Development of antibody technology to identify natural killer cell surface antigens in Xenopus Laevis

Natural killer (NK)-like lymphocytes have recently been identified in thymectomised (Tx) Xenopus which are capable of spontaneous cytotoxicity towards the MHC- deficient, allogeneic thymus tumour cell line B(_3)B(_7). This Thesis describes attempts to raise antibodies to Xenopus NK cell surface antigens by phage display and hybridoma technology. The phage display technique was optimised for raising antibodies to novel, cellular antigens in a trial run using the Xenopus thymus tumour cell line B(_3)B(_7). Having isolated a phage antibody which was shown by flow cytometry to bind B(_3)B(_7) cells, the technique was then used to try and raise antibodies to Xenopus NK cells. Isolation of an NIC-specific phage antibody was not achieved but phage antibody XL-6 was raised, which bound an antigen on Xenopus lymphocytes. Phage antibody XL-6, and soluble scFv derived from this, were able to identify a putative mature T cell population in the thymus and may be specific for an amphibian homologue of the mammalian leukocyte common antigen CD45. Hybridoma technology was used to isolate three monoclonal antibodies, 1F8, 4D4 and 1G5, which were shown by flow cytometric analysis to identify a putative NK cell population in control and Tx Xenopus. Following immunomagnetic purification, 1F8- positive spleen cells from control and Tx animals were shown to kill the MHC- deficient tumour target B(_3)B(_7), confirming that this antibody was specific for Xenopus NK cells. Western blotting experiments showed that 1F8, 4D4 and 1G5 identified a doublet of protein bands at 72 and 74 kilodaltons in Xenopus gut lymphoid lysates. Initial attempts to isolate cDNA encoding a Xenopus NK cell surface antigen through immunoscreening a xenopus gut cDNA expression library with antibody 1G5 were unsuccessful as was an attempt to clone a Xenopus homologue of the mammalian NK receptor NKR-Pl by PGR

TNFR2 ligation in human T regulatory cells enhances IL2-induced cell proliferation through the non-canonical NF-κB pathway.

Human T regulatory cells (T regs) express high levels of TNF receptor 2 (TNFR2). Ligation of TNFR2 with TNF, which can recognise both TNFR1 and TNFR2, or with a TNFR2-selective binding molecule, DARPin 18 (D18) activates canonical NF-κB signalling, assessed by IκBα degradation, and the magnitude of the response correlates with the level of TNFR2 expression. RNA-seq analysis of TNF- or D18-treated human T regs revealed that TNFR2 ligation induces transcription of NFKB2 and RELB, encoding proteins that form the non-canonical NF-κB transcription factor. In combination with IL2, D18 treatment is specific for T regs in (1) stabilising NF-κB-inducing kinase protein, the activator of non-canonical NF-κB signalling, (2) inducing translocation of RelB from cytosol to nucleus, (3) increasing cell cycle entry, and (4) increasing cell numbers. However, the regulatory function of the expanded T regs is unaltered. Inhibition of RelB nuclear translocation blocks the proliferative response. We conclude that ligation of TNFR2 by D18 enhances IL2-induced T regs proliferation and expansion in cell number through the non-canonical NF-κB pathway

Structure of the trypanosome transferrin receptor reveals mechanisms of ligand recognition and immune evasion.

To maintain prolonged infection of mammals, African trypanosomes have evolved remarkable surface coats and a system of antigenic variation1. Within these coats are receptors for macromolecular nutrients such as transferrin2,3. These must be accessible to their ligands but must not confer susceptibility to immunoglobulin-mediated attack. Trypanosomes have a wide host range and their receptors must also bind ligands from diverse species. To understand how these requirements are achieved, in the context of transferrin uptake, we determined the structure of a Trypanosoma brucei transferrin receptor in complex with human transferrin, showing how this heterodimeric receptor presents a large asymmetric ligand-binding platform. The trypanosome genome contains a family of around 14 transferrin receptors4, which has been proposed to allow binding to transferrin from different mammalian hosts5,6. However, we find that a single receptor can bind transferrin from a broad range of mammals, indicating that receptor variation is unlikely to be necessary for promiscuity of host infection. In contrast, polymorphic sites and N-linked glycans are preferentially found in exposed positions on the receptor surface, not contacting transferrin, suggesting that transferrin receptor diversification is driven by a need for antigenic variation in the receptor to prolong survival in a host

A single dose of antibody-drug conjugate cures a stage 1 model of African trypanosomiasis.

Infections of humans and livestock with African trypanosomes are treated with drugs introduced decades ago that are not always fully effective and often have severe side effects. Here, the trypanosome haptoglobin-haemoglobin receptor (HpHbR) has been exploited as a route of uptake for an antibody-drug conjugate (ADC) that is completely effective against Trypanosoma brucei in the standard mouse model of infection. Recombinant human anti-HpHbR monoclonal antibodies were isolated and shown to be internalised in a receptor-dependent manner. Antibodies were conjugated to a pyrrolobenzodiazepine (PBD) toxin and killed T. brucei in vitro at picomolar concentrations. A single therapeutic dose (0.25 mg/kg) of a HpHbR antibody-PBD conjugate completely cured a T. brucei mouse infection within 2 days with no re-emergence of infection over a subsequent time course of 77 days. These experiments provide a demonstration of how ADCs can be exploited to treat protozoal diseases that desperately require new therapeutics

Deep Sequencing of B Cell Receptor Repertoires From COVID-19 Patients Reveals Strong Convergent Immune Signatures.

Deep sequencing of B cell receptor (BCR) heavy chains from a cohort of 31 COVID-19 patients from the UK reveals a stereotypical naive immune response to SARS-CoV-2 which is consistent across patients. Clonal expansion of the B cell population is also observed and may be the result of memory bystander effects. There was a strong convergent sequence signature across patients, and we identified 1,254 clonotypes convergent between at least four of the COVID-19 patients, but not present in healthy controls or individuals following seasonal influenza vaccination. A subset of the convergent clonotypes were homologous to known SARS and SARS-CoV-2 spike protein neutralizing antibodies. Convergence was also demonstrated across wide geographies by comparison of data sets between patients from UK, USA, and China, further validating the disease association and consistency of the stereotypical immune response even at the sequence level. These convergent clonotypes provide a resource to identify potential therapeutic and prophylactic antibodies and demonstrate the potential of BCR profiling as a tool to help understand patient responses

Phenotypic screening reveals TNFR2 as a promising target for cancer immunotherapy.

Antibodies that target cell-surface molecules on T cells can enhance anti-tumor immune responses, resulting in sustained immune-mediated control of cancer. We set out to find new cancer immunotherapy targets by phenotypic screening on human regulatory T (Treg) cells and report the discovery of novel activators of tumor necrosis factor receptor 2 (TNFR2) and a potential role for this target in immunotherapy. A diverse phage display library was screened to find antibody mimetics with preferential binding to Treg cells, the most Treg-selective of which were all, without exception, found to bind specifically to TNFR2. A subset of these TNFR2 binders were found to agonise the receptor, inducing iκ-B degradation and NF-κB pathway signalling in vitro. TNFR2 was found to be expressed by tumor-infiltrating Treg cells, and to a lesser extent Teff cells, from three lung cancer patients, and a similar pattern was also observed in mice implanted with CT26 syngeneic tumors. In such animals, TNFR2-specific agonists inhibited tumor growth, enhanced tumor infiltration by CD8+ T cells and increased CD8+ T cell IFN-γ synthesis. Together, these data indicate a novel mechanism for TNF-α-independent TNFR2 agonism in cancer immunotherapy, and demonstrate the utility of target-agnostic screening in highlighting important targets during drug discovery.GW, BM, SG, JC-U, AS, AG-M, CB, JJ, RL, AJL, SR, RS, LJ, VV-A, RM and RWW were funded by MedImmune; JP and VB were funded by AstraZeneca PLC; JW, RSA-L and JB were funded by NIHR Cambridge Biomedical Research Centre and Kidney Research UK; JS and JF were funded by Retrogenix Ltd

A receptor for the complement regulator factor H increases transmission of trypanosomes to tsetse flies

Abstract: Persistent pathogens have evolved to avoid elimination by the mammalian immune system including mechanisms to evade complement. Infections with African trypanosomes can persist for years and cause human and animal disease throughout sub-Saharan Africa. It is not known how trypanosomes limit the action of the alternative complement pathway. Here we identify an African trypanosome receptor for mammalian factor H, a negative regulator of the alternative pathway. Structural studies show how the receptor binds ligand, leaving inhibitory domains of factor H free to inactivate complement C3b deposited on the trypanosome surface. Receptor expression is highest in developmental stages transmitted to the tsetse fly vector and those exposed to blood meals in the tsetse gut. Receptor gene deletion reduced tsetse infection, identifying this receptor as a virulence factor for transmission. This demonstrates how a pathogen evolved a molecular mechanism to increase transmission to an insect vector by exploitation of a mammalian complement regulator

Multiplexed Affinity Characterization of Protein Binders Directly from a Crude Cell Lysate by Covalent Capture on Suspension Bead Arrays.

The precise determination of affinity and specificity is a crucial step in the development of new protein reagents for therapy and diagnostics. Paradoxically, the selection of protein binders, e.g., antibody fragments, from large combinatorial repertoires is a rapid process compared to the subsequent characterization of selected clones. Here we demonstrate the use of suspension bead arrays (SBA) in combination with flow cytometry to facilitate the post-selection analysis of binder affinities. The array is designed to capture the proteins of interest (POIs) covalently on the surface of superparamagnetic color-coded microbeads directly from expression cell lysate, based on SpyTag-SpyCatcher coupling by isopeptide bond formation. This concept was validated by analyzing the affinities of a typical phage display output, i.e., clones consisting of single-chain variable fragment antibodies (scFvs), as SpyCatcher fusions in 12- and 24-plex SBA formats using a standard three-laser flow cytometer. We demonstrate that the equilibrium dissociation constants (Kd) obtained from multiplexed SBA assays correlate well with experiments performed on a larger scale, while the antigen consumption was reduced >100-fold compared to the conventional 96-well plate format. Protein screening and characterization by SBAs is a rapid and reagent-saving analytical format for combinatorial protein engineering to address specificity maturation and cross-reactivity profiling of antibodies.Acknowledgements (....) This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) and the EU’s Horizon 2020 programme. TH and LL received individual postdoctoral EU Marie-Curie fellowships. FH is an ERC Advanced Investigator (695669)

Skin test reactions in cutaneous leishmaniasis and chagas disease

Ministério da Saúde. Fundação Serviços de Saúde Pública. Instituto Evandro Chagas. Belém, PA, Brasil.Ministério da Saúde. Fundação Serviços de Saúde Pública. Instituto Evandro Chagas. Belém, PA, Brasil.London School of Hygiene and Tropical Medicine. Keppel Street, London, UK