PDCD1 and neoplasm: Strain tracking analysis has revealed inter-individual variations in the colonization of dominant donor microbes in recipients post-FMT, which appears unrelated to the response to anti-PD-1 immunotherapy.105 Certain recipients may fail to mount a response to tumors, irrespective of the microbiome composition, due to immunodeficiency or insufficient tumor immunogenicity.54 Of note, the efficacy of FMT may be associated with the recipient’s immune response to donor microbes.