Design and expression of polymeric immunoglobulin fusion proteins: a strategy for targeting low-affinity Fcgamma receptors

A polymeric immunoglobulin-antigen fusion protein strategy for enhancing vaccine immunogenicity

In this study, a strategy based on polymeric immunoglobulin G scaffolds (PIGS) was used to produce a vaccine candidate for Mycobacterium tuberculosis. A genetic fusion construct comprising genes encoding the mycobacterial Ag85B antigen, an immunoglobulin γ-chain fragment and the tailpiece from immunoglobulin μ chain was engineered. Expression was attempted in Chinese Hamster Ovary (CHO) cells and in Nicotiana benthamiana. The recombinant protein assembled into polymeric structures (TB-PIGS) in N. benthamiana, similar in size to polymeric IgM. These complexes were subsequently shown to bind to the complement protein C1q and FcγRs with increased affinity. Modification of the N-glycans linked to TB-PIGS by removal of xylose and fucose residues that are normally found in plant glycosylated proteins also resulted in increased affinity for low-affinity FcγRs. Immunization studies in mice indicated that TB-PIGS are highly immunogenic with and without adjuvant. However, they did not improve protective efficacy in mice against challenge with M. tuberculosis compared to conventional vaccination with BCG, suggesting that additional or alternative antigens may be needed to protect against this disease. Nevertheless, these results establish a novel platform for producing polymeric antigen-IgG γ-chain molecules with inherent functional characteristics that are desirable in vaccines.

Rapid immune responses to a botulinum neurotoxin Hc subunit vaccine through in vivo targeting to antigen-presenting cells

The clostridial botulinum neurotoxins (BoNTs) are the most potent protein toxins known. The carboxyl-terminal fragment of the toxin heavy chain (Hc) has been intensively investigated as a BoNT vaccine immunogen. We sought to determine whether targeting Hc to antigen-presenting cells (APCs) could accelerate the immune responses to vaccination with BoNT serotype A (BoNT/A) Hc. To test this hypothesis, we targeted Hc to the Fc receptors for IgG (FcγRs) expressed by dendritic cells (DCs) and other APCs. Hc was expressed as a fusion protein with a recombinant ligand for human FcγRs (R4) to produce HcR4 or a similar ligand for murine FcγRs to produce HcmR4. HcR4, HcmR4, and Hc were produced as secreted proteins using baculovirus-mediated expression in SF9 insect cells. In vitro receptor binding assays showed that HcR4 effectively targets Hc to all classes of FcγRs. APCs loaded with HcR4 or HcmR4 are substantially more effective at stimulating Hc-reactive T cells than APCs loaded with nontargeted Hc. Mice immunized with a single dose of HcmR4 or HcR4 had earlier and markedly higher Hc-reactive antibody titers than mice immunized with nontargeted Hc. These results extend to BoNT neutralizing antibody titers, which are substantially higher in mice immunized with HcmR4 than in mice immunized with Hc. Our results demonstrate that targeting Hc to FcγRs augments the pace and magnitude of immune responses to Hc.

A novel Fc gamma receptor ligand augments humoral responses by targeting antigen to Fc gamma receptors

Generating efficient antibody (Ab) responses against weak antigens remains challenging. Ab responses require antigen (Ag) uptake by antigen-presenting cells (APC), followed by presentation of processed Ag to T cells. Limited uptake of antigenic peptides by APC constrains Ab responses. Here we improve vaccine efficacy by targeting Ag to Fcgamma receptors (FcgammaR) using R4, a recombinant FcgammaR ligand. R4 has four repeats per chain of the hinge region and CH2 domain (HCH2) of human IgG1. HCH2 encompasses the FcgammaR binding site. The repeats are linked to the human IgG1 framework. To test R4 in augmenting Ag uptake, we expressed human serum albumin domain 1 (HSA1) at the N terminus of R4 to produce HSA1R4. HSA1R4 (50 microg) administered to mice in Ribi adjuvant induces up to 1100-fold higher HSA1-specific IgG titers than HSA1 (p<0.001). HSA1R4 (250 ng) induces up to 130 times more anti-HSA1 Ab than HSA1Fc, a protein with HSA1 linked to the IgG1 framework (p<0.001). HSA-reactive T cells proliferate more briskly to HSA1R4 than to HSA1Fc (p<0.008). Immunization with HSA1R4 yields greater T cell reactivity to HSA1 ex vivo than immunization with HSA1Fc (p<0.004). Linking antigenic peptides to linear HCH2 polymers may facilitate vaccine development.

Neutralizing antibodies in multiple sclerosis: a complex impact on interferon responses, magnetic resonance imaging findings and clinical outcomes

Interferon beta (IFN-β) therapy reduces relapse rate, MRI lesion development, and delays the progression of disability in relapsing forms of multiple sclerosis. As with other protein therapies, some patients develop neutralizing antibodies (NAbs) that could limit the efficacy of IFN-β. The clinical impact of NAbs is hotly debated. Non-standardized NAb assays, NAb persistence and disappearance, plus a six-month lag before a clinical effect, different IFN-β species and formulations, variable trial duration, have made interpretation of the significance of NAbs a challenging task. There is a correlation between the presence of NAb and reduced efficacy of IFN-β therapy in two- to four-year trials. However, patients destined to become NAb positive do better in the first year of IFN-β therapy. Patients with clinical worsening have surprisingly low NAb frequency and titers. Understanding the true clinical implications of NAbs will require well-controlled longitudinal studies instead of simple cross-sectional analyses, plus innovative trial designs with immune biomarkers. Multiple Sclerosis 2007; 13: S53—S62. http://msj.sagepub.com

Stably Transformed Insect Cell Lines: Tools for Expression of Secreted and Membrane‐anchored Proteins and High‐throughput Screening Platforms for Drug and Insecticide Discovery

Insect cell-based expression systems are prominent amongst current expression platforms for their ability to express virtually all types of heterologous recombinant proteins. Stably transformed insect cell lines represent an attractive alternative to the baculovirus expression system, particularly for the production of secreted and membrane-anchored proteins. For this reason, transformed insect cell systems are receiving increased attention from the research community and the biotechnology industry. In this article, we review recent developments in the field of insect cell-based expression from two main perspectives, the production of secreted and membrane-anchored proteins and the establishment of novel methodological tools for the identification of bioactive compounds that can be used as research reagents and leads for new pharmaceuticals and insecticides.

Preparative electrophoresis: a general method for the purification of polyclonal antibodies

Antibodies were purified from normal rabbit, sheep, goat, rat, human and bovine serum using preparative electrophoresis on a Gradiflow in a single-step process using an asymmetrical cartridge with three different pore size polyacrylamide membranes. Recoveries in each case were over 80% and were higher than those obtained using affinity chromatography on protein A, protein G or protein L. Degree of purity was at least comparable with these methods. These results suggest that preparative electrophoresis can be considered a general method for the purification of research quantities of antibodies from multiple serum sources and may be particularly useful where the reactivity with protein A, G or L is unknown.