Methods are disclosed for treating a subject with a tumor. These methods include administering to the subject a therapeutically effective amount of CD8+CD39+CD103+ T cells. Methods also are disclosed for isolating a nucleic acid encoding a T cell receptor (TCR) that specifically binds a tumor cell antigen. These methods include isolating CD8+CD39+CD103+ T cells from a sample from a subject with a tumor expressing the tumor cell antigen, and cloning a nucleic acid molecule encoding a TCR from the CD8+CD39+CD103+ T cells. In addition, methods are disclosed for expanding CD8+CD39+CD103+ T cells. In additional embodiments, methods are disclosed for determining if a subject with a tumor will respond to a checkpoint inhibitor. The methods include detecting the presence of CD8+CD39+CD103+ T cells in a biological sample from a subject.