Monitoring Circulating γδ T Cells in Cancer Patients to Optimize γδ T Cell-Based Immunotherapy

The success of γδ T cell-based immunotherapy, where the cytotoxic activity of circulating γδ T lymphocytes is activated by nitrogen-containing bisphosphonates (n-BP), or possibly by bispecific antibodies or the combination of both, requires a profound knowledge of patients' γδ T cells. A possible influence of radio- or chemotherapy on γδ T cells as well as their reported exhaustion after repetitive treatment with n-BP or their lack of response to various cancers can be easily determined by the monitoring assays described in this perspective article. Monitoring the absolute cell numbers of circulating γδ T cell subpopulations in small volumes of whole blood from cancer patients and determining γδ T cell cytotoxicity using the Real-Time Cell Analyzer can give a more comprehensive assessment of a personalized tumor treatment. Possible future directions such as the combined usage of n-BP or phosphorylated antigens together with bispecific antibodies that selectively target γδ T cells to tumor-associated antigens, will be discussed. Such strategies induce expansion and enhance γδ T cell cytotoxicity and might possibly avoid their exhaustion and overcome the immunosuppressive tumor microenvironment.