Expression, purification, and functional analysis of an antigen-targeting fusion protein composed of CD40 ligand and the C-terminal fragment of ovalbumin

Recent advances in antigen targeting to antigen-presenting cells in veterinary medicine

Advances in antigen targeting in veterinary medicine have gained traction over the years as an alternative approach for diseases that remain a challenge for traditional vaccines. In addition to the nature of the immunogen, antigen-targeting success relies heavily on the chosen receptor for its direct influence on the elicited response that will ensue after antigen uptake. Different approaches using antibodies, natural or synthetic ligands, fused proteins, and DNA vaccines have been explored in various veterinary species, with pigs, cattle, sheep, and poultry as the most frequent models. Antigen-presenting cells can be targeted using a generic approach, such as broadly expressed receptors such as MHC-II, CD80/86, CD40, CD83, etc., or focused on specific cell populations such as dendritic cells or macrophages (Langerin, DC-SIGN, XCR1, DC peptides, sialoadhesin, mannose receptors, etc.) with contrasting results. Interestingly, DC peptides show high specificity to DCs, boosting activation, stimulating cellular and humoral responses, and a higher rate of clinical protection. Likewise, MHC-II targeting shows consistent results in enhancing both immune responses; an example of this strategy of targeting is the approved vaccine against the bovine viral diarrhea virus in South America. This significant milestone opens the door to continuing efforts toward antigen-targeting vaccines to benefit animal health. This review discusses the recent advances in antigen targeting to antigen-presenting cells in veterinary medicine, with a special interest in pigs, sheep, cattle, poultry, and dogs.

Anti-CD40 Antibody Fused to CD40 Ligand Is a Superagonist Platform for Adjuvant Intrinsic DC-Targeting Vaccines

CD40 is a potent activating receptor expressed on antigen-presenting cells (APCs) of the immune system. CD40 regulates many aspects of B and T cell immunity via interaction with CD40L expressed on activated T cells. Targeting antigens to CD40 via agonistic anti-CD40 antibody fusions promotes both humoral and cellular immunity, but current anti-CD40 antibody-antigen vaccine prototypes require co-adjuvant administration for significant in vivo efficacy. This may be a consequence of dulling of anti-CD40 agonist activity via antigen fusion. We previously demonstrated that direct fusion of CD40L to anti-CD40 antibodies confers superagonist properties. Here we show that anti-CD40-CD40L-antigen fusion constructs retain strong agonist activity, particularly for activation of dendritic cells (DCs). Therefore, we tested anti-CD40-CD40L antibody fused to antigens for eliciting immune responses in vitro and in vivo. In PBMC cultures from HIV-1-infected donors, anti-CD40-CD40L fused to HIV-1 antigens preferentially expanded HIV-1-specific CD8+ T cells versus CD4+ T cells compared to analogous anti-CD40-antigen constructs. In normal donors, anti-CD40-CD40L-mediated delivery of Influenza M1 protein elicited M1-specific T cell expansion at lower doses compared to anti-CD40-mediated delivery. Also, on human myeloid-derived dendritic cells, anti-CD40-CD40L-melanoma gp100 peptide induced more sustained Class I antigen presentation compared to anti-CD40-gp100 peptide. In human CD40 transgenic mice, anti-CD40-CD40L-HIV-1 gp140 administered without adjuvant elicited superior antibody responses compared to anti-CD40-gp140 antigen without fused CD40L. In human CD40 mice, compared to the anti-CD40 vehicle, anti-CD40-CD40L delivery of Eα 52-68 peptide elicited proliferating of TCR I-Eα 52-68 CD4+ T cells producing cytokine IFNγ. Also, compared to controls, only anti-CD40-CD40L-Cyclin D1 vaccination of human CD40 mice reduced implanted EO771.LMB breast tumor cell growth. These data demonstrate that human CD40-CD40L antibody fused to antigens maintains highly agonistic activity and generates immune responses distinct from existing low agonist anti-CD40 targeting formats. These advantages were in vitro skewing responses towards CD8+ T cells, increased efficacy at low doses, and longevity of MHC Class I peptide display; and in mouse models, a more robust humoral response, more activated CD4+ T cells, and control of tumor growth. Thus, the anti-CD40-CD40L format offers an alternate DC-targeting platform with unique properties, including intrinsic adjuvant activity.

Strategies for Optimizing the Production of Proteins and Peptides with Multiple Disulfide Bonds

Bacteria can produce recombinant proteins quickly and cost effectively. However, their physiological properties limit their use for the production of proteins in their native form, especially polypeptides that are subjected to major post-translational modifications. Proteins that rely on disulfide bridges for their stability are difficult to produce in Escherichia coli. The bacterium offers the least costly, simplest, and fastest method for protein production. However, it is difficult to produce proteins with a very large size. Saccharomyces cerevisiae and Pichia pastoris are the most commonly used yeast species for protein production. At a low expense, yeasts can offer high protein yields, generate proteins with a molecular weight greater than 50 kDa, extract signal sequences, and glycosylate proteins. Both eukaryotic and prokaryotic species maintain reducing conditions in the cytoplasm. Hence, the formation of disulfide bonds is inhibited. These bonds are formed in eukaryotic cells during the export cycle, under the oxidizing conditions of the endoplasmic reticulum. Bacteria do not have an advanced subcellular space, but in the oxidizing periplasm, they exhibit both export systems and enzymatic activities directed at the formation and quality of disulfide bonds. Here, we discuss current techniques used to target eukaryotic and prokaryotic species for the generation of correctly folded proteins with disulfide bonds.

The MsrAB reducing pathway of Streptococcus gordonii is needed for oxidative stress tolerance, biofilm formation, and oral colonization in mice

The ability of Streptococcus gordonii to cope with oxidative stress is important for survival and persistence in dental plaque. In this study, we used mutational, phenotypic, and biochemical approaches to characterize the role of a methionine sulfoxide reductase (MsrAB) and proteins encoded by genes in the msrAB operon and an adjacent operon in oxidative stress tolerance in S. gordonii. The results showed that MsrAB and four other proteins encoded in the operons are needed for protection from H₂O₂ and methionine sulfoxide. These five proteins formed a reducing pathway that was needed for oxidative stress tolerance, biofilm formation, and oral colonization in mice. In the pathway, MsrAB was the enzyme that repaired oxidatively damaged proteins, and the two thioredoxin-like lipoproteins (SdbB and Sgo_1177) and two CcdA proteins were proteins that maintained the catalytic cycle of MsrAB. Consistent with the role in oxidative stress tolerance, the production of MsrAB, SdbB, and Sgo_11777 was induced in aerobic growth and planktonic cells.

Codon optimization significantly enhanced the expression of human 37-kDa iLRP in Escherichia coli

37-kDa immature laminin receptor protein (iLRP), the precursor of 67-kDa laminin receptor protein (LRP), is overexpressed on the surface of most cancer cells and recognized as a universal tumor antigen. The role makes it a potential target for cancer immunotherapy, which has been well-studied. Our study aimed to produce high quality of human iLRP in bacteria so that the needs in research of its clinical application could be met. The powerful system for heterologous protein expression, pET system was used. Two types of DNA sequences encoding the same amino acid sequences were separately cloned into the vector pET30a(+). One of the resulting vectors includes the wild-type iLRP, and other one includes the codon-optimized iLRP. The expression by both genes was then compared in Escherichia coli BL21(DE3). Our results revealed that the performance of codon optimization was crucial for the expression of human iLRP in Escherichia coli. The yield was significantly enhanced up to 300 mg/L of bacterial culture by this approach.