Clinical Immunogenicity Risk Assessment for a Fusion Protein.

This document highlights some relevant factors in the assessment of immunogenicity risk of fusion protein therapeutics. Our aim is to highlight specific risks associated with this type of molecule, while also aligning with general risk assessment factors, through a hypothetical case study, where the therapeutic molecule of interest is a Receptor-Fc Fusion protein (RFF) expressed within a typical manufacturing process in Chinese Hamster Ovary Cells (CHO). Given that the components are comprised of endogenous sequences, the risk of developing an ADA response to this molecule is generally considered to be low. However, the consequences of such an immune response may be more severe, specifically, if there is cross reactivity with the endogenous receptor, inducing cell lysis, or if any ADA act as an agonist to trigger receptor signaling. The risk factors described below are not meant to provide a comprehensive list, but rather a framework for factors that should be considered. Immunogenicity risk is difficult to quantify and relies on a comprehensive analysis of both product and patient-related factors. The goal is not necessarily to quantify risk, but rather to demonstrate an understanding of factors that may pose a risk, implement a strategy to minimize risk factors and then align overall risk with a bioanalytical immunogenicity monitoring strategy. The consequences resulting from unexpected outcome will likely depend on severity and impact on patient safety. An immunogenicity risk assessment is an ongoing and continuous process throughout clinical development with the goal of maximizing the safety of patients.

Clinical Immunogenicity Risk Assessment Strategy for a Low Risk Monoclonal Antibody.

This article provides a theoretical case-study risk assessment report for a low-risk monoclonal antibody (mAb) therapeutic. In terms of risk, there are considerations around risks to safety, but also risks regarding effects on pharmacokinetics (PK), pharmacodynamics (PD), and efficacy. Much of the discussion in this document is around the risk of immunogenicity incidence. A higher incidence of immunogenicity would necessitate a detailed review of the PK, efficacy and safety in anti-drug antibody (ADA) positive and ADA negative subjects, in order to evaluate potential effects. The publication is intended to provide a framework of some the current thought processes around assessing immunogenicity risk and for building strategies to mitigate those risks. For this example, we have created a hypothetical antibody, ABC-123, targeting a membrane protein on antigen presenting cells, for the treatment of rheumatoid arthritis (RA). This hypothetical antibody therapeutic is provided as an example for the purposes of risk assessment for a low risk molecule, although any application of similar approach would be case by case.

An in vitro FcRn- dependent transcytosis assay as a screening tool for predictive assessment of nonspecific clearance of antibody therapeutics in humans.

A cell-based assay employing Madin-Darby canine kidney cells stably expressing human neonatal Fc receptor (FcRn) heavy chain and ß2-microglobulin genes was developed to measure transcytosis of monoclonal antibodies (mAbs) under conditions relevant to the FcRn-mediated immunoglobulin G (IgG) salvage pathway. The FcRn-dependent transcytosis assay is modeled to reflect combined effects of nonspecific interactions between mAbs and cells, cellular uptake via pinocytosis, pH-dependent interactions with FcRn, and dynamics of intracellular trafficking and sorting mechanisms. Evaluation of 53 mAbs, including 30 marketed mAb drugs, revealed a notable correlation between the transcytosis readouts and clearance in humans. FcRn was required to promote efficient transcytosis of mAbs and contributed directly to the observed correlation. Furthermore, the transcytosis assay correctly predicted rank order of clearance of glycosylation and Fv charge variants of Fc-containing proteins. These results strongly support the utility of this assay as a cost-effective and animal-sparing screening tool for evaluation of mAb-based drug candidates during lead selection, optimization, and process development for desired pharmacokinetic properties.