Why Immunogenicity in Drug Development Matters

Immunogenicity, why do we keep talking about it? Immunogenicity can, in the simplest of terms, be described as a subject’s ability to generate antibodies specific to the dosed protein therapeutic. Immunogenicity can be either a wanted or unwanted reaction. Wanted immunogenicity is the desired immune response, such as when a vaccine triggers the body to develop protection against future exposure to a pathogen. In contrast, **unwanted immunogenicity** occurs when the immune system reacts against a therapeutic drug. This leads to the production of ADAs, which can potentially compromise the drug’s safety and efficacy. While stating it this way understates the complexity of the immune system and the methods needed to detect and characterize the anti-drug antibody (ADA) response, it is, at the core, the question being asked.

Understanding ADAs and Their Impact

Frequently, the ADA or immunogenicity assay development is secondary, as the primary focus of a project is to understand the absorption, distribution, metabolism, and excretion (ADME) of a dosed therapeutic, which is evaluated in Pharmacokinetics. Additionally, understanding the pharmacodynamics of the drug allows investigators to make critical decisions regarding go/no-go checkpoints early in a drug development program. While these assays are important and provide great value to a development program, the ADA assay and the information gleaned from that analysis are equally important in the safety assessment and efficacy in developing a comprehensive view of the drug/subject interaction.

When ADA Testing Begins: The Preclinical Phase

The reasons immunogenicity is needed and how it can impact a drug development program differ depending on where a drug candidate is in its life cycle. The first instance where ADA may be needed is in the so-called “pivotal tox studies”.  These are the rodent and non-human primate studies that are performed following the FDA 21CFR part 58 (GLP) guidelines.

While the animals are being dosed with a human protein, and the emergence of ADA is not predictive of what will happen in humans, the effect ADA has on the PK parameters can be useful both in understanding the effect of an ADA response as well as providing an explanation for aberrant exposures or elimination profiles. It is at this point (even if no non-clinical ADA assay is developed) that one should begin activities to enable method development for clinical studies.

ADA Assays in Clinical Development

After preclinical studies are complete, an IND (Investigational New Drug) filing is submitted to the FDA in order to obtain approval to start clinical trials. Once an IND is filed and there are plans to dose humans, the need for an ADA becomes paramount.

Before the IND Filing: Positive Control Prep

A central element of early ADA assay development is the generation of surrogate antibodies or positive controls. These materials are used as reference reagents in the development and validation of the assay, enabling consistent and accurate detection of anti-drug antibodies in clinical samples.

Key considerations in this process include:

  • Purpose: Surrogate antibodies act as stand-ins for actual patient-derived ADA responses, allowing assay performance to be characterized in the absence of real clinical samples.
  • Source: These antibodies are typically generated by immunizing animals (e.g., rabbits or rodents) with the therapeutic drug or a related immunogen.
  • Characterization: Once generated, surrogate antibodies must be purified and extensively characterized for specificity, affinity, and isotype to ensure they mimic likely clinical ADA responses.
  • Use in Assay Development: Positive controls are used to establish key assay parameters such as sensitivity, specificity, precision, and drug tolerance during method development, optimization, and validation.

By initiating the surrogate antibody generation program well ahead of the IND submission, the development team ensures that a fit-for-purpose ADA assay will be in place and ready for use by the time clinical dosing begins.

After IND Filing: ADA’s Role in PK & Safety

The information that is obtained from the assessment of samples for ADA will help inform not only the pharmacokinetics PK, but also the safety profile of the drug and determine if an antibody response is persistent (i.e., sustained over time without decreasing) or transient (i.e., can be managed or diminishes over time, allowing continued dosing without long-term adverse effects on drug exposure. Additional immunogenicity evaluations are conducted to further characterize the safety profile of the therapeutic. These evaluations determine the relative concentration of ADA, so a correlation can potentially be drawn between ADA prevalence and observed safety events. Further analyses assess where on the protein (e.g., in the case of a fusion protein) the ADA is binding, whether the ADA is neutralizing, and whether it interferes with the drug’s ability to bind its intended target or exert its therapeutic effect.

FDA Guidance on ADA Assays

In 2019, the FDA set forth guidance for the industry on ADA assay development and validation.  The guidance provides recommendations for the development and validation of assays used to detect ADAs during clinical trials.  This guidance covers various types of ADA assays, including screening, confirmatory, titration, and neutralization assays, as well as discussing the parameters evaluated in these methods

How KCAS Bio Supports Immunogenicity Strategy

Nonclinical Through Late-Stage Expertise

KCAS Bio is a CRO that not only understands how to develop an ADA assay for your unique protein therapeutic but can assist you in the development of an immunogenicity testing strategy starting at the non-clinical through late clinical phases.

Overcoming Common Challenges

Some of the services we offer regarding immunogenicity are method development and validation, including a statistically robust method for determining a cut point for your assay that exceeds FDA expectations, resolving endogenous interferences, improving drug tolerance challenges, etc.  When your program is approaching the critical phase of development, we will ensure you have the best assays to enable the success of your therapeutic protein program.

Conclusion: Immunogenicity Is Not Optional

Immunogenicity is a critical part of biologic drug development. Understanding and monitoring ADA responses ensures the safety and efficacy of a therapeutic. Planning early and maintaining a strong immunogenicity strategy throughout development supports better decision-making and increases the chances of clinical success.