The association between the composition of the gut microbiota and the anti-tumor efficacy of ICI-targeted immunotherapy is further strengthened by the findings of several studies, albeit with one exception (87), that prior or concomitant administration of antibiotics impacts negatively on the therapeutic benefit of CTLA-4- and PD-1/PD-L1-targeted MAbs (84, 88–90). Here, PDCD1 is linked to neoplasm.