Regulatory T cells (Tregs) are a population of T cells that exert a suppressive effect on a variety of immune cells and non-immune cells. The suppressive effects of Tregs are detrimental to anti-tumor immunity. Our laboratory has been at the front-edge of studying human cancer-specific Treg cells and developing reagents to target cancer Treg cells for overcoming resistance to immunotherapy. Recent investigations into cancer-associated Tregs have identified common yet heterogeneous populations of tumor-infiltrating Tregs. Using advanced single-cell sequencing technology, we profiled immune cells from renal clear cell carcinoma (ccRCC) patients and identified distinct transcriptional tumor-infiltrating Treg cell fates, with a particular suppressive subset showing distinct gene signature relative to PBMC Tregs. We demonstrate these Tregs have preferential suppressive effects. Gene signatures derived from the TI-Treg subset had superior ability to predict survival in ccRCC and other cancer types. The research project will focus on the understanding of TI-Treg function in cancer and the mechanism how TI-Tregs influence anti-cancer immunity. Another effort is to develop new targeting antibodies and inhibitors for TI-Tregs for cancer immunotherapy.