Inhibition of Interleukin-17 Promotes Differentiation of CD25- Cells Into Stable T Regulatory Cells in Patients With Autoimmune Hepatitis

BACKGROUND & AIMS: Patients with autoimmune hepatitis (AIH) have reduced numbers and function of CD4(+)CD25(high)FOXP3(+) T regulatory cells (Tregs). Tregs can be generated from CD25(-) (ngTreg) cells, which suppress the immune response less efficiently than Tregs. We investigated whether their differentiation into T-helper (Th)17 cells, an effector subset that has the same CD4(+) progenitors as Tregs, accounts for the reduced suppressive functions of ngTregs. We investigated whether blocking interleukin (IL)-17 increased the immunosuppressive activity of Tregs. METHODS: ngTregs were generated from 36 patients with AIH and 23 healthy subjects (controls). During Treg differentiation, expression of IL-17 was inhibited by physical removal of IL-17-secreting cells, exposure to recombinant transforming growth factor beta or neutralizing antibodies against IL-6 and IL-1 beta (to promote differentiation of ngTregs vs Th17 cells), small inhibitory RNAs specific for the Th17 transcription factor RORC, or a combination of all these approaches. RESULTS: ngTregs from patients with AIH contained greater proportions of IL-17(+) and RORC+ cells than Tregs from controls. All approaches to inhibit IL-17 increased expression of FOXP3 by ngTregs and their suppressive functions. Inhibition of IL-17 led to development of ngTregs that were phenotypically stable and did not acquire proinflammatory properties after exposure to IL-6 and IL-1 beta. CONCLUSIONS: Blocking Th17 allows ngTregs to differentiate into functionally stable immune inhibitory cells; this approach might be developed for therapy of patients with AIH.