Other metabolites produced by specific species of microbes can modify the activity of therapeutic agents, including PD-1 (PDCD1)/PD-L1 (CD274) targeting immunotherapies, in melanomas and other tumor types (Johnson et al. 2016; Gopalakrishnan et al. 2017; Routy et al. 2017). The gene discussed is PDCD1; the disease is neoplasm.