Engineered Bovine Antibodies in the Development of Novel Therapeutics, Immunomodulators and Vaccines

Broadly Neutralizing Bovine Antibodies: Highly Effective New Tools against Evasive Pathogens?

Potent antibody-mediated neutralization is critical for an organism to combat the vast array of pathogens it will face during its lifetime. Due to the potential genetic diversity of some viruses, such as HIV-1 and influenza, standard neutralizing antibodies are often ineffective or easily evaded as their targets are masked or rapidly mutated. This has thwarted efforts to both prevent and treat HIV-1 infections and means that entirely new formulations are required to vaccinate against influenza each year. However, some rare antibodies isolated from infected individuals confer broad and potent neutralization. A subset of these broadly neutralizing antibodies possesses a long complementarity-determining 3 region of the immunoglobulin heavy chain (CDR H3). This feature generates unique antigen binding site configurations that can engage conserved but otherwise inaccessible epitope targets thus neutralizing many viral variants. Remarkably, ultralong CDR H3s are a common feature of the cow antibody repertoire and are encoded by a single variable, diversity, joining (VDJ) recombination that is extensively diversified prior to antigen exposure. Recently, it was shown that cows rapidly generate a broadly neutralizing response upon exposure to HIV-1 and this is primarily mediated by these novel ultralong antibody types. This review summarises the current knowledge of these unusual CDR H3 structures and discusses their known and potential future uses.

Cognizance of Molecular Methods for the Generation of Mutagenic Phage Display Antibody Libraries for Affinity Maturation

Antibodies leverage on their unique architecture to bind with an array of antigens. The strength of interaction has a direct relation to the affinity of the antibodies towards the antigen. In vivo affinity maturation is performed through multiple rounds of somatic hypermutation and selection in the germinal centre. This unique process involves intricate sequence rearrangements at the gene level via molecular mechanisms. The emergence of in vitro display technologies, mainly phage display and recombinant DNA technology, has helped revolutionize the way antibody improvements are being carried out in the laboratory. The adaptation of molecular approaches in vitro to replicate the in vivo processes has allowed for improvements in the way recombinant antibodies are designed and tuned. Combinatorial libraries, consisting of a myriad of possible antibodies, are capable of replicating the diversity of the natural human antibody repertoire. The isolation of target-specific antibodies with specific affinity characteristics can also be accomplished through modification of stringent protocols. Despite the ability to screen and select for high-affinity binders, some 'fine tuning' may be required to enhance antibody binding in terms of its affinity. This review will provide a brief account of phage display technology used for antibody generation followed by a summary of different combinatorial library characteristics. The review will focus on available strategies, which include molecular approaches, next generation sequencing, and in silico approaches used for antibody affinity maturation in both therapeutic and diagnostic applications.

Exceptionally long CDR3H of bovine scFv antigenized with BoHV-1 B-epitope generates specific immune response against the targeted epitope

We discovered that some bovine antibodies are amongst the largest known to exist due to the presence of an exceptionally long CDR3H (≥49 amino acids) with multiple cysteines that provide a unique knob and stalk structure to the antigen binding site. The large CDR3H size, unlike mouse and human, provides a suitable platform for antigenization with large configurational B-epitopes. Here we report the identification of a B-epitope on the gC envelope protein of bovine herpes virus type-1 (BoHV-1) recognized by a bovine IgG1 antibody. The identified 156 amino acid long gC fragment (gC156) was expressed as a recombinant protein. Subsequently, a functional scFv fragment with a 61 amino-acid long CDR3H (scFv1H12) was expressed such that gC156 was grafted into the CDR3H, replacing the "knob" region (gC156scFv1H12 or Ag-scFv). Importantly, the Ag-scFv could be recognized by a neutralizing antibody fragment (scFv3-18L), which suggests that the engraftment of gC156 into the CDR3H of 1H12 maintained the native conformation of the BoHV-1 B-epitope. A 3D model of gC156 was generated using fold-recognition approaches and this was grafted onto the CDR3H stalk of the 1H12 Fab crystal structure to predict the 3D structure of the Ag-scFv. The grafted antigen in Ag-scFv is predicted to have a compact conformation with the ability to protrude into the solvent. Upon immunization of bovine calves, the antigenized scFv (gC156scFv1H12) induced a higher antibody response as compared to free recombinant gC156. These observations suggest that antigenization of bovine scFv with an exceptionally long CDR3H provides a novel approach to developing the next generation of vaccines against infectious agents that require induction of protective humoral immunity.