Using single cell sequencing, it has been found that the majority of tumor infiltrating Treg cells are uniformly highly activated comparing with those in periphery tissues (22), with lower level of CD45RA and CCR7 expression, and highly enriched for a range of co-stimulatory molecules such as CD27, ICOS, OX40, 41BB, GITR, and co-inhibitory molecules such as CTLA4, PD1, LAG3, and TIGIT. The gene discussed is CTLA4; the disease is neoplasm.