起(qi)(qi)的(de)主要作用是(shi)(shi)識(shi)別受(shou)體。
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圖5:由60個VP3裝配成的AAV2衣殼的拓撲結構
(Tseng, Y. S. and M. Agbandje-McKenna (2014). Front Immunol 5: 9.)
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圖6:AAV2 VP3單體的拓撲結構。9個VRs被用不同的顏色標記:
I,紫色;II,藍色;III,黃色;IV,紅色;V,黑色;VI,粉紅色;VII,青色;VIII,綠色;IX,巧克力色
(Gurda, B. L., et al. (2013). J Virol 87(16): 9111-9124.)
4.衣殼修飾(shi)的工程化AAV
特定的VP亞基已被作為衣殼修飾的靶點,例如去除免疫原基序,整合標簽或熒光基團和重新靶向等。
AAV2是研究相對成熟的血清型。以AAV2為骨架,在公共VP3區,大量研究表明,I-587(VP1氨基酸數)和I-588為較常用的衣殼修飾位置,因為這2個位置地處三倍凸起附近,可以接受長達34個氨基酸長度的肽鏈插入,而不影響衣殼化和基因組包裝。而且,外源肽鏈的插入使得AAV2第一受體結合基序被修飾,最終賦予AAV2變體新的靶向性。Buning, H.等人匯總了在I-587和I-588處插入肽鏈的AAV2變體(表1)。維真生物現擁有表1所列的所有AAV Cap質粒,數量近70種(zhong),可直接進行(xing)AAV病毒包(bao)裝。
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表1:在I-587和I-588處插入肽鏈的AAV2變體
Serotype | Position | Name | Target Cell Type | Insert |
AAV2 | I-587 | AAV-I-587 | β1-integrin positive tumor cells | QAGTFALRGDNPQG |
AAV2 | I-587 | AAV-588NGR | CD13-positive tumor cells | NGRAHA |
AAV2 | I-587 | AAV-MO7A | tumor cells | RGDAVGV |
AAV2 | I-587 | AAV-MO7T | tumor cells | RGDTPTS |
AAV2 | I-587 | AAV-MecA | tumor cells | GENQARS |
AAV2 | I-587 | AAV-MecB | tumor cells | RSNAVVP |
AAV2 | I-587 | rRGD587 | αv integrin positive tumor cells | CDCRGDCFC |
AAV2 | I-587 | AAV-C4 | tumor cells | PRGTNGP |
AAV2 | I-587 | AAV-D10 | tumor cells | SRGATTT |
AAV2 | I-587 | AAV-SIG | endothelial cells | SIGYPLP |
AAV2 | I-587 | AAV-MTP | endothelial cells | MTPFPTSNEANL |
AAV2 | I-587 | AAV-QPE | endothelial cells | QPEHSST |
AAV2 | I-587 | AAV-VNT | endothelial cells | VNTANST |
AAV2 | I-587 | AAV-CNH | endothelial cells | CNHRYMQMC |
AAV2 | I-587 | AAV-CAP | endothelial cells | CAPGPSKSG |
AAV2 | I-587 | AAV-EYH | smooth muscle cells | EYHHYNK |
AAV2 | I-587 | AAV587MTP | skeleton muscle cells | ASSLNIA |
AAV2 | I-587 | AAV-r3.45 | neuronal stem cells | TQVGQKT |
AAV2 | I-587 | AAV2-LSS | CNS | LPSSLQK |
AAV2 | I-587 | AAV2-PPS | CNS | DSPAHPS |
AAV2 | I-587 | AAV2-TLH | CNS | GWTLHNK |
AAV2 | I-587 | AAV2-GMN | CNS | GMNAFRA |
AAV2 | I-587 | AAV-Kera1 | keratinocytes | RGDTATL |
AAV2 | I-587 | AAV-Kera2 | keratinocytes | PRGDLAP |
AAV2 | I-587 | AAV-Kera3 | keratinocytes | RGDQQSL |
AAV2 | I-587 | AAV-588Myc | none | EQLSISEEDL |
AAV2 | I-587 | AAV2.N587_R588insBAP | adaptor | GLNDIFEAQKIEWHE |
AAV2 | I-587 | AAV2Ald13 | adaptor | LCTPSRAALLTGR |
AAV2 | I-587 | DMD4 | vaccine | QVSHWVSGLAEGSFG |
AAV2 | I-587 | DMD6 | vaccine | LSHTSGRVEGSVSLL |
AAV2 | I-588 | A588-RGD4C | av integrin-positive tumor cells | CDCRGDCFC |
AAV2 | I-588 | A588-RGD4CGLS | av-integrin positive tumor cells | CDCRGDCFC |
AAV2 | I-588 | AAV-VTAGRAP | tumor cells | VTAGRAP |
AAV2 | I-588 | AAV-APVTRPA | tumor cells | APVTRPA |
AAV2 | I-588 | AAV-DLSNLTR | tumor cells | DLSNLTR |
AAV2 | I-588 | AAV-NQVGSWS | tumor cells | NQVGSWS |
AAV2 | I-588 | AAV-EARVRPP | tumor cells | EARVRPP |
AAV2 | I-588 | AAV-NSVSLYT | tumor cells (CML) | NSVSLYT |
AAV2 | I-588 | AAV-LS1 | tumor cells (CML), CD34+cells | NDVRSAN* |
AAV2 | I-588 | AAV-LS2 | tumor cells (CML), CD34+cells | NESRVLS |
AAV2 | I-588 | AAV-LS3 | tumor cells (CML), CD34+cells | NRTWEQQ |
AAV2 | I-588 | AAV-LS4 | tumor cells (CML), CD34+cells | NSVQSSW |
AAV2 | I-588 | AAV-RGDLGLS | tumor cells | RGDLGLS |
AAV2 | I-588 | AAV-RGDMSRE | tumor cells | RGDMSRE |
AAV2 | I-588 | AAV-ESGLSQS | tumor cells | ESGLSQS |
AAV2 | I-588 | AAV-EYRDSSG | tumor cells | EYRDSSG |
AAV2 | I-588 | AAV-DLGSARA | tumor cells | DLGSARA |
AAV2 | I-588 | AAV-GPQGKNS | tumor cells | GPQGKNS |
AAV2 | I-588 | AAV-NSSRDLG | endothelial cells | NSSRDLG |
AAV2 | I-588 | AAV-NDVRAVS | endothelial cells | NDVRAVS# |
AAV2 | I-588 | AAV-PRSTSDP | lung (maybe endothelial cells) | PRSTSDP |
AAV2 | I-588 | AAV-DIIRA | endothelial cells | DIIRA |
AAV2 | I-588 | AAV-SYENV | endothelial cells | SYENVASRRPEG |
AAV2 | I-588 | AAV-PENSV | endothelial cells | PENSVRRYGLEE |
AAV2 | I-588 | AAV-LSLAS | endothelial cells | LSLASNRPTATS |
AAV2 | I-588 | AAV-NDVWN | endothelial cells | NDVWNRDNSSKRGGTTEAS |
AAV2 | I-588 | AAV-NRTYS | endothelial cells | NRTYSSTSNSTSRSEWDNS |
AAV2 | I-588 | rAAV2-ESGHGYF | pulmonary endothelial cells | ESGHGYF |
AAV2 | I-588 | AAV-GQHPRPG | cardiomyoblasts | GQHPRPG+ |
AAV2 | I-588 | AAV-PSVSPRP | cardiomyoblasts | PSVSPRP |
AAV2 | I-588 | AAV2-VNSTRLP | cardiomyoblasts | VNSTRLP |
AAV2 | I-588 | AAV-LSPVR | cardiomyoblasts | LSPVRPG |
AAV2 | I-588 | AAV-MSSDP | cardiomyoblasts | MSSDPRRPPRDG |
AAV2 | I-588 | AAV-GARPS | cardiomyoblasts | GARPSEVTTRPG |
AAV2 | I-588 | AAV-GNEVL | cardiomyoblasts | GNEVLGTKPRAP |
AAV2 | I-588 | AAV-KMRPG | cardiomyoblasts | KMRPGAMGTTGEGTRVTRE |
AAV2 | I-588 | AAV588MTP | skeleton muscle | ASSLNIA |
除(chu)了I-587和I-588外,I-453、I-520&I-584、I-584、I-585也已被(bei)成功用于(yu)開發新細胞靶向性(xing)工程化AAV(表(biao)2)。
表2:非I-587和I-588衣殼變體
Serotype | Position | Name | Target Cell Type | Insert |
AAV2 | I-453 | rRGD453ko | av integrin-positive tumor cells | CDCRGDCFC |
AAV2 | I-453 | AAV-MNVRGDL | endothelial cells | MNVRGDL |
AAV2 | I-453 | AAV-ENVRGDL | endothelial cells | ENVRGDL |
AAV2 | I-520 and I-584 | A520/N584 (RGD) | av integrin-positive tumor cells | CDCRGDCFC |
AAV2 | I-584 | A584-RGD4C | av integrin-positive tumor cells | CDCRGDCFC |
AAV2 | I-584 | A584-RGD4CALS | av integrin-positive tumor cells | CDCRGDCFC |
AAV2 | I-585 | AAV-?IV-NGR | CD13-positive tumor cells | NGRAHA |
AAV2 | I-585 | AAV-PTP | Plectin-positive tumor cells | KTLLPTP |
正如研究背景中(zhong)所(suo)述,體(ti)內(nei)預存中(zhong)和抗(kang)(kang)(kang)(kang)體(ti)是限制AAV廣(guang)泛臨床應(ying)用的(de)(de)(de)一(yi)大障礙。血清(qing)學研究表明,大多數人(ren)都接觸過野生型AAV,因此體(ti)內(nei)可能已經形成針對AAV的(de)(de)(de)中(zhong)和抗(kang)(kang)(kang)(kang)體(ti)。這(zhe)些(xie)中(zhong)和抗(kang)(kang)(kang)(kang)體(ti)可能會干擾AAV進入(ru)靶細胞、細胞內(nei)運輸和細胞核內(nei)的(de)(de)(de)解包裝,從而阻止了(le)轉導(dao)。據報道,抗(kang)(kang)(kang)(kang)AAV抗(kang)(kang)(kang)(kang)體(ti)在(zai)人(ren)群中(zhong)的(de)(de)(de)流行(xing)率約為(wei)(wei)40-80%。其中(zhong),抗(kang)(kang)(kang)(kang)AAV2的(de)(de)(de)中(zhong)和抗(kang)(kang)(kang)(kang)體(ti)在(zai)人(ren)群中(zhong)相對更(geng)流行(xing)。為(wei)(wei)了(le)克服這(zhe)個障礙,科學工(gong)作者以其他(ta)低免疫原(yuan)性血清(qing)型為(wei)(wei)骨(gu)架,并參考AAV2的(de)(de)(de)衣殼修(xiu)飾位點,開(kai)發了(le)一(yi)系列(lie)新(xin)的(de)(de)(de)工(gong)程化AAV(表3)。
表3:非AAV2骨架的工程化AAV
Serotype | Position | Name | Target Cell Type | Insert |
AAV1 | I-590 | BAP-AAV1 | Scavidin displaying BT4C (rat glioma) | GLNDIFEAQKIEWHE |
AAV1 | I-590 | BAP-AAV1 | endothelial cells | GLNDIFEAQKIEWHE plus CDCRGDCFC(RGD4C) |
AAV1 | I-590 | AAV1-RGD | tumor cells, endothelial cells | CDCRGDCFC |
AAV1 | I-590 | AAV1-RGD/BAP (90/10) (mosaic capsid) | tumor cells, endothelial cells | CDCRGDCFC and GLNDIFEAQKIEWHE |
AAV1 | I-590 | Tet1c-AAV1 (mosaic capsid) | tetanus toxin GT1b receptor positive cells | HLNILSTLWKYR |
AAV1 | I-590a | AAV1.9-3-SKAGRSP | fibroblast | SKAGRSP |
AAV5 | I-575 | BAP-AAV4 | tumor cells | GLNDIFEAQKIEWHE |
AAV6 | I-585 | AAV6-RGD | tumor cells | RGD |
AAV6 | I-585 plus Y705-731F+T492V | AAV6-RGD-Y705-731F+T492V | tumor cells | RGD |
AAV6 | I-585plus Y705-731F+T492V+K531E | AAV6-RGD-Y705-731F+T492V+K531E | tumor cells | RGD |
AAV8 | I-585c | AAV2/8-BP2 | on-bipolar cells | PERTAMSLP |
AAV8 | I-590 | AAV8-ESGLSOS | tumor cells | ESGLSOS135 |
AAV8 | I-590 | AAV8-ASSLNIA | heart (weakly improved transduction) | ASSLNIA122 |
AAV8 | I-590d | AAV8-GQHPRPG | heart (weakly improved transduction) | GQHPRPG86 |
AAV8 | I-590d | AAV8-SEGLKNL | liver | SEGLKNL |
AAV9 | I-589 | AAV-SLRSPPS | endothelial cells, smooth muscle cells | SLRSPPS |
AAV9 | I-589 | AAV-RGDLRVS | endothelial cells, smooth muscle cells | RGDLRVS |
AAV9 | I-589d | AAV9-NDVRAVS | endothelial cells | NDVRAVS82 |
AAV9 | I-589d | AAV9-ESGLSOS | tumor cells (weak targeting) | ESGLSOS135 |
AAV9 | I-588 | AAV-PHP.B | CNS | TLAVPFK |
AAV9 | I-588 | AAV-PHP.A | CNS | YTLSQGW |
AAV9 | I-588 | AAV9-7m8 | retinal cells | LGETTRP80 |
AAV9P1 | not disclosed | AAV9P1 | neuronal progenitor cells | RGDLGLS |
如(ru)若了解(jie)靶向(xiang)同(tong)一類細胞的所(suo)有血清型間的效果差異,請(qing)參(can)考Reference 2中(zhong)對應的參(can)考文獻。
目前AAV基(ji)(ji)因(yin)(yin)藥物的(de)(de)臨床(chuang)研究大(da)多數采用(yong)的(de)(de)是天(tian)然(ran)(ran)的(de)(de)衣殼(ke),這些衣殼(ke)極易(yi)成(cheng)為(wei)宿主酶的(de)(de)作用(yong)靶點(dian)(dian),從而(er)(er)影響(xiang)它(ta)們的(de)(de)整(zheng)體(ti)性(xing)能。此(ci)外(wai),天(tian)然(ran)(ran)AAV血清型(xing)具有組織親噬性(xing),但通常(chang)趨向性(xing)比較廣泛。因(yin)(yin)此(ci),必須使(shi)用(yong)高(gao)劑(ji)量(liang)(liang)的(de)(de)病(bing)毒(du)才能達到治療效(xiao)果。而(er)(er)且,AAV載體(ti)的(de)(de)包裝容量(liang)(liang)和大(da)多數人群中已存的(de)(de)中和抗(kang)體(ti)進一(yi)步限制了(le)AAV的(de)(de)臨床(chuang)應用(yong)。為(wei)了(le)克服這些限制,科學工(gong)作者(zhe)將(jiang)研究的(de)(de)重點(dian)(dian)聚焦在工(gong)程(cheng)化AAV,以進一(yi)步提高(gao)其安全性(xing)、有效(xiao)性(xing)和特異性(xing),從而(er)(er)推動(dong)基(ji)(ji)因(yin)(yin)治療領(ling)域的(de)(de)快(kuai)(kuai)速(su)發(fa)展(zhan)。在當今(jin)基(ji)(ji)因(yin)(yin)治療的(de)(de)研究熱潮下,為(wei)了(le)加快(kuai)(kuai)您的(de)(de)科研進程(cheng),我們建立了(le)工(gong)程(cheng)化AAV庫,旨(zhi)在為(wei)基(ji)(ji)因(yin)(yin)治療的(de)(de)發(fa)展(zhan)貢(gong)獻自己的(de)(de)一(yi)份力。
6.參考文獻
1. Lugin, M. L., et al. (2020). "Synthetically Engineered Adeno-Associated Virus for Efficient, Safe, and Versatile Gene Therapy Applications." ACS Nano 14(11): 14262-14283.
2. Buning, H. and A. Srivastava (2019). "Capsid Modifications for Targeting and Improving the Efficacy of AAV Vectors." Mol Ther Methods Clin Dev 12: 248-265.
3. Pipe, S., et al. (2019). "Clinical Considerations for Capsid Choice in the Development of Liver-Targeted AAV-Based Gene Transfer." Mol Ther Methods Clin Dev 15: 170-178.
4. Tseng, Y. S. and M. Agbandje-McKenna (2014). "Mapping the AAV Capsid Host Antibody Response toward the Development of Second Generation Gene Delivery Vectors." Front Immunol 5: 9.
5. Gurda, B. L., et al. (2013). "Capsid antibodies to different adeno-associated virus serotypes bind common regions." J Virol 87(16): 9111-9124.