Indeed, studies have demonstrated that the efficacy of CTLA4 blockade partly depends on the host microbiota by showing, for example, that fecal microbiota transplantation (FMT) from patients with multiple myeloma treated with CTLA4 blockade into germ-free mice reduced tumor size in a manner that depended on the presence of distinct Bacteroides species [16]. This evidence concerns the gene CTLA4 and plasma cell myeloma.