PDF file, 251K, Supplemental Figure 1. CD56+CD16+ NK cells isolation from buffy coats. Suppelmental Figure 2. IFN-alpha treatment impairs STAT1 activation in Treg. Supplemental Figure 3. IFN-alpha did not affect Foxp3 expression in Treg. Supplemental Figure 4. Pharmacological repression of cAMP production in Treg does not affect ZAP-70 phosphorylation.
ARTICLE ABSTRACTIFN-α is an antineoplastic agent in the treatment of several solid and hematologic malignancies that exerts strong immune- and autoimmune-stimulating activity. However, the mechanisms of immune activation by IFN-α remain incompletely understood, particularly with regard to CD4+CD25highFoxp+ regulatory T cells (Treg). Here, we show that IFN-α deactivates the suppressive function of human Treg by downregulating their intracellular cAMP level. IFN-α–mediated Treg inactivation increased CD4+ effector T-cell activation and natural killer cell tumor cytotoxicity. Mechanistically, repression of cAMP in Treg was caused by IFN-α–induced MAP–ERK kinase (MEK)/extracellular signal-regulated kinase (ERK)–mediated phosphodiesterase 4 (PDE4) activation and accompanied by downregulation of IFN receptor (IFNAR)-2 and negative regulation of T-cell receptor signaling. IFN-α did not affect the anergic state, cytokine production, Foxp3 expression, or methylation state of the Treg-specific demethylated region (TSDR) within the FOXP3 locus associated with a stable imprinted phenotype of human Treg. Abrogated protection by IFN-α–treated Treg in a humanized mouse model of xenogeneic graft-versus-host disease confirmed IFN-α–dependent regulation of Treg activity in vivo. Collectively, the present study unravels Treg inactivation as a novel IFN-α activity that provides a conceivable explanation for the immune-promoting effect and induction of autoimmunity by IFN-α treatment in patients with cancer and suggests IFN-α for concomitant Treg blockade in the context of therapeutic vaccination against tumor antigens. Cancer Res; 73(18); 5647–56. ©2013 AACR.