Low-dose IL-2 therapy limits the reduction in absolute numbers of circulating regulatory T cells in rheumatoid arthritis

Abstract

Background: Circulating regulatory T cells (Tregs) are responsible for mediating immune tolerance and maintaining immunological homeostasis. Decreases in Tregs may be involved in the onset of rheumatoid arthritis (RA). Low-dose interleukin-2 (IL-2) has been considered for the treatment of inflammatory diseases mediated by T cells. This study focused on the status of circulating CD4⁺T subsets and the clinical feasibility of IL-2 therapies in patients with RA.

Methods: The subjects included 888 patients with RA and 100 healthy controls (HCs); 233 RA patients received IL-2 treatment with 0.5 million international units (MIU)/day from days 1 through 5. The demographic features, disease activity, and levels of CD4+T cells measured by modified flow cytometry were collected in all RA patients before and after treatment.

Results: RA patients had lower absolute Treg counts (but not Th17) compared with HCs, which was associated with disease activity; previously treated RA patients had the fewest circulating Tregs (p < 0.05). Patients treated with low-dose IL-2 had a three-fold increase in absolute anti-inflammatory Treg counts, as well as a two-fold increase in the other CD4⁺T subsets. Moreover, post-treatment levels of markers of disease activity in RA patients treated with IL-2 were significantly lower than the baseline values (p < 0.001), with no apparent side effects.

Conclusion: Decreased absolute counts of circulating CD4⁺T lymphocyte subsets were observed in patients with RA. Circulating Tregs, which mediate immune tolerance, may be involved in the pathogenesis and progression of RA; however, this was ameliorated by low-dose IL-2, without obvious side effects.

Plain language summary: Low-dose IL-2 treatment for rheumatoid arthritis • Circulating Tregs may be involved in the pathogenesis and progression of RA.• The absolute count of Tregs was significantly correlated with disease activity measures.• Low-dose IL-2 was able to effectively expade Tregs and help for RA patients' symptoms remission without evaluated side effects.

Keywords: immunoregulation; low-dose IL-2; regulatory T cells; rheumatoid arthritis.

Figure 1.

Changes in the absolute counts of peripheral CD4+T subsets among new (n = 188) and previously treated (n = 700) patients with RA and healthy controls (n = 100). (a) The absolute count of CD4+T cells was significantly decreased in previously treated patients with RA compared with new RA patients. (b) The absolute count of Th1 cells from previously treated patients with RA was significantly lower than that of healthy individuals and new RA patients. New RA patients had a similar level of Th1 cells as healthy controls. (c, d) There were no significant differences in the absolute counts of Th2 or Th17 cells between RA patients and healthy controls. (e) RA patients, both new and previously treated, had decreased absolute counts of Tregs compared with healthy controls; the fewest circulating Tregs were from previously treated RA patients. (f, g) The Th1/Th2 ratio was significantly lower, and the Th17/Treg ratio significantly higher, in patients with RA. Previously treated patients had the lowest Th1/Th2 ratio. *p < 0.05, **p < 0.01, ***p < 0.001. Significance values are asymptotic (two-sided tests) and the significance level is p < 0.05. RA, rheumatoid arthritis; Tregs, regulatory T cells.

Figure 2.

Correlation between the absolute count of circulating Tregs and disease activity. (a–e) The absolute count of Tregs in peripheral blood was negatively correlated with markers of disease activity, including TJC, SJC, ESR, CRP, and DAS28, in patients with RA. Significance values are asymptotic (2-sided tests) and the significance level is p < 0.05. CRP, C-reactive protein; DAS28, disease activity score-28; ESR, erythrocyte sedimentation rate; SJC, swollen joint counts; RA, rheumatoid arthritis; TJC, tender joint counts; Treg, regulatory T cells.

Figure 3.

Efficacy of short-term, low-dose IL-2 treatment in regulating levels of CD4+T subsets. (a–e) Absolute counts of peripheral CD4+T and its subsets, especially Tregs, were significantly higher in RA patients after IL-2 treatment compared with baseline. (f, g) The Th17/Treg ratio decreased significantly in RA patients after IL-2 treatment, whereas the ratio of Th1/Th2 was not significantly different. Within-group comparisons were made using the paired samples t test before and after IL-2 therapy. ***p < 0.001. Significance values are asymptotic (two-sided tests) and the significance level is p < 0.05. IL-2, interleukin-2; RA, rheumatoid arthritis; Tregs, regulatory T cells.