Correlation Between Chimeric Antigen Receptor T‐Cell Pharmacokinetic Data Measured by Flow Cytometry and Quantitative Polymerase Chain Reaction

ABSTRACT Chimeric antigen receptor (CAR)‐T cells have antitumor efficacy in hematological and solid malignancies. Unlike small molecules or antibodies, CAR‐T cells have unique kinetic profiles (distribution, expansion, contraction, and persistence). To quantify these dynamics, flow cytometry and qPCR are commonly used, each with distinct advantages and limitations. We analyzed the correlation between flow cytometry and qPCR quantification of CAR‐T cells in subjects from 4 phase 1 clinical studies (individually and combined). We also explored factors that affect calculations of CAR‐T cells and CAR transgene copy number, how these affect pharmacokinetic (PK) parameters determination for clinical studies, and associations with pharmacodynamic factors such as cytokine levels. We demonstrate that CAR transgene copy number is more highly correlated with the ratio of CAR‐T cells to white blood cells (WBCs) than with the actual number of CAR‐T cells, indicating that CAR transgene copy number is related to the percentage of CAR‐T cells in blood. The low level of correlation between CAR transgene copy number and CAR‐T cells may be due to differences in the ratio of CAR‐T cells to WBCs at some time points. Meanwhile, flow cytometry and qPCR PK values correlated with cytokine levels; flow cytometry data had a higher correlation coefficient ( r ) and lower p ‐values than qPCR data. These findings increase our understanding of potential causes of inconsistencies in PK and pharmacodynamic parameters analyzed during studies of CAR‐T cell therapy.