Immunogenicity of biological therapeutics in regulatory perspective

Immunogenicity risk assessment?

Quality, safety and efficacy should be evaluated for new drugs to be approved. And from a safety point of view, immunogenicity of biological therapeutics has been largely concerned by regulatory authorities, so sponsors are supposedly to provide regulatory authority with a plan for immunogenicity risk assessment on IND submission. Immunogenicity is humoral response of human immune system to administrated drug molecule and or any impurities present in drug substance and or product, that are characterized by its source: product- or process-related impurities. In terms of quality and safety, impurities must be identified and characterized whether they have deleterious effect or any risk including immunogenic potential. Therefore, immunogenicity risk assessment is not a stand-alone task but concomitantly required for the specifications to be approved by regulatory authorities. During early phase of development, immunogenicity risk can be assessed with an in-silico method to predict the reactivity of drug product and or impurities with T-cells, so amino acid sequences with high immunogenic potential could be replaced with non-reactive sequences as a preventive measurement. And the result could be asked to be verified with a validated analytical method, such as ELISPOT assay. On the other hand, anti-drug antibody (ADA) assay is a method to detect humoral immune response whether our body physically produces antibodies against drug and or impurities. Therefore, the method validation of ADA assay is therefore necessary and the US FDA has provided a related guidance.?

Principle of ADA assay and statistics

ADA assay is an immunoassay like ELISA to determine ADA positive or negative also quantity thereof in samples, if necessary. It generally consists of three consecutive analytical procedures: screening, confirmatory and titration and each procedure requires a cut-point to discriminate samples are to be or not to be further analyzed. In brief, if sample’s signal is at or higher than the screening cut-point value and then the sample should be analyzed in confirmatory run, to determine whether the first (screening) result is true or not; if true on confirmatory its quantity should also be measured.?

Regarding estimation of the screening cut-point of ADA assay, the US FDA recommends to use 90% one-sided low confidence interval of 95th percentile or upper bound of 95th percentile of data of drug-na?ve sample. In addition, the FDA also recommends to analysis the data structure of ADA assay validation result, in order to calculate false positive rate correctly by using random effect model in a recently published paper. The screening cut-point should provide at least 5% of false-positive rate in both validation and study sample analysis. The method proposed by FDA for the screening cut-point estimation is statistically well-introduced and easy to apply directly to current ADA assay validation practice. However, in our experiences, it may still be a challenge for many biotech companies without statistical support.?

To support this, GCCL will provide a short article for non-statistical readers who are interested in statistics of ADA assay development and validation on request. If more supports are needed, Bioanalytical team of GCCL, with CMC knowledge for biopharmaceutical manufacturing, analysis and statistics, can provide consultation on client’s decision making for ADA assay development, validation and immunogenicity risk assessment.?