Structure-guided antibody cocktail for prevention and treatment of COVID-19.

Development of effective therapeutics for mitigating the COVID-19 pandemic is a pressing global need. Neutralizing antibodies are known to be effective antivirals, as they can be rapidly deployed to prevent disease progression and can accelerate patient recovery without the need for fully developed host immunity. Here, we report the generation and characterization of a series of chimeric antibodies against the receptor-binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Some of these antibodies exhibit exceptionally potent neutralization activities in vitro and in vivo, and the most potent of our antibodies target three distinct non-overlapping epitopes within the RBD. Cryo-electron microscopy analyses of two highly potent antibodies in complex with the SARS-CoV-2 spike protein suggested they may be particularly useful when combined in a cocktail therapy. The efficacy of this antibody cocktail was confirmed in SARS-CoV-2-infected mouse and hamster models as prophylactic and post-infection treatments. With the emergence of more contagious variants of SARS-CoV-2, cocktail antibody therapies hold great promise to control disease and prevent drug resistance.

Reversal of pancreatic desmoplasia by a tumour stroma-targeted nitric oxide nanogel overcomes TRAIL resistance in pancreatic tumours.

OBJECTIVE: Stromal barriers, such as the abundant desmoplastic stroma that is characteristic of pancreatic ductal adenocarcinoma (PDAC), can block the delivery and decrease the tumour-penetrating ability of therapeutics such as tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), which can selectively induce cancer cell apoptosis. This study aimed to develop a TRAIL-based nanotherapy that not only eliminated the extracellular matrix barrier to increase TRAIL delivery into tumours but also blocked antiapoptotic mechanisms to overcome TRAIL resistance in PDAC. DESIGN: Nitric oxide (NO) plays a role in preventing tissue desmoplasia and could thus be delivered to disrupt the stromal barrier and improve TRAIL delivery in PDAC. We applied an in vitro-in vivo combinatorial phage display technique to identify novel peptide ligands to target the desmoplastic stroma in both murine and human orthotopic PDAC. We then constructed a stroma-targeted nanogel modified with phage display-identified tumour stroma-targeting peptides to co-deliver NO and TRAIL to PDAC and examined the anticancer effect in three-dimensional spheroid cultures in vitro and in orthotopic PDAC models in vivo. RESULTS: The delivery of NO to the PDAC tumour stroma resulted in reprogramming of activated pancreatic stellate cells, alleviation of tumour desmoplasia and downregulation of antiapoptotic BCL-2 protein expression, thereby facilitating tumour penetration by TRAIL and substantially enhancing the antitumour efficacy of TRAIL therapy. CONCLUSION: The co-delivery of TRAIL and NO by a stroma-targeted nanogel that remodels the fibrotic tumour microenvironment and suppresses tumour growth has the potential to be translated into a safe and promising treatment for PDAC.

α-2,6-sialic acid/IgG anti-dsDNA ratios correlate with human lupus disease activity and possible mechanisms: A pilot study.

OBJECTIVE: To study the association of α2,6-sialic acid (SIA) content in serum IgG anti-dsDNA with human systemic lupus erythematosus disease activity index (SLEDAI) and the effect of sialylated and desialylated (deSIA) IgG anti-dsDNA on lupus B cells. METHODS: Blood from lupus patients was collected to determine the ratio of SIA in isolated IgG anti-dsDNA over serum IgG anti-dsDNA (SIA/IgG anti-dsDNA) ratios, which were plotted against SLEDAI using a receiver-operating-characteristics curve. Lupus B cells were cultured in vitro with chimeric sialylated IgG anti-dsDNA and its deSIA form. Culture supernatants were assayed for anti-inflammatory IL-10 and SIA/IgG anti-dsDNA ratios, which were compared among different pre-treatment groups using t-tests. RESULTS: The area-under-the-curve (AUC) for anti-dsDNA levels against SLEDAI was 0.791 positively (95% confidence interval [C.I.]: 0.699-0.884) and SIA/IgG anti-dsDNA ratios against SLEDAI yielded an AUC of 0.705 inversely (95% C.I: 0.601-0.809): not significantly different. SIA/IgG anti-dsDNA ratios discriminated significantly between patients without and patients with proteinuria (p = .046). SIA/IgG anti-dsDNA ratios correlated significantly and positively with serum C3c and C4 levels. Pre-treatment with IgG anti-dsDNA and its immune complexes (dsDNA/IgG anti-dsDNA IC) induced higher IL-10 from lupus B cells than medium pre-treatment (most p < .01 from day 2 to day 5 culture). DeSIA IgG anti-dsDNA IC induced lower IL-10 (p < .05) and lower SIA/IgG anti-dsDNA ratios (p < .001) from lupus B cells than medium and dsDNA pre-treatment. CONCLUSION: α2,6-SIA/IgG anti-dsDNA ratios inversely forecasted SLEDAI scores. Possible mechanisms may be due to the different effects of sialylated and deSIA IgG anti-dsDNA on lupus B cells in terms of IL-10 secretion and SIA/IgG anti-dsDNA ratios.

Identification of COVID-19 B-cell epitopes with phage-displayed peptide library.

BACKGROUND: Coronavirus disease 19 (COVID-19) first appeared in the city of Wuhan, in the Hubei province of China. Since its emergence, the COVID-19-causing virus, SARS-CoV-2, has been rapidly transmitted around the globe, overwhelming the medical care systems in many countries and leading to more than 3.3 million deaths. Identification of immunological epitopes on the virus would be highly useful for the development of diagnostic tools and vaccines that will be critical to limiting further spread of COVID-19. METHODS: To find disease-specific B-cell epitopes that correspond to or mimic natural epitopes, we used phage display technology to determine the targets of specific antibodies present in the sera of immune-responsive COVID-19 patients. Enzyme-linked immunosorbent assays were further applied to assess competitive antibody binding and serological detection. VaxiJen, BepiPred-2.0 and DiscoTope 2.0 were utilized for B-cell epitope prediction. PyMOL was used for protein structural analysis. RESULTS: 36 enriched peptides were identified by biopanning with antibodies from two COVID-19 patients; the peptides 4 motifs with consensus residues corresponding to two potential B-cell epitopes on SARS-CoV-2 viral proteins. The putative epitopes and hit peptides were then synthesized for validation by competitive antibody binding and serological detection. CONCLUSIONS: The identified B-cell epitopes on SARS-CoV-2 may aid investigations into COVID-19 pathogenesis and facilitate the development of epitope-based serological diagnostics and vaccines.

Development of therapeutic antibodies for the treatment of diseases.

It has been more than three decades since the first monoclonal antibody was approved by the United States Food and Drug Administration (US FDA) in 1986, and during this time, antibody engineering has dramatically evolved. Current antibody drugs have increasingly fewer adverse effects due to their high specificity. As a result, therapeutic antibodies have become the predominant class of new drugs developed in recent years. Over the past five years, antibodies have become the best-selling drugs in the pharmaceutical market, and in 2018, eight of the top ten bestselling drugs worldwide were biologics. The global therapeutic monoclonal antibody market was valued at approximately US$115.2 billion in 2018 and is expected to generate revenue of $150 billion by the end of 2019 and $300 billion by 2025. Thus, the market for therapeutic antibody drugs has experienced explosive growth as new drugs have been approved for treating various human diseases, including many cancers, autoimmune, metabolic and infectious diseases. As of December 2019, 79 therapeutic mAbs have been approved by the US FDA, but there is still significant growth potential. This review summarizes the latest market trends and outlines the preeminent antibody engineering technologies used in the development of therapeutic antibody drugs, such as humanization of monoclonal antibodies, phage display, the human antibody mouse, single B cell antibody technology, and affinity maturation. Finally, future applications and perspectives are also discussed.

Novel human Ab against vascular endothelial growth factor receptor 2 shows therapeutic potential for leukemia and prostate cancer.

Vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed in tumor-associated endothelial cells, where it modulates tumor-promoting angiogenesis, and it is also found on the surface of tumor cells. Currently, there are no Ab therapeutics targeting VEGFR2 approved for the treatment of prostate cancer or leukemia. Therefore, development of novel efficacious anti-VEGFR2 Abs will benefit cancer patients. We used the Institute of Cellular and Organismic Biology human Ab library and affinity maturation to develop a fully human Ab, anti-VEGFR2-AF, which shows excellent VEGFR2 binding activity. Anti-VEGFR2-AF bound Ig-like domain 3 of VEGFR2 extracellular region to disrupt the interaction between VEGF-A and VEGFR2, neutralizing downstream signaling of the receptor. Moreover, anti-VEGFR2-AF inhibited capillary structure formation and exerted Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity in vitro. We found that VEGFR2 is expressed in PC-3 human prostate cancer cell line and associated with malignancy and metastasis of human prostate cancer. In a PC-3 xenograft mouse model, treatment with anti-VEGFR2-AF repressed tumor growth and angiogenesis as effectively and safely as US FDA-approved anti-VEGFR2 therapeutic, ramucirumab. We also report for the first time that addition of anti-VEGFR2 Ab can enhance the efficacy of docetaxel in the treatment of a prostate cancer mouse model. In HL-60 human leukemia-xenografted mice, anti-VEGFR2-AF showed better efficacy than ramucirumab with prolonged survival and reduced metastasis of leukemia cells to ovaries and lymph nodes. Our findings suggest that anti-VEGFR2-AF has strong potential as a cancer therapy that could directly target VEGFR2-expressing tumor cells in addition to its anti-angiogenic action.

Advancement and applications of peptide phage display technology in biomedical science.

Combinatorial phage library is a powerful research tool for high-throughput screening of protein interactions. Of all available molecular display techniques, phage display has proven to be the most popular approach. Screening phage-displayed random peptide libraries is an effective means of identifying peptides that can bind target molecules and regulate their function. Phage-displayed peptide libraries can be used for (i) B-cell and T-cell epitope mapping, (ii) selection of bioactive peptides bound to receptors or proteins, disease-specific antigen mimics, peptides bound to non-protein targets, cell-specific peptides, or organ-specific peptides, and (iii) development of peptide-mediated drug delivery systems and other applications. Targeting peptides identified using phage display technology may be useful for basic research and translational medicine. In this review article, we summarize the latest technological advancements in the application of phage-displayed peptide libraries to applied biomedical sciences.

Hyaluronic acid-covered ferric ion-rich nanobullets with high zoledronic acid payload for breast tumor-targeted chemo/chemodynamic therapy.

Due to the heterogeneity of the tumor microenvironment, the clinical efficacy of tumor treatment is not satisfied, highlighting the necessity for new strategies to tackle this issue. To effectively treat breast tumors by tumor-targeted chemo/chemodynamic therapy, herein, the Fe3+-rich MIL-88B nanobullets (MNs) covered with hyaluronic acid (HA) were fabricated as vehicles of zoledronic acid (ZA). The attained ZA@HMNs showed a high ZA payload (ca 29.6 %), outstanding colloidal stability in the serum-containing milieu, and accelerated ZA as well as Fe3+ release under weakly acidic and glutathione (GSH)-rich conditions. Also, the ZA@HMNs consumed GSH by GSH-mediated Fe3+ reduction and converted H2O2 into OH via Fenton or Fenton-like reaction with pH reduction. After being internalized by 4T1 cells upon CD44-mediated endocytosis, the ZA@HMNs depleted intracellular GSH and degraded H2O2 into OH, thus eliciting lipid peroxidation and mitochondria damage to suppress cell proliferation. Also, the ZA@HMNs remarkably killed macrophage-like RAW 264.7 cells. Importantly, the in vivo studies and ki67 and GPX4 staining of tumor sections demonstrated that the ZA@HMNs efficiently accumulated in 4T1 tumors to hinder tumor growth via ZA chemotherapy combined with OH-mediated ferroptosis. This work presents a practicable strategy to fabricate ZA@HMNs for breast tumor-targeted chemo/chemodynamic therapy with potential clinical translation.

PEGylated chitosan-coated nanophotosensitizers for effective cancer treatment by photothermal-photodynamic therapy combined with glutathione depletion.

The combination of photothermal therapy (PTT) and photodynamic therapy (PDT) has emerged as a promising strategy for cancer treatment. However, the poor photostability and photothermal conversion efficiency (PCE) of organic small-molecule photosensitizers, and the intracellular glutathione (GSH)-mediated singlet oxygen scavenging largely decline the antitumor efficacy of PTT and PDT. Herein, a versatile nanophotosensitizer (NPS) system is developed by ingenious incorporation of indocyanine green (ICG) into the PEGylated chitosan (PEG-CS)-coated polydopamine (PDA) nanoparticles via multiple π-π stacking, hydrophobic and electrostatic interactions. The PEG-CS-covered NPS showed prominent colloidal and photothermal stability as well as high PCE (ca 62.8 %). Meanwhile, the Michael addition between NPS and GSH can consume GSH, thus reducing the GSH-induced singlet oxygen scavenging. After being internalized by CT26 cells, the NPS under near-infrared laser irradiation produced massive singlet oxygen with the aid of thermo-enhanced intracellular GSH depletion to elicit mitochondrial damage and lipid peroxide formation, thus leading to ferroptosis and apoptosis. Importantly, the combined PTT and PDT delivered by NPS effectively inhibited CT26 tumor growth in vivo by light-activated intense hyperthermia and redox homeostasis disturbance. Overall, this work presents a new tactic of boosting antitumor potency of ICG-mediated phototherapy by PEG-CS-covered NPS.

Correction: Development of a Humanized Antibody with High Therapeutic Potential against Dengue Virus Type 2.

[This corrects the article DOI: 10.1371/journal.pntd.0001636.].

Astrocyte elevated gene-1 is associated with metastasis in head and neck squamous cell carcinoma through p65 phosphorylation and upregulation of MMP1.

BACKGROUND: The survival rate of head and neck squamous cell carcinoma (HNSCC) at advanced stage is poor, despite contemporary advances in treatment modalities. Recent studies have indicated that astrocyte elevated gene-1 (AEG-1), a single transmembrane protein without any known functional domains, is overexpressed in various malignancies and is implicated in both distant metastasis and poor survival. RESULTS: High expression of AEG-1 in HNSCC was positively correlated with regional lymph node metastasis and a poor 5-year survival rate. Knockdown of AEG-1 in HNSCC cell lines reduced their capacity for colony formation, migration and invasion. Furthermore, decreased tumor volume and metastatic foci were observed after knockdown of AEG-1 in subcutaneous xenografts and pulmonary metastasis assays in vivo, respectively. We also demonstrated that AEG-1 increased phosphorylation of the p65 subunit of NF-κB, and regulated the expression of MMP1 in HNSCC cells. Moreover, compromised phosphorylation of the p65 (RelA) subunit of NF-κB at serine 536 was observed upon silencing of AEG-1 in both HNSCC cell lines and clinical specimens. CONCLUSION: High expression of AEG-1 is associated with lymph node metastasis and its potentially associated mechanism is investigated.

Molecular mimicry of human endothelial cell antigen by autoantibodies to nonstructural protein 1 of dengue virus.

The pathogenesis of dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS), both serious complications of dengue virus (DV) infection, remains unclear. In this study, we found that anti-DV NS1 (nonstructural protein 1) polyclonal antibodies cross-reacted with human umbilical vein endothelial cells (HUVECs). We further identified a complex-specific mAb, DB16-1, which could recognize DV NS1 and cross-react with HUVECs and human blood vessels. The target protein of DB16-1 was further purified by immunoaffinity chromatography. LC-MS/MS analysis and co-immunoprecipitation revealed that the target protein of DB16-1 was human LYRIC (lysine-rich CEACAM1 co-isolated). Our newly generated anti-LYRIC mAbs bound to HUVECs in a pattern similar to that of DB16-1. The B-cell epitope of DB16-1 displayed a consensus motif, Lys-X-Trp-Gly (KXWG), which corresponded to amino acid residues 116-119 of DV NS1 and mimicked amino acid residues 334-337 in LYRIC. Moreover, the binding activity of DB16-1 in NS1 of DV-2 and in LYRIC disappeared after the KXWG epitope was deleted in each. In conclusion, DB16-1 targeted the same epitope in DV NS1 and LYRIC protein on human endothelial cells, suggesting that it might play a role in the pathogenesis of DHF/DSS. Future studies on the role of the anti-NS1 antibody in causing vascular permeability will undoubtedly be performed on sera collected from individuals before, during, and after the endothelial cell malfunction phase of a dengue illness.

Structural basis of interleukin-17B receptor in complex with a neutralizing antibody for guiding humanization and affinity maturation.

Upregulation of interleukin-17 receptor B (IL-17RB) is known to be oncogenic, while other IL-17 receptors and ligands are generally involved in pro-inflammatory pathways. We identify a mouse neutralizing monoclonal antibody (mAb) D9, which blocks the IL-17RB/IL-17B pathway and inhibits pancreatic tumorigenesis in an orthotopic mouse model. The X-ray crystal structure of the IL-17RB ectodomain in complex with its neutralizing antibody D9 shows that D9 binds to a predicted ligand binding interface and engages with the A'-A loop of IL-17RB fibronectin III domain 1 in a unique conformational state. This structure also provides important paratope information to guide the design of antibody humanization and affinity maturation of D9, resulting in a humanized 1B12 antibody with marginal affinity loss and effective neutralization of IL-17B/IL-17RB signaling to impede tumorigenesis in a mouse xenograft model.

NOTCH1 signaling promotes protein stability of HER3 through the AKT pathway in squamous cell carcinoma of head and neck.

Epidermal growth factor receptor (EGFR) remains the sole druggable molecular target other than the PD1/PD-L1 pathway with meaningful clinical benefit in squamous cell carcinoma of head and neck (SCCHN). Human epidermal growth factor receptor 3 (HER3) confers the resistance to EGFR-targeted treatment in SCCHN. Thus, it is essential to determine the distribution and regulatory mechanisms of HER3 in SCCHN. We explored the prevalence of HER3 expression and its distribution within SCCHN by immunohistochemical staining and clinicopathological correlations were analyzed. The regulatory mechanism of HER3 expression was then dissected in vitro, using RT-PCR, Western blotting, and immunoprecipitation in a set of SCCHN cell lines. Subsequent in vivo validation in the murine model was also performed. We found that concomitant high expression of HER3 and its ligand NRG1 in SCCHN is associated with the increased presence of regional lymphatic metastasis and the majority of HER3 is located on the differentiated tumor cells. Further investigation revealed that HER3 is under positive control of NOTCH1 through transcriptional activation and inhibition of protein degradation through the polyubiquitination machinery via AKT pathway and USP8 deubiquitinating enzyme. In addition, loss of function of NOTCH1 suppresses HER3 expression through increased phosphorylation of serine 473 of AKT in SCCHN cells, and promotes the aggressiveness of the tumor cells. These data indicated that the level of HER3 is regulated by NOTCH1 in SCCHN both transcriptionally and post-translationally, and NOTCH1 is in a higher hierarchy in the regulatory system of the AKT pathway. Since NOTCH1 is inactivated in approximately 10% of SCCHN cases and this aberration strongly impacts the AKT pathway and diminishes HER3, exclusion of patients with NOTCH1-inactivated SCCHN may be beneficial for future clinical trials of HER3-targeting antibodies.

Novel anti-EGFR scFv human antibody-conjugated immunoliposomes enhance chemotherapeutic efficacy in squamous cell carcinoma of head and neck.

BACKGROUND AND OBJECTIVES: Squamous cell carcinoma of head and neck (SCCHN) is the fifth most prevalent cancer worldwide. Because the anatomical complexity of this region, complete surgical resection is often not achievable and conventional chemotherapy would aid locoregional control and mitigate distant metastasis. Nonetheless, the nonspecific cytotoxicity and short in vivo half-life of conventional chemotherapeutic drugs limit their effects. Given the high frequency of overexpression of wild type epidermal growth factor receptor (EGFR), we exploit EGFR as a homing beacon for drug delivery system with cytotoxic payloads. MATERIALS AND METHODS: We generated fully human anti-EGFR single chain variable fragment (scFv)-conjugated immunoliposomes (IL) containing doxorubicin and vinorelbine and tested their anti-neoplastic efficacy in vitro and in vivo. RESULT: Our IL enhanced endocytosis and significantly reduced the half maximal inhibitory concentrations of the therapeutic payloads when compared to non-targeting liposomal counterparts in various cell lines of SCCHN. Furthermore, median survival time was significantly prolonged in subcutaneous and orthotopic SCCHN xenograft murine models treated with our IL formulations than those treated with non-targeting counterparts (94 days versus 60 days and 72 days versus 56 days, respectively) without evident increased systemic toxicity. CONCLUSION: The therapeutic index of the chemotherapeutic payloads was augmented by our EFGR-targeting IL formulation and they are warranted for further development and preclinical trial.

Imaging and biodistribution of radiolabeled SP90 peptide in BT-483 tumor bearing mice.

The objective of this study was to evaluate radiolabeled DOTA-SP90 as a radiotracer for breast cancer. The in vitro competition assay showed that radiolabeled DOTA-SP90 had significant binding affinity to BT-483 cancer cells. Biodistribution, nanoSPECT/CT and nanoPET/CT imaging results indicated that radiolabeled DOTA-SP90 can accumulate in tumors. In addition, radiolabeled DOTA-SP90 peptides can also detect metastatic tumors. Therefore, radiolabeled SP90 peptide may provide the potential capability as diagnostic agent for breast cancer patients.

Extracellular domain of EpCAM enhances tumor progression through EGFR signaling in colon cancer cells.

Epithelial cell adhesion molecule (EpCAM) is highly expressed in colon cancers, but its role in cancer progression remains to be elucidated. In this work, we found that the extracellular domain of EpCAM (EpEX) activated EGFR and downstream ERK1/2 signaling to promote colon cancer cell migration and proliferation, as well as tumor growth. Mechanistically, we discovered that EpEX-EGFR-ERK1/2 signaling positively regulated intramembrane proteolysis (RIP) of EpCAM and shedding of the intracellular domain (EpICD). Treatment with an EGFR inhibitor ablated the EpEX-induced phosphorylation of ERK1/2 and AKT. Additionally, treatment with inhibitors of either EGFR or MEK decreased EpEX-induced EpICD shedding and further revealed that EpICD is necessary for nuclear accumulation of ß-catenin and the induction of HIF1α target gene expression in vitro and in vivo. Moreover, an anti-EpCAM neutralizing monoclonal antibody, EpAb2-6, inhibited the nuclear translocation of EpICD and ß-catenin and induced apoptosis in colon cancer cells. Importantly, analysis of colorectal cancer tissues showed that nuclear accumulation of EpICD was highly correlated with metastasis and poor prognosis, suggesting that it may play an important functional role in cancer progression. Thus, we provide novel insights into the mechanisms and functions of EpEX-mediated signaling, which may be considered as a promising target for the treatment of colon cancer.

Generation and Characterization of Antinonstructural Protein 1 Monoclonal Antibodies and Development of Diagnostics for Dengue Virus Serotype 2.

Dengue virus (DENV) circulates in tropical and subtropical areas around the world, where it causes high morbidity and mortality. There is no effective treatment of infection, with supportive care being the only option. Furthermore, early detection and diagnosis are important to facilitate clinical decisions. In this study, seven monoclonal antibodies (mAbs) recognizing nonstructural protein 1 (NS1) of DENV were generated by hybridoma techniques. These antibodies can be divided into two groups: serotype-specific (DB6-1, DB12-3, and DB38-1) and nonspecific (consisting of antibodies DB16-1, DB20-6, DB29-1, and DB41-2). The B-cell epitopes of DB20-6 and DB29-1 were identified by phage display and site-directed mutagenesis, and its binding motif, WXXWGK, was revealed to correspond to amino acid residues 115-120 of the DENV-2 NS1 protein. A diagnostic platform, consisting of a serotype-specific capture antibody and a complex detection antibody, exhibited a detection limit of about 1 ng/mL, which is sufficient to detect NS1 in clinical serum samples from dengue patients. This diagnostic platform displayed better specificity and sensitivity than two examined commercial NS1 diagnostic platforms. In summary, our results indicate that these newly generated mAbs are suitable for detection of NS1 protein of DENV-2 in clinical samples.

An Epitope-Substituted DNA Vaccine Improves Safety and Immunogenicity against Dengue Virus Type 2.

Dengue virus (DENV), a global disease, is divided into four serotypes (DENV1-4). Cross-reactive and non-neutralizing antibodies against envelope (E) protein of DENV bind to the Fcγ receptors (FcγR) of cells, and thereby exacerbate viral infection by heterologous serotypes via antibody-dependent enhancement (ADE). Identification and modification of enhancing epitopes may mitigate enhancement of DENV infection. In this study, we characterized the cross-reactive DB21-6 and DB39-2 monoclonal antibodies (mAbs) against domain I-II of DENV; these antibodies poorly neutralized and potently enhanced DENV infection both in vitro and in vivo. In addition, two enhancing mAbs, DB21-6 and DB39-2, were observed to compete with sera antibodies from patients infected with dengue. The epitopes of these enhancing mAbs were identified using phage display, structural prediction, and mapping of virus-like particle (VLP) mutants. N8, R9, V12, and E13 are the reactive residues of DB21-6, while N8, R9, and E13 are the reactive residues of DB39-2. N8 substitution tends to maintain VLP secretion, and decreases the binding activity of DB21-6 and DB39-2. The immunized sera from N8 substitution (N8R) DNA vaccine exerted greater neutralizing and protective activity than wild-type (WT)-immunized sera, both in vitro and in vivo. Furthermore, treatment with N8R-immunized sera reduced the enhancement of mortality in AG129 mice. These results support identification and substitution of enhancing epitope as a novel strategy for developing safe dengue vaccines.

Development of a humanized antibody with high therapeutic potential against dengue virus type 2.

BACKGROUND: Dengue virus (DENV) is a significant public health threat in tropical and subtropical regions of the world. A therapeutic antibody against the viral envelope (E) protein represents a promising immunotherapy for disease control. METHODOLOGY/PRINCIPAL FINDINGS: We generated seventeen novel mouse monoclonal antibodies (mAbs) with high reactivity against E protein of dengue virus type 2 (DENV-2). The mAbs were further dissected using recombinant E protein domain I-II (E-DI-II) and III (E-DIII) of DENV-2. Using plaque reduction neutralization test (PRNT) and mouse protection assay with lethal doses of DENV-2, we identified four serotype-specific mAbs that had high neutralizing activity against DENV-2 infection. Of the four, E-DIII targeting mAb DB32-6 was the strongest neutralizing mAb against diverse DENV-2 strains. Using phage display and virus-like particles (VLPs) we found that residue K310 in the E-DIII A-strand was key to mAb DB32-6 binding E-DIII. We successfully converted DB32-6 to a humanized version that retained potency for the neutralization of DENV-2 and did not enhance the viral infection. The DB32-6 showed therapeutic efficacy against mortality induced by different strains of DENV-2 in two mouse models even in post-exposure trials. CONCLUSIONS/SIGNIFICANCE: We used novel epitope mapping strategies, by combining phage display with VLPs, to identify the important A-strand epitopes with strong neutralizing activity. This study introduced potential therapeutic antibodies that might be capable of providing broad protection against diverse DENV-2 infections without enhancing activity in humans.