You are what you eat and translate: Feeding the code to fight cancer and viruses.

How nutrients shape gene expression has remained a fundamental question. Wu et al.1 show that extracellular arginine directly remodels the tRNA-codon axis, controlling codon-dependent translation of major histocompatibility complex class I mRNA independently of canonical amino acid stress signaling. This nutrient-sensing mechanism regulates immunity in colorectal cancer and viral infection while revealing new opportunities for therapeutic intervention.