HAVCR2 and neoplasm: Second, JQ1 as a BET molecule was loaded onto ultrasmall Cu2−xSe nanoparticles (the resultant nanoparticles were abbreviated as CS‐J NPs), and used to decrease not only PD‐1 and TIM‐3 on T cells through downregulation of TET2 expression, but also PD‐L1 on tumor cells.