Generation of human sequence antibodies in OmniChicken against the highly conserved mammalian target BDNF using three distinct discovery workflows

Generation of antibodies against highly conserved mammalian targets remains a substantial challenge in the therapeutic antibody space. Naïve and synthetic libraries address this need through rounds of in vitro affinity maturation. In vivo affinity matured antibodies from hyperimmunization often fail to generate diverse repertoires against conserved targets. Phylogenetically distant species offer an alternative strategy to obtain in vivo affinity-matured antibodies against conserved targets. We used OmniChicken, a transgenic chicken that expresses fully human heavy and light immunoglobulin genes, to generate antibodies against brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family that is dysregulated in chronic pain syndromes and neurological diseases such as Alzheimer's disease. Mature BDNF is 100% conserved between humans and mice. Following immunization of a cohort of OmniChickens, splenocytes were screened using three discovery workflows: Gel Encapsulated Microenvironment (GEM) and xPloration®, which are both single B cell screening platforms, and phage display. In total, we isolated 110 unique antibodies representing 29 unique VH and 32 unique VL lineages, many of which overlapped across the three platforms. Assessment of immunogenicity, including T cell epitope content and "humanness" showed that the cohort compared favorably with a clinical reference set, while biophysical analysis was consistent with good developability characteristics. EC50s were comparable to a benchmark clone, R3bH01, previously developed from a wild-type chicken. Finally, an ELISA-based IC50 assay identified clones from each platform with neutralizing activity. Overall, all three discovery workflows identified diverse lineages of antibodies with desirable developability properties and functionally relevant binding characteristics.