4.13.8 Immunogenicity assays

Biosimilarity: The FDA Perspective

192 The speci city of ADAs is assessed using competitive con rmatory assays utilizing both intact drugs (originator and biosimilar) and a relevant speci c domain of the drug. Additionally, potential cross-reactivity to endogenous proteins is considered if the drug contains an endogenous protein sequence. In those instances where ADAs do not affect the disposition kinetics, additional characterization of ADA is not warranted, but if the disposition pro les are affected, more detailed studies are conducted to demonstrate the similarity of ADAs between the biosimilar and the originator product. If ADA response is detected, but no PK changes are observed, additional characterization of the positive reaction may not be necessary. If the effects of the ADA interference with the PK assessment are demonstrated differently between the originator and the biosimilar, this would require additional investigation and risk mitigation.

The biopharmaceutical scientist can choose from several technologies to perform immunogenicity testing. A second antigen-bridging assay has been preferred since such a method, once optimized, can be applied to immunogenicity testing in any host species. Thus, the same IM assay can be used for early animal studies and clinical studies in humans. Each technology platform has its advantages and disadvantages. ELISA is a well-proven, low-cost, open technology platform for detecting high-af nity ADAs. It has superior drug tolerance, but may miss low-af nity ADAs due to the requirement of high sample dilution and multiple wash steps that may disrupt weakly bound ADA-drug complexes. ELISA can detect ADAs after acid dissociation of drugcomplexed antibodies. A surface plasmon resonance (Biacore) IM assay has been shown to be ef cient in the detection of low-af nity ADAs but overall is not as sensitive as ELISA due to the label-free assay con guration and the requirement for sample dilution. It shows higher drug tolerance for low-af nity ADAs, but it cannot be used with acid dissociation of circulating complexes. The method requires investment in costly dedicated instrumentation. Similar problems also exist in the Bio-Layer Interferometry Dip and Read–based IM assays. Electrochemiluminescence IM assay is very similar to ELISA in performance with the claims of improved sensitivity from the use of an electrochemiluminescent label. However, similar shortcomings with the detection of low-af nity ADAs due to the need for sample dilution and a nal wash step still exist in addition to a signi cantly higher cost of equipment and reagents, when compared to regular ELISA. The method requires investment in costly dedicated instrumentation.