The simplified secretory-IgA (SSIgA) format is especially interesting; it is a stable multivalent IgA format made up of four VHH-IgA chain one J chain and a secretory component, more suitable for application at the mucosal surfaces like the gastric mucosa. Our current efforts are focused on further optimizing the expression to obtain high amounts of assembled sSIgA by exploring efficient plant transformation with the constituting components. For instance, we have observed extreme difference in levels of assembled sSIgA in plants cotransformants with 3 T-DNAs each encoding one of the components compared with one T-DNA containing the the three constituting elements in tandem. Further, other factors like the influence of gene copy number of each component and the protein expression on the efficiency of assembly of sSIgA will be determined. Aiming toward eventual valorization, we are investigating the production of antibodies in the seeds of protein-rich seed crop plants like soybean and pea. In collaboration with the Lab of Inge Broer (University of Rostock), pea transformants were obtained, and in the service facility of Kan Wang (Iowa State University) soya transformants were generated with 3 different antibody constructs. Comparing different expression cassettes, the possibilities and opportunities of each platform are being evaluated. Further, the seed produced antibodies in these different platforms are being characterized for their functionality, proteolysis and glycosylation profile, and the stability of the different formats of plant-made antibodies are being studied in various conditions and environments. It was already demonstrated that the recombinant antibodies stored in intact seeds are stable over several years. Now, a biochemical heat resistance profile on functionality will be made for purified antibodies and for antibodies in the seed matrix. In parallel, together with the Callewaert lab (Unit of Medical Biotechnology, VIB-Ghent University), we are developing novel strategies for glyco-engineering in plants as the plant-specific N-glycans may represent immunogenic epitopes for humans and animals when used as injectables. This is especially important when the seeds would be used to stockpile therapeutic recombinant antibodies that could be purified in emergencies like disease outbreaks (cfr the ZMapp antibodies protecting against ebola).
Our group demonstrated that designer simple monomeric, dimeric and secretory antibodies, devoid of light chains and based on IgAs, are efficiently produced in Arabidopsis seeds.