Keywords:
bispecific biotherapeutics,clinical antidrug antibody characterization,multidomain,biotherapeutics,pre-existing antidrug antibody,treatment-emergent antidrug antibody
Antibody engineering has dramatically evolved in recent years, resulting in current conventional antibody therapeutics having fewer immune-related adverse effects observed in the clinic. However, the advanced antibody engineering technologies have also created a great variety of novel antibody-based therapeutics with bispecific and multispecific domains entering to the clinic [1]. While having multiple specificities in the same molecule that are capable of binding to multiple different molecular antigens, or two different epitopes on the same antigen, may provide additional efficacy benefit over combination therapy, more bioengineering modifications and complex manufacturing processes are required for multidomain biotherapeutics compared with the conventional monospecific antibody therapeutics. As a result, multidomain biotherapeutics may potentially hold greater risk for immunogenicity and present unique challenges for immunogenicity analysis. Some clinical data have highlighted immunogenicity as one of the key challenges in the development of multidomain biotherapeutics. A recent publication reported that the bispecific antibody LY3415244 showed increased immunogenicity as compared with the two parental antibodies, in which all 12 patients developed treatment-emergent antidrug antibodies (TE-ADAs) to LY3415244 [2]. In addition, pre-existing antidrug antibodies (PE-ADAs) to LY3415244 were also detected in serum samples from normal human donors and the enrolled patients unexposed to the drug [2,3]. Another clinical trial also reported that strong immunogenic responses were observed for a bispecific antibody, which were unexpected as similar findings were not observed in the two previously studied parental molecules [4]. Therefore, there is an increasing need for immunogenicity investigation of multidomain biotherapeutics as part of drug development in the pharmaceutical and biotechnology industry. To guide the industry on the development of this rapidly growing class of biotherapeutics, the US FDA in 2021 published regulatory guidance on bispecific antibody development programs [5]. Although the guidance is intended for bispecific antibodies, the principles discussed in the guidance may also be applied to other types of bispecific protein products and multispecific products. In general, many aspects of a bispecific antibody development program will be like monospecific monoclonal antibody development programs. However, the guidance notes that an immune response to one domain may inhibit a specific function while leaving others intact. Therefore, it recommends that when examining immune responses to bispecific antibodies, it may be appropriate to develop multiple assays to measure immune responses to different domains of bispecific antibodies. This recommendation is in alignment with other guidelines from the FDA and European Medicines Agency on bioanalysis for bispecific/multispecific biotherapeutics [6,7]. The guidance also encourages the industry and other stakeholders to engage the FDA to discuss their individual bispecific antibody development programs. As such, the challenge facing the bioanalytical community is how to apply the FDA’s guidance in the immunogenicity assessment process. To address the challenge, at the 2021 Workshop on Recent Issues in Bioanalysis (WRIB), a hot-topic discussion was devoted to multidomain biotherapeutics and bispecific antibody immunogenicity. Given the industry’s limited experience with immunogenicity of multidomain antibodies, the resultant 2021 WRIB white paper recommends that customized bioanalytical strategies and methodologies be planned based on the target biology and mechanism of action, phase of development and key reagent availability [8]. At the 2023 WRIB, continued discussion on the topic was held to provide the global bioanalytical community with the current industry/regulator consensus in support of clinical immunogenicity assessment of multidomain biotherapeutics [9]. Although the industry and regulatory agencies are generally aligned in a risk-based approach to the immunogenicity assessment of multidomain biotherapeutics, at this time the bioanalytical practices in the development of multidomain biotherapeutics have not been harmonized in terms of bioanalytical strategies and methodologies. At Boehringer Ingelheim, we have supported several multidomain biotherapeutic programs for their clinical immunogenicity assessment. In this commentary, we will present our risk-based approach on clinical antidrug antibody (ADA) detection and characterization of multidomain biotherapeutics. Additionally, case studies will be provided that describe the reagents and tools along with the methods used to characterize domain specificity and identify the location of PE-ADAs in clinical ADA samples. We will also share our strategy for the development of an orthogonal clinical ADA method to differentiate PE-ADAs from TE-ADAs in clinical ADA samples.