Heavy chain-only immunoglobulins are naturally produced in camelids and sharks and their potential uses have intrigued the biomedical field for years. Because the structure does not utilize light chain, the antigen-binding region (VH of heavy chain-only, or VHH) is half the size of a traditional antibody, allowing for unique interactions with antigenic epitopes. Chicken immunoglobulins have a standard heterodimeric structure comprised of both heavy and light chains, and do not naturally include VHH forms. We have developed an engineered chicken that produces VHH antibodies with human variable regions. In these birds, the human VH contains select framework mutations to provide stability and a truncated light chain that facilitates immunoglobulin secretion in the absence of the VL domain. Productive B-cell development is observed in these transgenic birds, which express normal levels of serum IgM and reduced levels of IgY. When three different targets were immunized into the VHH chickens, robust immune responses were observed. Recovered antigen-specific VHH antibodies offered a diverse repertoire of VHH sequences, broad epitope coverage, and binding affinities reaching single-digit nM KD.
