Involvement of Ocular Surface in Graft-Versus-Host Disease: A Review
Hematopoietic stem cell transplantation (HSCT) is a promising curative therapy for hematologic malignancies and other disorders of blood and bone marrow. Historically, HSCT was referred to as bone marrow transplantation (BMT) because bone marrow was the sole source of transplanted hematopoietic stem cells (HSCs). The accuracy of HSCs is high, and they can be harvested from peripheral blood and umbilical cord blood. More recently, experimental HSCT has been investigated for its role in organ transplantation. For the treatment of hematologic malignancies, the aim is to destroy cancer cells through a combination of chemotherapy and graft-versus-tumor (GVT) effect. Despite advances, this treatment modality is limited by organ cytotoxicity and graft-versus-host disease (GVHD), and tumor escape.
Graft-Versus-Host Disease (GVHD)
GVHD is the most common complication of allogeneic transplantation but can also be observed after syngeneic and autologous transplantation. It is also the major cause of post-transplant morbidity and mortality. GVHD occurs when donor T cells target the genetically defined proteins of recipient host cells. These proteins usually consist of highly polymorphic Human Leukocyte Antigens (HLA), encoded by the major histocompatibility complex (MHC). The corresponding HLAs of MHC class I, A, B, and C, are expressed on nearly all nucleated cells in the human body. Whereas HLAs corresponding to Class II MHC, DR, DQ, and DP, is primarily expressed on the hematopoietic cells such as B cells, monocytes, and dendritic cells except in the cases of inflammation or tissue injury. Despite HLA matching, some patients may develop acute GVHD due to minor histocompatibility antigens.
This expert review by Bruscolin et al. summarizes clinical features, management, current treatment modalities, and the future of ocular GVHD.
Classification of GVHD
Currently, GVHD is classified based on clinical manifestations. The two major types are, acute GVHD and chronic GVHD.
Acute GVHD
Acute GVHD (aGVHD) is an immediate multi-organ inflammation, most commonly seen within the first 100 days of HSCT. Although aGVHD can affect any part of the human body, the most important clinical consequences involve skin, liver, and intestine. Martin et al. in their comprehensive review reported skin, GI, and liver involvement to be 81%, 54%, and 50% respectively, at the onset of aGVHD in patients who underwent transplantation. When acute GVHD affects the skin, it often appears as a skin rash that may advance to blistering, ulceration, or desquamation. Ulceration of the GI tract usually results in bloody diarrhea, vomiting, or severe abdominal pain. Acute GVHD can destroy liver bile ducts, leading to jaundice and liver failure. There is controversy about acute GVHD of the eyes, and this is a topic for future studies.
Gam et al reported that single‐nucleotide polymorphism (SNPs) may affect the expression of proteins that modulate the immune response and influence the outcome of acute GVHD. Boieri et al. demonstrated that pathogenesis of acute GVHD proceeds in three phases.
Phase I: Includes activation of antigen-presenting cells (APCs) due to the tissue damage, followed by the production of pro-inflammatory cytokines. For example, tumor necrosis factor‐α (TNF‐α), interferon‐γ (IFN‐γ), and interleukins (IL) 1 and 6. Choi et al. reported an increment in TNF‐α receptor‐1 at one week after transplantation and correlates with GVHD onset. Furthermore, it has been suggested that an injury at oral, gastrointestinal, or ocular mucosa may activate APCs.
Phase II: This is the crucial phase involving donor T cells activation, proliferation, differentiation, and migration. Peyer’s patches within the small intestine are probably the first sites of donor T cells and recipient APCs. As indicated by numerous studies the activated T cells produce Th1 cytokines (IL‐2 and IFN‐γ), which are known to promote acute GVHD. A preclinical study demonstrated that the unbalance between Th1 and Th2 responses may induce the onset of acute GVHD.
Phase III: The T cells move from the site of activation to target organs and mediate apoptosis through cytotoxic T lymphocytes (CD8+ or CD4+) and natural killer cells. Jabs et al. reported the presence of inflammatory infiltration of mononuclear T lymphocytes in conjunctival GVHD. There are also reports of increased levels of cytokines like IL‐12, IL‐6, and TNF‐α in the tear of acute GVHD patients.
Chronic GVHD
GVHD occurring more than 100 days after HSCT. Chronic GVHD (cGVHD) is of autoimmune nature which involves the skin (75%), mouth (50-60%), liver (29-50%) along with associated ocular involvement in 40 – 60% of cases. The cGVHD usually is a continuation of aGVHD, though it can occur de novo (30%) involving one single organ or widespread in several organs.
The pathogenesis of cGVHD is much more complex; it mimics scleroderma, neuromyelitis, Sjogren syndrome, primary biliary cirrhosis, wasting syndrome, inflammatory bowel disease, bronchiolitis obliterans, or Graves’ disease. Therefore, for better explanation of pathogenesis, a three-phase-based concept was developed.
Phase I: Involves elucidating pre-existing inflammations. It overlaps with aGVHD development and is mediated by innate immunity responses resulting in inflammation or tissue damage caused by infections, cytotoxic medications, or Th1/Th2. Experimental studies suggested that Th1/Th2 mediated tissue damage may release damage molecules such as ATP, nucleic acids, and HMGBI, which in turn, trigger TLR, NOD-like receptors, and inflammasome pathways. Multiple INF-inducible genes and receptors are found to be upregulated during cGVHD onset. Evidence also suggests that IFN-gamma mediated expression of CXCL9, CXCL10, and CXCL11 recruits more Th1 and NK cells into tissues for cell death. Recently, anti-LG3 and endothelin-1 were found to be potential markers of vascular inflammation, and this may contribute to cGVHD pathogenesis.
Phase II: Involves the deregulation of adaptive immunity. The thymus gland damage plays a key role in this phase. Thymus dysfunction reduces the heterogeneity of tissue-specific auto-antigens present in cGVHD target sites such as the skin, liver, salivary glands, lungs, eyes, and GI tract. Few studies investigated the role of B lymphocytes on cGVHD pathogenesis. B-cell receptor (BCR) and B-cell activating factor (BAFF) play crucial roles in the fate and survival of B lymphocytes. High BAFF levels were reported in the plasma of cGVHD patients. It was also reported that BAFF directly promotes TLR7 and TLR9 expression, thus providing a positive outcome in terms of B cell proliferation, and cytokine production.
Despite their role in mediating humoral immunity, B lymphocytes act as antigen-presenting cells (APCs) and take part in the secretion of regulatory cytokines and chemokines. The actual role of B lymphocytes in cGVHD is complex. Recent studies showed the role of Regulatory B cells (Bregs) in cGVHD pathogenesis. The Bregs’ presence after 100 days of transplantation correlates with the probability of developing cGVHD. Another study reported high levels of transitional CD19+/CD21− B lymphocytes and lower levels of memory CD19+/CD27+ B lymphocytes in active cGVHD patients.
Phase III: The third phase of chronic GVHD pathogenesis is based on deregulated biological processes in response to inflammation resulting in fibrosis, scarring, and tissue/organ dysfunction. Since extracellular matrix (ECM) is essential for initiating the healing process, it is considered an active factor in cell-ECM interactions. Other prerequisites for tissue/organ healing are vascular remodeling and restoration of the epithelial cells. Evidence shows that ECM-producing fibroblasts are activated by cellular effectors such as TNF-alpha, IL-6, and IL-1-beta. TGF-beta, PDGF, or matrix-metalloproteinases (MMPs) are also found to mediate ECM production. Experimental studies reported MMP3’s role in promoting epithelial-mesenchymal transition. Importantly, MMP3 concentration increases during cGVHD onset, making it a biomarker of tissue fibrosis in active cGVHD cases. Some authors also reported the role of Th2 and Th17 CD4+ lymphocytes in activating profibrotic pathways through the production of IL-13 and IL-17.
Diagnostic Criteria for Graft-Versus-Host Disease
The diagnosis of graft-versus-host disease is usually made clinically, supported by biopsy or relevant tests. Schirmer’s test, tear break-up time (TBUT), corneal and conjunctival staining, and tear film osmolarity are used in diagnosing graft-versus-host disease.
According to 2014 NIH criteria, the diagnosis requires (i) distinction from other diagnoses where the clinical manifestation resembles GVHD, (ii) presence of at least one clinical sign, or (iii) one distinctive manifestation. Some of the distinctive manifestations used in the diagnosis of cGVHD:
- Skin cGVHD: Poikiloderma, lichenoid changes, and scleroderma
- Oral cGVHD: Hyperkeratotic patches
- Gastrointestinal cGVHD: Stenosis in the esophagus and esophageal web
- Musculoskeletal GVHD: Fasciitis, joint stiffness, or contractures
Lack of validated biomarkers limits differential diagnosis of GVHD. However, some promising data from clinical trials identified biomarkers that could predict or differentiate GVHD from other diagnoses which may mimic GVHD. For example, hepatocyte growth factor (HGF) to diagnose liver acute graft versus host disease; CXCL9, CXCL10, and CXCL11 for chronic GVHD.
Ocular Manifestation of Graft-Versus-Host Disease
Incidence
Ocular involvement is common in patients with chronic GVHD, with an incidence of 40-60%. Ocular GVHD (oGVHD) can occur in both acute and chronic forms. In a retrospective study of 283 patients who underwent HSCT between 2005 and 2020, about 50% developed ocular GVHD in the first five years. The cumulative incidence was reported to be 19.7% at 1st year, 29.3% at 2nd year, 40.7% at 3rd year, 47.2% at 4th year, and 49.7% at 5th year. Significant predictors of ocular GVHD were age, female sex, use of Peripheral blood stem cell (PBSC) for transplantation, and acute GVHD. Another single-center by Y. Inamoto et al. defined ocular GVHD based on the parameters such as new-onset dry eye symptoms, tear breakup time (≤5 seconds), mean Schirmer test value (≤5 mm at 5 minutes), vital staining grade (I or higher), and corneo-conjunctival inflammation. Using this definition, the incidence of ocular GVHD was 16% within 100 days of HCT, and the cumulative incidence was 35% at 2 years. An incidence of 33% was reported in a single-center study of 635 patients with the Schirmer test as one of the diagnostic criteria. In a prospective multicenter study of patients with chronic GVHD, ocular involvement was found in 51% of patients.
Signs and Symptoms
Ocular GVHD may involve the cornea, conjunctiva, lacrimal as well as the Meibomian glands, and rarely the uvea, the sclera, and the retina. Manifestations of ocular GVHD range from dry eyes to severe cicatricial conjunctivitis and corneal ulceration, melting, and perforation. The most commonly reported biological process of ocular GVHD is the dysfunction of lacrimal and Meibomian glands. In ocular GVHD patients, severe dry eyes may cause blurry vision, photophobia, gritty sensation, burning, pain, redness, and excessive tearing. These symptoms significantly reduce the patients’ overall quality of life. Thus, close monitoring and early diagnosis are necessary to avoid severe complications and to improve quality of life.
The National Institutes of Health (NIH) consensus noted that ocular manifestations are insufficient to establish an accurate diagnosis of aGVHD or cGVHD. However, numerous studies showed that keratoconjunctivitis sicca (KCS), commonly known as dry eye, typically develops within 3-9 months after HCT. Conjunctival infection was also reported to be a common sign of ocular GVHD. Jabs, D. A. et al. reported a decreased survival of GVHD patients with conjunctival involvement in comparison with all marrow transplant recipients. Jabs, D. A. et al. also proposed that the conjunctiva may mirror oral, intestinal, and lung mucosal membranes. Symptoms such as irritation, burning, pain, redness, photophobia, blurry vision, and excessive tearing were also reported to be associated with ocular GVHD.
NIH severity scoring is used to establish the severity and progression of GVHD and to determine treatment. Organs and tissues are scored on a 4-point scale (0 to 3).
- Score 0: No involvement or symptoms
- Score 1: Mild involvement
- Score 2: Moderate involvement
- Score 3: Severe functional compromise
Ocular graft‐versus‐host disease: Management & Treatment
There is a huge unmet need in the management of graft-versus-host disease and research into better options continues. Currently, corticosteroids are used as first-line therapy for treating acute and chronic GVHD. However, complete remission is observed in only 40-50% of cases. Furthermore, higher doses and longer treatment cause side effects, including immunosuppression, bone thinning, and hyperglycemia.
Intense lubrication is important not only for maintaining the integrity of the ocular surface, but also for preventing friction, discomfort, and inflammations. Preservative-free artificial tears, or viscous eye drops, and topical ointment are recommended to prevent dryness and epithelial damage. These drops also help to improve visual function. An ophthalmic suspension of hyaluronic acid- and dexpanthenol is recommended for patients with severe KCS. Mucin secretagogue eye drops (eg, 3% diquafosol sodium or 2% rebamipide) have been used in patients with dry eye disease and ocular GVHD. Some studies showed autologous serum eye drops can double as anti-inflammatory and nutritive agents; they are rich in epitheliotropic growth factors, some cytokines, nerve growth factors, and tissue inhibitors of matrix metalloproteinases.
Punctal occlusion with collagen or silicone plugs can help with lubrication. Y. Inamoto et al. reported that permanent punctal occlusion by thermal cauterization or surgical occlusion can be effective in some patients. In patients with blepharitis, topical anti-inflammatory therapy with calcineurin inhibitors is recommended. Low-dose oral tetracycline/doxycycline is found effective in inducing tear secretion by the meibomian gland.
Randomized studies have shown that topical cyclosporine A (CsA) can be used for KCS treatment. CsA may help increase the density of conjunctival goblet cells, and reduce punctate keratopathy. The recommended dose of CsA eye drops for cGVHD cases is 0.05% or 0.1% (twice daily).
Second-line therapies involving anti-thymocyte globulins (ATGs), MMF, and inhibitors of IL-2 and TNF α, are also used, but there is insufficient data to support their role in GVHD treatment.
Graft-versus-host disease: The Future
Considering the increment in HSCT there remains an urgent need to optimize conventional therapies and develop novel methods for improving the efficacy of GVHD treatment.
Promising new directions include recombinant deoxyribonuclease (DNase) eye drops. Though the safety and efficacy are under investigation, researchers found that DNase eye drops can help reduce the symptoms of ocular graft-versus-host disease by inhibiting neutrophil extracellular traps pathway.
Novel inhibitory agents (e.g. Janus kinase, Bruton’s tyrosine kinase, and Rho-kinase inhibitors) targeting GVHD pathways are still under research.
Lifitegrast, an LFA-1 antagonist was approved by the FDA for use in Dry Eye Disease (DED) as a 5% (50 mg/ml) ophthalmic solution. By inhibiting the binding of LFA-1 to ICAM-1, Lifitegrast prohibits T-cell activation, cytokine release, and formation of the immunological synapse, thereby decreasing the ocular inflammatory cycle
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