來(lái)自美國(guó)基因科技公司(GENENTECH INC.)的研究人員在新研究中繞過(guò)抗體合成的常規(guī)法則,，合成了一種能夠通過(guò)血腦屏障的且具有雙特異性的新型基因工程抗體,。這一新技術(shù)或可在將來(lái)推動(dòng)科學(xué)家們開(kāi)發(fā)出基于抗體的腦病治療新方法。研究人員在5月25日的《科學(xué)—轉(zhuǎn)化醫(yī)學(xué)》（Science Translational Medicine）同時(shí)發(fā)表了兩篇文章，詳述地描述了這一抗體的設(shè)計(jì)過(guò)程,。
抗體是生物體內(nèi)免疫系統(tǒng)用于中和有害的外源物質(zhì)的一種特異的蛋白質(zhì),，捕獲天然抗體或人工制備高度特異性的抗體一直是蛋白質(zhì)組學(xué)研究中的熱點(diǎn)領(lǐng)域,。近年來(lái)各個(gè)研究機(jī)構(gòu)及企業(yè)的研究人員也在致力于構(gòu)建具有多靶向性的抗體,。
“合成雙特異性抗體的新浪潮即將來(lái)到，”Genentech公司的神經(jīng)生物學(xué)家Ryan Watts說(shuō)道：“它們將成為這一領(lǐng)域中的研究熱點(diǎn),。”
血腦屏障是機(jī)體參與固有免疫的一個(gè)重要的內(nèi)部屏障,，它能夠阻擋病原生物和其他大分子由血循環(huán)進(jìn)入腦組織和腦室,。從而保護(hù)腦組織避免循環(huán)血液中有毒物質(zhì)的損害,。由于抗體通常無(wú)法通過(guò)血腦屏障,，因此在大腦中抗體的濃度約比在血液中要低一千倍,。
在新研究中,，Watts等合成了一種能通過(guò)血腦屏障且具有雙蛋白質(zhì)靶向性的抗體。其靶向的β分泌酶（β-secretase）是當(dāng)前阿爾茨海默癥治療的一個(gè)重要的藥物開(kāi)發(fā)靶點(diǎn),。過(guò)去的研究證實(shí)β-secretase在大腦的淀粉樣肽生成中起重要作用,。
這一抗體靶向的第二種蛋白質(zhì)則是轉(zhuǎn)鐵蛋白受體（transferrin receptor）。在正常情況轉(zhuǎn)鐵蛋白受體可通過(guò)與轉(zhuǎn)鐵蛋白的相互作用介導(dǎo)大腦中的鐵攝取,。研究人員利用轉(zhuǎn)鐵蛋白將抗體輸送至大腦中，從而確保其能在大腦中作用于β-secretase,。
研究人員證實(shí)這種雙特性抗體能在阿爾茨海默癥模型小鼠中很好地發(fā)揮作用,。在每天接受一次抗體注射后,，小鼠大腦中的β淀粉樣蛋白的濃度下降了47%。
“我們?cè)O(shè)計(jì)合成這一新型抗體是基于一種獨(dú)特的理念,，挑戰(zhàn)了抗體工程中的一個(gè)重要的法則,，”Watts說(shuō),。
抗體與抗原之間的相互作用力通常被稱(chēng)之為抗體的親和力（affinity）。親和力越高則表明抗體與抗原之間的相互作用力越強(qiáng),。長(zhǎng)期以來(lái)大多數(shù)的抗體工程技術(shù)人員都致力于合成出具有高親和力的抗體,，從而確?？贵w能與抗原緊密的結(jié)合,。
Watts和另一位抗體工程人員Mark Dennis在最初是希望能夠合成出對(duì)轉(zhuǎn)鐵蛋白具有高親和力的抗體,。然而他們卻發(fā)現(xiàn)這些高親和力的抗體被阻止在血管中無(wú)法通過(guò)腦組織。Dennis由此推測(cè)抗體有可能是被轉(zhuǎn)鐵蛋白受體截留在了血管中,，于是他開(kāi)始設(shè)計(jì)合成低親和力的抗體,。正如Dennis所預(yù)想的一樣,，合成的低親和力抗體能夠更廣泛地分布到大腦中,。
“這是一個(gè)極好的范例，它表明在考慮多特異性蛋白質(zhì)治療時(shí),，我們必須拋開(kāi)某些我們從單克隆抗體中學(xué)習(xí)到的規(guī)則和模式,，”這一研究的負(fù)責(zé)人David Hilbert說(shuō)。
目前Hilbert正在努力研發(fā)能同時(shí)識(shí)別5種不同靶蛋白的多特異性抗體,。Hilbert認(rèn)為多特異性抗體的設(shè)計(jì)理念還可運(yùn)用到其他的領(lǐng)域，例如癌干細(xì)胞中,。科學(xué)家們通常根據(jù)其表達(dá)的細(xì)胞表面標(biāo)志蛋白來(lái)識(shí)別癌干細(xì)胞,。然而由于這些表面標(biāo)志有時(shí)候也存在于其他的一些健康細(xì)胞中,。常規(guī)的高親和力單克隆抗體會(huì)在靶向癌細(xì)胞的同時(shí)殺傷健康細(xì)胞,，而低親和力的多靶向性抗體則能夠更具有選擇性地靶向癌干細(xì)胞,。（生物谷Bioon.com）
生物谷推薦原文：
Science Translational Medicine DOI： 10.1126/scitranslmed.3002254
A Therapeutic Antibody Targeting BACE1 Inhibits Amyloid-β Production in Vivo
Atwal, Jasvinder K.; Chen, Yongmei; Chiu, Cecilia; Mortensen, Deborah L.; Meilandt, William J.; Liu, Yichin; Heise, Christopher E.; Hoyte, Kwame; Luk, Wilman; Lu, Yanmei; Peng, Kun; Wu, Ping; Rouge, Lionel; Zhang, Yingnan; Lazarus, Robert A.; Scearce-Levie, Kimberly; Wang, Weiru; Wu, Yan; Tessier-Lavigne, Marc; Watts, Ryan J.
Reducing production of amyloid-β (Aβ) peptide by direct inhibition of the enzymes that process amyloid precursor protein (APP)is a central therapeutic strategy for treating Alzheimer’s disease. However, small-molecule inhibitors of the β-secretase(BACE1) and γ-secretase APP processing enzymes have shown a lack of target selectivity and poor penetrance of the blood-brainbarrier (BBB). Here, we have developed a high-affinity, phage-derived human antibody that targets BACE1 (anti-BACE1) and isanti-amyloidogenic. Anti-BACE1 reduces endogenous BACE1 activity and Aβ production in human cell lines expressing APP andin cultured primary neurons. Anti-BACE1 is highly selective and does not inhibit the related enzymes BACE2 or cathepsin D.Competitive binding assays and x-ray crystallography indicate that anti-BACE1 binds noncompetitively to an exosite on BACE1and not to the catalytic site. Systemic dosing of mice and nonhuman primates with anti-BACE1 resulted in sustained reductionsin peripheral Aβ peptide concentrations. Anti-BACE1 also reduces central nervous system Aβ concentrations in mouse and monkey,consistent with a measurable uptake of antibody across the BBB. Thus, BACE1 can be targeted in a highly selective manner throughpassive immunization with anti-BACE1, providing a potential approach for treating Alzheimer’s disease. Nevertheless, therapeuticsuccess with anti-BACE1 will depend on improving antibody uptake into the brain.
Science Translational Medicine DOI： 10.1126/scitranslmed.3002230
Boosting Brain Uptake of a Therapeutic Antibody by Reducing Its Affinity for a Transcytosis Target
Yu, Y. Joy; Zhang, Yin; Kenrick, Margaret; Hoyte, Kwame; Luk, Wilman; Lu, Yanmei; Atwal, Jasvinder; Elliott, J. Michael; Prabhu, Saileta; Watts, Ryan J.; Dennis, Mark S.
Monoclonal antibodies have therapeutic potential for treating diseases of the central nervous system, but their accumulationin the brain is limited by the blood-brain barrier (BBB). Here, we show that reducing the affinity of an antibody for thetransferrin receptor (TfR) enhances receptor-mediated transcytosis of the anti-TfR antibody across the BBB into the mousebrain where it reaches therapeutically relevant concentrations. Anti-TfR antibodies that bind with high affinity to TfR remainassociated with the BBB, whereas lower-affinity anti-TfR antibody variants are released from the BBB into the brain and showa broad distribution 24 hours after dosing. We designed a bispecific antibody that binds with low affinity to TfR and withhigh affinity to the enzyme β-secretase (BACE1), which processes amyloid precursor protein into amyloid-β (Aβ) peptides includingthose associated with Alzheimer’s disease. Compared to monospecific anti-BACE1 antibody, the bispecific antibody accumulatedin the mouse brain and led to a greater reduction in brain Aβ after a single systemic dose. TfR-facilitated transcytosis ofthis bispecific antibody across the BBB may enhance its potency as an anti-BACE1 therapy for treating Alzheimer’s disease.
