Two independent reports from MIT researchers showed that delivering mRNAs encoding key trophic factors to hepatocytes transiently restored T cell numbers and function in aged mice, improving vaccine responses and enhancing cancer immunotherapy efficacy. The approach repurposes the liver as a temporary secretory organ to compensate for thymic involution. The teams used lipid nanoparticle (LNP) delivery of mRNAs encoding DLL1, FLT3L and IL‑7 and reported expanded naive and stem‑like T cell populations, improved vaccine responsiveness, and better tumor control in mouse models. The studies found no clear signs of autoimmunity or systemic toxicity in treated animals and were published in Nature and related journals. Authors emphasized the transient nature of the intervention and its potential to augment immunotherapies and vaccines in elderly patients. Translational steps will require safety evaluation of repeated hepatic mRNA expression, dosing windows, and the impact on human thymic and peripheral T cell biology.