Soluble IgG Receptors
“We are in the process of upscaling production of the Fc gamma receptor protein (FcgR) for use in clinical trials,” says Peter Sondermann, Ph.D., CSO at SuppreMol (www.suppremol.com). The company’s goal is to address a range of autoimmune disorders through the use of Fc receptor-based therapies. In IgG-mediated autoimmune diseases, humoral and cellular effector functions, interacting through the Fc part of the immune complexed IgGs, can react against host tissues. To interrupt the cycle of this destructive process, the company has developed SM101, a soluble human FcγRIIb receptor that interferes with the interaction of immune complexed IgG with FcγR-expressing cells and complement.
SuppreMol’s strategy for the treatment of autoimmune diseases is based on the fact that soluble Fcγ receptors in the circulation may compete with the cellular Fcγ receptors for the immune complexes. By introducing augmented levels of the receptor proteins into the patients’ circulation, Dr. Sondermann argues that they prevent the binding of the immune complexes to the cell and inhibit the feedback loop of autoantibody production, formation of additional immune complexes, and restimulation of immune cells.
For clinical trials, it was necessary to produce large quantities of the protein through an improved production train. “We initially developed a GMP 20–30 g/batch method, which we scaled up to 300 g/batch. This was required because the previous process was not scalable. We are now able to expand our protocols to any volume that we want, up to the 100,000 L range.” Further modification of the fermentation fed batch process increased cell density by a factor of five and also improved downstream processing per volume to a five- to sevenfold more efficient level than before.
During their efforts to upscale production of the receptor protein, the SuppreMol scientists did not have to contend with glycosylation, so they were able to employ an E. coli expression system, with the protein produced in inclusion bodies. But even though the Fc receptors are not glycosylated, it was necessary to resolve the post-translation problem of correct disulfide bridge formation and subsequent folding and formation of the polypeptide chain to yield an active product.
At the downstream end, Dr. Sondermann and his colleagues employ classical chromatographic separation, since inclusion bodies that are prepared just by a simple centrifugation of the cell lysate already contain almost exclusively the target protein. Therefore, the purification does not require an affinity matrix or an affinity tag fused to the product.
“We believe that our approach constitutes a generalized therapy for the treatment of autoimmune dysfunction, so we are investigating other indications, including primary immune thrombocytopenia. But it is incumbent upon us that we choose subsequent applications very carefully, given that every autoimmune disease is unique.”
“It is essential to maintain a consistent and well-documented glycosylation pattern during product scale-up,” says Daryl Fernandes, D. Phil., CEO at Ludger. “Yet this can be a monumental challenge, due to the complexity and variability of glycosylation and its sensitivity to fermentation conditions and variation in downstream processing.”
Especially for very complex drugs such as EPO (erythropoeitin) and Factor VIII, inconsistency in glycosylation can be the cause of failed batches with out-of-specification patterns. Frequently, biopharma companies and regulatory authorities disagree on the consequences to patients of alterations in drug glycosylation following scale-up and other manufacturing changes, leading to delays in approval. Even when regulators and therapeutics companies agree, detailed characterization studies may be required, which significantly increase the time to market.
“We start working with clients at the very earliest stages of development to optimize safety and efficacy profiles of their therapeutics by glycoengineering and process optimization.It gives us the best chance to help our clients to work on the glycosylation patterns of their drug early on, making good choices during drug development (particularly scale-up), and shortening the time to market.”