Evaluating Immunogenicity Risk Due to Host Cell Protein Impurities in Antibody-Based Biotherapeutics.

A potential risk factor for immunogenicity of a biotherapeutic is the low levels of host cell protein (HCP) impurities that remain in the product following the purification process. During process development, significant attention has been devoted to removing HCPs due to their potential safety risk. Samples from different purification steps of several monoclonal antibodies (mAbs) purified by one type of platform were evaluated for their residual Chinese Hamster Ovary (CHO) cell-derived HCP content. HCPs in both in-process (high levels of HCP) and highly purified (low levels of HCP) samples were identified and quantitated by proteomic analysis via mass spectrometry. The responses to HCPs were evaluated in an in vitro assay using PBMC from a population of healthy and disease state individuals. Results indicated that samples with up to 4000 ppm HCP content (levels 200 times greater than the drug substance) did not pose a higher immunogenicity risk than highly purified mAb samples. As an orthogonal method to predict immunogenicity risk, in silico algorithms that probe amino acid sequence for foreign epitope content were used to evaluate over 20 common HCPs (identified in the different mAb samples). Only a few HCPs were identified as high risk by the algorithms; however, the in vitro assay results indicated that the concentration of these HCPs from in-process biotherapeutic mAb samples was not sufficient to stimulate an immune response. This suggests that high levels of HCP in mAb biotherapeutics purified by this type of platform do not increase the potential risk of immunogenicity of these molecules. Insights from these studies can be applied to HCP control and risk assessment strategies.