Upregulation of MCT4 (also known as solute carrier family 16 member 4 or SLC16A4), a major lactate transporter, contributes to the immunosuppressive phenotype including M2 macrophage polarization and T cell hypofunction observed in a Lkb1-deficient Kras-driven lung cancer mouse model (Qian et al., 2023). The gene discussed is SLC16A4; the disease is lung carcinoma.