抗H9亚型禽流感病毒血凝素单克隆抗体的制备和鉴定

目的:获得分泌抗H9亚型禽流感病毒(AIV)血凝素单克隆抗体的杂交瘤细胞。方法:以H9N2亚型AIV为免疫原,免疫6～8周龄雌性BALB/c小鼠,取其脾细胞与骨髓瘤细胞Sp2/0-Ag-14,在PEG4000的作用下进行细胞融合,通过血凝抑制(HI)试验筛选分泌抗H9亚型AIV血凝素单克隆抗体的杂交瘤细胞。结果:经过连续3～4次克隆化,获得能稳定分泌抗H9亚型AIV血凝素的单克隆抗体细胞系6株,分别命名为1B2、1C10、1G2、2B7、2E3和5E11。6株细胞培养上清HI效价为24～28,腹水HI效价为210～213。除1G2为IgM外,其余5株均为IgG1。Western blotting结果显示,1B2、1C10、2B7和2E3能与AIVH9蛋白在Mr为75000处反应,表明其是针对AIVH9亚型血凝素蛋白的单抗。特异性试验表明该6株单抗均只与H9亚型AIV发生特异性HI反应,而不与其他14个HA亚型的AIV及新城疫病毒、传染性支气管炎病毒发生交叉反应,显示出良好的特异性。结论:制备了针对H9亚型禽流感病毒血凝素的单克隆抗体,为禽流感的快速诊断和病毒的抗原性分析等奠定了基础。     

一株抗H5亚型禽流感病毒血凝素蛋白单克隆抗体的广谱中和活性

以H5N1禽流感病毒株Ck/HK/Yu22/02作为抗原,应用常规杂交瘤技术和血凝抑制实验筛选出抗H5亚型禽流感病毒血凝素蛋白的单抗8H5,单抗8H5经免疫荧光鉴定具有很好的H5特异性.选择33株2002～2006年不同地域,不同宿主中分离的不同遗传变异亚系的H5N1病毒代表株,对单抗8H5分别进行血凝抑制实验及中和试验分析,结果显示单抗8H5对所有H5亚型病毒均有较强反应,而对非H5亚型标准病毒株均不反应,说明8H5是一株广谱性抗H5特异性中和单抗,并提示单抗8H5的HA识别表位可能是一个相当保守的中和表位.并且单抗8H5双抗夹心系统的初步评价显示了其在诊断应用上的前景.     

H5亚型禽流感病毒单抗-生物素捕获ELISA的建立

目的建立一种单克隆抗体介导的、经生物素—亲和素系统放大的H5亚型禽流感病毒捕获ELISA检测方法,为进一步研究检测试剂盒提供基础。方法用亲和层析法纯化抗禽流感病毒H5亚型血凝素单克隆抗体,包被微量反应板,用于捕获病毒抗原,再用生物素标记的单抗和酶标亲和素来检测病毒血凝素抗原,经方阵试验优化ELISA反应体系。用该方法检测H1—H15亚型AIV标准毒株和H5、H7、H9亚型AIV分离株,并与血凝和血凝抑制试验比较,评价其敏感性和特异性。结果纯化后的单抗具有良好的反应活性,生物素标记单抗工作浓度为1∶5000;ELISA对H5亚型AIV的检出限为025个血凝单位。该ELISA反应体系能检出H5N3标准株和所有20株国内H5亚型AIV分离株,而与其他14个血凝素亚型的AIV标准株、15个H9亚型AIV分离株和2个H7亚型AIV分离株均无交叉反应。结论初步建立了检测H5亚型禽流感病毒的单抗—生物素捕获ELISA方法,为研制试剂盒和进一步应用试验提供了基础。     

抗禽流感病毒H5N1亚型单克隆抗体制备初报

目的制备禽流感H5N1亚型病毒的单克隆抗体,为相关研究提供工具。方法以禽流感H5N1亚型病毒免疫BALBc小鼠,取其脾细胞和SP20细胞融合,用血凝抑制试验(HI)和酶联免疫反应(ELISA)检测培养上清,并将阳性融合细胞稀释克隆化3次直至100%孔均为阳性,筛选阳性克隆株,运用免疫荧光法评估单克隆抗体检测病毒感染的犬肾细胞(MDCK)。结果得到三株稳定分泌抗体的细胞并命名为F8、F9、G11,抗体亚型鉴定结果分别为IgG1、IgG2a和IgG2b;在免疫荧光法单克隆抗体能够检测出感染MDCK细胞的病毒。结论建立了3株抗禽流感H5N1亚型病毒的单克隆抗体细胞株,其产生的一株高特异性的McAbG11能够用于H5N1亚型禽流感病毒感染诊断,并可能应用于禽流感病毒H5N1亚型感染的防治。     

抗H5N1亚型禽流感病毒血凝素单克隆抗体的制备及鉴定

目的建立稳定分泌抗H5N1亚型禽流感病毒血凝素单克隆抗体的杂交瘤细胞系,为进一步研究禽流感诊断技术奠定基础。方法以纯化的H5亚型禽流感病毒按常规方法免疫BALBc小鼠,最后一次免疫后第3天取其脾细胞与SP20细胞在聚乙二醇作用下融合,用选择性培养、有限稀释法克隆和血凝抑制试验进行筛选,对获得阳性克隆株用ELISA方法进行亚型鉴定,并用37株H5、H7、H9亚型AIV测定其特异性、覆盖性。结果最后获得了3株分泌特异性抗体的杂交瘤细胞,命名为1E5、4A4、4B1,经长期体外培养和冻存后复苏能稳定地分泌抗体。经鉴定,其亚型均为IgG1、kappa链。腹水HI效价1∶210～1∶216,细胞培养上清HI效价1∶26～1∶28。3株杂交瘤所分泌的单克隆抗体均能与本中心保存的全部20株H5亚型禽流感病毒分离株发生反应,而与15株H9亚型禽流感病毒分离株、2株H7亚型禽流感病毒分离株以及H1H4、H6H15亚型禽流感病毒标准毒株均不反应,与鸡新城疫病毒、鹅新城疫病毒、鹅腺病毒和鸡产蛋下降综合征病毒等均无交叉反应。结论所获3株单克隆抗体可用于禽流感病毒特异性诊断试剂的研制。     

人源中和性抗高致病性禽流感病毒H5N1基因工程全抗体的研制

运用噬菌体表面呈现技术,从禽流感病人恢复期血中获得淋巴细胞,通过基因工程手段,构建了人源抗H5NI禽流感病毒基因工程抗体文库.用纯化的人源H5N1禽流感病毒颗粒(A/Anhui/1/2005)及重组血凝素蛋白HA(A/Viet Nam/1203/2004)对Fab噬菌体抗体库进行富集筛选,成功地获得了抗禽流感病毒H5N1血凝素蛋白HA的人源单抗Fab段基因,并在大肠杆菌中获得有效表达.通过序列测定确定抗体轻重链型别,然后将阳性克隆的轻链和重链Fd段基因分别克隆入全抗体表达载体pAC-L-Fc后转染昆虫Sf9细胞,利用杆状病毒/昆虫细胞系统实现全抗体的分泌型表达.用ELISA、IFA和流式细胞术对所获人源单抗的功能特性进行鉴定.结果表明,我们获得了2株特异性针对H5N1禽流感病毒血凝素蛋白HA而与甲1型和甲3型人流感病毒无交叉反应的人源单抗(AVFlulgG01、AVFlulgG03).微量中和试验结果表明,除A/Guangdong/1/2006外,AVFlu-IgG01能够广泛地中和HA基因进化上属于Clade 2的中国南方、北方及中部地区的H5N1禽流感病毒分离株,同时还对属于Clade Ⅰ的越南H5N1分离株A/Viet Nam/1203/2004具有中和活性;AVFluIgG03虽然不能中和A/Viet Nam/1203/2004,但是对属于Clade 2的所有中国H5N1分离株均具有中和作用.人源中和性抗禽流感病毒H5N1基因工程全抗体的获得不仅为高致病性禽流感病毒H5N1的预防和治疗带来了希望,同时也为其疫苗研制提供了新的思路.     

抗H5亚型禽流感病毒单链抗体在毕赤酵母中的分泌型表达和生物活性分析

在本实验室研制出的多株针对H5N1亚型禽流感血凝素单抗中,13D4单抗对所有H5亚型病毒均有血凝抑制和中和活性,具有特异性高、反应性强和识别广的特点,且在小鼠实验中显示了对各种代表株禽流感的感染和发病均具有良好的治疗效果。在此研究基础上,本实验通过基因工程构建含有13D4单链抗体(scFv)基因的毕赤酵母表达载体,实现目的蛋白的分泌性表达和纯化。经过竞争法和血凝抑制检测其活性,表明获得的单链抗体具有与原始鼠源抗体相近的反应活性和相同的识别表位。H5N1广谱中和单抗13D4的单链抗体的成功构建,为进一步研制针对H5N1禽流感病毒的治疗性抗体奠定了基础。     

高致病性禽流感病毒H5N1中和抗体的单链抗体构建与活性鉴定

在本实验室研制出的多株针对H5N1血凝素的鼠单抗中,10F7对34株H5N1病毒株都有血凝抑制和中和活性,具有特异性高、反应性强、识别谱广的特点。通过基因工程构建10F7单链抗体(scFv)表达重组质粒,在大肠杆菌中表达并纯化scFv,经血凝抑制实验及中和实验检测其活性。结果在针对3株病毒的血凝抑制实验中,10F7scFv蛋白对其中2株H5N1病毒均显示出结合活性,而对H9毒株没有反应。在针对7株H5N1病毒的中和实验中,10F7scFv对5株病毒具有较好的中和能力。H5N1广谱中和抗体10F7的单链抗体构建,为进一步研制针对H5N1禽流感病毒的治疗性抗体奠定了基础。     

甲型H1N1流感病毒血凝素蛋白单抗杂交瘤细胞株的制备与初步鉴定

目的:建立具有高特异、高效价的甲型H1N1流感病毒血凝素蛋白(HA)单抗的杂交瘤细胞株。方法:以纯化的昆虫杆状病毒表达的甲型H1N1流感病毒HA蛋白为免疫原免疫BALB/c小鼠,取脾细胞与Sp2/0小鼠骨髓瘤细胞融合,通过有限稀释法筛选阳性克隆,经ELISA和Western blot分析单抗的特性和特异性。结果:获得6株甲型H1N1流感HA抗原特异单克隆抗体杂交瘤细胞株,抗原肽库ELISA检测结果表明其中3株(1E12,3F12,1C11)单抗只与甲型H1N1流感HA抗原肽库反应,不与H5N1病毒HA抗原肽库反应;Western blot分析表明,单抗1B3只特异识别甲型H1N1流感HA抗原,而与其他季节性甲流病毒(H1,H3)及人禽流感H5N1病毒不反应。结论:所获杂交瘤细胞株特异性强,效价高,分泌抗体性能稳定,为分析甲型H1N1流感病毒抗原性位点、建立诊断试剂奠定了基础。     

H5N1型禽流感病毒广谱中和单克隆抗体的筛选及其中和机制初步研究

利用杆状病毒-昆虫细胞表达H5N1型禽流感病毒的血凝素蛋白(HA),纯化后的重组蛋白HA免疫小鼠并制备杂交瘤单克隆抗体,用H5N1型禽流感病毒的全病毒进行筛选,成功地获得了抗H5N1型禽流感病毒血凝素蛋白HA的单抗.MDCK细胞微量中和试验表明,单抗8G10D7可对clade2和clade9的H5N1型禽流感病毒起中和作用.Western-blot及血凝抑制实验进一步证明了该单抗的结合位点位于HA蛋白的HA1亚基上.鸡胚感染病毒预防试验结果表明,8G10D7对禽来源的和人来源的H5N1型禽流感病毒均可达到100%的保护率;在治疗试验组中,8G10D7对禽来源的病毒感染具有较高的保护率,可达100%,对人来源的H5N1型禽流感病毒最高也可达87.5%的保护率.该抗体的获得不仅为H5N1型高致病性禽流感病毒的预防和治疗带来了希望,同时其中和位点的发现也为以后亚单位疫苗的研制提供新的思路.     

Human monoclonal antibodies to pandemic 1957 H2N2 and pandemic 1968 H3N2 influenza viruses

Investigation of the human antibody response to the 1957 pandemic H2N2 influenza A virus has been largely limited to serologic studies. We generated five influenza virus hemagglutinin (HA)-reactive human monoclonal antibodies (MAbs) by hybridoma technology from the peripheral blood of healthy donors who were born between 1950 and 1968. Two MAbs reacted with the pandemic H2N2 virus, two recognized the pandemic H3N2 virus, and remarkably, one reacted with both the pandemic H2N2 and H3N2 viruses. Each of these five naturally occurring MAbs displayed hemagglutination inhibition activity, suggesting specificity for the globular head domain of influenza virus HA. When incubated with virus, MAbs 8F8, 8M2, and 2G1 each elicited H2N2 escape mutations immediately adjacent to the receptor-binding domain on the HA globular head in embryonated chicken eggs. All H2N2-specific MAbs were able to inhibit a 2006 swine H2N3 influenza virus. MAbs 8M2 and 2G1 shared the V(H)1-69 germ line gene, but these antibodies were otherwise not genetically related. Each antibody was able to protect mice in a lethal H2N2 virus challenge. Thus, even 43 years after circulation of H2N2 viruses, these subjects possessed peripheral blood B cells encoding potent inhibiting antibodies specific for a conserved region on the globular head of the pandemic H2 HA.     

Mapping of Epitopes Exposed on Intact Human Immunodeficiency Virus Type 1 (HIV-1) Virions: a New Strategy for Studying the Immunologic Relatedness of HIV-1

To study the antigenic conservation of epitopes of human immunodeficiency virus type 1 (HIV-1) isolates of different clades, the abilities of human anti-HIV-1 gp120 and gp41 monoclonal antibodies (MAbs) to bind to intact HIV-1 virions were determined by a newly developed virus-binding assay. Eighteen human anti-HIV MAbs, which were directed at the V2, V3 loop, CD4-binding domain (CD4bd), C5, or gp41 regions, were used. Nine HIV-1 isolates from clades A, B, D, F, G, and H were used. Microtiter wells were coated with the MAbs, after which virus was added. Bound virus was detected after lysis by testing for p24 antigen with a noncommercial p24 enzyme-linked immunosorbent assay. The anti-V3 MAbs strongly bound the four clade B viruses and viruses from the non-B clades, although binding was weaker and more sporadic with the latter. The degrees of binding by the anti-V3 MAbs to CXCR4- and CCR5-tropic viruses were similar, suggesting that the V3 loops of these two categories of viruses are similarly exposed. The anti-C5 MAbs bound isolates of clades A, B, and D. Only weak and sporadic binding of all the viruses tested with anti-CD4bd, anti-V2, and anti-gp41 MAbs was detected. These results suggest that V3 and C5 structures are shared and well exposed on intact virions of different clades compared to the CD4bd, V2, and gp41 regions.     

Epitope mapping of the hemagglutinin molecule of a highly pathogenic H5N1 influenza virus by using monoclonal antibodies

We mapped the hemagglutinin (HA) antigenic epitopes of a highly pathogenic H5N1 influenza virus on the three-dimensional HA structure by characterizing escape mutants of a recombinant virus containing A/Vietnam/1203/04 (H5N1) ΔHA and neuraminidase genes in the genetic background of A/Puerto Rico/8/34 (H1N1) virus. The mutants were selected with a panel of eight anti-HA monoclonal antibodies (MAbs), seven to A/Vietnam/1203/04 (H5N1) virus and one to A/Chicken/Pennsylvania/8125/83 (H5N2) virus, and the mutants’ HA genes were sequenced. The amino acid changes suggested three MAb groups: four MAbs reacted with the complex epitope comprising parts of the antigenic site B of H3 HA and site Sa of H1 HA, two MAbs reacted with the epitope corresponding to the antigenic site A in H3 HA, and two MAbs displayed unusual behavior: each recognized amino acid changes at two widely separate antigenic sites. Five changes were detected in amino acid residues not previously reported as changed in H5 escape mutants, and four others had substitutions not previously described. The HA antigenic structure differs substantially between A/Vietnam/1203/04 (H5N1) virus and the low-pathogenic A/Mallard/Pennsylvania/10218/84 (H5N2) virus we previously characterized (N. V. Kaverin et al., J. Gen. Virol. 83:2497-2505, 2002). The hemagglutination inhibition reactions of the MAbs with recent highly pathogenic H5N1 viruses were consistent with the antigenic-site amino acid changes but not with clades and subclades based on H5 phylogenetic analysis. These results provide information on the recognition sites of the MAbs widely used to study H5N1 viruses and demonstrate the involvement of the HA antigenic sites in the evolution of highly pathogenic H5N1 viruses, findings that can be critical for characterizing pathogenesis and vaccine design.     

Detection of circulating Asian H5N1 viruses by a newly established monoclonal antibody

Monoclonal antibodies (MAbs) against the recently emerged Asian H5N1 virus (A/crow/Kyoto/53/2004) were generated. From five anti-hemagglutinin (HA) MAbs, four antibodies (3C11, 4C12, 3H12, and 3H4) broadly in vitro recognized and neutralized H5 subtypes, including H5N1. By contrast, the 4G6 MAb specifically reacted with H5N1-HA and not with H5N2- or H5N3-HAs from previous epidemics. The 4G6 MAb was useful for immunofluorescence assays but not for immunoblotting, suggesting that this antibody recognizes a conformational epitope of the H5N1-HA protein. An intensive epitope-mapping analysis demonstrated that the 4G6 MAb recognizes Asp59, which is highly conserved among currently circulating H5N1 lineages. Further, a 4G6-based antigen capture enzyme-linked immunosorbent assay detected H5N1 even that derived from clade 2.2 (A/chicken/Egypt/CL-61/2007) from infected chicken lung before virus isolation. Taken together, these results suggest that the established MAbs, especially 4G6, are useful for rapid and specific detection of Asian H5N1 viruses.     

Molecular Basis for Broad Neuraminidase Immunity: Conserved Epitopes in Seasonal and Pandemic H1N1 as Well as H5N1 Influenza Viruses

Influenza A viruses, including H1N1 and H5N1 subtypes, pose a serious threat to public health. Neuraminidase (NA)-related immunity contributes to protection against influenza virus infection. Antibodies to the N1 subtype provide protection against homologous and heterologous H1N1 as well as H5N1 virus challenge. Since neither the strain-specific nor conserved epitopes of N1 have been identified, we generated a panel of mouse monoclonal antibodies (MAbs) that exhibit different reactivity spectra with H1N1 and H5N1 viruses and used these MAbs to map N1 antigenic domains. We identified 12 amino acids essential for MAb binding to the NA of a recent seasonal H1N1 virus, A/Brisbane/59/2007. Of these, residues 248, 249, 250, 341, and 343 are recognized by strain-specific group A MAbs, while residues 273, 338, and 339 are within conserved epitope(s), which allows cross-reactive group B MAbs to bind the NAs of seasonal H1N1 and the 1918 and 2009 pandemic (09pdm) H1N1 as well as H5N1 viruses. A single dose of group B MAbs administered prophylactically fully protected mice against lethal challenge with seasonal and 09pdm H1N1 viruses and resulted in significant protection against the highly pathogenic wild-type H5N1 virus. Another three N1 residues (at positions 396, 397, and 456) are essential for binding of cross-reactive group E MAbs, which differ from group B MAbs in that they do not bind 09pdm H1N1 viruses. The identification of conserved N1 epitopes reveals the molecular basis for NA-mediated immunity between H1N1 and H5N1 viruses and demonstrates the potential for developing broadly protective NA-specific antibody treatments for influenza.     

Fab MAbs specific to HA of influenza virus with H5N1 neutralizing activity selected from immunized chicken phage library

Hemagglutinin protein (HA) was considered to be the primary target for monoclonal antibody production. This protein not only plays an important role in viral infections, but can also be used to differentiate H5N1 virus from other influenza A viruses. Hence, for diagnostic and therapeutic applications, it is important to develop anti-HA monoclonal antibody (MAb) with high sensitivity, specificity, stability, and productivity. Nine unique Fab MAbs were generated from chimeric chicken/human Fab phage display library constructed from cDNA derived from chickens immunized with recombinant hemagglutinin protein constructed from H5N1 avian influenza virus (A/Vietnam/1203/04). The obtained Fab MAbs showed several characteristics for further optimization and development—three clones were highly specific to only H5N1 virus. This finding can be applied to the development of H5N1 diagnostic testing. Another clone showed neutralization activity that inhibited H5N1 influenza virus infection in Madin-Darby canine kidney (MDCK) cells. In addition, one clone showed strong reactivity with several of the influenza A virus subtypes tested. The conversion of this clone to whole IgG is a promising study for a cross-neutralization activity test.     

Tetrasialoganglioside GQ1b Reactive Monoclonal Antibodies: Their Characterization and Application for Quantification of GQ1b in Some Cell Lines of Neuronal and Adrenal Origin(S)

Seven monoclonal antibodies (MAbs) directed to tetrasialoganglioside (GQ1b) were established, purified GQ1b being used for immunization and hybridoma screening. All of the MAbs reacted strongly with GQ1b, although they also reacted with other gangliosides, with different specificities and reactivities. Some MAbs (1H10, 2C7, and 3F4) reacted with GD3, GT1a, GQ1b, and GP1c. MAb 1H4 showed broad specificity. It reacted with GD3, GD1b, GD2, GT1a, GT1b, GO1b, GQ1c, and GP1c. MAbs 7F5, 4E7, and 4F10 recognized GT1a, GQ1b, and GP1c. MAb 4F10 was more specific for GQ1b than the other MAbs. Using MAb 4F10, we determined, by means of an immunoassay, the quantities of endogenous GQ1b in some neuronal and adrenal cell lines, GOTO (human neuroblastoma), Neuro2a (mouse neuroblastoma), and PC12 (rat pheochromocytoma). PC12 and Neuro2a cells contained at least 5.1 X 10(6) and 3.9 X 10(5) molecules/cell of GQ1b, respectively. In contrast, no GQ1b was detected in GOTO cells, which are known for their specific neuritogenic response to this particular ganglioside when exogenously added.     

Cross-protection of newly emerging HPAI H5 viruses by neutralizing human monoclonal antibodies: A viable alternative to oseltamivir

Newly emerging highly pathogenic avian influenza (HPAI) H5N2, H5N3, H5N5, H5N6, H5N8 and H5N9 viruses have been spreading in poultry and wild birds. The H5N6 viruses have also caused 10 human infections with 4 fatal cases in China. Here, we assessed the cross-neutralization and cross-protection of human and mouse monoclonal antibodies against 2 viruses: a HPAI H5N8 virus, A/chicken/Netherlands/14015526/2014 (NE14) and a HPAI H5N6 virus, A/Sichuan/26221/2014 (SC14). The former was isolated from an infected chicken in Netherlands in 2014 and the latter was isolated from an infected human patient in Sichuan, China. We show that antibodies FLA5.10, FLD21.140, 100F4 and 65C6, but not AVFluIgG01, AVFluIgG03, S139/1 and the VRC01 control, potently cross-neutralize the H5N8 NE14 and H5N6 SC14 viruses. Furthermore, we show that a single injection of >1 mg/kg of antibody 100F4 at 4 hours before, or 20 mg/kg antibody 100F4 at 72 hours after, a lethal dose of H5N8 NE14 enables mice to withstand the infection. Finally, we show that a single injection of 0.5 or 1 mg/kg antibody 100F4 prophylactically or 10 mg/kg 100F4 therapeutically outperforms a 5-day course of 10 mg/kg/day oseltamivir treatment against lethal H5N8 NE14 or H5N6 SC14 infection in mice. Our results suggest that further preclinical evaluation of human monoclonal antibodies against newly emerging H5 viruses is warranted.     

Critical epitopes in transmissible gastroenteritis virus neutralization.

Purified transmissible gastroenteritis (TGE) virus was found to be composed of three major structural proteins having relative molecular weights of 200,000, 48,000, and 28,000. The peplomer glycoprotein was purified by affinity chromatography with the monoclonal antibody (MAb) 1D.G3. A collection of 48 MAbs against TGE virus was developed from which 26, 10, and 3 were specific for proteins E2, N, and E1, respectively. A total of 14 neutralizing MAbs of known reactivity were E2 protein specific. In addition, MAb 1B.C11, of unknown specificity, was also neutralizing. These MAbs reduced the virus titer 10(2)- to 10(9)-fold. Six different epitopes critical in TGE virus neutralization were found, all of which were conformational based on their immunogenicity and antigenicity. Only the epitope defined by MAb 1G.A7 was resistant to sodium dodecyl sulfate treatment, although it was destroyed by incubation in the presence of both the detergent and beta-mercaptoethanol. The frequency of MAb-resistant (mar) mutants selected with four MAbs (1G.A7, 1B.C11, 1G.A6, and 1E.F9) ranged from 10(-6) to 10(-7), whereas the frequency of the putative mar mutant defined by MAb 1B.B11 was lower than 10(-9). Furthermore, the epitopes defined by these MAbs and by MAbs 1H.C2 and 1A.F10, were present in 11 viral isolated with different geographical locations, years of isolation, and passage numbers (with the exception of two epitopes absent or modified in the TOY 56 viral isolate), suggesting that the critical epitopes in TGE virus neutralization were highly conserved.     

Broad and potent neutralizing antibody responses elicited in natural HIV-2 infection

Compared with human immunodeficiency virus type 1 (HIV-1), little is known about the susceptibility of HIV-2 to antibody neutralization. We characterized the potency and breadth of neutralizing antibody (NAb) responses in 64 subjects chronically infected with HIV-2 against three primary HIV-2 strains: HIV-2(7312A), HIV-2(ST), and HIV-2(UC1). Surprisingly, we observed in a single-cycle JC53bl-13/TZM-bl virus entry assay median reciprocal 50% inhibitory concentration (IC(50)) NAb titers of 1.7 × 10(5), 2.8 × 10(4), and 3.3 × 10(4), respectively. A subset of 5 patient plasma samples tested against a larger panel of 17 HIV-2 strains where the extracellular gp160 domain was substituted into the HIV-2(7312A) proviral backbone showed potent neutralization of all but 4 viruses. The specificity of antibody neutralization was confirmed using IgG purified from patient plasma, HIV-2 Envs cloned by single-genome amplification, viruses grown in human CD4(+) T cells and tested for neutralization sensitivity on human CD4(+) T target cells, and, as negative controls, env-minus viruses pseudotyped with HIV-1, vesicular stomatitis virus, or murine leukemia virus Env glycoproteins. Human monoclonal antibodies (MAbs) specific for HIV-2 V3 (6.10F), V4 (1.7A), CD4 binding site (CD4bs; 6.10B), CD4 induced (CD4i; 1.4H), and membrane-proximal external region (MPER; 4E10) epitopes potently neutralized the majority of 32 HIV-2 strains bearing Envs from 13 subjects. Patient antibodies competed with V3, V4, and CD4bs MAbs for binding to monomeric HIV-2 gp120 at titers that correlated significantly with NAb titers. HIV-2 MPER antibodies did not contribute to neutralization breadth or potency. These findings indicate that HIV-2 Env is highly immunogenic in natural infection, that high-titer broadly neutralizing antibodies are commonly elicited, and that unlike HIV-1, native HIV-2 Env trimers expose multiple broadly cross-reactive epitopes readily accessible to NAbs.