Introduction
SARS-CoV-2 is a positive-sense, single stranded RNA in theCoronaviridae family of viruses1.2. Most cases of infection present with mild disease phenotype with self-limiting symptoms largely consisting of fever, fatigue, dry cough, headache, and diarrhea1,2. However, roughly 14% of patients develop a severe disease phenotype requiring hospitalization, most commonly due to dyspnea and hypoxia3,4. Characteristic laboratory features of this virus are leukopenia, prolonged prothrombin time, and elevated serum concentrations of D-dimer, lactate dehydrogenase (LDH), ferritin, and c-reactive protein (CRP)5. Chest computed tomography classically demonstrates bilateral ground glass opacities1. A critical component of the pathogenesis of SARS-CoV-2 consists of a hyperactive immune response to the virus resulting in a sudden, acute increase in pro-inflammatory cytokines, termed “the cytokine storm”6. Key pro-inflammatory cytokines upregulated in this process include interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α)6. IL-6 is one of the most highly expressed cytokines in SARS-CoV-2 infection and elevated serum levels of IL-6 are associated with a poor prognosis7-9. Elevated cytokine levels prompt an influx of various immune cells into the site of infection, leading to tissue destruction and multiorgan damage10. Immune mediated tissue destruction is thought to be a contributing factor to the development of several life-threatening complications, such as acute respiratory distress syndrome, septic shock, and multiorgan failure11.
Primary myelofibrosis (PMF) is an acquired stem cell neoplasm with ineffective hematopoiesis, bone marrow fibrosis and splenomegaly. Clonal populations of dysplastic megakaryocytes and myeloid cells release inflammatory cytokines that are responsible for clonal evolution, symptom burden, progressive myelofibrosis and extramedullary splenic hematopoiesis12. Risk factors for acquired PMF include smoking, excessive alcohol intake, exposure to radiation, or exposure to industrial solvents13. Common gene mutations found in patients with PMF include Janus kinase 2 (JAK2V617F), calreticulin (CALR), thrombopoietin receptor (MPL515L/K), and ten-eleven translocation 2 (TET2). The early phase of PMF is termed the pre-fibrotic phase when patients have traditionally been thought to be asymptomatic. This phase is characterized by a hypercellular marrow with megakaryocytic hyperplasia and minimal fibrosis12. However, recent studies by Mesa have shown that most patients with myeloproliferative neoplasms, and particularly myelofibrosis, are symptomatic at onset.14 At later stages of disease progression, myelofibrosis develops due to the release of excessive amounts of growth factors from megakaryocytes and monocytes resulting in fibroblast proliferation, collagen synthesis and an increasing degree of fibrosis12. Patients may express cytokine related hypercatabolic symptoms such as fatigue, weight loss, fever, and chills, together with abdominal discomfort from splenomegaly. Splenomegaly is primarily due to extramedullary hematopoiesis but can also be due to splanchnic vein thrombosis12. Treatment largely depends on disease burden; while many patients are observed without treatment, young, high risk patients may receive allogenic stem cell transplant15. For other patients, therapies are designed to dampen the excessive inflammatory marrow milieu16. On the molecular level, Janus kinases (JAKs) mediate cytokine production through various downstream signaling pathways, such as the signal transducer and activator of transcription (STAT) pathway17. The JAKs consists of four tyrosine kinases that consists of JAK1, JAK2, JAK3, and tyrosine kinase 2 (TYK2). They transmit extracellular signals, such as proinflammatory cytokines, to the nucleus by activating STAT. Ultimately, these extracellular signals result in a transcriptional response of target genes from cellular DNA18. In this pathway, receptors bind to various cytokines that, in turn, trigger and orchestrate innate immune responses19. Additionally, interferon acts through the JAK-STAT pathway to target genes responsible for antiviral and adaptive immune responses20. The JAK2V617F variant, a gain-of-function mutation, causes constitutive activation of tyrosine kinase domain of JAK2 leading to dysregulated immune response21. This mutation is present in majority of patients with myeloproliferative neoplasms. JAK inhibitors ruxolitinib and fedratinib are FDA approved for the treatment of PMF22. The immunosuppressive effects of JAK inhibition vary based on the specificity and dosage of each drug, which also accounts for the range in toxicology profiles. Ruxolitinib is a JAK 1-2 inhibitor that causes a reduction in cytokine production. This drug was shown to decrease spleen size and disease-related symptoms compared to placebo in the double-blind COMFORT-I trial consisting of 309 patients with intermediate-2 or high-risk myelofibrosis. Ruxolitinib is primarily utilized in the treatment of myelofibrosis, but it is also licensed for patients with polycythemia vera intolerant or refractory to hydroxyurea. However, ruxolitinib is also utilized off label for diseases involving cytokine release as the primary pathogenesis, including graft versus host disease and hemophagocytic lymphohistiocytosis23,24. Fedratinib is a selective oral JAK 2 inhibitor that has demonstrated similar results as ruxolitinib in placebo-controlled, randomized phase II and III clinical trials22. However, four patients developed neurological symptoms during clinical trials and fedratinib now carries a black block warning for serious and fatal encephalopathy, including Wernicke encephalopathy25. Prior to administering fedratinib, thiamine levels must be measured and replenished. Multiple small molecule JAK inhibitors are also utilized in the treatment of many inflammation-driven pathologies, such as inflammatory bowel disease, rheumatoid arthritis, and psoriasis26. Another molecular component in inflammation regulation is interferon which for decades has been used successfully in the treatment of patients with myeloproliferative neoplasms. Interferon normalizes cell counts in the majority of patients within a few months. Interferon also improves megakaryocytic dysfunction in part through induction of IFITM327. This led to treatment of early phase PMF with interferon28-30. Eighty percent stabilization, partial response or remission were observed in phase 2 studies. Architectural reversion of the marrow fibrosis after treatment was noted. Recent studies have demonstrated efficacy of ruxolitinib and interferon α2 combination PMF treatment with an acceptable toxicity profile31. Combination therapy was shown to elicit complete remissions in 3 out of 18 patients and complete hematologic response in 11 out of 12 patients32.
JAK/STAT pathway inhibitors have been proposed as a therapy to target the hyperinflammation associated with SARS-CoV-217. This hyperinflammation seen in SARS-CoV-2 is similarly observed in cytokine release syndrome (CRS), characterized by elevated IL-6, IL-2, IL-7, IL-10, and more1,33. Elevations in serum cytokine and chemokine levels correlate with disease severity and adverse clinical outcome1. Specifically, increased levels of IL-6 have been reported in patients with severe SARS-CoV-2 and have been associated with increased mortality7-9. IL-6 plays pivotal role in CRS through JAK-STAT signaling that results in altered immune regulation and oxidative stress18. Therefore, many treatments are aimed at ameliorating the cytokine storm by inhibiting the JAK-STAT pathway. Ruxolitinib has been shown to significantly reduce IL-6 and CRP levels in patients with myelofibrosis, with a relatively mild side effect profile and is therefore being considered as a treatment option for SARS-CoV-234. Of note, there is concern for increased risk of infection in patients treated with JAK inhibitors, as JAK-STAT signaling is responsible for the signal transduction of type I interferon18. Interferons are crucial for preventing viral replication in the early stage of infection in addition to enhancing antibacterial immunity35. This was evidenced by previous studies reporting increased incidence of bacterial infections, particularly urinary tract infections in patients treated with JAK inhibitors36. Interferons may be protective early in SARS-CoV-2 infection and damaging later in the infection. Thus, the effects of interferon in COVID-19 patients is likely complex and time dependent.
We present the case of an 83-year-old woman found to be SARS-CoV-2 positive who was asymptomatic while taking ruxolitinib for co-existing PMF but displayed a prolonged period of nasal swab PCR positivity. Culture failed to reveal infectious virions. Administration of pegylated interferon was followed by rapid clearance of viral RNA by PCR. We hypothesize that the combination of ruxolitinib with interferon may be useful in the acute COVID-19 setting to induce viral clearance with reduced risk of cytokine storm.