1.研究背景
基因治療是一種新型的治療手段,它可以治療多種疾病,包括癌癥、遺傳性疾病、神經(jīng)性疾病、感染性疾病、心血管疾病和自身免疫性疾病等,它針對(duì)的是疾病的根源而不僅僅是疾病的癥狀。如此有效的治療方法有什么特殊性呢?其實(shí)很簡單,它就是將外源正常基因借助一定的技術(shù)或者載體導(dǎo)入靶細(xì)胞,從而糾正或補(bǔ)償缺陷和異?;蛞鸬募膊?,以達(dá)到治療疾病的目的(圖1)。
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圖1:基因治療的示意圖(來源于:https://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(shí)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(yàn)數(shù)據(jù)庫(ClinicalTrials.gov)中的一系列臨床前和臨床研究均證實(shí)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(jìn)化的。而且,體內(nèi)預(yù)存的中和抗體和AAV載體的承載能力進(jìn)一步限制了AAV載體的廣泛應(yīng)用。目前,科學(xué)家們研究的重點(diǎn)主要集中在工程化AAV載體,用于提高其安全性、靶向性和轉(zhuǎn)導(dǎo)效率。工程化AAV載體的構(gòu)建方法多種多樣,本篇我們將重點(diǎn)跟大家分享衣殼修飾的工程化AAV載體(圖3)。
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圖3:工程化AAV載體的示意圖
2.AAV基因組結(jié)構(gòu)
了解AAV基因組結(jié)構(gòu)是構(gòu)建工程化AAV的基礎(chǔ)。野生型AAV含有約4.7kb的單鏈線性DNA基因組,三個(gè)基因Rep, Cap和X的兩端各由145bp的ITR組成,可形成T型的發(fā)夾結(jié)構(gòu)(圖4)。Rep基因編碼病毒轉(zhuǎn)錄調(diào)控、復(fù)制和包裝必需的四個(gè)調(diào)控蛋白:Rep78, Rep68, Rep52 和Rep40。Cap基因編碼三個(gè)重疊的結(jié)構(gòu)蛋白(VP1, VP2, VP3,其表達(dá)比例為1:1:10)和VPs入核必需的裝配激活蛋白AAP(assembly-activating protein)。X基因編碼基因組復(fù)制中具有支持功能的蛋白質(zhì)。
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圖4:AAV2載體的基因組結(jié)構(gòu)
(Buning, H. and A. Srivastava (2019). Mol Ther Methods Clin Dev 12: 248-265.)
3.AAV衣殼結(jié)構(gòu)
AAV衣殼結(jié)構(gòu)的解析有助于理解AAV如何感染細(xì)胞和確定工程化AAV衣殼修飾的位置。腺相關(guān)病毒的衣殼呈T=1二十面體(二十面體是由20個(gè)三角形圍成的凸多面體,每5個(gè)三角形圍出一個(gè)五倍頂,通過每一對(duì)相對(duì)著的五倍頂有一個(gè)五倍旋轉(zhuǎn)軸;通過每一對(duì)相對(duì)著的三角形中心有1個(gè)三倍旋轉(zhuǎn)軸;通過每一對(duì)相對(duì)著的棱的中點(diǎn)有1個(gè)二倍旋轉(zhuǎn)軸)。它由60個(gè)VP單體通過這些旋轉(zhuǎn)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(gòu)成。
AAV衣殼表面的顯著特征是二倍凹地,三倍凸起和五倍通道(圖5)。圓柱形通道連通衣殼內(nèi)外,是AAV DNA進(jìn)入衣殼的地方,它參與 Rep 蛋白結(jié)合、衣殼蛋白裝配、VP1 N 末端外露、AAV病毒感染等多個(gè)過程;二倍凹地是病毒衣殼最薄的地方;三倍凸起的主要作用是識(shí)別受體。
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圖5:由60個(gè)VP3裝配成的AAV2衣殼的拓?fù)浣Y(jié)構(gòu)
(Tseng, Y. S. and M. Agbandje-McKenna (2014). Front Immunol 5: 9.)
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圖6:AAV2 VP3單體的拓?fù)浣Y(jié)構(gòu)。9個(gè)VRs被用不同的顏色標(biāo)記:
I,紫色;II,藍(lán)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.衣殼修飾的工程化AAV
特定的VP亞基已被作為衣殼修飾的靶點(diǎn),例如去除免疫原基序,整合標(biāo)簽或熒光基團(tuán)和重新靶向等。
AAV2是研究相對(duì)成熟的血清型。以AAV2為骨架,在公共VP3區(qū),大量研究表明,I-587(VP1氨基酸數(shù))和I-588為較常用的衣殼修飾位置,因?yàn)檫@2個(gè)位置地處三倍凸起附近,可以接受長達(dá)34個(gè)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(jié)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(xiàn)擁有表1所列的所有AAV Cap質(zhì)粒,數(shù)量近70種,可直接進(jìn)行AAV病毒包裝。
包裝表1所列AAV血清型,年中讓利僅需8折,還送免費(fèi)對(duì)照!
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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 |
除了I-587和I-588外,I-453、I-520&I-584、I-584、I-585也已被成功用于開發(fā)新細(xì)胞靶向性工程化AAV(表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 |
正如研究背景中所述,體內(nèi)預(yù)存中和抗體是限制AAV廣泛臨床應(yīng)用的一大障礙。血清學(xué)研究表明,大多數(shù)人都接觸過野生型AAV,因此體內(nèi)可能已經(jīng)形成針對(duì)AAV的中和抗體。這些中和抗體可能會(huì)干擾AAV進(jìn)入靶細(xì)胞、細(xì)胞內(nèi)運(yùn)輸和細(xì)胞核內(nèi)的解包裝,從而阻止了轉(zhuǎn)導(dǎo)。據(jù)報(bào)道,抗AAV抗體在人群中的流行率約為40-80%。其中,抗AAV2的中和抗體在人群中相對(duì)更流行。為了克服這個(gè)障礙,科學(xué)工作者以其他低免疫原性血清型為骨架,并參考AAV2的衣殼修飾位點(diǎn),開發(fā)了一系列新的工程化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 |
如若了解靶向同一類細(xì)胞的所有血清型間的效果差異,請參考Reference 2中對(duì)應(yīng)的參考文獻(xiàn)。
目前AAV基因藥物的臨床研究大多數(shù)采用的是天然的衣殼,這些衣殼極易成為宿主酶的作用靶點(diǎn),從而影響它們的整體性能。此外,天然AAV血清型具有組織親噬性,但通常趨向性比較廣泛。因此,必須使用高劑量的病毒才能達(dá)到治療效果。而且,AAV載體的包裝容量和大多數(shù)人群中已存的中和抗體進(jìn)一步限制了AAV的臨床應(yīng)用。為了克服這些限制,科學(xué)工作者將研究的重點(diǎn)聚焦在工程化AAV,以進(jìn)一步提高其安全性、有效性和特異性,從而推動(dòng)基因治療領(lǐng)域的快速發(fā)展。在當(dāng)今基因治療的研究熱潮下,為了加快您的科研進(jìn)程,我們建立了工程化AAV庫,旨在為基因治療的發(fā)展貢獻(xiàn)自己的一份力。
6.參考文獻(xiàn)
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.