Background

Sjögren’s syndrome is a chronic autoimmune disease that primarily affects exocrine glands, particularly the salivary and lacrimal glands. This leads to dry mouth and eyes as a common symptom in patients. However, it is often associated with musculoskeletal disorders and Inflammatory processes damage to other body systems [1]. The diagnosis of Sjogren’s syndrome is based on a combination of dryness symptoms and autoimmune features, including T-cell activity (confirmed by a positive salivary gland biopsy) or B-cell activity (demonstrated by the presence of autoantibodies) [2]. In most cases, Sjogren’s syndrome occurs independently of other inflammatory and autoimmune diseases and is referred to as primary Sjogren’s syndrome. However, it can also occur together with other autoimmune diseases such as thyroid disease, rheumatoid vasculitis and systemic lupus erythematosus, which is referred to as secondary Sjogren’s syndrome [3]. An increased prevalence of dry eye is observed in patients with autoimmune diseases, including Sjogren’s syndrome. Approximately 8% of the population is affected by this disease, 78% of whom are women [4,5]. Dry eye is typically due to instability of the tear film, with the thickness of the lipid layer being a key factor in this stability [6]. Chronic inflammation combined with decreased secretion of tear fluid and increased evaporation contribute to its development [7]. Patients with dry eye may complain of foreign body sensation, pain, sensitivity to light, blurred vision and difficulty opening the eyes. [8] Tears contain various growth factors and essential compounds, including epidermal growth factors, vitamin A, neurotrophic factors, albumin, and specific and non-specific antimicrobial substances such as lysozyme, lactoferrin, alpha-lysine and protein-based antimicrobial components. These elements play an important role in maintaining the health of the epithelial surface of the eye [9,10]. Lysozyme destroys bacteria by hydrolyzing the peptidoglycan layer of bacterial cell walls. In addition, lysozyme also has antifungal properties due to its ability to degrade chitin [10,11]. Alpha-lysine disrupts cell membranes by an unclear mechanism, and its concentration in tears is higher than in serum or plasma [12]. Lactoferrin reversibly binds to two iron atoms, limiting bacterial access to iron, which is critical for their growth and metabolism [13]. Specific antimicrobial components in tears include immunoglobulins A, G and M [14].

The tear film provides a smooth optical surface for the refraction of light, nourishes the cornea and plays a crucial role in the eye’s defense system. A lack of tear production or a change in tear composition can lead to eye damage and pathological conditions [15].

Long-term ocular complications resulting from exposure to chemical warfare agents include photophobia (73.2%), perceived visual deterioration (72.5%), dry eye sensation (66.4%), foreign body sensation (61.1%), excessive tearing (46.3%) and pain (43%). Slit lamp findings indicate meibomian gland dysfunction (96%), eyelid inflammation, tear abnormalities and dry ocular surfaces (80–90%). Chronic eyelid inflammation and decreased tear secretion are two key factors contributing to the progression of these ocular complications. The likelihood of chemical-induced keratopathy increases with higher initial exposure, higher degree of disability and longer duration of ocular involvement [16].

Initial ocular symptoms of chemical agent exposure include lacrimation, edema, ocular discharge, and even blindness, which may gradually resolve over the course of days or weeks. However, residual keratopathy may remain, leading to long-term effects in affected individuals (DMGK). Patients often suffer from dry eye symptoms [17].

Current treatments for dry eye syndrome include artificial tears, topical corticosteroids, cyclosporine A, therapeutic contact lenses, protective eyewear, punctal occlusion and tarsorrhaphy. However, these methods do not provide the essential growth factors and components found in natural tears [18].

Eye drops derived from the umbilical cord blood of healthy mothers contain high levels of cytokines, vitamin A, growth factors, neurotrophic factors and essential tear components, as well as antibacterial and antifungal agents such as IgG, lysozyme and other compounds. These drops create a suitable environment for the growth and regeneration of damaged cells and tissues. They are preservative-free, safe and effective in promoting the repair and regeneration of damaged epithelial cells and improving epithelial diseases [9,19,20].

Human umbilical cord blood serum (HUCB) eye drops are a safe and effective treatment rich in growth factors, essential tear components, neurotrophic and defensive factors. These drops not only provide the necessary tear components, but also provide an ideal environment for the regeneration and repair of damaged tissue. With a structural composition very similar to natural tears, they have shown significant efficacy in the treatment of dry eyes and ocular surface disorders.

However, its specific therapeutic effects in patients with Sjogren’s syndrome — a condition characterized by combined lacrimal gland dysfunction and ocular surface damage — and in chemical warfare veterans suffering from severe dry eye and extensive ocular surface damage, including corneal and conjunctival lesions, have not yet been thoroughly investigated. Although the underlying causes differ (autoimmune vs. chemical injury), both conditions share common pathogenic mechanisms — including epithelial damage, tear film instability, and chronic inflammation. Therefore, investigating HUCB serum in these two distinct but mechanistically related populations provides an opportunity to evaluate its regenerative potential across different etiologies of severe dry eye.

This study aims to investigate the effects of HUCB eye drops:

1. The improvement and repair of damaged ocular surface tissue.
2. The restoration of vision diminished by damage to the ocular surface tissue.
3. The relief of severe dry eye symptoms in patients with Sjogren’s syndrome and chemical warfare veterans.

Both subjective and objective tests will be used to evaluate these outcomes. The results of this study may also have application to other eye conditions associated with severe dry eye and ocular surface damage, such as Stevens-Johnson syndrome, keratoconjunctivitis sicca, burns, and chemical warfare or industrial exposure injuries.

Materials and methods

Procedure

In brief, all the assessments and evaluations are presented in Table 1.

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Table 1. Project assessment and time steps.

https://doi.org/10.1371/journal.pone.0337186.t001

Recruitment and baseline assessment.

Individuals who visit Baqiyatallah Hospital and meet the criteria for participation in the study will be assessed by a rheumatologist. Those with a confirmed diagnosis of Sjögren’s syndrome, based on rheumatological factors and clinical findings, including a combination of dry eye symptoms and autoimmune characteristics (such as T-cell activity, confirmed by a positive salivary gland biopsy, or B-cell activity, confirmed by the presence of autoantibodies), will be referred to the ophthalmology clinic. If they agree to participate, they will be included in the study.

Additionally, individuals with moderate to severe mustard gas chemical eye injuries who exhibit dry eye symptoms, as diagnosed by an experienced ophthalmologist, will also be included in the study.

For the control group, standard treatments for dry eye, such as artificial tears and topical corticosteroid drops, will be used, and the changes will be monitored. A convenience sampling method will be used, and the study’s purpose will be clearly explained to participants. Written informed consent will be obtained from all participants.

Umbilical cord serum droplets.

After childbirth, umbilical cord blood was collected directly as part of this study by the research team at Baqiyatallah University of Medical Sciences, Tehran, Iran. The collection took place in affiliated hospitals under ethical approval and informed written consent from the donor mothers. All cord blood samples were obtained in sterile containers without anticoagulants and were immediately processed under controlled laboratory conditions.

We included women aged 18–45 without any current known infection who underwent elective cesarean section. Also, in laboratory conditions, the donated umbilical cord blood samples are screened for contagious viral pathogens such as Human Immunodeficiency Virus (HIV), syphilis, and hepatitis B and C viruses. These samples will be taken in the same timeline as the rest of the study. We began recruitment of eligible donor mothers on April 1, 2025, and estimate that it will be completed by July 31, 2025.

The virus-free umbilical cord blood is incubated for two to four hours at room temperature, followed by the blood centrifugation process. After centrifugation, the yellow supernatant (serum) is carefully separated into a new sterile tube, and the remaining sediment (red blood cells and other cellular debris) should be discarded. Thermal inactivation should then be carried out at 56°C for 30 minutes on the collected serum. Following inactivation, filtration is performed, and the serum is stored at −20°C for future clinical use.

Serum eye drops, including autologous serum eye drops (ASEDs) and umbilical cord blood serum (UCBS), are advanced biologic treatments used to manage severe ocular surface diseases.

Opened serum drops should be stored in the refrigerator at 4°C within 7 days to ensure safety and effectiveness due to the lack of preservatives and risk of contamination, while unopened drops should be kept at −20°C for up to 3 months. The serum drops are administered 6–10 times a day, and if necessary, preservative-free artificial tears may also be recommended [25].

Discussion

This randomized controlled trial aims to evaluate the efficacy of human umbilical cord blood (HUCB) serum eye drops in improving ocular surface health, restoring vision, and alleviating severe dry eye symptoms in patients with Sjogren’s syndrome and chemical warfare veterans. By incorporating both subjective and objective outcome measures, this study will provide a comprehensive assessment of HUCB eye drops’ therapeutic potential.

The novelty of this study lies in its investigation of HUCB eye drops as a regenerative treatment for severe dry eye, particularly in patients with underlying autoimmune and chemically induced ocular surface damage. Unlike conventional treatments, HUCB serum eye drops offer essential growth factors, neurotrophic components, and antimicrobial agents that closely mimic natural tears, potentially promoting ocular surface repair and regeneration more effectively.

One of the strengths of this study is its randomized and controlled design, which includes validated assessment tools, a well-defined patient population, and a structured follow-up protocol. The inclusion of both Sjogren’s syndrome patients and chemical warfare veterans broadens the applicability of the findings, with potential implications for other severe ocular surface disorders, such as Stevens-Johnson syndrome and industrial chemical exposure injuries.

This study is open-label because the physical properties and storage conditions of umbilical cord blood serum differ visibly from conventional artificial tears, making participant blinding infeasible. However, the ophthalmologist and optometrist responsible for clinical assessments will remain blinded to treatment allocation to minimize measurement bias. Furthermore, objective ophthalmic parameters (TBUT, fluorescein staining, SM tube test) are included as secondary outcomes to complement the subjective OSDI score. The absence of participant blinding is acknowledged as a limitation, and results based on subjective measures will be interpreted with caution. Although a longer follow-up period would provide valuable information about the durability of treatment effects, this pilot study was designed primarily to assess short-term feasibility and preliminary efficacy. Due to resource and logistical constraints, extending follow-up beyond 60 days was not possible. The results of this trial will, however, inform the design and timing of follow-up assessments in a future larger-scale RCT with a longer observation period.

In conclusion, this study has the potential to advance treatment options for patients with severe dry eye and ocular surface damage. If successful, the findings may support the integration of HUCB serum eye drops into clinical practice as a safe and effective alternative for managing complex ocular surface diseases.

Supporting information

Acknowledgments

During the preparation of this work the authors used ChatGPT (developed by OpenAI, 2025) in order to improve the readability and language of this paper. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.