Detection of PD-1 for flow cytometry immunophenotyping using commercial antibodies in clinical studies with check point inhibitors

Abstract Precision for Medicine (Precision) has optimized the use of commercial anti-PD-1 and anti-IgG4 reagents to detect both free PD-1 and/or Pembro-bound PD-1 in pharmacodynamic studies when Pembrolizumab, a concomitant check point inhibitor, is used in combination with a new therapy. Precision has developed and qualified flow immunophenotyping assays to quantify PD-1 on CD4+ and CD8+ T cells using a commercial PD-1 clone (PD1.3.1.3) and an anti-IgG4. This enabled detection of both free and drug bound PD-1 receptor. We compared detection of PD-1 in PHA stimulated healthy donors treated with saturating Pembrolizumab or no drug treatment. There was not a significant difference observed in PD-1 quantification in the presence or absence of Pembrolizumab, which demonstrated that our approach was able to accurately measure total PD-1 whether free or bound. As Pembrolizumab was titrated from the saturating concentration there was a dose-dependent decrease in detection of PD-1. Here we will demonstrate the detection of PD-1 using the above methodology compared to other commercial PD-1 antibody clones. In clinical trials which incorporate checkpoint inhibitors like either PD-1 or PD-L1, the selection of commercial reagents are key considerations to detect these receptors when designing a sensitive, selective, and accurate biomarker assay.