Two independent reports show transient hepatic expression of key trophic factors via mRNA delivery can rejuvenate aged T cell populations and enhance vaccine and cancer immunotherapy responses in mice. Teams led by Feng Zhang delivered combinations of DLL1, FLT3L, and IL‑7 to the liver using LNPs and observed expanded, more diverse T‑cell repertoires and improved antitumor immunity. The studies highlight a strategy of repurposing the liver as a therapeutic factory to compensate for thymic involution in aging. Authors report stronger vaccine responses and better outcomes in aged animals receiving checkpoint inhibitors. Translational questions remain about dosing, duration, and safety of systemic trophic factor expression, but the approach points to a modular mRNA application beyond vaccines.