Ustekinumab For the Treatment of Giant Cell Arteritis: Comment on the Article by Matza et al

New Insights into the Pathogenesis of Giant Cell Arteritis: Mechanisms Involved in Maintaining Vascular Inflammation

The giant cell arteritis (GCA) pathophysiology is complex and multifactorial, involving a predisposing genetic background, the role of immune aging and the activation of vascular dendritic cells by an unknown trigger. Once activated, dendritic cells recruit CD4 T cells and induce their activation, proliferation and polarization into Th1 and Th17, which produce interferon-gamma (IFN-γ) and interleukin-17 (IL-17), respectively. IFN-γ triggers the production of chemokines by vascular smooth muscle cells, which leads to the recruitment of additional CD4 and CD8 T cells and also monocytes that differentiate into macrophages. Recent data have shown that IL-17, IFN-γ and GM-CSF induce the differentiation of macrophage subpopulations, which play a role in the destruction of the arterial wall, in neoangiogenesis or intimal hyperplasia. Under the influence of different mediators, mainly endothelin-1 and PDGF, vascular smooth muscle cells migrate to the intima, proliferate and change their phenotype to become myofibroblasts that further proliferate and produce extracellular matrix proteins, increasing the vascular stenosis. In addition, several defects in the immune regulatory mechanisms probably contribute to chronic vascular inflammation in GCA: a defect in the PD-1/PD-L1 pathway, a quantitative and qualitative Treg deficiency, the implication of resident cells, the role of GM-CSF and IL-6, the implication of the NOTCH pathway and the role of mucosal‑associated invariant T cells and tissue‑resident memory T cells.

The Th17 Pathway in Vascular Inflammation: Culprit or Consort?

The involvement of IL-17A in autoimmune and inflammatory diseases has prompted the development of therapeutic strategies to block the Th17 pathway. Promising results came from their use in psoriasis and in ankylosing spondylitis. IL-17A acts on various cell types and has both local and systemic effects. Considering the premature mortality observed during chronic inflammatory diseases, IL-17A action on vascular cells was studied. Both in vitro and in vivo results suggest that this cytokine favors inflammation, coagulation and thrombosis and promotes the occurrence of cardiovascular events. These observations led to study the role of IL-17A in diseases characterized by vascular inflammation, namely allograft rejection and vasculitis. Increased circulating levels of IL-17A and histological staining reveal that the Th17 pathway is involved in the pathogenesis of these diseases. Vasculitis treatment faces challenges while the use of steroids has many side effects. Regarding results obtained in giant cell arteritis with IL-6 inhibitors, a cytokine involved in Th17 differentiation, the use of anti-IL-17 is a promising strategy. However, lessons from rheumatoid arthritis and multiple sclerosis must be learnt before targeting IL-17 in vasculitis, which may be culprit, consort or both of them.

Advances in the Treatment of Giant Cell Arteritis

Giant cell arteritis (GCA) is the most common vasculitis among elderly people. The clinical spectrum of the disease is heterogeneous, with a classic/cranial phenotype, and another extracranial or large vessel phenotype as the two more characteristic patterns. Permanent visual loss is the main short-term complication. Glucocorticoids (GC) remain the cornerstone of treatment. However, the percentage of relapses with GC alone is high, and the rate of adverse events affects more than 80% of patients, so it is necessary to have alternative therapeutic options, especially in patients with worse prognostic factors or high comorbidity. MTX is the only DMARD that has shown to reduce the cumulative dose of GC, while tocilizumab is the first biologic agent approved due to its ability to decrease the relapse rate and lower the cumulative GC doses. However, apart from the IL-6 pathway, there are other pro-inflammatory cytokines and growth factors involved in the typical intima hyperplasia and vascular remodeling of GCA. Among them, the more promising targets in GCA treatment are the IL12/IL23 axis antagonists, IL17 inhibitors, modulators of T lymphocytes, and inhibitors of either the JAK/STAT pathway, the granulocyte-macrophage colony-stimulating factor, or the endothelin, all of which are updated in this review.

Literature Commentary

In this issue of Journal of Neuro-Ophthalmology, M. Tariq Bhatti, MD, and Mark L. Moster, MD will discuss the following 6 articles: Li L, Dmytriw AA, Krings T, Feng Y, Jiao L. Visualization of the human intracranial vasa vasorum in vivo using optical coherence tomography. JAMA Neurol. 2020;77:903-905.Lee KE, Zehri A, Soldozy S, Syed H, Catapano JS, Maurer R, Albuquerque FC, Liu KC, Wolfe SQ, Brown S, Levitt MR, Fargen KM. Dural venous sinus stenting for treatment of pediatric idiopathic intracranial hypertension. J Neurointerv Surg. [published online ahead of print July 30, 2020] doi:10.1136/neurintsurg-2020-016183.Matza MA, Fernandes AD, Stone JH, Unizony SH. Ustekinumab for the treatment of giant cell arteritis. Arthritis Care Res (Hoboken). [published online ahead of print April 5, 2020] doi:10.1002/acr.24200.Kunchok A, Aksamit AJ Jr, Davis JM III, Kantarci OH, Keegan BM, Pittock SJ, Weinshenker BG, McKeon A. Association between tumor necrosis factor inhibitor exposure and inflammatory central nervous system events. JAMA Neurol. 2020;77:937-946.Mac Grory B, Nackenoff A, Poli S, Spitzer MS, Nedelmann M, Guillon B, Preterre C, Chen CS, Lee AW, Yaghi S, Stretz C, Azher I, Paddock J, Bakaeva T, Greer DM, Shulman JG, Kowalski RG, Lavin P, Mistry E, Espaillat K, Furie K, Kirshner H, Schrag M. Intravenous fibrinolysis for central retinal artery occlusion: a cohort study and updated patient-level meta-analysis. Stroke. 2020;51:2018-2025.Lopez-Chiriboga S, Sechi E, Buciuc M, Chen JJ, Pittock SJ, Lucchinetti CF, Flanagan EP. Long-term outcomes in patients with myelin oligodendrocyte glycoprotein immunoglobulin G-associated disorder. JAMA Neurol. [published online ahead of print August 31, 2020] doi:10.1001/jamaneurol.2020.3115.