Patient selection for cancer immunotherapy requires precise, quantitative readouts of biomarker expression in intact tumors that can be reliably compared across multiple subjects over time. The current clinical standard biomarker for assessing immunotherapy response is programmed death-ligand-1 (PD-L1) expression, typically quantified using immunohistochemistry. This method, however, only provides snapshots of PD-L1 expression status in microscopic regions of ex vivo specimens. While various targeted probes have been investigated for in vivo imaging of PD-L1, non-specific probe accumulation within the tumor microenvironment (TME) has hindered accurate quantification, limiting the utility for preclinical and clinical studies. Here, we demonstrated that in vivo time-domain (TD) fluorescence imaging of an anti-PD-L1 antibody tagged with the near-infrared fluorophore IRDye 800CW (αPDL1-800) can yield quantitative estimates of baseline tumor PD-L1 heterogeneity across untreated mice, as well as variations in PD-L1 expression in mice undergoing clinically relevant anti-PD1 treatment. The fluorescence lifetime (FLT) of PD-L1 bound αPDL1-800 was significantly longer than the FLT of nonspecifically accumulated αPDL1-800 in the TME. This FLT contrast allowed quantification of PD-L1 expression across mice both in superficial breast tumors using planar FLT imaging and in deep-seated liver tumors (>5 mm depth) using the asymptotic TD algorithm for fluorescence tomography. These findings suggest that fluorescence lifetime imaging can accelerate the preclinical investigation and clinical translation of new immunotherapy treatments by enabling robust quantification of receptor expression across subjects.

中文翻译：

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荧光寿命成像能够对 PD-L1 表达和肿瘤间异质性进行体内定量


癌症免疫治疗的患者选择需要完整肿瘤中生物标志物表达的精确、定量读数，这些读数可以随着时间的推移在多个受试者之间进行可靠的比较。目前用于评估免疫治疗反应的临床标准生物标志物是程序性死亡配体 1 （PD-L1） 表达，通常使用免疫组织化学进行量化。然而，这种方法仅提供离体标本微观区域 PD-L1 表达状态的快照。虽然已经研究了各种靶向探针用于 PD-L1 的体内成像，但肿瘤微环境 （TME） 内的非特异性探针积累阻碍了准确定量，限制了临床前和临床研究的效用。在这里，我们证明，用近红外荧光团 IRDye 800CW （αPDL1-800） 标记的抗 PD-L1 抗体的体内时域 （TD） 荧光成像可以产生未治疗小鼠中基线肿瘤 PD-L1 异质性的定量估计，以及接受临床相关抗 PD1 治疗的小鼠中 PD-L1 表达的变化。PD-L1 结合的 αPDL1-800 的荧光寿命 （FLT） 显著长于 TME 中非特异性积累的 αPDL1-800 的荧光寿命 （FLT）。这种 FLT 对比允许使用平面 FLT 成像在浅表乳腺肿瘤中量化小鼠的 PD-L1 表达，以及使用用于荧光断层扫描的渐近 TD 算法在深部肝肿瘤 （>5 mm 深度） 中表达。这些发现表明，荧光寿命成像可以通过实现跨受试者受体表达的稳健量化来加速新免疫疗法的临床前研究和临床转化。