The present disclosure provides methods for measuring the number of CD4+ OX40+ Foxp3+ lymphocytes in a sample containing cancer cells and lymphocytes obtained from a subject by labeling lymphocytes that show CD4 expression in the sample, then labeling lymphocytes that show OX40 expression in the sample, then labeling lymphocytes that show Foxp3 expression in the sample, then measuring the number of CD4+ OX40+ Foxp3+ lymphocytes in the sample. Further provided are methods for determining the prognosis of a subject, predicting responsiveness of a subject having cancer to an OX40 agonist treatment, and methods for treating or delaying progression of cancer based on the number of CD4+ OX40+ Foxp3+ lymphocytes in a sample.
