Peripheral blood biomarker for evaluating anti-tumor immune effect of radiation therapy

A method of using a composition of a cell subpopulation in a sample obtained from a subject who has undergone radiation therapy as an indicator of radiation therapy-induced immune activation in the subject, comprising:

• analyzing the composition of the cell subpopulation in the sample obtained from the subject;
• wherein the presence/absence of immune activation in the subject is indicated by comparing an amount of a CD4+ T cell subpopulation correlated with dendritic cell stimulation in an antitumor immune response in the sample with a baseline, and the CD4+ T cell subpopulation correlated with dendritic cell stimulation in an antitumor immune response is a cell subpopulation within a CD62LlowCD4+ T cell population,
• wherein an increase in the amount of the cell subpopulation in the sample relative to the baseline indicates that immunity is activated by radiation therapy in the subject,
• wherein no increase in the amount of the cell subpopulation in the sample relative to the baseline indicates that immunity is not activated by radiation therapy in the subject,
• wherein radiation therapy-induced immune activation in the subject further indicates that cancer immunotherapy comprising one or more immune checkpoint inhibitors should be administered to the subject at that point in time,
• wherein the one or more immune checkpoint inhibitors comprise a PD-1 inhibitor, a PD-L1 inhibitor, and/or a CTLA-4 inhibitor, and
• wherein no radiation therapy-induced immune activation in the subject further indicates that radiation therapy should be re-administered to the subject.