Immunogenicity Risk Assessment of Generic Teriparatide Impurities

Aimee E. Mattei^1*Brian J Roberts¹Sandra Lelias¹Shah Miah²Kristina Howard³James L. Weaver³Daniela Verthelyi³Eric Pang³Katie Edwards⁴Anne Searls De Groot^1*

• ¹EpiVax (United States), Providence, Rhode Island, United States
• ²Oakland University William Beaumont School of Medicine, Rochester, United States
• ³United States Food and Drug Administration, Silver Spring, Maryland, United States
• ⁴University of Rochester, Rochester, New York, United States

Abstract Teriparatide is one of several generic peptides named in a recent Food and Drug Administration (FDA) guidance (FDA-2017-D-5767-0002) that recommends a potential strategy to inform the immunogenicity risk assessment for synthetic generic peptides without requiring clinical studies to assess immunogenicity. More specifically, the guidance states that for abbreviated new drug applications (ANDAs), once the sameness of the active pharmaceutical ingredient (API) between their product and the reference licensed drug is established, generic drug developers can mitigate the residual risk of an unwanted immunogenicity response by using in silico and in vitro tools to characterize the risk of any differences in product and process related impurities between the reference listed and generic drug products. With regards to the product-related impurities, a stated concern is that sequence modifications may create new T cell epitopes that could drive unwanted immune responses. Specifically, the guidance describes limits for the relative abundance of each impurity and requests that each new impurity over a certain concentration threshold be evaluated for potential T cell-driven immunogenicity using orthogonal methods that evaluate their ability to bind Human Leukocyte Antigen (HLA) as well as their capacity to elicit a T cell response. One such orthogonal immunogenicity risk assessment approach was applied to teriparatide (TPT) and several theoretical or observed product-related impurities in the case study described here. First, the immunogenic potential of TPT and selected impurities were assessed using three in silico tools: EpiMatrix, ClustiMer and JanusMatrix. Second, an in vitro method was used to evaluate the binding affinity of TPT and the selected TPT impurities to different class II HLA DRs in vitro. Third, a human peripheral blood mononuclear cell (PBMC) T cell assay was used to compare T cell proliferation in response to individual impurities or the reference teriparatide drug product, Forteo® in vitro. The orthogonal approaches identified multiple impurities as being more immunogenic than TPT. In a novel finding, the in silico analysis identified a potentially tolerogenic sequence in TPT that was associated with lower-than-expected de novo immune responses to TPT impurities in vitro.