An increased aTreg fraction could represent a possible marker of more severe CLL disease, characterised by serious infectious complications, as the disease course of a subgroup of our CLL patients with higher aTreg percentages among CD4+FOXP3+ T cells at the start of therapy was characterised by more frequent episodes of severe infections during the follow-up. Here, FOXP3 is linked to B-cell chronic lymphocytic leukemia.