Fluorescence Lifetime Imaging Enables In Vivo Quantification of PD-L1 Expression and Intertumoral Heterogeneity

Patient selection for cancer immunotherapy requires precise, relevant anti–PD-1 treatment. The fluorescence lifetime (FLT) quantitative readouts of biomarker expression in intact tumors of PD-L1–bound αPDL1-800 was significantly longer than the that can be reliably compared across multiple subjects over FLT of nonspecifically accumulated αPDL1-800 in the tumor time. The current clinical standard biomarker for assessing microenvironment. This FLT contrast allowed quantification of immunotherapy response is PD-L1 expression, typically PD-L1 expression across mice both in superficial breast tumors quantified using IHC. This method, however, only provides using planar FLT imaging and in deep-seated liver tumors snapshots of PD-L1 expression status in microscopic regions of (>5 mm depth) using the asymptotic time-domain algorithm ex vivo specimens. Although various targeted probes have been for fluorescence tomography. These findings suggest that investigated for in vivo imaging of PD-L1, nonspecific probe FLT imaging can accelerate the preclinical investigation and accumulation within the tumor microenvironment has hin- clinical translation of new immunotherapy treatments by endered accurate quantification, limiting the utility for preclinical abling robust quantification of receptor expression across and clinical studies. Here, we demonstrated that in vivo time- subjects. domain fluorescence imaging of an anti–PD-L1 antibody tagged with the near-infrared fluorophore IRDye 800CW Significance: Fluorescence lifetime imaging can quantify PD(αPDL1-800) can yield quantitative estimates of baseline tumor L1 expression across multiple mice undergoing anti–PD-1 PD-L1 heterogeneity across untreated mice, as well as varia- treatment, providing a critically needed noninvasive imaging tions in PD-L1 expression in mice undergoing clinically method to quantify immunotherapy targets in vivo.