PDCD1 and neoplasm: Although sucralose may have some effects directly upon T-cell activation (Supplementary Fig. S8; ref. 27), our data suggest that sucralose consumption interacts directly with gut microbiota to diminish sensitivity to anti–PD-1 therapy and is both necessary and sufficient to drive degradation of key amino acids, CD8+ T-cell dysfunction, increased tumor growth, and reduced response to anti–PD-1.