applied genome‐wide CRISPR screening in primary human T cells and identified multiple negative regulators, including suppressor of cytokine signalling 1, transcription elongation factor B polypeptide 2, RAS p21 protein activator 2 (RASA2) and cbl proto‐oncogene B,183 and ablation of these targets enhanced both proliferation and in vitro anti‐cancer function of T cells. Here, RASA2 is linked to cancer.