Recently, we and others highlighted that HLA-DR+CD38+ CD4+ T cells are associated with intestinal inflammation in a subset of IBD patients.32,33 In the present study, we observed the enrichment of HLA-DR+CD38+ CD4+ T cells in virtually all CD-associated fistulas; moreover, in a subset of these patients, this was accompanied by the presence of HLA-DR+CD38+ CD8+ T cells. Here, CD38 is linked to inflammatory bowel disease.