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COVID-19, Kawasaki and the Cytokine Storm

by Sabina Paglialunga, PhD – Director, Scientific Affairs, Celerion

SARS-CoV-2 symptoms include fever, cough and shortness of breath. The disease is especially hard on vulnerable populations such as the elderly and those with underlying health conditions like obesity and hypertension. Now, developing reports indicate that children may also be at great risk than originally thought.  


Into the Eye of the Storm

The virus primarily enters the body via the respiratory tract, and into lung cells through ACE2 receptors.  To counteract, the body mounts an immune response to defend against the foreign virus.  However, this attack tends to occur several days after initial infection, by when significant amount of viral shedding has already occurred, contributing to the wide spread of the disease.  As part of the defense process, there is an influx of immune cells, which include macrophages and T cells to the respiratory tract, leading to an overall systemic upregulation of pro-inflammatory cytokines (e.g. IL-6, IL-1β, TNFα) as well as interferon (IFN) signaling and production anti-viral factors. The resulting immune response drives B cells to create antibodies against SARS-CoV-2. These antibodies recognize the virus, neutralize and clear it from the body.  

While many infected individuals are asymptomatic or present with mild symptoms. Since the ACE2 receptors are also expressed in gastrointestinal tissues, abdominal symptoms are associated with COVID-19.  More severe cases will result in pneumonia, sepsis, acute respiratory distress syndrome (ARDS) requiring hospitalization and even death. Researchers have found that a hyper-immune response is associated with the most severe COVID-19 cases. Early studies from China reported patients in intensive care units (ICU) had dramatically elevated levels of IL-6, IL-10 and TNFα, accompanied by a reduction in CD4+ and CD8+ T cells [1]. This hyper-, pro-inflammatory state is often referred to as the cytokine storm or cytokine release syndrome (CRS). In this state, pro-inflammatory cytokines are released in excess amounts, creating an exaggerated cytokine response.  This can lead to not only damage to the virus and infected host cell but also healthy cells too. In the lungs, destruction of areole cells can result in hypoxia and ARDS, which may lead to death.  Similar finding of increased levels in IL-2, IL-7, G-CSF, CXCL10, MCP-1, MIP-1α, and CXCL10, CCL7 were subsequently reported, suggesting the hyper-inflammation associated with severe COVID-19 exacerbates lung damage [2, 3]. The cytokine storm is thought to be driven by IL-6 [4]. In that respect, the virus also infects monocytes, macrophages and dendritic cells that can result in their activation and further secretion of IL-6. 


Navigating the Current Pandemic with Past Coronavirus Experience 

The raging cytokine storm also contributed to morbidity in patients infected with other Coronaviruses. There are seven known human coronaviruses.  The 229E, HKU1, NL63, OC43 strains are associated with the common cold, however more virulent forms  have resulted in major past outbreaks; SARS (Severe Acute Respiratory Syndrome) in 2002 and MERS (Middle Eastern Respiratory Syndrome) in 2012. SARS, MERS and COVID-19 viruses originated in bats then transitioned in an intermediate host before jumping to humans (reviewed in [5, 6]). The SARS-CoV-2 virus shares similar sequence identity to the SARS virus (SARS-CoV) and may provide insight into the current pandemic and cytokine storm. 

SARS-CoV-2 binds ACE2 receptors more efficiently than the SARS-CoV 2003 strain but less efficiently than the strain first identified in 2002, as mutations in SARS-CoV created a less virulent form. It is too early to tell how or if any mutations in SARS-CoV-2 will affect infection and mortality rates. The reproductive number (R0), number of cases directly generated by one infected individual, as well as complication and mortality rates for SARS, MERS and COVID-19 is listed in Table 1. While the infection rate of COVID-19 is much greater than SARS and MERS, the mortality rate is expected to be lower. On the other hand, ARDS-specific complication of COVID-19 is anticipated to be similar to SARS and MERS. 

Table 1. Virulence of SARS, MERS & COVID-19

Characteristics SARS MERS COVID-19*
Reproductive number (R0)  1.7 – 1.9 <1.0 2.0 – 2.5
ICU admission (% cases) 23 – 24% 53 – 89% 24%
ARDS-specific complication (% cases) 20%  20 – 30%  18 – 30% 
Mortality rate 14 – 15% 35% 2 – 4%

Adapted from [5-7].  *Current estimated values.  

 

A key lesson learned from previous outbreaks is how Coronaviruses commandeer the host cells immune response unleashing the cytokine storm. Both SARS-CoV and MERS-CoV encode accessory proteins known to antagonize IFN and suppress its signaling [8]. Diminished IFN response, allows for unchecked and rapid viral replication in which a surge of cytokines and chemokines are eventually and robustly released in a last ditch attempt to kill the virus contributing to the cytokine storm. Moreover, this dampening of the IFN response is strongly associated with disease severity [9].   In a second strike, the SARS-CoV virus also encoded accessory proteins that activate NLRP3 inflammasome, which drives IL-1β and promotes expression of other pro-inflammatory cytokines such as TNFα and IL-6 (reviewed in [6]). These strategic viral battle maneuvers are postulated to contribute to the cytokine storm that is being observed with the current COVID-19 pandemic.


The Next Wave: Kawasaki Disease-like Symptoms in Children

While early reports suggested that children were spared from COVID-19, a number of significant severe COVID-19 cases in pediatric populations have emerged [10, 11].  More urgently, is the rise of multisystem inflammatory syndrome in children (MIS-C) clusters arising in the US and EU associated with COVID-19. As of May 12, 2020 there were over 50 cases reported in New York City alone. With the current situation escalating rapidly, on May 14, 2020 the CDC issued a health advisory for MIS-C.  The disorder is associated with active infection or antibodies against SARS-CoV-2 [12], or COVID-19 exposure within 4 weeks prior to the onset of symptoms. Clinically, MIS-C is defined as persistent fever, requiring hospitalization with multisystem involvement (cardiac, renal, respiratory, hematologic, gastrointestinal, dermatologic or neurological) and Kawasaki disease-like symptoms. 

Kawasaki disease is a rare, vasculitis disorder affecting young children that can lead to coronary artery aneurysm, thrombosis and sudden death if left unchecked. It is the leading cause of acquired heart disease in pediatric populations in developed countries. Disease diagnosis is established by presence of persistent fever along with four of five signs and symptoms; bilateral conjunctivitis, strawberry tongue and/or dried cracked lips, polymorphous exanthema, cervical lymphadenopathy, swelling of hands and feet. While the exact etiology is still not fully understood, it is thought that Kawasaki disease may arise from an infectious trigger (bacterial or viral), resulting in upregulation of the immune system in a genetically susceptible individual (reviewed in [13]). 

Kawasaki disease has been previously reported with acute viral infection of the respiratory system, resulting in dysregulated immune response as observed in with the cytokine storm [13]. A children’s hospital retrospective review of Kawasaki disease admission from 2009 to 2013 linked the disease with rhinovirus and parainfluenza and to a lesser extent human coronaviruses strains 229E, NL63, OC43 [14]. Therefore, it is conceivable that SARS-CoV-2 may represent the infectious trigger during the current crisis. Similar to the cytokine storm described above, Kawasaki disease patients also have remarkably increased CRP, IL-6, IL-10 and IFNγ [13], and potential involvement of an acute B cell response [15].  Indeed, the first case of Kawasaki disease with concurrent COVID-19 infection was reported in a 6-month old infant with elevated CRP. The patient also had a continuous fever, lack of appetite, mild congestion, and met the classic Kawasaki disease criteria [16]. In addition, RT-PCR testing confirmed positive result for COVID-19 infection. 

While the incidence of past Kawasaki disease cases tended to be seasonal and were more prevalent in Asian countries and Asian races in the US [13]. Genome-wide association studies have identified candidate loci [17], however the genetic factors contributing to pathogenesis of the disease are not fully understood. Moreover, it is still too early to determine if genetic susceptibility plays a role in the rash MIS-C observed in the current COVID-19 pandemic as children of many ethnicities have reported disease symptoms [12, 16]. 


Quieting the Storm: Immunosuppressant Drugs

Since disease severity appears to be driven by a cytokine surge, it suggests that anti-inflammatory treatments may quell the cytokine storm and improve disease prognosis.  During the SARS outbreak, immunosuppressants such as corticosteroids resulted in more harm than good and are therefore not recommended for the treatment of COVID-19 [18]. For that reason, clinicians are expanding their toolbox and looking to therapies targeting pro-inflammatory cytokine. Tocilizumab, a marketed IL-6 receptor antagonist, is indicated for CSR, and was recently reported to improve COVID-19 patient outcomes in a small open-label study in China. Further randomized controlled trials are now underway with Tocilizumab, as well as with other  direct IL-6 antagonists such as Siltuximab and Sarilumab and indirect inhibitors such as Ruxolitinib. Additional immunosuppressant drugs such as anti-IL-1 anti-IL-17, anti-TNFα are also currently being explored as potential treatment under the compassionate use authority or off-label, with randomized clinical trials starting soon.  A recent GlobalData* database search retrieved nearly 75 COVID-19 planned or ongoing trials with interleukin inhibitors. Moreover, there may be a role for novel anti-inflammatory drugs in COVID-19 treatment.  Across all stages of development, sponsors are promptly advancing their program to help the fight. In response and support of this effort, the FDA issued guidance for industry on developing treatment and preventative COVID-19 drugs. While, immunosuppressant drugs will not be a cure for COVID-19, only a vaccine or anti-viral drug can annihilate the virus, anti-inflammatory therapies can play an important role in reducing the need for ventilators and preventing mortality.  

For children presenting with classic Kawasaki disease criteria, treatment guidelines include intravenous immunoglobulin and high dose aspirin [16]. Refectory Kawasaki disease may be treated with corticosteroids, although this approach remains controversial due to the risks associated with steroids [13]. Alternative therapies aiming to suppress the pro-inflammatory state include TNFα inhibitors such as Infliximab, Abciximab and Etanercept. Overall, treatment with these anti-inflammatory drugs led to improved outcome, reduction in fever and reduced risk of coronary artery aneurysms (reviewed in [13]. It remains to be seen how TNFα inhibitors will be deployed in the current pandemic. 


Biomarkers beaming like a Lighthouse

Another area under intense investigation is the use of biomarkers. Cardiac biomarkers such as N-terminal pro-B-type natriuretic peptide (NT-proBNP) indicate cardiac stress can be useful to assess cardiac risk associated with Kawasaki disease. Furthermore, identifying early prognostic biomarkers of COVID-19 severity is important for clinicians to initiate therapy before critical care is needed.  Low lymphocyte count as well as the serum levels of D-dimers, ferritin, CRP and IL-6 may help stratify mild from severe cases [19, 20]. C-reactive protein (CRP), an acute-phase inflammatory protein synthesized by IL-6-dependent signaling and indicator of IL-6 bioactivity. CRP can be used to predict the cytokine storm severity and monitor IL-6 blockade efficacy [21]. Therefore, monitoring chemokines and inflammatory cytokines may not only be helpful to risk stratify for disease severity but also demonstrate target engagement and proof-of-mechanism for immunosuppressant and anti-inflammatory drugs in development. 


A Fleet of Bioanalytical Platforms 

In addition to measuring cytokines in serum, COVID-19 testing will help launch us out of social isolation.  A SARS-CoV-2 qPCR test can confirm the presence of the virus and antibody testing can determine if someone was already exposed and may have immunity to SARS-CoV-2. For clinical trials, it is important that these assays meet stringent validation criteria as well as demonstrate good sensitivity and specificity.  

Utilizing an advanced array of bioanalytical tools, Celerion provides full bioanalytical solutions for small and large molecule assays as well as genetic and cell-based assays. For the health and safety of our participants and staff, we provide COVID-19 testing at our Clinical Pharmacology Units in Lincoln, NE, Phoenix, AZ and Belfast, UK. These tests are validated and performed in our very own Bioanalytical laboratory.  Critical to the current pandemic, we offer analytically validated cytokine and chemokine assays utilizing a sophisticated automated electrochemiluminescence (ECL) platform. 

View our list of analytically validated COVID-19 biomarkers here: https://www.celerion.com/2020/04/27/capturing-the-cytokine-storm-using-biomarkers-in-covid-19-trials 


Celerion is on Deck!

As a full-service CRO and leader in early phase drug development, Celerion is ready to serve our biotech and pharma partners develop life-saving treatments during these extraordinary times. Our mission is to focus every day on helping our clients get their drugs to market, so that they touch the lives of our family, friends and people in need around the world.


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*GlobalData search: Infectious disease therapy area; Coronavirus disease 2019 (COVID-19) indication; planned, ongoing not recruiting, ongoing recruiting, ongoing recruiting by invitation trial status; L04AC Interleukin inhibitors ATC classification. Search date 01May2020. GlobalData, John Carpenter House, UK.


Acknowledgments

Thank you to Celerion scientists Aernout van Haarst, Sumit Kar, Fred Pritchard, Michelle Combs and Lorraine Rusch for editorial assistance.