IL15 and lymphopenia: In this study, we demonstrate a key role both in vitro and in vivo for IL-15 in enhancing the phosphorylation of ULK1 and up-regulating the expression of Atg7 and LAL, indicating that lymphopenia promotes Tm cell formation via IL-15 dependent activation of the ULK1/Atg7 autophagy pathway for maintenance of their memory metabolism.