How does the recombinant human interferon beta induce antibodies in immune tolerant mice?

Therapeutic proteins revolutionized the treatment of severe diseases like multiple sclerosis, diabetes, haemophilia and many more. Unfortunately, their usage is often limited due to the formation of anti drug antibodies (ADAs), which may block the activity of these protein drugs and may lead to immune-related side effects. In order to better understand the mechanism underlying the formation of ADAs we performed a series of experiments in immune tolerant transgenic mice. These mice express a specific human protein and therefore build tolerance towards it, like humans do. Formation of ADAs against the corresponding therapeutic protein therefore occurs via a similar mechanism as in patients. Our results show that for recombinant human interferon beta products, immunogenicity strongly depends on the route of administration and ADA production increases with increasing dose and frequency of injections. Also we show that ADA response, especially during its early stages, is CD4+ T-cell dependent. Nonetheless, several characteristics usually associated with CD4+ T-cell dependent responses (formation of memory, susceptibility for adjuvant stimulation) are lacking. Commonly used immune adjuvants fail to enhance the ADA production, and even if they increased ADA production no apparent immunological memory is formed. In addition, we show that protein aggregation alters biodistribution of the drug as aggregates are retained at the site of injection after intramuscular and subcutaneous administration. Also aggregates are probably taken up by immune cells of the lungs, liver and spleen after intaperitoneal and/or intravenous administration. Taken together, the data described in this thesis emphasize that the mechanism underlying immunogenicity of therapeutic proteins is a novel, undescribed mechanism and not a classical immune response. Full understanding of this mechanism is necessary to improve efficiency and safety of existing and newly developed therapeutic proteins.