Plant expression of chicken secretory antibodies derived from combinatorial libraries.

Delivery of secretory IgA antibodies (sIgA) to mucosal surfaces is a promising strategy to passively prevent infectious diseases. Plants have been proposed as biofactories for such complex immunoglobulin molecules. Recently, the molecular characterization of all four monomers of chicken sIgA (IgA immunoglobulin heavy and light chains, J-chain and secretory component) has been completed, allowing recombinant, up scaled production of chicken sIgA and extension of passive immune strategies to poultry. To test the suitability of the plant cell factory for bulk production of chicken sIgA, we studied the expression of chicken IgA, dIgA and sIgA in planta. To that end, new cassettes were designed that allowed the grafting of immunoglobulin variable regions derived from combinatorial libraries into full-size chicken IgA frames ready for plant expression. Using this system, 10 individual phage display clones, which had previously been selected against Eimeria acervulina antigens, were transferred "from phage to plant". Plant-made chicken antibodies showed strong differences in expression levels, which seemed governed mainly by the stability of their respective light chains. Finally, with the co-expression of chicken IgA heavy and light chains, J-chain and secretory component in N. benthamiana leaves we showed that plant cells are suitable biofactories for the production of assembled chicken sIgA complexes.