Unlike small-molecule drugs, large molecule therapeutics face a high chance of detection by the immune system, and are therefore more apt to trigger alarms. The resulting immune responses can range from largely benign to life-threatening, which is why immunogenicity testing has become a critical requirement in the biologics development process. But, the development and implementation of such assays can be technically challenging, and this is causing differing industry opinions around the use of cell-based functional assays vs. non-cell-based competitive ligand binding assays for NAb detection.

The Turning Tide
Cell-based assays have become the traditional mainstay for characterizing drug efficacy and safety within the context of immunogenicity. In fact, regulatory agencies generally prefer cell-based assays because when designed correctly, they mimic the drug’s mechanism of action in vitro. However, I am beginning to see the tides turn within the field on this a bit, with more choosing to use ligand binding in place of challenging cell-based assay development as a first step for assessing drug impact.

The Ligand Binding Advantage
For example, at the recent Annual Immunogenicity BioAssay Summit in Baltimore, a presentation was given that showed the results of a study comparing a ligand-binding assay against a cell-based platform for the detection of in vitro NAb against the monoclonal antibody benralizumab, in which the ligand-binding assay was found to be more sensitive, drug-tolerant, and robust.

When Cell-Based is Best
Although comparative studies like the above are causing the industry to take notice of the potential uses of ligand binding assays for immunogenicity testing, they may still not be a suitable alternative to cell-based assays when the focus needs to be functional. Biosimilar development a good example of this, because the assay used must provide evidence that the originator molecule and biosimilar are functionally equivalent.

Since researchers first discovered a rare neutralizing antibody (NAb) response to the recombinant erythropoietin protein used to treat anemia, which also neutralized endogenous erythropoietin and resulted in pure red cell aplasia, immunogenicity testing has become an absolutely necessary part of developing effective, safe biologics. Designing the proper assay for such testing requires a solid understanding of the underlying drug mechanism of action, because the variety of methods used for modeling are as varied as the mechanisms themselves.

You can read more about the discussions from the Eight Annual Immunogenicity BioAssay Summit in a GEN article I recently contributed to titled “Cell-Based Assays Keep Biosimilars on Track”.