Sumathy Velumani

Monoclonal Antibodies against the Fusion Peptide of Hemagglutinin Protect Mice from Lethal Influenza A Virus H5N1 Infection

ABSTRACT The HA2 glycopolypeptide (gp) is highly conserved in all influenza A virus strains, and it is known to play a major role in the fusion of the virus with the endosomal membrane in host cells during the course of viral infection. Vaccines and therapeutics targeting this HA2 gp could induce efficient broad-spectrum immunity against influenza A virus infections. So far, there have been no studies on the possible therapeutic effects of monoclonal antibodies (MAbs), specifically against the fusion peptide of hemagglutinin (HA), upon lethal infections with highly pathogenic avian influenza (HPAI) H5N1 virus. We have identified MAb 1C9, which binds to GLFGAIAGF, a part of the fusion peptide of the HA2 gp. We evaluated the efficacy of MAb 1C9 as a therapy for influenza A virus infections. This MAb, which inhibited cell fusion in vitro when administered passively, protected 100% of mice from challenge with five 50% mouse lethal doses of HPAI H5N1 influenza A viruses from two different clades. Furthermore, it caused earlier clearance of the virus from the lung. The influenza virus load was assessed in lung samples from mice challenged after pretreatment with MAb 1C9 (24 h prior to challenge) and from mice receiving early treatment (24 h after challenge). The study shows that MAb 1C9, which is specific to the antigenically conserved fusion peptide of HA2, can contribute to the cross-clade protection of mice infected with H5N1 virus and mediate more effective recovery from infection.

Low antibody titers 5 years after vaccination with the CYD-TDV dengue vaccine in both pre-immune and naïve vaccinees

ABSTRACT Globally, dengue virus (DENV) is one of the most widespread vector-borne viruses. Dengue disease affects populations in endemic areas and, increasingly, tourists who travel to these countries, but there is currently no approved vaccine for dengue. A phase 3 efficacy trial with Sanofi-Pasteurs recombinant, live-attenuated, tetravalent dengue vaccine (CYD-TDV) conducted in South East Asia showed an overall efficacy of 56% against virologically confirmed dengue infections of any severity and any of the 4 serotypes, but the long-term protection of the vaccine has yet to be demonstrated. To address longevity of antibody titers and B cell memory, we recalled study participants from an earlier CYD immunogenicity study (Phase 2) conducted in Singapore that enrolled healthy volunteers in the year 2009. Depending on the age group, 57–84% of the participants initially generated a neutralizing antibody titer ≥ 10 to all 4 DENV serotypes 28 d after the third and final dose. We observed very low antibody titers in blood samples collected from 23 vaccinees 5 y after the first dose, particularly titers of antibodies binding to virus particles compared with those binding to recombinant E protein. The in vivo efficacy of plasma antibodies against DENV-2 challenge was also tested in a mouse model, which found that only 2 out of 23 samples were able to reduce viremia. Although the sample size is too small for general conclusions, dengue immune memory after vaccination with CYD-TDV appears relatively low.

Kinome siRNA screen identifies novel cell-type specific dengue host target genes

Dengue is a global emerging infectious disease, with no specific treatment available. To identify novel human host cell targets important for dengue virus infection and replication, an image-based high-throughput siRNA assay screening of a human kinome siRNA library was conducted using human hepatocyte cell line Huh7 infected with a recent dengue serotype 2 virus isolate BR DEN2 01-01. In the primary siRNA screening of 779 kinase-related genes, knockdown of 22 genes showed a reduction in DENV-2 infection. Conversely, knockdown of 8 genes enhanced viral infection. To assess host cell specificity, the confirmed hits were tested in the DENV-infected monocytic cell line U937. While the expression of EIF2AK3, ETNK2 and SMAD7 was regulated in both cell lines after infection, most kinases were hepatocyte-specific. Monocytic cells represent initial targets of infection and an antiviral treatment targeting these cells is probably most effective to reduce initial viral load. In turn, infection of the liver could contribute to pathogenesis, and the novel hepatocyte-specific human targets identified here could be important for dengue infection and pathogenesis.

A potent neutralizing antibody with therapeutic potential against all four serotypes of dengue virus

A therapy for dengue is still elusive. We describe the neutralizing and protective capacity of a dengue serotype-cross-reactive antibody isolated from the plasmablasts of a patient. Antibody SIgN-3C neutralized all four dengue virus serotypes at nano to picomolar concentrations and significantly decreased viremia of all serotypes in adult mice when given 2 days after infection. Moreover, mice were protected from pathology and death from a lethal dengue virus-2 infection. To avoid potential Fc-mediated uptake of immune complexes and ensuing enhanced infection, we introduced a LALA mutation in the Fc part. SIgN-3C-LALA was as efficient as the non-modified antibody in neutralizing dengue virus and in protecting mice while antibody-dependent enhancement was completely abrogated. The epitope of the antibody includes conserved amino acids in all three domains of the glycoprotein, which can explain its cross-reactivity. SIgN-3C-LALA neutralizes dengue virus both pre and post-attachment to host cells. These attributes likely contribute to the remarkable protective capacity of SIgN-3C.Dengue: A single vaccine candidate for all strainsAn antibody-vaccine candidate has been discovered that neutralizes and confers protection against all four strains of dengue virus. Katja Fink, of the Singapore Immunology Network and Nanyang Technological University, Singapore, describes this as the first time a highly neutralizing antibody has shown efficacy against all four strains. Fink’s team, consisting of scientists from institutions across the country, tested the candidate (SIgN-3C-LALA) in both pre-exposure and post-exposure mouse models. The findings showed it reduced blood-virus levels, protected from lethal infection, and also offered improved safety—without compromising efficacy—the latter by way of intentional mutations to the antibody’s structure. As the global cost of dengue treatment is as high as 9 billion US

Immune predictors of cancer progression.

per year, further study is needed to evaluate the suitability of the antibody candidate for the treatment of dengue in humans.

Plasmablasts During Acute Dengue Infection Represent a Small Subset of a Broader Virus-specific Memory B Cell Pool

The immune system has multiple, complex, and sometimes opposing roles during cancer progression. While immune-compromised individuals have a higher incidence of cancers, inflammation is also associated with increased risk of disease progression. It is becoming apparent that simple measures of immune responses in the blood are of limited use in cancer. Instead, the importance of the exact identity and functional characteristics of tumor-infiltrating immune cells is increasingly recognized. This realization has led to recent studies that have revealed a critical role for chemokine expression in the tumor microenvironment and suggested a therapeutic potential of manipulating intratumoral expression of chemokines to alter the local immune milieu.

Skin dendritic cell and T cell activation associated with dengue shock syndrome

Dengue is endemic in tropical countries worldwide and the four dengue virus serotypes often co-circulate. Infection with one serotype results in high titers of cross-reactive antibodies produced by plasmablasts, protecting temporarily against all serotypes, but impairing protective immunity in subsequent infections. To understand the development of these plasmablasts, we analyzed virus-specific B cell properties in patients during acute disease and at convalescence. Plasmablasts were unrelated to classical memory cells expanding in the blood during early recovery. We propose that only a small subset of memory B cells is activated as plasmablasts during repeat infection and that plasmablast responses are not representative of the memory B cell repertoire after dengue infection.

Protective Capacity of the Human Anamnestic Antibody Response during Acute Dengue Virus Infection

The pathogenesis of severe dengue remains unclear, particularly the mechanisms underlying the plasma leakage that results in hypovolaemic shock in a small proportion of individuals. Maximal leakage occurs several days after peak viraemia implicating immunological pathways. Skin is a highly vascular organ and also an important site of immune reactions with a high density of dendritic cells (DCs), macrophages and T cells. We obtained skin biopsies and contemporaneous blood samples from patients within 24 hours of onset of dengue shock syndrome (DSS), and from healthy controls. We analyzed cell subsets by flow cytometry, and soluble mediators and antibodies by ELISA; the percentage of migratory CD1a+ dermal DCs was significantly decreased in the DSS patients, and skin CD8+ T cells were activated, but there was no accumulation of dengue-specific antibodies. Inflammatory monocytic cells were not observed infiltrating the skin of DSS cases on whole-mount histology, although CD14dim cells disappeared from blood.

Complete human CD1a deficiency on Langerhans cells due to a rare point mutation in the coding sequence.

ABSTRACT Half of the worlds population is exposed to the risk of dengue virus infection. Although a vaccine for dengue virus is now available in a few countries, its reported overall efficacy of about 60% is not ideal. Protective immune correlates following natural dengue virus infection remain undefined, which makes it difficult to predict the efficacy of new vaccines. In this study, we address the protective capacity of dengue virus-specific antibodies that are produced by plasmablasts a few days after natural secondary infection. Among a panel of 18 dengue virus-reactive human monoclonal antibodies, four groups of antibodies were identified based on their binding properties. While antibodies targeting the fusion loop of the glycoprotein of dengue virus dominated the antibody response, two smaller groups of antibodies bound to previously undescribed epitopes in domain II of the E protein. The latter, largely serotype-cross-reactive antibodies, demonstrated increased stability of binding at pH 5. These antibodies possessed weak to moderate neutralization capacity in vitro but were the most efficacious in promoting the survival of infected mice. Our data suggest that the cross-reactive anamnestic antibody response has a protective capacity despite moderate neutralization in vitro and a moderate decrease of viremia in vivo. IMPORTANCE Antibodies can protect from symptomatic dengue virus infection. However, it is not easy to assess which classes of antibodies provide protection because in vitro assays are not always predictive of in vivo protection. During a repeat infection, dengue virus-specific immune memory cells are reactivated and large amounts of antibodies are produced. By studying antibodies cloned from patients with heterologous secondary infection, we tested the protective value of the serotype-cross-reactive “recall” or “anamnestic” response. We found that results from in vitro neutralization assays did not always correlate with the ability of the antibodies to reduce viremia in a mouse model. In addition, a decrease of viremia in mice did not necessarily improve survival. The most protective antibodies were stable at pH 5, suggesting that antibody binding in the endosomes, after the antibody-virus complex is internalized, might be important to block virus spread in the organism.

Publisher Correction: A potent neutralizing antibody with therapeutic potential against all four serotypes of dengue virus

To the Editor: The family of CD1 molecules is structurally similar to MHC class I molecules, but the 2 protein families mediate fundamentally different immune functions. MHC class I molecules present peptides to T cells, whereas CD1 molecules present lipids to natural killer T cells and other CD1-restricted T cells. CD1a is highly expressed on human Langerhans cells (LCs), a specialized mononuclear phagocyte that is prevalent in the epithelial cell layer of the skin and mucosal surfaces. Epidermal LCs can function as classical antigen-presenting cells (APCs) to induce naive T-cell responses in draining lymph nodes, but also have a regulatory function in the skin via local induction of regulatory T cells and maintenance of epithelial barrier integrity. Human dermal dendritic cells (DCs) also express CD1a, but in much lower amounts compared with LCs. CD1a dermal DCs, which coexpress CD1c, have been shown to efficiently stimulate CD4 and CD8 T cells in vitro. However, immune deficiencies due to selective CD1a defects have not been previously described, and it has proved difficult to dissect the specific role of CD1a in immune regulation. During the course of a clinical study that involvedanalysis ofAPC subsets in human skin biopsies by flow cytometry, we identified a healthy Vietnamese individual, donor 007, who showed complete absence of CD1a expression on skinAPCs (Fig 1,A). This case presented an opportunity to study the biological significance of CD1a expression. To check whether LCs were absent altogether in donor 007, we obtained a second skin biopsy, separated the epidermis from the underlying structures, and stained the epidermal tissues with antibodies binding to CD1a and to HLA-DR. Donor 007 LCs displayed intense HLA-DR staining with typical dendritic morphology, but CD1a staining was minimal (Fig 1, B). We next addressed whether the CD1a deficiency represented a generic expression defect, using monocyte-derived dendritic cells (moDCs) as a model. In keeping with our earlier observations, moDCs from donor 007 showed no surface CD1a expression by flow cytometry or immunohistochemistry (see Fig E1, A, in this article’s Online Repository at www.jacionline.org), in contrast to moDCs derived from a normal healthy control donor. Staining with other anti-human CD1a clones, OKT6 and NA1/34-HLK, showed the same result as staining with clone HI149 (see Figs E2 and E3 in this article’s Online Repository at www. jacionline.org). In addition, no costain with early endosome antigen-1 and CD1awas observed, excluding CD1a accumulation in early endosomes in donor 007 (Fig E1, B). To address whether the CD1a defect was caused by a mutation in the CD1a gene, we invited the parents and all 4 siblings of