Viruses are nasty little things that you cannot see by eye but if you inhale, swallow or absorb them, they can make you very sick. Influenza (the flu) is one of those viruses that once it gets inside you (we call this infection), causes a highly contagious disease of the breathing organs and can spread rapidly from person to person around the world. We are interested to understand our body’s natural response to flu, mainly by investigating the fighters of our immune system called CD8+ T cells. If we have the flu, previously infantile CD8+ T cell fighters are activated and grow up into mature, efficient fighters of virus-infected cells. This growing up process can be seen in changes in the appearance of the fighters as well as the development of new skills, enabling the T cell fighters to kill virus-infected cells and clear the infection, allowing us to recover and get well again. But how do infantile T cells mature to be fully-fledged T cell fighters? This is all determined by turning particular genes on and off (we call this the genetic program of cells). This program is regulated by different building blocks that interact with DNA to help or hinder gene expression. One of these building blocks is SATB1. SATB1 is very important as mice that do not have this building block die early after birth. However, less is known about the exact function of SATB1 in the process of making efficient CD8+ T cell fighters during flu infection. Our study is looking at the importance of SATB1 for these CD8+ T cell fighters. Understanding the processes involved in shaping optimal CD8+ T cell fighters against the flu will help us to find ways to ultimately protect us from getting sick with severe flu disease.