Highlight
Key points
– In a single-center perspective-controlled trial (Xue et al., J Am Acad Dermatol 2024), adding subcutaneous low-dose interleukin-2 (0.5 million IU every other day for 8 weeks) to standard systemic corticosteroids shortened time to disease control in moderate-to-severe bullous pemphigoid (BP).
– Mean time to disease control was 7.6 ± 3.0 days with IL-2 versus 10.43 ± 3.06 days in controls (P = .008); total systemic corticosteroid exposure was lower in the IL-2 group and no serious infections were reported during the study period.
– Study limitations (single-center, open-label, small sample, short follow-up) temper conclusions; findings are hypothesis-generating and support larger randomized trials focused on durability, safety, and steroid-sparing potential in an elderly population.
Background: clinical context and unmet need
Bullous pemphigoid is the most common subepidermal autoimmune blistering disease and predominantly affects older adults. It is characterized by autoantibodies directed against hemidesmosomal components (BP180 and BP230), complement activation, and inflammatory cell recruitment that lead to tense subepidermal blisters, pruritus, and significant morbidity. Standard therapy relies heavily on systemic corticosteroids and, in refractory or steroid-sparing strategies, adjunctive immunosuppressants (e.g., azathioprine, mycophenolate mofetil, doxycycline, biologics such as rituximab in selected cases).
Because BP patients are typically elderly with multiple comorbidities, prolonged systemic corticosteroid exposure increases the risk of infection, diabetes, hypertension, osteoporosis, and other complications. New approaches that control disease more rapidly, reduce cumulative steroid doses, and restore immunologic tolerance are therefore highly desirable.
Regulatory T cells (Tregs) are central to maintaining peripheral tolerance. Prior studies have demonstrated reduced numbers or impaired function of Tregs in peripheral blood and lesional skin of patients with BP, providing a plausible immunologic target. Low-dose interleukin-2 (IL-2) preferentially expands and activates Tregs because of their high IL-2 receptor alpha (CD25) expression; this strategy has shown proof-of-concept in other immune-mediated conditions to restore immune regulation without broadly suppressing protective immunity.
Study design
Design: Single-center, perspective-controlled, open-label trial reported by Xue et al. (J Am Acad Dermatol 2024).
Population: 43 patients with moderate-to-severe bullous pemphigoid were enrolled. Baseline disease severity stratification dictated corticosteroid starting doses (0.5 mg/kg/day for moderate disease, 1.0 mg/kg/day for severe disease).
Interventions and comparators: Both groups received systemic corticosteroids (initial dose per severity) and allowed immunosuppressants for the control group as clinically indicated. The treatment group received, in addition to standard corticosteroid therapy, subcutaneous low-dose IL-2 at a dose of 0.5 million IU (half million IU) every other day for 8 weeks.
Endpoints: The primary outcome was time (number of days) to achieve disease control. Secondary outcomes included other clinical responses (e.g., lesion healing, pruritus improvement), total systemic corticosteroid exposure, and safety outcomes (notably infections).
Key findings
Primary outcome: Patients in the IL-2 treatment group achieved disease control more rapidly than controls. Mean time to disease control was 7.60 ± 3.00 days in the IL-2 group versus 10.43 ± 3.06 days in the control group (P = .008). This represents a clinically meaningful acceleration in early response.
Steroid exposure: The trial reports that total systemic corticosteroid use was less in the treatment group compared with controls. The manuscript did not provide detailed cumulative dose curves or standardized steroid-equivalent quantification in the summary information provided here; nevertheless, the reported steroid-sparing effect is clinically important given the older age and comorbidity burden of typical BP patients.
Safety: Importantly, no serious infections were detected in the IL-2 treatment group during the study period. No signal of unexpected short-term toxicity from low-dose IL-2 was reported in this cohort. The study duration and sample size limit conclusions about rarer or longer-term adverse events.
Other clinical outcomes: The investigators reported earlier treatment responses overall in the IL-2 arm. Detailed secondary outcome data (e.g., rates of complete remission, time to relapse, pruritus scores, quality-of-life measures) are not fully described in the summary here; readers should consult the full publication for numeric secondary results and subgroup analyses.
Interpretation and biological plausibility
The study’s findings are biologically plausible. Low-dose IL-2 preferentially stimulates Tregs and has been employed in pilot studies and early-phase trials in other immune-mediated diseases to restore immune homeostasis and induce clinical benefit. In BP, where Treg deficiency or dysfunction has been observed in blood and skin, expansion of functional Tregs could suppress autoreactive effector T cells and downstream B cell autoantibody production, reduce tissue inflammation, and accelerate lesion healing.
Mechanistically, IL-2’s dose-dependent effects are critical: low doses favor Treg expansion and regulatory pathways, while higher doses can activate effector T cells and natural killer cells. The dosing regimen used in this study—0.5 million IU subcutaneously every other day for 8 weeks—aims to exploit the Treg-selective window.
Expert commentary and study limitations
Strengths: The trial addresses a high-priority unmet need — safer, steroid-sparing treatments for BP — and provides the first clinical evidence suggesting that low-dose IL-2 may accelerate disease control in moderate-to-severe cases. The pragmatic, real-world combination with standard corticosteroid dosing increases clinical relevance.
Limitations: Several important limitations temper interpretation and direct applicability.
- Design: The study was single-center, open-label, and perspective-controlled rather than randomized and blinded. This increases the risk of selection bias, performance bias, and observer bias in outcome assessment.
- Size and power: With 43 participants total, the trial is small and not powered to detect less frequent safety events (e.g., opportunistic infections, malignancy risk) or to robustly evaluate relapse rates and long-term remission.
- Duration: Follow-up was short. BP is a disease with potential relapses; the durability of responses and long-term steroid-sparing benefits remain unknown.
- Details: The summary provides limited granular data on cumulative steroid doses, standardized secondary endpoints, or immunologic correlates (e.g., Treg counts/function before and after therapy), which would strengthen mechanistic inference.
- Generalizability: Single-center design and potential heterogeneity in adjunctive immunosuppressant use in the control arm may limit broader applicability across different healthcare settings and patient populations.
Clinical implication: The accelerated time to disease control and reduced steroid exposure reported are clinically relevant signals. However, given the limitations, these results should be viewed as preliminary and hypothesis-generating. Clinicians should not change practice based on a single small open-label study; instead, the trial supports the rationale for randomized, placebo-controlled studies with larger samples, longer follow-up, predefined steroid tapering algorithms, and immunologic monitoring.
Recommendations for future research
Key priorities for subsequent studies include:
- Well-powered randomized, double-blind, placebo-controlled trials evaluating low-dose IL-2 plus standardized corticosteroid regimens versus corticosteroids alone with predefined steroid-sparing endpoints.
- Longer follow-up to assess relapse rates, sustained remission, and late adverse events — particularly infection and malignancy in older adults.
- Detailed immunophenotyping (peripheral and ideally lesional skin) to document Treg expansion, functional changes, and downstream effects on autoantibody production and complement activation.
- Evaluation of optimal dosing regimens, duration of IL-2 therapy, and combination strategies (e.g., with doxycycline, nicotinamide, or targeted biologics) that maximize efficacy while preserving safety.
- Subgroup analyses to identify patients most likely to benefit (age strata, baseline Treg status, disease severity, comorbidities).
Conclusion
The single-center perspective-controlled trial by Xue et al. provides preliminary evidence that subcutaneous low-dose IL-2 (0.5 million IU every other day for 8 weeks) added to standard systemic corticosteroids accelerates clinical disease control in moderate-to-severe bullous pemphigoid and is associated with reduced total steroid exposure and no serious infections during the study period. The findings align with the mechanistic rationale of Treg restoration in BP but are limited by the study’s open-label design, small size, and short follow-up.
Clinicians should regard these results as promising but preliminary. Larger randomized controlled trials with longer follow-up and correlative immunologic studies are needed before low-dose IL-2 can be recommended routinely for BP. If future studies confirm efficacy and safety, low-dose IL-2 could become an important tool to achieve faster control and reduce corticosteroid-related harms in a vulnerable elderly population.
Funding and clinicaltrials.gov
The published report (Xue et al., J Am Acad Dermatol. 2024 Dec;91(6):1113-1117) should be consulted for detailed funding disclosures and protocol registration. Funding sources and clinical trial registration were not detailed in the brief provided here; readers should review the full article for that information.
References
1. Xue R, Li G, Zhou Y, Wang B, Xu Y, Zhao P, Teng L, Zheng J, Liu H, Ji S, Elston DM, Liang Y. Efficacy and safety of low-dose interleukin 2 in the treatment of moderate-to-severe bullous pemphigoid: A single center perspective-controlled trial. J Am Acad Dermatol. 2024 Dec;91(6):1113-1117. doi: 10.1016/j.jaad.2024.08.033. Epub 2024 Aug 23. PMID: 39182680.
Note: Additional background on low-dose IL-2 biology and prior clinical experience in other immune-mediated diseases can inform interpretation; readers should consult the wider literature and current reviews for context and mechanistic detail.
