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Exploitation of interactions with the neonatal Fc receptor to manipulate biological half-lives for therapeutic applications

Time: Fri 2019-09-20 10.30

Location: Oskar Kleins Auditorium, Roslagstullsbacken 21, Albanova University Center, Stockholm (English)

Subject area: Biotechnology

Doctoral student: Shengze Yu , Protein Engineering, Gräslund group

Opponent: Professor Mats Ohlin,

Supervisor: Professor Torbjörn Gräslund, Biokemi och biokemisk teknologi, Bioteknologi, Albanova VinnExcellence Center for Protein Technology, ProNova

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Protein engineering provides powerful tools to create useful proteins with desired properties. In this thesis, rational design principles have been used for development of fusion proteins that can interact with the neonatal Fc receptor (FcRn) for potential medical applications. 

FcRn is widely expressed in the human body. The natural ligands of FcRn are immunoglobulin G (IgG) and serum albumin (SA). FcRn can bind to both proteins in a pH dependent manner and endow them with an unusually long half-life in vivo. Protein building blocks interacting directly or indirectly with FcRn may potentially be used to either piggy-back on the FcRn-system for extension of the in vivo half-life or to saturate the system to decrease the in vivo half-life of the natural ligands. In this thesis, I have explored an FcRn binding affibody molecule (ZFcRn) and/or an albumin binding domain (ABD) for these purposes. 

In study I and II, the prolactin receptor was found to often be expressed in glioblastoma multiforme tumors from patients as well as in glioblastoma multiforme cells lines. We investigated a novel antagonist of the prolactin receptor in vitro and found that it could block signaling through the receptor as well as cellular invasiveness. An antagonist of prolactin receptor could thus potentially become a drug for treatment of glioblastoma multiforme. However, the antagonist will likely have a short plasma half-life due to its small molecular size, which limits its usability. Therefore, it was expressed as a fusion to ABD, which interacts indirectly with FcRn. The produced fusion protein was found to be able to block signaling through the prolactin receptor in vitro and also had a prolonged plasma half-life in vivo

The goal of study III was to investigate the properties of human growth hormone (hGH) when it was expressed as a protein fusion with ZFcRn, interacting directly with FcRn, and/or ABD. The fusion proteins, ZFcRn-hGH, ABD-hGH, and ZFcRn-ABD-hGH could be recombinantly expressed and successfully purified to homogeneity. They had the expected binding abilities to FcRn, SA and hGH receptor. They were all found to be able to induce signaling over the plasma membrane in a model cell line. 

Patients suffering from many autoimmune diseases produce particular IgG molecules, which are responsible for the disease symptoms. A potential treatment could be to increase the catabolism of these IgGs to relieve disease symptoms. In study IV, an FcRn interacting affibody molecule was investigated for IgG depletion by blocking the IgG/FcRn interaction. In vitro, we first found that the affibody molecule shares a common binding site with IgG on FcRn, which indicates that the affibody should be able to block IgG from binding to FcRn. In vivo, we injected large amounts of the affibody molecules in different formats in mice and found up to 39% reduction of total endogenous IgG. In a clinical setting, reduction of total IgG level would also reduce the disease causing IgGs, and potentially ameliorate the symptoms of IgG-driven autoimmune diseases. 

Taken together, I have in this thesis explored application of FcRn interacting molecules for extension of biological half-lives of therapeutically relevant proteins and reduction of total IgG level by FcRn blocking.