Free IgE Assay

About the Assay:

It is a pharmacodynamic marker used for clinical trials. Since allergy trial readouts are somewhat subjective, it was important to have a PD marker to see if anti-IgE was suppressing the ability of IgE to bind to its target. When Xolair moved into development, we developed a free IgE ELISA for human samples. The first generation assay was sensitive to ~24 ng/mL. It was not clear whether this sensitivity was adequate, so after implementing the first generation assay, we continued work to make the assay more sensitive. The second generation assay had its lower limit of detection at single ng/mL levels.

What makes it unique:

Once correlations could be done with the clinical data, we concluded that the target free IgE concentration for efficacy was right around the low end of the original assay. We showed that the assay significantly disrupts complexes in vitro, and so the results cannot be treated as quantitative.