Optimization of a whole blood phenotyping assay for enumeration of peripheral blood leukocyte populations in multicenter clinical trials

• We develop one antibody staining panel that enumerates all major blood leukocytes.
• We define assay variables relevant to clinical trials that affect cell counts.
• Some assay variables have a greater effect on certain cell populations than others.
• Data from the staining panel correlates highly with complete blood count data.
• The panel can be used in experimental medicine trials to profile immune responses.

Vaccination with viral vectors or adjuvants can induce early changes in circulating peripheral blood leukocytes that are predictive of a protective immune response. In this study, we define an 11-color whole blood antibody staining Trucount Panel (TP1) to enumerate and phenotype the major leukocyte populations in a human vaccine experimental medicine trial setting. TP1 can be prepared up to 8 weeks prior to use, enabling bulk preparation at a central laboratory and distribution to clinical sites. Cells in whole blood must be stained within 4 h of draw to accurately detect the major cell populations. Staining of cells with TP1 followed by storage and shipping at −80 °C to a central laboratory has little to no effect on the cell concentrations observed. We also present data from an HIV vaccine multicenter clinical trial obtained using the optimized TP1 assay protocol and show that the data produced accurately correlates with complete blood count (CBC) data. Taken together, these data indicate the optimized TP1 panel assay can be used in a multicenter clinical trial setting to increase our understanding of systemic responses to vaccination or disease.