A new mRNA and lipid nanoparticle (mRNA-LNP) platform could selectively reprogram in vivo cytotoxic effector T cells (Teff), the cells responsible for eliminating infected or tumor cells. To achieve this, scientists at the University of Pennsylvania conjugated LNPs with fractalkine, a molecule that binds to the CX3CR1 receptor, which is a marker of Teff cells. Using this strategy, the researchers delivered an mRNA encoding new proteins such as IL‑2 or human CD62 L‑selectin, opening the door to temporarily reprogramming these cells within the body, both in the blood and in lymphoid tissue, where they reside and become activated.