MIT researchers reported that transient liver delivery of mRNAs encoding key trophic factors (DLL1, FLT3L, IL‑7) restored naive and stem‑like T cell populations in aged mice, improving vaccine responses and cancer immunotherapy outcomes. The study used lipid nanoparticle‑mediated hepatic expression to compensate for thymic involution and reconstitute supportive systemic signals; treated aged animals showed broader T cell receptor diversity and stronger functional responses without clear autoimmunity signals in preclinical readouts. Authors propose the approach as a modular strategy to transiently supply missing systemic factors and enhance immune competence in older hosts.