Improvement of Treg immune response after treatment with tocilizumab in giant cell arteritis

Abstract

Objectives: To study the percentage, suppressive function and plasticity of Treg in giant cell arteritis (GCA), and the effects of glucocorticoids and tocilizumab.

Methods: Blood samples were obtained from 40 controls and 43 GCA patients at baseline and after treatment with glucocorticoids + IV tocilizumab (n = 20) or glucocorticoids (n = 23). Treg percentage and phenotype were assessed by flow cytometry. Suppressive function of Treg was assessed by measuring their ability to inhibit effector T-cell (Teff) proliferation and polarisation into Th1 and Th17 cells.

Results: Treg (CD4⁺CD25^highFoxP3⁺) frequency in total CD4⁺ T cells was decreased in active GCA patients when compared to controls (2.5% vs. 4.7%, P < 0.001) and increased after treatment with tocilizumab but worsened after treatment with glucocorticoids alone. Treg lacking exon 2 of FoxP3 were increased in GCA patients when compared to controls (23% vs. 10% of total Treg, P = 0.0096) and normalised after treatment with tocilizumab + glucocorticoids but not glucocorticoids alone. In GCA patients, Treg were unable to control Teff proliferation and induced ˜50% increase in the amount of IL-17⁺ Teff, which was improved after in vitro blockade of the IL-6 pathway by tocilizumab.

Conclusion: This study reports quantitative and functional disruptions in the regulatory immune response of GCA patients and demonstrates that, unlike glucocorticoids, tocilizumab improves Treg immune response.

Keywords: Treg; giant cell arteritis; interleukin‐6; tocilizumab.