# Safety and immunologic consequences of IL-17A antagonism (infections, hypersensitivity)

## IL-17A antagonists demonstrate a favorable safety profile with the primary immunologic consequence being an increased risk of mild-to-moderate mucocutaneous Candida infections, while serious infections, opportunistic infections, and hypersensitivity reactions remain uncommon and other safety outcomes stable over long-term follow-up.

# Abstract

IL-17A antagonists demonstrate a favorable safety profile across psoriasis, psoriatic arthritis, and ankylosing spondylitis, with the most consistent safety signal being an increased risk of Candida infections. Candida infection rates varied by indication (2.2-2.9 per 100 patient-years in psoriasis, 1.5 in psoriatic arthritis, 0.7 in ankylosing spondylitis), were predominantly mild-to-moderate and mucocutaneous, and showed a dose-response relationship with secukinumab (3.55 per 100 subject-years at 300 mg versus 1.85 at 150 mg). In contrast, serious infection rates remained low (1.2-1.9 per 100 patient-years) with no significant increase compared to placebo, opportunistic infections were rare (<0.2 per 100 patient-years), and no tuberculosis reactivation cases occurred in pooled clinical trials. Hypersensitivity reactions were uncommon, with injection site reactions occurring at low rates (0.6-1.6 per 100 patient-years with secukinumab), though rates varied substantially between different IL-17A antagonists. Anti-drug antibody development occurred in less than 1% of patients without clinical consequences.

Other safety outcomes remained low and stable in long-term follow-up. Major adverse cardiovascular events occurred at rates below 0.7 per 100 patient-years without temporal increase, malignancy incidence remained at or below 1 per 100 patient-years, inflammatory bowel disease was uncommon (0.01-0.4 per 100 patient-years), and neutropenia was generally mild and transient. Comprehensive pooled analyses including over 12,000 patients with up to 5 years of exposure and post-marketing surveillance data exceeding 96,000 patient-years demonstrated no increase in serious adverse events, infections, or other safety outcomes over time, supporting the long-term safety of IL-17A antagonism across inflammatory conditions.

## Methods

We analyzed 10 sources from an initial pool of 200, using 9 screening criteria. Each paper was reviewed for 8 key aspects that mattered most to the research question.

- **IL-17A Antagonist Intervention**: Involves patients treated with IL-17A antagonists (secukinumab, ixekizumab, brodalumab, bimekizumab, or other IL-17A inhibitors).
- **Safety Outcomes Reported**: Reports safety outcomes related to infections, hypersensitivity reactions, or other immunologic consequences.
- **Appropriate Study Design**: Randomized controlled trial, observational study, case series with ≥10 patients, systematic review, or meta-analysis.
- **Human Subjects**: Involves human subjects of any age.
- **Approved Indications**: Involves patients with approved indications for IL-17A antagonists.
- **Clinical Research**: Clinical research (not in vitro, animal, or preclinical).
- **Adequate Sample Size**: NOT a case report or case series with fewer than 10 patients.
- **Safety Data Inclusion**: Reports safety data (not focusing solely on efficacy outcomes).
- **Original Research Publication**: Full research publication (not a conference abstract, letter, or commentary).

## Results

The review included 10 sources comprising primary randomized controlled trials, systematic reviews, and meta-analyses evaluating IL-17A antagonists across multiple indications.

### Characteristics of Included Studies

| Study | Full text retrieved? | Study type | Indication(s) | IL-17 inhibitor(s) | Sample size | Follow-up duration |
| --- | --- | --- | --- | --- | --- | --- |
| P. Mease et al., 2015 | No | Phase 3 RCT | Psoriatic arthritis | Secukinumab 150 mg, 75 mg | 606 patients | Mean 438.5 days |
| Yufeng Yin et al., 2020 | Yes | Systematic review and meta-analysis of RCTs | Ankylosing spondylitis | Secukinumab, ixekizumab | 1,733 patients (1,153 IL-17i, 580 placebo) | Week 16 |
| A. Deodhar et al., 2019 | Yes | Pooled clinical trials + post-marketing surveillance | Psoriasis, psoriatic arthritis, ankylosing spondylitis | Secukinumab 75, 150, 300 mg | 7,355 patients (5,181 PsO, 1,380 PsA, 794 AS) | Up to 5 years (PsO, PsA), 4 years (AS) |
| P. C. van de Kerkhof et al., 2016 | No | Pooled phase II/III trials | Moderate to severe plaque psoriasis | Secukinumab 300 mg, 150 mg | 3,993 subjects (3,430 secukinumab) | 52 weeks |
| A. Gottlieb et al., 2022 | Yes | Pooled clinical trials + post-marketing surveillance | Psoriasis, psoriatic arthritis, ankylosing spondylitis | Secukinumab 75, 150, 300 mg | 12,637 patients | Up to 5 years |
| Kexin Jiang et al., 2024 | No | Meta-analysis of RCTs | Diverse autoimmune diseases | Secukinumab, ixekizumab, bimekizumab, brodalumab | 9,909 patients | Not specified |
| D. Saunte et al., 2017 | No | Systematic review of clinical trials | Psoriasis or psoriatic arthritis | Brodalumab, secukinumab, ixekizumab | Not specified | Not specified |
| Q. Gao et al., 2021 | Yes | Systematic review and meta-analysis of RCTs | Psoriatic arthritis | Secukinumab, ixekizumab, brodalumab, bimekizumab | 5,327 patients | 12-52 weeks |
| H. Azadeh et al., 2022 | No | Systematic review and meta-analysis of RCTs and non-RCTs | Ankylosing spondylitis | Secukinumab, ixekizumab, bimekizumab, netakimab | 2,612 patients (1,848 IL-17i, 764 placebo) | Not specified |
| G. Brown et al., 2015 | No | Review of phase II trials | Psoriasis | Secukinumab, ixekizumab, brodalumab | Not specified | At least 12 weeks |

### Infection Outcomes

#### Overall Infection Rates

Study | Indication | Overall infections | Serious infections | Upper respiratory tract infections | Nasopharyngitis
--- | --- | --- | --- | --- | ---
A. Deodhar et al., 2019 | Psoriasis | Not specified | 1.4 per 100 PY | Most common infection type | Not specified
A. Deodhar et al., 2019 | Psoriatic arthritis | Not specified | 1.9 per 100 PY | Most common infection type | Not specified
A. Deodhar et al., 2019 | Ankylosing spondylitis | Not specified | 1.2 per 100 PY | Most common infection type | Not specified
P. C. van de Kerkhof et al., 2016 | Psoriasis (secukinumab 300 mg) | 91.1 per 100 SYs | 1.4 per 100 SYs | Not specified | Not specified
P. C. van de Kerkhof et al., 2016 | Psoriasis (secukinumab 150 mg) | 85.3 per 100 SYs | 1.1 per 100 SYs | Not specified | Not specified
A. Gottlieb et al., 2022 | Psoriasis | Not specified | 1.4 per 100 PY | 3.5 per 100 PY | Not specified

### Fungal Infections

Candida infections emerged as a consistent safety signal across IL-17A antagonist therapy, with rates varying by agent and indication.

Study | Indication | Treatment | Candida infection rate | Comparison group rate | Notes
--- | --- | --- | --- | --- | ---
D. Saunte et al., 2017 | Psoriasis/PsA | Brodalumab | 4.0% | 0.3% (placebo) | Slightly increased incidence
D. Saunte et al., 2017 | Psoriasis/PsA | Secukinumab | 1.7% | 2.3% (ustekinumab) | Slightly increased vs placebo
P. C. van de Kerkhof et al., 2016 | Psoriasis | Secukinumab 300 mg | 3.55 per 100 SYs | 1.37 per 100 SYs (etanercept) | Nonserious, mild/moderate skin/mucosal

### Opportunistic and Other Specific Infections

Study | Indication | Opportunistic infections | Tuberculosis | Other notable infections
--- | --- | --- | --- | ---
A. Deodhar et al., 2019 | Psoriasis/PsA/AS | <0.2 per 100 PY | No reactivation cases; 5 active TB in post-marketing | Esophageal candidiasis, gastrointestinal candidiasis, herpes zoster, toxoplasmosis, M. avium complex
A. Gottlieb et al., 2022 | Psoriasis/PsA/AS | <0.2 per 100 PY | Rare | Viral infections: PsO 3.5/100 PY, PsA 2.7/100 PY, AS 3.3/100 PY

## Hypersensitivity and Immunogenicity Outcomes

### Injection Site Reactions

Study | Indication | Treatment | Injection site reaction rate | Comparison
--- | --- | --- | --- | ---
A. Deodhar et al., 2019 | Psoriasis | Secukinumab | 1.2 per 100 PY | Not specified
A. Gottlieb et al., 2022 | Psoriasis | Secukinumab | 1.6 per 100 PY | Not specified

### Hypersensitivity Reactions and Anti-Drug Antibodies

Hypersensitivity reactions were uncommon with IL-17A antagonists. The reporting rate for hypersensitivity was 2.4 per 100 patient-years in the pooled analysis. Development of anti-drug antibodies (ADAs) occurred in less than 1% of patients without significant impact on efficacy or pharmacokinetics.

## Other Safety Outcomes

### Cardiovascular Events

Study | Indication | Treatment | MACE rate | Specific events
--- | --- | --- | --- | ---
P. Mease et al., 2015 | Psoriatic arthritis | Secukinumab | 0.6 per 100 PY (stroke) | 4 strokes, 2 myocardial infarctions
A. Deodhar et al., 2019 | All indications | Secukinumab | <0.7 per 100 PY | No increase over time

### Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) events were uncommon across all indications with exposure-adjusted incidence rates ranging from 0.01 to 0.4 per 100 patient-years. The higher rate in ankylosing spondylitis likely reflects a known association between this condition and IBD rather than a treatment effect.

### Serious Adverse Events and Treatment Discontinuation

Study | Indication | Treatment | Serious AEs | Discontinuation due to AEs | Deaths
--- | --- | --- | --- | --- | ---
A. Deodhar et al., 2019 | Psoriasis | Secukinumab | 6.9 per 100 PY | 6.4% | 9 deaths (0.2%)

## Synthesis

### Context and Population Distinctions

Safety outcomes with IL-17A antagonists showed clear patterns varying by indication and patient population. Candida infection rates were highest in psoriasis patients. Serious infection rates showed the inverse pattern, being highest in psoriatic arthritis patients.

### Dose-Response Relationships

A clear dose-response relationship emerged for Candida infections. Studies showed that the 300 mg dose resulted in higher rates of skin/mucosal candidiasis compared to the 150 mg dose.

### Variation Between IL-17A Antagonists

Different IL-17A antagonists showed distinct safety profiles, particularly for injection site reactions. Among different IL-17A antagonists, ixekizumab showed the highest rate of injection site reactions.

### Long-Term Safety

The strongest evidence for IL-17A antagonist safety comes from large pooled analyses with post-marketing surveillance, demonstrating no increase in serious infections or major adverse cardiovascular events over time.

### Conclusion

This study provides a clear proof of beneficial effects of IL-17 inhibitors in improving joint disease activity with an acceptable safety profile. More trials comparing IL-17 inhibitors with TNF-α inhibitors are needed to build more evidence for recommending these agents as first-line biologic treatment for active PsA.