MIT researchers reported in Nature that transient liver‑targeted mRNA delivery of trophic factors (DLL1, FLT3L, IL‑7) restored naive and stem‑like T cell populations in aged mice, improving vaccine responses and enhancing the efficacy of cancer immunotherapy. Instead of attempting thymic regeneration, the team reprogrammed hepatic cells to secrete key immune‑support signals, producing durable functional improvements without overt toxicity. The approach used LNP‑mediated mRNA expression in hepatocytes to reconstitute systemic immune support. Preclinical results showed larger and more diverse T cell repertoires and better responses to vaccination and checkpoint blockade. The platform presents a translational path to transiently augment immunity in older patients, but human safety, dosing regimen and durability remain to be established.