CD8+ T cell differentiation into effector and memory T cells is critical for tumor immunity, pathogen response, and vaccine effectiveness, but to date researchers have not been able to use standard methods to study the factors involved in the process without first extensively manipulating naive T cells ex vivo, making the biology difficult to understand. ӳý researchers Nick Haining, Glenn Cowley, David Root, Arlene Sharpe, and colleagues, including first author Jernej Godec of Dana-Farber Cancer Institute, describe overcoming this obstacle in a recent .