Selective IL-2 Responsiveness of Regulatory T Cells Through Multiple Intrinsic Mechanisms Supports the Use of Low-Dose IL-2 Therapy in Type 1 Diabetes

Low-dose interleukin-2 (IL-2) inhibited unwanted immune responses in several clinical settings and is currently being tested in patients with type 1 diabetes (T1D). Low-dose IL-2 selectively targets regulatory T cells (Tregs), but the mechanisms underlying this selectivity are poorly understood. We show that IL-2-dependent STAT5 activation in Tregs from healthy individuals and patients with T1D occurred at an similar to 10-fold lower concentration of IL-2 than that required by T memory (T-M) cells or by in vitro-activated T cells. This selective Treg responsiveness is explained by their higher expression of IL-2 receptor subunit alpha (IL-2R alpha) and gamma chain and also endogenous serine/threonine phosphatase protein phosphates 1 and/or 2A activity. Genome-wide profiling identified an IL-2-dependent transcriptome in human Tregs. Quantitative assessment of selected targets indicated that most were optimally activated by a 100-fold lower concentration of IL-2 in Tregs versus CD4(+) T-M cells. Two such targets were selectively increased in Tregs from T1D patients undergoing low-dose IL-2 therapy. Thus, human Tregs possess an IL-2-dependent transcriptional amplification mechanism that widens their selective responses to low IL-2. Our findings support a model where low-dose IL-2 selectively activates Tregs to broadly induce their IL-2/1L-2R gene program and provide a molecular underpinning for low-dose IL-2 therapy to enhance Tregs for immune tolerance in T1D.