A Spotlight on immunogenicity: an interview with Joyce Slusser

Joyce Slusser is a Senior Scientist and Principle Investigator at KCAS Bioanalytical and Biomarker Services (KS, USA). Slusser joined KCAS in 2016 bringing with her the knowledge and expertise to expand KCAS’ flow cytometry and tissue culture offerings. Her proficiency in flow cytometry stems from years in the lab at two medical colleges and as a Consulting Scientist in a corporate setting. Over the past 20 years, she has gained experience across multiple species and platforms both in research settings and in clinical settings. Her education is rooted in immunology, virology, hematology and oncology. Joyce has published over 15 articles and is an active member of the International Society of Analytical Cytometry, International Clinical Cytometry Society, American Association of Immunologists and founder of Great Plains Analytical Cytometry Association.

1. Could you introduce yourself and explain what began your interest in immunogenicity?

My name is Dr Joyce Slusser and I first started thinking about immunogenicity in a virology class in high school. The mystery lay in how to choose the bit needed for immunization, which would work for most of the population; how to choose that epitope from the myriad of biologic materials, why would a single epitope not work for all of the population, why is one person’s immunity stronger or longer-lasting than another’s? This of course led me to learn immunology, which opened up an even bigger mystery: self/non-self-discrimination! Finally this leads us to today’s topic, which is focused on the ability to detect an adaptive response to dosed drugs.

2. What technologies do you use to investigate immunogenicity at KCAS?

The preferred platform is Meso Scale Diagnostics, MSD, which is an Electro Chemi Luminescence instrument, ECL. This platform has become the industry standard as it allows the ability to detect high affinity antibodies, as well as antibodies with lower affinity to the drug.

While not a technology, a critical aspect of investigating immunogenicity is the employment of statistics to quantify the noise of a method or the background and set a meaningful ‘cut point’ based on a normal population that allows us to ensure a sample is in fact positive for an anti-drug antibody (ADA). Additionally, in order to ensure we always err on the side of patient safety, our statistical approach allows us to set the positive/negative cut point to have a 5% false positive rate, which will be confirmed and characterized in subsequent analyses.

3. What are the challenges you face when assessing immunogenicity?

One challenge commonly experienced with ADA methods is something termed ‘drug tolerance’. This is the ability to detect antibodies to the dosed therapeutic in the presence of said therapeutic. The reason this is challenging is that the reagents used in many immunogenicity assays is the drug itself with different labels on it.

There are several methodologies we employ to improve the drug tolerance and sensitivity to reach the required level below 100 ng/ml, including using a technique called acid disassociation to break the circulating immune complexes allowing the antibody to be readily detected. In this methodology, we expose the sample to a weak acid for a prescribed amount of time then neutralize the sample in the presence of excess concentrations of the critical labeled assay reagents.

Another challenge that we see today is related to less traditional biotherapeutic modalities, such as enzyme therapeutics. These patients can have a higher than average pre-existing reactivity making it difficult to find an appropriate negative control for a specific disease population. In these cases, it is necessary to use disease matrix and establish the cut point using the disease population.

Finally, one last challenge that we deal with when developing and validating immunogenicity methods is handling fusion proteins. These types of therapeutics not only have ADA that can show up to the different distinct domains of a fusion protein but also have a ‘neo-domain’ that can be difficult to identify without having multiple individual constructs of the fusion protein to use if domain specificity is needed.

4. How does KCAS’s portfolio of services help with these challenges?

KCAS scientists have a diverse background of study and experience, which allow us to look at each challenge with a different set of eyes; we are quick to find, explore, brainstorm and resolve any challenges that arise. KCAS knows the regulatory requirements and our scientists and QC departments work together to resolve and overcome issues.

Our labs are equipped to develop and validate the immunogenicity assay at any stage during your drug development program from non-clinical toxicology, up to and including neutralizing antibody assays for use in the clinic.

5. What are your top three tips for studying immunogenicity?

Understanding the risk an anti-drug antibody to your dosed therapeutic poses to the patient population (i.e. is the drug a recombinant protein already found in the circulation or is it a novel protein with little to no homology to known endogenous proteins).

The route of administration can affect the risk for formation of anti-drug antibodies and the subclass.

Our scientists familiarize themselves with the patient population and the disease model. Are the patients’ immune systems compromised, is there expected to be a high level of pre-existing reactivity due to the disease state, is the antibody specific enough to identify therapeutic induced ADA in autoimmune patients?

6. Where do you hope this field will be in 5–10 years’ time?

I’d like to see immune monitoring move forward to add to the understanding and characterization of new biologic compounds and immunogenicity testing routinely using a neutralizing bioassay. KCAS offers a number of methods: flow cytometry, cell imaging, cytokine profiling, for example, as companion testing to ensure treatments are safe and effective.


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