We have all been engulfed by the c金哥urrent SARS-CoV-2 pandem微費ic with the lives of mi船議llions affected. To date, COV光信ID-19 has resulted in almost 8 mi筆討llion confirmed cases with o志體ver 400,000 deaths. Considerabl吃算e effort and money have been 媽的invested in trying to understa花業nd the mode of infectio做和n, pathogenicity and immune re頻火activity in order to develop th街的erapeutics and vaccines.
Mice have been studied in the labo熱廠ratory for over 100 years and du可離e to their genetic simi章小larity with human時睡s, have proven to be the家制 model organism of cho懂月ice for understandi友錯ng human development, homeostasis路間 and disease. The lack of useful mouse 船商models to study COVID-19 is compounded 睡南by the fact that司去 mouse ACE2 pro文的tein, unlike ACE2 in human and b習黃at that acts as the receptor for SARS-C小分oV-2 entry (1), does not 就公facilitate cell來照ular entry of SARS-CoV-2 in m也對ouse (2). This is analogous 年購to MERS-CoV, which was also sh志電own to be incapable of很計 infecting murine c身喝ells, leading several groups to 坐知develop mouse models that can facilit商去ate viral entry (3冷就,4). This included the g小大eneration of a tr他錯ansgenic knockin mouse that expresses不水 the MERS-CoV receptor 商新DPP4 and a model whereby mice a門動re transduced with adenovirus c上現arrying the hum請那an DPP4 gene, t風放hus sensitizing 湖開them to MERS-CoV infection. Such 用線models successfully recapitulat熱麗ed the human diseas信為e as did SARS mouse models expressin們河g human ACE2 (hACE2) (5). However, the商光 use of such hACE2 mode東爸ls to study the current SARS-照南CoV-2 appears restr文做icted as demonstrate也厭d by poor pathogen師山esis. The develop制了ment of a new mouse mo學動del that displays計北 the hallmarks of COVID-19 upo女是n SARS-CoV-2 infection is cle個弟arly of importance.
Adenovirus is a 制很preferred system for gene deliv車多ery into most mammalian cel匠業ls since it does not integra東鄉te into the genome and, b外人y design, is ren分店dered replication incompetent. In 呢要a very recent paper, Sun et al 下錯(6) modified an exist信自ing approach (7) to develop a COVID-19空業 mouse model whereby adenoviru內醫s expressing hACE2 under the cont雜影rol of a CMV promoter (Ad話女5-ACE2) is administer嗎窗ed intranasally to靜爸 6-8 week old BALB/c mice followed by我話 infection with SARS山嗎-CoV-2 isolated from COVID-19 pat坐商ients. In line with pre如飛vious work (8,9), hACE2 expression 去關was observed in the alveolar epithe路著lium and to a l窗少esser extent the湖笑 airway epithelium.&nb金有sp; In contrast to contro門車l mice that only rec秒冷eived empty Ad5 virus, Ad5-ACE2-transd術窗uced and SARS-CoV-2-in喝線fected BALB/c mice developed p低你neumonia, characterised by breath上家ing difficulties and s來鐵ignificant (20%) weight loss. Im頻爸portantly, C57BL/6 mice, which, unli也化ke BALB/c, are not immunocompr兒妹omised, showed a similar ph錯好enotype. Lung pathology o司南f both models revealed inf友道lammatory infiltrate得雜s, necrosis and alveolar edema consi明風stent with recent reports of severe森知 gross lung damage in SARS-CoV-2 huma樹樹n lungs.
To better understand how SARS-CoV-2 int紙飛eracts with the innate immune sys月場tem, knockout (KO) mice師電 lacking components of民如 the interferon-1 (IFN-1) signallin多你g pathway were infe輛報cted with SARS-CoV-2 f土歌ollowing sensiti化鄉zation with Ad5-ACE2. Genetic deplet船些ion of interfer好件on-α/β receptor (IFNAR-/- mice) 男笑led to delayed viral clearance and atte從黃nuated inflammation in contras樂如t to mice lacking type II I國妹FN (IFN-γ), which remain裡理ed asymptomatic. A more d畫北ramatic phenotype was ob西男served in STAT1 KO mice with SARS-CoV-志這2 infection leading to exacerbate從樹d weight loss, enhanced lung i地厭nflammation and delayed virus clea司看rance. In support of開子 previous work, a pr服答otective role of IFN-1 against SAR林筆S-CoV-2 was proposed since pr高秒e-treatment of mice w話業ith the potent IFN-1 inducer r如習esulted in a better 件們clinical outcome.
To identify changes in gene expre拍一ssion resulting from 愛時SARS-CoV-2 infe話我ction, lungs from Ad5-ACE2-transd朋大uced mice were anal唱路ysed by RNA-Seq 2 da大照ys post-infection. A total of 間門3056 genes differentiall我綠y expressed compared to Ad下校5-Empty transduced mice were observed. 呢船Consistently, genes associat金又ed with inflamm弟理ation and innate美錯 and adaptive immunity we路微re upregulated together照長 with genes involved in媽笑 T cell migration行說 (CD4 and CD8). Im照讀muno-depletion of CD4+ and CD8+商相 T cells confirmed the requir費公ement for both arms鐘習 of the immune respons謝高e. T cell epitopes were identified 醫站in the N protein and S1 region of the S煙什 protein, as demon校銀strated by the respon中些se of T cells harvested fr有家om infected mou得他se lungs to peptide pools enco森樂mpassing SARS-CoV-2 s什呢tructural and accessory 腦花ORFs. Additionally舞們, a number of c坐低ytokines and chemokin林人es shown to be ov有自er expressed in COVID-19 patients (10)做電 were also upregulated.
Therapeutic intervention市自 and vaccine deve話又lopment were evalua也村ted with detection of neutralizi歌鄉ng antibodies in mice sensit國老ized to Ad5-hACE2. Using the V家匠enezuelan equin廠來e encephalitis repli資算con particle (VRP) v路微accine platform, SARS-CoV-2 titers we個跳re greatly reduced in BALB/c an山湖d C57BL/6 models following i北銀mmunization with VRPs e師自xpressing SARS-雜什CoV-2 spike protei討月n (VRP-S). 坐姐 In contrast, no increase in男術 virus clearance was o爸答bserved following新數 immunization with VRPs expressi大厭ng transmembrane, nucleocapsid or e外市nvelope proteins of SARS-CoV-2制山. The potential therapy of 自個plasma transfer was also c微他haracterised in Ad5-hACE2 mice 報低with plasma from 3 C雨很OVID-19 patients adm也綠inistered one day prior to inf時跳ection. Compared to plasma from a non-上如infected donor, plasma from SARS-Co熱高V-2 infected patients prevented we金年ight loss and lung damage together w小分ith increased v那為irus clearance. No effect was ob離暗served with plasma from patients who知西 survived infec舊自tions of SARS a到月nd MERS. Lastly, a similar reg呢光ime was applied for treatment 下大of the U.S. Food家姐 and Drug Administration approved drug,家藍 Remdesivir. Treatment with Remdesivir 計可improved clinical outcome in infecte歌公d Ad5-hACE2-tran鄉快sduced mice.
In summary, the work here de理路scribes a mouse model that recapi司長tulates pneumonia seen in COVID-19 pa海上tients. Further studies are requir門畫ed for understandin學會g the different contr報刀ibutions of STAT and IFN-1 signalling 放空as is the need to address target刀山ing of non-pulmonary target cells (1師可1). However, this n都舞ewly developed SARS-CoV-2 sensitization計腦 model, together w唱校ith a similar mo內老del by Hassan e還刀t al (12), should prove extrem刀在ely useful for deciphe那票ring the molecular媽高 mechanisms involve為個d in viral clearance as well as ther對見apeutic interventi弟場on and vaccine development黑大.
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