Abstract
Despite the recent implementation of immunotherapies into clinical practice of various tumor types, the immunobiology of tumors and in particular the role and clinical relevance of the different immune cell populations and their function still remained unclear. Therefore, an in depth analysis of the complex landscape of immune cell populations and their soluble mediators in the peripheral blood and tumor microenvironment of cancer patients is urgently needed. Mass cytometry has revolutionized the immune phenotyping in particular in settings where simultaneous breadth and detailed characterization of the phenotype and function of immune cell (sub)populations with limited sample size is required, such as monitoring of patients' response to immunotherapies. Since mass cytometry is a powerful multiplex approach to decipher tumor intrinsic and tumor extrinsic effects of tumor immunotherapies, this review summarizes the use of this technology for determination of the frequency and functional status of immune cell populations within the tumor and in the blood leading to the identification of intratumoral/peripheral immune signatures that might serve as biomarkers (i) for treatment response and/or failure, (ii) for the stratification of tumor patients or (iii) for the identification of novel therapeutic targets.