A low baseline proportion of peripheral blood CD4+ Tregs has been reported to be associated with anti-CTLA-4-related colitis (Shahabi et al., 2013), while eosinophils had already been found in biopsy specimens from patients with anti-CTLA-4-induced hepatitis, rash and colitis (Berman et al., 2010; Lacouture et al., 2014; Johncilla et al., 2015). Here, CTLA4 is linked to colitis.