Biology subjects

Ejemel, M.

Publications and source records attributed to Ejemel, M..

6 recordsLinked to original sources

bioRxiv2026

INHIBITION OF LIGAND-DEPENDENT BMP SIGNALING BLUNTS MELANOMA GROWTH

Treatments for advanced melanoma have markedly improved, but a significant proportion of patients still receive little to no survival benefit with standard-of-care therapies due to resistance and relapse1-5. The discovery and development of novel targets and therapies are needed to continue to improve patient outcomes in advanced melanoma. The identification of ligand-dependent BMP signaling that inhibits differentiation and promotes survival of melanoma cells suggests it is a potential therapeutic target that could complement current therapies6. Expression of the BMP ligand GDF6 (a.k.a BMP13) is responsible for this activity, and its expression is correlated with poor outcomes for melanoma patients. Here, we describe a novel monoclonal antibody targeting GDF6 that causes melanoma cell differentiation and death and blunts tumor growth in vivo. Together, these results indicate BMP-directed therapy has significant potential as a novel therapy for patients with advanced melanoma.

Cancer Biology↗

bioRxiv2022

Structural Elucidation of a Protective B cell Epitope on Outer Surface Protein C (OspC) of the Lyme disease spirochete, Borreliella burgdorferi

Outer surface protein C (OspC) plays a pivotal role in mediating tick-to-host transmission and infectivity of the Lyme disease spirochete, Borreliella burgdorferi. OspC is a helical-rich homodimer that interacts with tick salivary proteins, as well as components of the mammalian immune system. Several decades ago, it was shown that the OspC-specific monoclonal antibody, B5, was able to passively protect mice from experimental tick-transmitted infection by B. burgdorferi strain B31. However, B5s epitope has never been elucidated, despite widespread interest in OspC as a possible Lyme disease vaccine antigen. Here we report the crystal structure of B5 antigen-binding fragments (Fabs) in complex with recombinant OspC type A (OspCA). Each OspC monomer within the homodimer was bound by a single B5 Fab in a side-on orientation, with contact points along OspCs -helix 1 and -helix 6, as well as interactions with the loop between a-helices 5 and 6. In addition, B5s complementarity-determining region (CDR) H3 bridged the OspC-OspC homodimer interface, revealing the quaternary nature of the protective epitope. To provide insight into the molecular basis of B5 serotype specificity, we solved the crystal structures of recombinant OspC types B and K and compared them to OspCA. This study represents the first structure of a protective B cell epitope on OspC and will aid in the rational design of OspC-based vaccines and therapeutics for Lyme disease. IMPORTANCEThe spirochete, Borreliella burgdorferi, is the causative agent of Lyme borreliosis, the most common tickborne disease in the United States. The spirochete is transmitted to humans during the course of a tick taking a bloodmeal. After B. burgdorferi is deposited into the skin of a human host, it replicates locally and spreads systemically, often resulting in clinical manifestations involving the central nervous system, joints, and/or heart. Antibodies directed against B. burgdorferis outer surface protein C (OspC) are known to block tick-to-host transmission, as well as dissemination of the spirochete within a mammalian host. In this report, we reveal the first atomic structure of one such antibody in complex with OspC. Our results have implications for the design of a Lyme disease vaccine capable to interfering with multiple stages in B. burgdorferi infection.

immunology↗

bioRxiv2021

Allosteric modulation of the SARS-CoV-2 spike conformation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects cells through binding to angiotensin-converting enzyme 2 (ACE2). This interaction is mediated by the receptor-binding domain (RBD) of the viral spike (S) glycoprotein. Structural and dynamic data have shown that S can adopt multiple conformations, which controls the exposure of the ACE2-binding site in the RBD. Here, using single-molecule Forster resonance energy transfer (smFRET) imaging we report the effects of ACE2 and antibody binding on the conformational dynamics of S from the Wuhan-1 strain and the B.1 variant (D614G). We find that D614G modulates the energetics of the RBD position in a manner similar to ACE2 binding. We also find that antibodies that target diverse epitopes, including those distal to the RBD, stabilize the RBD in a position competent for ACE2 binding. Parallel solution-based binding experiments using fluorescence correlation spectroscopy (FCS) indicate antibody-mediated enhancement of ACE2 binding. These findings inform on novel strategies for therapeutic antibody cocktails.

biophysics↗

bioRxiv2020

Oral administration of a single anti-CfaE nanobody provides broadly cross-protective immunity against major pathogenic Enterotoxigenic Escherichia coli strains

Enterotoxigenic Escherichia coli (ETEC) is estimated to cause approximately 380,000 deaths annually during sporadic or epidemic outbreaks worldwide. There is currently no vaccine licensed to prevent ETEC. Development of prophylaxis against ETEC is challenging due to the vast heterogeneity of the ETEC strains. The discovery of nanobodies has emerged as a successful new biologics in treating mucosal infectious disease as nanobodies can recognize conserved epitopes on hypervariable pathogens. In this study, we performed large screens using immunized llamas and a naive nanobody yeast display library against adhesins of colonization factors. Cross-protective nanobodies were selected with in vitro activities inhibiting mannose-resistant hemagglutination (MRHA) against all eleven major pathogenic ETEC strains. Oral administration of nanobodies led to significant reduction of bacterial colonization in animals challenged with multiple ETEC strains. Structural analysis revealed novel conserved epitopes as critical structural features for pan-ETEC vaccine design. Two of the lead nanobodies, 2R215 and 1D7, were further engineered as trimer or fused with human IgA Fc-fragments as fusionbodies. Oral administration of the trimers or fusionbodies protected mice from infection at a much lower dose compared to the monomeric format. Importantly, fusionbodies prevented infection as a pre-treatment when administrated 2 hours before ETEC challenge to the animals. Together, our study provides the first proof of concept that oral administration of a single nanobody could confer broad protection against major pathogenic ETEC strains. Technological advances in large-scale manufacturing of biological proteins in plants and microorganisms will make nanobody-based immunotherapy a potent and cost-effective prophylaxis or treatment for ETEC.

microbiology↗

bioRxiv2020

IgA MAb blocks SARS-CoV-2 Spike-ACE2 interaction providing mucosal immunity

COVID-19 caused by SARS-CoV-2 has become a global pandemic requiring the development of interventions for the prevention or treatment to curtail mortality and morbidity. No vaccine to boost mucosal immunity or as a therapeutic has yet been developed to SARS-CoV-2. In this study we discover and characterize a cross-reactive human IgA monoclonal antibody, MAb362. MAb362 binds to both SARS-CoV and SARS-CoV-2 spike proteins and competitively blocks hACE2 receptor binding, by completely overlapping the hACE2 structural binding epitope. Furthermore, MAb362 IgA neutralizes both pseudotyped SARS-CoV and SARS-CoV-2 in human epithelial cells expressing hACE2. SARS-CoV-2 specific IgA antibodies, such as MAb362, may provide effective immunity against SARS-CoV-2 by inducing mucosal immunity within the respiratory system, a potentially critical feature of an effective vaccine.

microbiology↗

bioRxiv2018

Identification and Characterization of Human Monoclonal Antibodies for Immunoprophylaxis Against Enterotoxigenic Escherichia coli Infection

BackgroundEnterotoxigenic Escherichia coli (ETEC) cause diarrheal illness in infants in the developing world and travelers to endemic countries including military personnel. ETEC infection of the host involves colonization of the small intestinal epithelium and toxin secretion leading to watery diarrhea. There is currently no vaccine licensed to prevent ETEC. CFA/I is one of the most common colonization factor antigens (CFAs). The CFA/I adhesin subunit, CfaE, is required for ETEC adhesion to host intestinal cells. Human antibodies against CfaE have potential to block colonization of ETEC and serve as an immunoprophylactic against ETEC-related diarrhea.\n\nMethodsMice transgenic for human immunoglobulin genes were immunized with CfaE to generate a panel of human monoclonal IgG1 antibodies (HuMAbs). The most potent IgG1 identified in the in vitro functional assays were selected and isotype switched to secretory IgA (sIgA) and tested in animal colonization assays via oral administration.\n\nResultsOver 300 unique anti-CfaE IgG1 HuMabs were identified. The lead IgG1 anti-CfaE HuMAbs completely inhibited hemagglutination and blocked adhesion of ETEC to Caco-2 cells. Epitope mapping studies revealed that HuMAbs recognized epitopes in the N-terminal domain of CfaE near the putative receptor binding site. Oral administration of anti-CfaE antibodies in either IgG or secretory IgA isotypes inhibited intestinal colonization in mice challenged with ETEC. A two to four log decrease of colony forming units was observed as compared to irrelevant isotype controls.\n\nConclusionsWe identified fully human monoclonal antibodies against CfaE adhesion domain that can be potentially employed as an immunoprophylaxis to prevent ETEC-related diarrhea.

microbiology↗