Circulating regulatory T cells in "clinical" monoclonal B-cell lymphocytosis.

Regulatory T-cells (Tregs) constitute a small subset of cells involved in antitumour immunity and are generally increased in patients with chronic lymphocytic leukemia (CLL). No data is available on Tregs in monoclonal B-cell lymphocytosis (MBL), a disease entity characterized by less than 5000/microL circulating clonal B-cells in absence of other features of lymphoproliferative disorders. We used multicolour flow cytometry to evaluate the number of circulating Tregs in 56 patients with "clinical" MBL, 74 patients with previously untreated CLL and 40 healthy subjects. MBL patients showed a lower absolute number of Tregs, compared to CLL patients, but slightly higher than controls. Moreover, the absolute cell number of Tregs directly correlated both with more advanced Rai/Binet clinical stages and peripheral blood B-cell lymphocytosis. Of note, the absolute number of Tregs was found lower in MBL patients than in CLL patients staged as 0/A Rai/Binet. The study showed that Treg increase gradually from normal subjects to "clinical" MBL patients and are significantly higher in CLL patients as compared to MBL patients. Moreover, a significant direct relationship was found between higher Treg values and a higher tumor burden expressed by B-lymphocytosis or more advanced clinical stages. In light of this data, MBL seems to be a preliminary phase preceding CLL. The progressive increase of Treg numbers might contribute both to the clinical evolution of MBL to overt CLL and to CLL progression.