CD4+ CD25^high Regulatory T Cells in Newly Diagnosed Patients with Acute Myeloid Leukemia.

Regulatory CD4+CD25+ T cells (T reg) are critical regulators of immune tolerance. Increasing evidence supports the existence of elevated numbers of regulatory T cells in cancer patients. Although the increase of T cells seems to be a characteristic feature in most tumors the functional role of Treg, especially in patients with hematologic malignancies, has been less well defined. Mutlicolor flow cytomerty was used to investigated the frequency and phenotype of CD4+ CD25^high T cells in the peripheral blood of thirty seven newly diagnosed acute myeloid leukemia (AML) patients (prior to any treatment) and thirty one healthy donors. The suppressive function of Treg was evaluated using CFSE-labeled fresh autologous CD4⁺CD25⁻ T cells activated with an anti-CD3 antibody as responders. The percentage of circulating CD4+ CD25^high Treg was higher (p < 0.0001) in the AML patients (2.9 ± 0.3%, range 0.1–7%) compared to healthy donors (0.4 ± 0.02%, range 0.1–1%). Percentages of T reg expressing Foxp3, CTLA-4, CD45 RO, Fas ligand (CD95) and GITR were significantly elevated in the circulation of AML patients compared to healthy donors: Foxp3 60vs32% p<0.001, CTLA-4 47vs21% p<0.01, CD45 RO 81vs53% p<0.002, Fas ligand 23vs4% p<0.001, GITR 65vs25% p<0.001. Suppression mediated by T reg co-incubated with proliferating autologous responders was also significantly higher (p<0.001) in AML than that mediated by control T reg (75 ± 6% vs 12% ± 4%). These results indicate that T reg accumulate in the periphery of patients with AML and mediate vigorous suppression. Modulation of the Treg suppressive activity, especially during the post-induction period, in AML patients may have therapeutic implications.