Among 14 phenotypically distinct populations of Treg cells, identified by 13-color immunophenotyping and unsupervised FlowSOM clustering, population 5, which was more abundant in our CLL patients, was CXCR5-positive and showed a CD45RA negative-memory phenotype similar to CXCR5+ Tfr cells. This evidence concerns the gene CXCR5 and B-cell chronic lymphocytic leukemia.