In particular, in a melanoma mouse model administration of commensal probiotics has shown to improve tumor control alone and in association with PD-L1 blockade; on the other hand tumors in antibiotic-treated or germ-free mice did not respond to CTLA-4 blockade (Sivan et al., 2015; Vetizou et al., 2015). This evidence concerns the gene CTLA4 and melanoma.