Flow cytometry in cancer immunotherapy: Applications, quality assurance, and future

Abstract

The recent success and enormous potential of immune checkpoint modulation demonstrate how powerful T-cells are in controlling tumor cell growth; with checkpoint blockade antibodies, antitumor effects mostly rely on the functional release of preexisting tumor-specific T-cells. In contrast, experimental therapeutic vaccination of cancer results in the induction of new antitumor T-cells. Both strategies are expected to synergize to increase the number of responding patients and to establish long-lasting tumor control, and clinical trials are ongoing. Immune monitoring is essential to all these approaches: it provides evidence of immunogenicity, identifies targeted antigens, guides the choice and dosage of vaccine components, and assesses the effects of immune modulators. Immune monitoring also has the potential to reveal early biomarkers of clinical efficacy. Hence, knowledge on the quantity and quality of induced tumor-antigen-specific (CD4+ and CD8+) T-cells and also the characterization of suppressive immune cell subsets are of high relevance for further developments in cancer immunotherapy. The canonical multiparameter assay for the characterization of immune cells is polychromatic flow cytometry, and it is ubiquitously used in tumor immunology and in immunotherapy trials. This chapter describes the main flow cytometry methods being applied in cancer immunotherapy, with an emphasis on recent progress in the field, challenges associated with maintenance of quality and performance, its promise to reveal biomarkers of clinical efficacy, and current developments in automated analysis that are reaching clinical cancer immunology.