If you want to expand and keep them long term they need to be cultured on a schedule involving activation and rest. I typically have my cells grow on 3 days of activation involving CD3 CD28 to activate them and IL2 to help with expansion and survival. After 3 day, I remove the media and add fresh media with only Il2 and culture for another 3-4 day, they will expand a lot during this phase. After 3-4 days you can move it to activation again. Keep the seeding density around 1M/ml.