Thioredoxin-Displayed Multipeptide Immunogens

Enhanced immunogenicity of a positively supercharged archaeon thioredoxin scaffold as a cell-penetrating antigen carrier for peptide vaccines

Polycationic resurfaced proteins hold great promise as cell-penetrating bioreagents but their use as carriers for the intracellular delivery of peptide immuno-epitopes has not thus far been explored. Here, we report on the construction and functional characterization of a positively supercharged derivative of Pyrococcus furiosus thioredoxin (PfTrx), a thermally hyperstable protein we have previously validated as a peptide epitope display and immunogenicity enhancing scaffold. Genetic conversion of 13 selected amino acids to lysine residues conferred to PfTrx a net charge of +21 (starting from the -1 charge of the wild-type protein), along with the ability to bind nucleic acids. In its unfused form, +21 PfTrx was readily internalized by HeLa cells and displayed a predominantly cytosolic localization. A different intracellular distribution was observed for a +21 PfTrx-eGFP fusion protein, which although still capable of cell penetration was predominantly localized within endosomes. A mixed cytosolic/endosomal partitioning was observed for a +21 PfTrx derivative harboring three tandemly repeated copies of a previously validated HPV16-L2 (aa 20-38) B-cell epitope grafted to the display site of thioredoxin. Compared to its wild-type counterpart, the positively supercharged antigen induced a faster immune response and displayed an overall superior immunogenicity, including a substantial degree of self-adjuvancy. Altogether, the present data point to +21 PfTrx as a promising novel carrier for intracellular antigen delivery and the construction of potentiated recombinant subunit vaccines.

Strategies for Generating Diverse Antibody Repertoires Using Transgenic Animals Expressing Human Antibodies

Therapeutic molecules derived from antibodies have become a dominant class of drugs used to treat human disease. Increasingly, therapeutic antibodies are discovered using transgenic animal systems that have been engineered to express human antibodies. While the engineering details differ, these platforms share the ability to raise an immune response that is comprised of antibodies with fully human idiotypes. Although the predominant transgenic host species has been mouse, the genomes of rats, rabbits, chickens, and cows have also been modified to express human antibodies. The creation of transgenic animal platforms expressing human antibody repertoires has revolutionized therapeutic antibody drug discovery. The observation that the immune systems of these animals are able to recognize and respond to a wide range of therapeutically relevant human targets has led to a surge in antibody-derived drugs in current development. While the clinical success of fully human monoclonal antibodies derived from transgenic animals is well established, recent trends have seen increasingly stringent functional design goals and a shift in difficulty as the industry attempts to tackle the next generation of disease-associated targets. These challenges have been met with a number of novel approaches focused on the generation of large, high-quality, and diverse antibody repertoires. In this perspective, we describe some of the strategies and considerations we use for manipulating the immune systems of transgenic animal platforms (such as XenoMouse^®) with a focus on maximizing the diversity of the primary response and steering the ensuing antibody repertoire toward a desired outcome.

Broadly neutralizing antiviral responses induced by a single-molecule HPV vaccine based on thermostable thioredoxin-L2 multiepitope nanoparticles

Vaccines targeting the human papillomavirus (HPV) minor capsid protein L2 are emerging as chemico-physically robust and broadly protective alternatives to the current HPV (L1-VLP) vaccines. We have previously developed a trivalent L2 vaccine prototype exploiting Pyrococcus furiosus thioredoxin (PfTrx) as a thermostable scaffold for the separate presentation of three distinct HPV L2(20–38) epitopes. With the aim of achieving a highly immunogenic, yet simpler and more GMP-production affordable formulation, we report here on a novel thermostable nanoparticle vaccine relying on genetic fusion of PfTrx-L2 with the heptamerizing coiled-coil polypeptide OVX313. A prototype HPV16 monoepitope version of this nanoparticle vaccine (PfTrx-L2-OVX313; median radius: 8.6 ± 1.0 nm) proved to be approximately 10-fold more immunogenic and with a strikingly enhanced cross-neutralization capacity compared to its monomeric counterpart. Vaccine-induced (cross-)neutralizing responses were further potentiated in a multiepitope derivative displaying eight different L2(20–38) epitopes, which elicited neutralizing antibodies against 10 different HPVs including three viral types not represented in the vaccine. Considering the prospective safety of the PfTrx scaffold and of the OVX313 heptamerization module, PfTrx-OVX313 nanoparticles lend themselves as robust L2-based immunogens with a high translational potential as a 3^rd generation HPV vaccine, but also as a novel and extremely versatile peptide-antigen presentation platform.

Secretory production of designed multipeptides displayed on a thermostable bacterial thioredoxin scaffold in Pichia pastoris

Internal grafting of designed peptides to scaffold proteins is a valuable strategy for a variety of applications including recombinant peptide antigen construction. A peptide epitope from human papillomavirus (HPV) minor capsid protein L2 displayed on thioredoxin (Trx) has been validated preclinically as a broadly protective and low-cost alternative HPV vaccine. Focusing on thioredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus (PfTrx) as a scaffold, we have constructed a modified Pichia pastoris expression vector and used a PfTrx fusion derivative containing three tandemly repeated copies of a 19 amino acids peptide epitope from HPV-L2 for expression optimization and biochemical-immunological characterization of the Pichia-produced PfTrx-L2 antigen. We show that PfTrx-L2 is produced at high levels (up to 100 mg from a 100 ml starting culture using a multi-cycle induction protocol) and secreted into the culture medium as a highly enriched (>70% pure), non-glycosylated polypeptide that can be purified to homogeneity in a single step. Oxidation and aggregation state, thermal stability and immunogenicity of the endotoxin-free PfTrx-L2 antigen produced in P. pastoris were tested and found to be identical to those of the same antigen produced in Escherichia coli. Secretory production of endotoxin-free PfTrx-peptides in P. pastoris represents a cost- and time-effective alternative to E. coli production. Specifically designed for peptide antigens, the PfTrx-expression vector and conditions described herein are easily transferable to a variety of applications centred on the use of structurally constrained bioactive peptides as immune as well as target-specific binder reagents.