The immune system makes a chemical called Interferon Gamma (IFNg). This molecule is renowned for increasing TAP and MHC in cells by a hitherto unknown method. Jefferies’ group discovered that IFNg bumps up histone acetylation of the TAP gene, which relaxes it, prompting it to turn on. The team reckons that IFNg reforms the behaviour of CBP, restoring its HAT activity. Not only fixing a fault (MHC loss), but understanding how (by activating CBP using IFNg) makes for a satisfyingly complete story. This confirms the potential of epigenetics, with respect to immune recognition and antigen processing, for cancer treatment.