A Novel DT40 Antibody Library for the Generation of Monoclonal Antibodies

Monoclonal antibody generation by controlled immunoglobulin gene rearrangements

Monoclonal antibodies (mAbs) are essential for various applications including experimental reagents, diagnostics, and therapeutics. Thus, the platform technologies that stably generate antigen-specific mAbs are increasingly crucial. We previously developed a method to generate mAbs, termed the "ADLib system", utilizing the avian-derived B cell line DT40. Avian immunoglobulin (Ig) genes diversify principally through gene conversion-a kind of homologous recombination. The ADLib system isolates antigen-specific clones from libraries constructed using DT40 cells treated with Trichostatin A (TSA), a histone deacetylase inhibitor that enhances gene conversion frequencies. The obtained antigen-specific clones are cultured without TSA to minimize further diversification. However, low-frequency spontaneous gene conversion still occurs, potentially leading to gradual changes in the specificity of the clones. To address this, we engineered conditional mutants of activation-induced deaminase (AID), the initiator of gene conversion, using auxin-inducible degron system which enables targeted protein degradation via the auxin-dependent ubiquitin-proteasome pathway. The addition of the phytohormone auxin led to the degradation of degron-tagged AID proteins, effectively halting gene conversion. Subsequently, we carried out the ADLib system using these clones and successfully isolated antigen-specific mAbs. These suggest that our AID conditional mutants provide a powerful tool for generating and stabilizing antigen-specific clones isolated by the ADLib system.

Molecular mechanisms of avian immunoglobulin gene diversification and prospect for industrial applications

Poultry immunoglobulin genes undergo diversification through homologous recombination (HR) and somatic hypermutation (SHM). Most animals share a similar system in immunoglobulin diversification, with the rare exception that human and murine immunoglobulin genes diversify through V(D)J recombination. Poultry possesses only one functional variable gene for each immunoglobulin heavy (HC) and light chains (LC), with clusters of non-productive pseudogenes upstream. During the B cell development, the functional variable gene is overwritten by sequences from the pseudo-variable genes via a process known as gene conversion (GC), a kind of HR. Point mutations caused in the functional variable gene also contribute to immunoglobulin diversification. This review discusses the latest findings on the molecular mechanisms of antibody gene diversification in poultry, using chickens as a model. Additionally, it will outline how these basic research findings have recently been applied especially in the medical field.

Methods and cell-based strategies to produce antibody libraries: current state

Antibodies are critical components of the adaptive immune system, whose therapeutic applications have been growing exponentially in the last years. Discovery and development of therapeutic antibodies encompasses in vivo immunization, synthetic libraries, and surface display methodologies. To overcome some of their limitations, several platforms in higher eukaryotic cells have been developed. Moreover, these platforms aim to replicate in the bench both primary and secondary antibody diversification mechanisms that occur in vivo. Here, we describe the latest strategies that have been used to mirror both naïve and affinity-maturated antibody repertoire. KEY POINTS: • Therapeutic antibodies are one of the most promising classes of drugs to fight diseases. • Antibodies discovered through hybridoma or display technologies require further engineering. • Innovative antibody discovery platforms in higher eukaryotic cells have been developed.