Randomized Trial Supports Sirolimus as Add-On Therapy for Systemic Lupus Erythematosus

Phase 3 SIRIUS trial results show that sirolimus (rapamycin) added to standard therapy significantly improves clinical and serologic outcomes in active systemic lupus erythematosus (SLE). At 24 weeks, 52.9% of sirolimus-treated patients achieved SRI-4 response vs 22.7% with placebo (P = .001). The mTOR inhibitor, already established for transplant rejection prevention, was successfully repurposed for lupus in this multicenter, double-blind, randomized controlled trial conducted at six centers in China.

📋 SIRIUS Trial Design: Phase 3 Randomized Controlled Study

The SIRIUS trial (presented as a late-breaking clinical abstract at the European Alliance of Associations for Rheumatology (EULAR) 2026 Annual Meeting in London) was a multicenter, randomized, double-blind, placebo-controlled Phase 3 study conducted at six centers in China.

• Inclusion criteria: Adults with active SLE (SLEDAI-2K score ≥4 despite standard treatment) plus serologic activity (anti-dsDNA >10 IU/mL and/or complement C3 ≤0.90 g/L)
• Intervention: Sirolimus 1.5 mg/day or matching placebo added to stable background therapy for 24 weeks, followed by crossover
• Primary endpoint: SLE Responder Index (SRI)-4 response at week 24
• Patient population: Mean age ~35 years, 94% women, mean time from diagnosis ~8.5 years

📊 Primary and Secondary Endpoint Results

📈 Additional Secondary Endpoints Favoring Sirolimus

⚠️ Safety Profile: Known and Manageable

🧬 Why Sirolimus? The mTOR Pathway in SLE Pathogenesis

Sirolimus (also known as rapamycin) is a well-established mTOR (mammalian target of rapamycin) inhibitor used for decades to prevent organ transplant rejection. Its mechanism of action in SLE is supported by evidence that the mTOR signaling pathway is “extensively” involved in lupus pathogenesis:

• mTOR hyperactivation is observed in T cells, B cells, and dendritic cells from SLE patients
• mTOR inhibition restores regulatory T cell (Treg) function and suppresses autoreactive lymphocytes
• Reduces autoantibody production and inflammatory cytokine release

Previous proof-of-concept studies (Lancet 2018, meta-analysis 2020) suggested sirolimus might be beneficial in SLE. The SIRIUS trial now provides Phase 3 randomized evidence supporting its efficacy as an add-on therapy.

💬 Expert Commentary: Implications for Clinical Practice

Commenting on the findings, Dr. Md Yuzaiful Md Yusof (Associate Professor, Leeds Institute of Rheumatic and Musculoskeletal Medicine, UK) — who was not involved in the study — noted:

• “These are important Phase 3 randomized trial results showing rapid efficacy and a large effect size of 30% between sirolimus and placebo at week 24.”
• “The low placebo response rate strengthens the findings.”
• “Other key secondary efficacy endpoints favored sirolimus too, with no major safety signals.”

Potential place in therapy: Dr. Md Yusof suggested sirolimus could be used in patients with active moderate-to-severe nonrenal disease who failed one conventional immunosuppressant — prior to biologics, as well as those with T-cell driven features (mucocutaneous disease, arthritis, serositis, cytopenia).

🔬 Scientific References & External Resources

• EULAR 2026 Late-breaking abstract: Li M, et al. “Sirolimus as add-on therapy for active systemic lupus erythematosus: a randomized, double-blind, placebo-controlled phase 3 trial (SIRIUS).” Presented June 10, 2026.
• PubMed — Sirolimus in SLE (including Lancet 2018 and 2020 meta-analysis)
• PubMed — mTOR pathway in SLE pathogenesis
• EULAR (European Alliance of Associations for Rheumatology) — Official meeting website
• ClinicalTrials.gov — Search for ongoing SLE studies