Treatment of Active Idiopathic Inflammatory Myopathies by Low-Dose Interleukin-2: A Prospective Cohort Pilot Study

INTRODUCTION: Treatment of idiopathic inflammatory myopathies (IIMs) is challenging due to a lack of safe and efficacious medication. Low-dose interleukin-2 (IL-2) treatment emerges as a new option in active IIMs. This study aims to explore the clinical and immunological effects of low-dose IL-2 in patients with active IIMs. METHODS: Eighteen patients with active IIMs were enrolled and received 1 × 10(6) IU of IL-2 subcutaneously every other day for 12 weeks on top of standard care. The primary endpoint for the trial was change in percentage of regulatory T (Treg) cells in total CD4(+) T cells at week 12. The secondary endpoints included the International Myositis Assessment and Clinical Studies (IMACS) definition of improvement (DOI), the 2016 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) myositis response criteria, safety, and steroid-sparing effect at weeks 12 and 24. RESULTS: With low-dose IL-2 treatment, 77.78% (14/18) patients achieved IMACS DOI and 83.33% (15/18) patients met the 2016 ACR/EULAR myositis response criteria at week 12. All individual core set measures (CSMs) including PhGA, PGA and HAQ-DI, muscle enzymes, MMT-8 and extramuscular activity were improved at week 12. The cutaneous dermatomyositis disease area and severity index activity score (CDASI-a) decreased significantly from 7 (4.5, 13) to 2 (0, 7) after IL-2 administration (P < 0.001). Proportion of Treg cells significantly increased with low-dose IL-2 treatment at week 12 (8.97% [5.77, 9.89%] vs. 15.2% [10.4, 17.3%], P = 0.009). There were no serious adverse events. CONCLUSIONS: Low-dose IL-2 was effective in active IIMs and well tolerated. The amelioration of disease activity may associate with promotion of Tregs. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT04062019. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40744-021-00301-3.