Mechanistic Study of Broadly Neutralizing Human Monoclonal Antibodies against Dengue Virus That Target the Fusion Loop

There are no available vaccines for dengue, the most important mosquito-transmitted viral disease. Mechanistic studies with anti-dengue virus (DENV) human monoclonal antibodies (hMAbs) provide a rational approach to identify and characterize neutralizing epitopes on DENV structural proteins that can serve to inform vaccine strategies. Here, we report a class of hMAbs that is likely to be an important determinant in the human humoral response to DENV infection. In this study, we identified and characterized three broadly neutralizing anti-DENV hMAbs: 4.8A, D11C, and 1.6D. These antibodies were isolated from three different convalescent patients with distinct histories of DENV infection yet demonstrated remarkable similarities. All three hMAbs recognized the E glycoprotein with high affinity, neutralized all four serotypes of DENV, and mediated antibody-dependent enhancement of infection in Fc receptor-bearing cells at subneutralizing concentrations. The neutralization activities of these hMAbs correlated with a strong inhibition of virus-liposome and intracellular fusion, not virus-cell binding. We mapped epitopes of these antibodies to the highly conserved fusion loop region of E domain II. Mutations at fusion loop residues W101, L107, and/or G109 significantly reduced the binding of the hMAbs to E protein. The results show that hMAbs directed against the highly conserved E protein fusion loop block viral entry downstream of virus-cell binding by inhibiting E protein-mediated fusion. Characterization of hMAbs targeting this region may provide new insights into DENV vaccine and therapeutic strategies.     

Epitope Mapping of Broadly Neutralizing HIV-2 Human Monoclonal Antibodies

Recent studies have shown that natural infection by HIV-2 leads to the elicitation of high titers of broadly neutralizing antibodies (NAbs) against primary HIV-2 strains (T. I. de Silva, et al., J. Virol. 86:930–946, 2012; R. Kong, et al., J. Virol. 86:947–960, 2012; G. Ozkaya Sahin, et al., J. Virol. 86:961–971, 2012). Here, we describe the envelope (Env) binding and neutralization properties of 15 anti-HIV-2 human monoclonal antibodies (MAbs), 14 of which were newly generated from 9 chronically infected subjects. All 15 MAbs bound specifically to HIV-2 gp120 monomers and neutralized heterologous primary virus strains HIV-2_7312A and HIV-2_ST. Ten of 15 MAbs neutralized a third heterologous primary virus strain, HIV-2_UC1. The median 50% inhibitory concentrations (IC₅₀s) for these MAbs were surprisingly low, ranging from 0.007 to 0.028 μg/ml. Competitive Env binding studies revealed three MAb competition groups: CG-I, CG-II, and CG-III. Using peptide scanning, site-directed mutagenesis, chimeric Env constructions, and single-cycle virus neutralization assays, we mapped the epitope of CG-I antibodies to a linear region in variable loop 3 (V3), the epitope of CG-II antibodies to a conformational region centered on the carboxy terminus of V4, and the epitope(s) of CG-III antibodies to conformational regions associated with CD4- and coreceptor-binding sites. HIV-2 Env is thus highly immunogenic in vivo and elicits antibodies having diverse epitope specificities, high potency, and wide breadth. In contrast to the HIV-1 Env trimer, which is generally well shielded from antibody binding and neutralization, HIV-2 is surprisingly vulnerable to broadly reactive NAbs. The availability of 15 human MAbs targeting diverse HIV-2 Env epitopes can facilitate comparative studies of HIV/SIV Env structure, function, antigenicity, and immunogenicity.     

Generation of Neutralizing Human Monoclonal Antibodies against Parvovirus B19 Proteins

Infections caused by human parvovirus B19 are known to be controlled mainly by neutralizing antibodies. To analyze the immune reaction against parvovirus B19 proteins, four cell lines secreting human immunoglobulin G monoclonal antibodies (MAbs) were generated from two healthy donors and one human immunodeficiency virus type 1-seropositive individual with high serum titers against parvovirus. One MAb is specific for nonstructural protein NS1 (MAb 1424), two MAbs are specific for the unique region of minor capsid protein VP1 (MAbs 1418-1 and 1418-16), and one MAb is directed to major capsid protein VP2 (MAb 860-55D). Two MAbs, 1418-1 and 1418-16, which were generated from the same individual have identity in the cDNA sequences encoding the variable domains, with the exception of four base pairs resulting in only one amino acid change in the light chain. The NS1- and VP1-specific MAbs interact with linear epitopes, whereas the recognized epitope in VP2 is conformational. The MAbs specific for the structural proteins display strong virus-neutralizing activity. The VP1- and VP2-specific MAbs have the capacity to neutralize 50% of infectious parvovirus B19 in vitro at 0.08 and 0.73 μg/ml, respectively, demonstrating the importance of such antibodies in the clearance of B19 viremia. The NS1-specific MAb mediated weak neutralizing activity and required 47.7 μg/ml for 50% neutralization. The human MAbs with potent neutralizing activity could be used for immunotherapy of chronically B19 virus-infected individuals and acutely infected pregnant women. Furthermore, the knowledge gained regarding epitopes which induce strongly neutralizing antibodies may be important for vaccine development.     

Identification and Characterization of Broadly Neutralizing Human Monoclonal Antibodies Directed against the E2 Envelope Glycoprotein of Hepatitis C Virus

Nearly all livers transplanted into hepatitis C virus (HCV)-positive patients become infected with HCV, and 10 to 25% of reinfected livers develop cirrhosis within 5 years. Neutralizing monoclonal antibody could be an effective therapy for the prevention of infection in a transplant setting. To pursue this treatment modality, we developed human monoclonal antibodies (HuMAbs) directed against the HCV E2 envelope glycoprotein and assessed the capacity of these HuMAbs to neutralize a broad panel of HCV genotypes. HuMAb antibodies were generated by immunizing transgenic mice containing human antibody genes (HuMAb mice; Medarex Inc.) with soluble E2 envelope glycoprotein derived from a genotype 1a virus (H77). Two HuMAbs, HCV1 and 95-2, were selected for further study based on initial cross-reactivity with soluble E2 glycoproteins derived from genotypes 1a and 1b, as well as neutralization of lentivirus pseudotyped with HCV 1a and 1b envelope glycoproteins. Additionally, HuMAbs HCV1 and 95-2 potently neutralized pseudoviruses from all genotypes tested (1a, 1b, 2b, 3a, and 4a). Epitope mapping with mammalian and bacterially expressed proteins, as well as synthetic peptides, revealed that HuMAbs HCV1 and 95-2 recognize a highly conserved linear epitope spanning amino acids 412 to 423 of the E2 glycoprotein. The capacity to recognize and neutralize a broad range of genotypes, the highly conserved E2 epitope, and the fully human nature of the antibodies make HuMAbs HCV1 and 95-2 excellent candidates for treatment of HCV-positive individuals undergoing liver transplantation.Hepatitis C virus (HCV) is a major cause of liver failure and infects more than 170 million people worldwide. HCV is a member of the Flaviviridae family and contains a 9.6-kb positive-strand RNA genome. The genome is translated into a single polypeptide that is cleaved by viral and cellular proteases into at least nine different proteins. The major HCV surface glycoproteins, E1 and E2, form a noncovalent heterodimer on the virion surface (23) and are believed to mediate viral entry via a complex set of poorly understood interactions with cellular coreceptors, including CD81 (28), claudin-1 (8), occludin (29), scavenger receptor class B type I (30), and others (38). The E2 glycoprotein has been shown to interact directly with receptors (38); currently, no function has been assigned to E1, although it is known to be required for viral infection. These viral glycoproteins provide an obvious target for neutralizing monoclonal antibodies (MAbs).Isolation of potently neutralizing HCV-specific MAbs has been complicated by the lack of an in vitro cell culture system to study the full infection cycle of the virus. Recently, systems have been developed that allow for the generation of infectious viral particles, highlighting the importance of E1 and E2 in viral binding and entry. A novel in vitro infection system employs HCV pseudotyped viral particles (HCVpp) generated from a lentivirus that are devoid of native glycoproteins and engineered to contain HCV glycoproteins E1 and E2 (4, 15). HCVpp specifically infect cell lines derived from human liver cells and can be neutralized by polyclonal and MAbs directed against the HCV envelope glycoproteins.HCVpp have allowed the identification of antibodies that can neutralize HCV infection in cell culture. E1 has proven to be a difficult target for MAb-mediated neutralization, possibly because it appears to have low immunogenicity (32), has no identified binding proteins on the cell surface, and has an undefined role in cell entry. Despite this challenge, two groups have identified HCV neutralizing MAbs directed to E1: these MAbs are H-111, which has moderate neutralizing activity (17), and the recently isolated IGH505 and IGH526, which neutralize numerous HCV genotypes (1a, 1b, 2a, 4a, 5a, and 6a but not 2b and 3a) (22). Although they are predicted to inhibit viral binding or fusion, the mechanism by which these E1-directed MAbs neutralize HCV infection is unclear.A diverse group of mouse anti-E2 antibodies, recognizing both linear and discontinuous epitopes, has been generated. Many of these MAbs showed broad neutralization of multiple HCV genotypes, but not surprisingly, several HCV isolates were refractory to neutralization. In contrast, AP33, a mouse MAb that largely recognizes a highly conserved linear epitope in the N terminus of E2 (amino acids 412 to 423), was identified as a broadly cross-reactive antibody that neutralized strains from all genotypes tested (1a, 1b, 2a, 2b, 3a, 4, 5, and 6), with the exception of one genotype 5 virus (UKN5.14.4; GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"AY894682","term_id":"58220837","term_text":"AY894682"}}AY894682) (24). Recently, several cross-reactive neutralizing MAbs have been identified that are of human origin and have the capacity to neutralize a significant fraction of the genotypes tested (1, 5, 12, 13, 27, 31) or to neutralize all genotypes tested (16, 20, 25). As with the vast majority of previously described human MAbs (HuMAbs), these MAbs recognize conformation-dependent epitopes of E2. One broadly neutralizing human antibody, AR3B, was tested in a mouse model of infection and showed significant protection from viremia (20). Given the known function of the E2 envelope glycoprotein, the high level of immunogenicity, the surface vulnerability, and the abundance of data pertaining to E2 and HCV neutralization, E2 provides a promising target for the development of fully human neutralizing antibodies.Liver deterioration due to HCV infection is the leading reason for liver transplantation in the United States. Unfortunately, it is highly likely that the transplanted liver will also become infected with HCV, and 10 to 25% of these patients develop cirrhosis within 5 years of transplant (9, 40). Here we describe the characterization of HuMAbs directed against the HCV E2 envelope glycoprotein, generated using transgenic mice. Based on epitope conservation and broad neutralization capacity, HuMAbs HCV1 and 95-2 provide excellent candidates for prevention of graft reinfection of HCV-infected individuals undergoing liver transplantation.     

人源中和性抗狂犬病毒基因工程抗体的研制

从具有高滴度狂犬病毒抗体的多位疫苗注射者采集外周血淋巴细胞,构建人源抗狂犬病毒Fab基因工程抗体文库。用纯化的狂犬aG和CTN株病毒颗粒富集筛选所得Fab噬菌体抗体文库,利用ELISA和间接免疫荧光法IFA鉴定所得人源单克隆抗体Fab段基因的功能特性,并通过序列测定确定所得抗体的轻链和重链的型别,成功获得11株抗狂犬病毒糖蛋白的人源单克隆Fab抗体。将其中5株人源单克隆Fab抗体的轻链和重链分别克隆入全抗体表达载体pAC-L-Fc后转染昆虫Sf9细胞,利用杆状病毒系统实现全抗体的分泌型表达。5株全抗体在体外与狂犬病毒CVS-11株的中和反应中均显示具有狂犬病毒中和活性。人源中和性抗狂犬病毒基因工程全抗体的获得为我国自行生产抗狂犬病单克隆抗体鸡尾酒奠定了物质基础。     

Pharmacokinetics and Immunogenicity of Broadly Neutralizing HIV Monoclonal Antibodies in Macaques

The identification of highly potent broadly neutralizing antibodies (bnAbs) against HIV-1, and success in preventing SHIV infection following their passive administration, have increased the likelihood that immunotherapeutic strategies can be adopted to prevent and treat HIV-1 infection. However, while broad and potent neutralizing activity is an essential prerequisite, in vivo properties such as good circulatory stability and non-immunogenicity are equally critical for developing a human treatment. In the present study, glycoforms of the bnAbs 10-1074, NIH45-46^G54W, 10E8, PGT121, PGT128, PGT145, PGT135, PG9, PG16, VRC01 and b12 were produced by Agrobacterium-mediated transient transfection of Nicotiana benthamiana and assessed following administration in rhesus macaques. The results indicate that (i) N-glycans within the VL domain impair plasma stability of plant-derived bnAbs and (ii) while PGT121 and b12 exhibit no immunogenicity in rhesus macaques after multiple injections, VRC01, 10-1074 and NIH45-46^G54W elicit high titer anti-idiotypic antibodies following a second injection. These anti-idiotypic antibodies specifically bind the administered bnAb or a close family member, and inhibit the bnAb in neutralization assays. These findings suggest that specific mutations in certain bnAbs contribute to their immunogenicity and call attention to the prospect that these mutated bnAbs will be immunogenic in humans, potentially compromising their value for prophylaxis and therapy of HIV-1.     

Human Monoclonal Antibodies against Highly Conserved HR1 and HR2 Domains of the SARS-CoV Spike Protein Are More Broadly Neutralizing

Immune sera from convalescent patients have been shown to be effective in the treatment of patients infected with Severe Acute Respiratory Syndrome Virus (SARS-CoV) making passive immune therapy with human monoclonal antibodies an attractive treatment strategy for SARS. Previously, using Xenomouse (Amgen British Columbia Inc), we produced a panel of neutralizing Human monoclonal antibodies (HmAbs) that could specifically bind to the ectodomain of the SARS-CoV spike (S) glycoprotein. Some of the HmAbs were S1 domain specific, while some were not. In this study, we describe non-S1 binding neutralizing HmAbs that can specifically bind to the conserved S2 domain of the S protein. However, unlike the S1 specific HmAbs, the S2 specific HmAbs can neutralize pseudotyped viruses expressing different S proteins containing receptor binding domain sequences of various clinical isolates. These data indicate that HmAbs which bind to conserved regions of the S protein are more suitable for conferring protection against a wide range of SARS-CoV variants and have implications for generating therapeutic antibodies or subunit vaccines against other enveloped viruses.     

Characterization of Two Human Monoclonal Antibodies Neutralizing Influenza A H7N9 Viruses

H7N9 was a cause of significant global health concern due to its severe infection and approximately 35% mortality in humans. By screening a Fab antibody phage library derived from patients who recovered from H7N9 infections, we characterized two human monoclonal antibodies (HuMAbs), HNIgGD5 and HNIgGH8. The epitope of these two antibodies was dependent on two residues in the receptor binding site at positions V186 and L226 of the hemagglutinin glycoprotein. Both antibodies possessed high neutralizing activity.     

Broadly Neutralizing Monoclonal Antibodies 2F5 and 4E10 Directed against the Human Immunodeficiency Virus Type 1 gp41 Membrane-Proximal External Region Protect against Mucosal Challenge by Simian-Human Immunodeficiency Virus SHIVBa-L

The membrane-proximal external region (MPER) of HIV-1, located at the C terminus of the gp41 ectodomain, is conserved and crucial for viral fusion. Three broadly neutralizing monoclonal antibodies (bnMAbs), 2F5, 4E10, and Z13e1, are directed against linear epitopes mapped to the MPER, making this conserved region an important potential vaccine target. However, no MPER antibodies have been definitively shown to provide protection against HIV challenge. Here, we show that both MAbs 2F5 and 4E10 can provide complete protection against mucosal simian-human immunodeficiency virus (SHIV) challenge in macaques. MAb 2F5 or 4E10 was administered intravenously at 50 mg/kg to groups of six male Indian rhesus macaques 1 day prior to and again 1 day following intrarectal challenge with SHIV_Ba-L. In both groups, five out of six animals showed complete protection and sterilizing immunity, while for one animal in each group a low level of viral replication following challenge could not be ruled out. The study confirms the protective potential of 2F5 and 4E10 and supports emphasis on HIV immunogen design based on the MPER region of gp41.Eliciting broadly neutralizing antibodies is an important goal of HIV vaccine design efforts, and the study of broadly neutralizing monoclonal antibodies (bnMAbs) can assist in that goal. Human bnMAbs against both gp120 and gp41 of the HIV-1 envelope spike have been described. Three bnMAbs to gp41, 2F5, 4E10, and Z13e1, have been identified and shown to recognize neighboring linear epitopes on the membrane proximal external (MPER) region of gp41 (3, 24, 25, 37, 47). In a comprehensive cross-clade neutralization study by Binley et al., 2F5 neutralized 67% and 4E10 neutralized 100% of a diverse panel of 90 primary isolates (2). Similar broad neutralization was seen against sexually transmitted isolates cloned from acutely infected patients (22). More recently, a comprehensive study showed that 2F5 neutralized 97 isolates from a 162-virus panel (60%) and that 4E10 neutralized 159 isolates (98%) (41). Although less potent, the monoclonal antibody Z13, isolated from an antibody phage display library derived from a bone marrow donor whose serum was broadly neutralizing (47), has cross-clade neutralizing activity. Z13e1 is an affinity-enhanced variant of the earlier-characterized MAb Z13 that is directed against an access-restricted epitope between and overlapping the epitopes of 2F5 and 4E10. Both MAbs 2F5 and 4E10 were originally obtained as IgG3 antibodies in hybridomas derived from peripheral blood mononuclear blood lymphocytes (PBMCs) of HIV-1-seropositive nonsymptomatic patients and were later class switched to IgG1 to enable large-scale manufacturing and to prolong in vivo half-life (3, 6, 32).Despite the interest in the MPER as a vaccine target, there is limited information on the ability of MPER antibodies to act antivirally in vivo either in established infection or prophylactically. A study using the huPBL-SCID mouse model showed limited impact from 2F5 when the antibody was administered in established infection (31). Passive administration of 2G12, 2F5, and 4E10 to a cohort of acutely and chronically infected HIV-1 patients provided little direct evidence of 2F5 or 4E10 antiviral activity, whereas the emergence of escape variants indicated unequivocally the ability of 2G12 to act antivirally (18, 39). Indirect evidence did, however, suggest that the MPER MAbs may have affected virus replication, as indicated by viral rebound suppression in a patient known to have a 2G12-resistant virus prior to passive immunization (39). Another study of 10 individuals passively administered 2G12, 2F5, and 4E10 before and after cessation of combination antiretroviral therapy (ART) showed similarly that 2G12 treatment could delay viral rebound, but antiviral activity by 2F5 and 4E10 was not clearly demonstrated (21). In prophylaxis, an early 2F5 passive transfer study with chimpanzees suggested that the antibody could delay or lower the magnitude of primary viremia following HIV-1 challenge (7). A study using gene transfer of 2F5 in a humanized SCID mouse model suggested that continuous plasma levels of approximately 1 μg/ml of 2F5 may significantly reduce viral loads in LAI- and MN-challenged mice (34). Protection studies of rhesus macaques using simian-human immunodeficiency virus SHIV_89.6PD challenge did not provide definitive direct evidence for MPER antibody-mediated protection. One of three animals was protected against intravenous (i.v.) challenge when 2F5 was administered in a cocktail with HIVIG and 2G12 (19), but all three animals treated with 2F5 alone at high concentration became infected. In a vaginal challenge study with SHIV_89.6PD (20), four of five animals were protected with a cocktail of HIVIG, 2F5, and 2G12, but a 2F5/2G12 combination protected only two of five animals. Further protection studies have used MPER MAbs in combination with other MAbs, leaving the individual contributions of these antibodies uncertain (1, 8).In our previous studies, we successfully used the SHIV/macaque model to demonstrate neutralizing antibody protection against mucosal challenge, and we have begun to explore how that protection is achieved (12, 30). Here, we conducted a protection study with the two broadly neutralizing MPER-directed antibodies 2F5 and 4E10. We show that the antibodies can prevent viral infection and thereby support the MPER as a vaccine target.     

戊型肝炎病毒中和性单克隆抗体的鉴定

阻断实验发现。用戊型肝炎病毒(HEV)衣壳蛋白重组抗原制备的8株抗HEV单克隆抗体(mAb),分别识别3个构象表位和2个线性表位。用抗体捕获反转录PCR方法证实,其中识别2个构象表位的3个mAb可以直接捕获HEV颗粒,表明这2个表位位于HEV颗粒的外表面。识别这两个表位的mAbSCll和8H3均可中和HEV对恒河猴的致病性和感染性。rnAb8C11缩短排毒时间的效应较明显,而mAb8H3延迟机体抗HEV抗体阳转时间的效应较明显。二者的中和效应具有较明显的协同作用。中和单抗8C11、8H3对戊肝不同感染时期的血清均有显著阻断作用,Fab片段的阻断作用与完整抗体类似,表明这两个mAb对应的中和表位是HEV体液免疫应答的优势表位。     

High-Avidity and Potently Neutralizing Cross-Reactive Human Monoclonal Antibodies Derived from Secondary Dengue Virus Infection

The envelope (E) protein of dengue virus (DENV) is the major target of neutralizing antibodies (Abs) and vaccine development. Previous studies of human dengue-immune sera reported that a significant proportion of anti-E Abs, known as group-reactive (GR) Abs, were cross-reactive to all four DENV serotypes and to one or more other flaviviruses. Based on studies of mouse anti-E monoclonal antibodies (MAbs), GR MAbs were nonneutralizing or weakly neutralizing compared with type-specific MAbs; a GR response was thus not regarded as important for vaccine strategy. We investigated the epitopes, binding avidities, and neutralization potencies of 32 human GR anti-E MAbs. In addition to fusion loop (FL) residues in E protein domain II, human GR MAbs recognized an epitope involving both FL and bc loop residues in domain II. The neutralization potencies and binding avidities of GR MAbs derived from secondary DENV infection were stronger than those derived from primary infection. GR MAbs derived from primary DENV infection primarily blocked attachment, whereas those derived from secondary infection blocked DENV postattachment. Analysis of the repertoire of anti-E MAbs derived from patients with primary DENV infection revealed that the majority were GR, low-avidity, and weakly neutralizing MAbs, whereas those from secondary infection were primarily GR, high-avidity, and potently neutralizing MAbs. Our findings suggest that the weakly neutralizing GR anti-E Abs generated from primary DENV infection become potently neutralizing MAbs against the four serotypes after secondary infection. The observation that the dengue immune status of the host affects the quality of the cross-reactive Abs generated has implications for new strategies for DENV vaccination.