Fluorescence imaging of tumor immune contexture in immune checkpoint blockade therapy

In the past decade, immunotherapy using immune checkpoint blockades (ICBs) has markedly changed the field of clinical oncology. However, the therapeutic efficacy of ICBs is closely related to the infiltration of immune cells in tumors and varies among different patients. There are still patients whose treatment effect is poor or even unresponsive. Due to different tumor immune contexture and highly complex regulation of immune network, immunoimaging techniques emerge and develop quickly. Fluorescence imaging, as a whole-body and non-invasive imaging technique, is regarded as a potential molecular imaging technique for immunotherapy by using a variety of fluorescent probes. In this review, we summarize the fluorescence imaging used in immune checkpoint blockade therapies: 1) evaluate the presence, subtype and abundance of T cells in tumors; 2) monitor the activation of T cell; 3) identify the immune regulators expressed on T and tumor cells. Moreover, for some theranostic nanoparticles, they could integrate fluorescence imaging and photoimmunotherapy as a whole.