of ADAs

Understanding biosimilarity

these PCs are generated by immunizing animals, preferably nonhuman primates. PCs are used for both assays when required. In those instances where the PTMs are signi cantly different between the biosimilar candidate and the originator product, separate PCs are recommended. It is noteworthy that a biosimilar product need is the same as the originator product regarding the PTMs; so these are real possibilities in their development. However, the PCs should come from the same species and be processed using identical methods; yet since they come from different animals of the same species, some differences in reactivity, af nity, and avidity are expected. For mAbs where there is a speci c immunogenic site, sensitivity of the two controls can be readily made to validate the controls. When two assays are used, additional matching for factors such as temperature, concentration of capture, and detection reagents is also made. It is important to note that while two assays are being developed, the attempts include temperatures, concentration of capture and detection reagents, and so on. If the format of the assay involves conjugation, then the process should be kept same for both assays.

4.13.7 Specificity and characterization of ADAs

ADAs may induce unwanted side effects, especially in biotechnologyderived pharmaceuticals, such as therapeutic antibodies and growth factors. Hence, ADA has been subjected to increasing scrutiny by the regulatory authorities using immunogenicity safety studies. The ADAs have been observed in preclinical and clinical studies resulting in signi cant changes in toxicology, PK, and ef cacy. These effects arise from the generation of drug-induced (neutralizing) autoantibodies against, e.g., EPO, FVIII (Factor VIII), and insulin; these can be responsible for allergic reactions, or even anaphylactic shock. The adverse immunological reactions may widely vary, depending on how the active ingredients are structured, produced, and applied. For example, the expression of anti-Fc antibodies, anti-idiotypic antibodies, or antibodies against glycosylated antigens may appear. The detection and the characterization assays for ADA must, therefore, be developed, customized, and optimized for each drug. The ADAs are determined using a formal stepwise approach that includes the following. • Screening assay (bridging, direct or competitive ELISA, cytokine pro le) • Con rmation assay (determination of speci city) • Characterization assay (class/isotypes of antibodies, neutralizing yes/no) The ultimate goal is to correlate the ADA response with clinical observations, to use the comprehensive data to evaluate the differences between the originator and the biosimilar and its impact on safety and ef cacy. 191