Targeting ectromelia virus and TNF/NF-κB or STAT3 signaling for effective treatment of viral pneumonia.

Viral causes of pneumonia pose constant threats to global public health, but there are no specific treatments currently available for the condition. Antivirals are ineffective when administered late after the onset of symptoms. Pneumonia is caused by an exaggerated inflammatory cytokine response to infection, but tissue necrosis and damage caused by virus also contribute to lung pathology. We hypothesized that viral pneumonia can be treated effectively if both virus and inflammation are simultaneously targeted. Combined treatment with the antiviral drug cidofovir and etanercept, which targets tumor necrosis factor (TNF), down-regulated nuclear factor kappa B-signaling and effectively reduced morbidity and mortality during respiratory ectromelia virus (ECTV) infection in mice even when treatment was initiated after onset of clinical signs. Treatment with cidofovir alone reduced viral load, but animals died from severe lung pathology. Treatment with etanercept had no effect on viral load but diminished levels of inflammatory cytokines and chemokines including TNF, IL-6, IL-1ß, IL-12p40, TGF-ß, and CCL5 and dampened activation of the STAT3 cytokine-signaling pathway, which transduces signals from multiple cytokines implicated in lung pathology. Consequently, combined treatment with a STAT3 inhibitor and cidofovir was effective in improving clinical disease and lung pathology in ECTV-infected mice. Thus, the simultaneous targeting of virus and a specific inflammatory cytokine or cytokine-signaling pathway is effective in the treatment of pneumonia. This approach might be applicable to pneumonia caused by emerging and re-emerging viruses, like seasonal and pandemic influenza A virus strains and severe acute respiratory syndrome coronavirus 2.

Poxvirus-encoded TNF receptor homolog dampens inflammation and protects from uncontrolled lung pathology during respiratory infection.

Ectromelia virus (ECTV) causes mousepox, a surrogate mouse model for smallpox caused by variola virus in humans. Both orthopoxviruses encode tumor necrosis factor receptor (TNFR) homologs or viral TNFR (vTNFR). These homologs are termed cytokine response modifier (Crm) proteins, containing a TNF-binding domain and a chemokine-binding domain called smallpox virus-encoded chemokine receptor (SECRET) domain. ECTV encodes one vTNFR known as CrmD. Infection of ECTV-resistant C57BL/6 mice with a CrmD deletion mutant virus resulted in uniform mortality due to excessive TNF secretion and dysregulated inflammatory cytokine production. CrmD dampened pathology, leukocyte recruitment, and inflammatory cytokine production in lungs including TNF, IL-6, IL-10, and IFN-γ. Blockade of TNF, IL-6, or IL-10R function with monoclonal antibodies reduced lung pathology and provided 60 to 100% protection from otherwise lethal infection. IFN-γ caused lung pathology only when both the TNF-binding and SECRET domains were absent. Presence of the SECRET domain alone induced significantly higher levels of IL-1ß, IL-6, and IL-10, likely overcoming any protective effects that might have been afforded by anti-IFN-γ treatment. The use of TNF-deficient mice and those that express only membrane-associated but not secreted TNF revealed that CrmD is critically dependent on host TNF for its function. In vitro, recombinant Crm proteins from different orthopoxviruses bound to membrane-associated TNF and dampened inflammatory gene expression through reverse signaling. CrmD does not affect virus replication; however, it provides the host advantage by enabling survival. Host survival would facilitate virus spread, which would also provide an advantage to the virus.

TNF deficiency dysregulates inflammatory cytokine production, leading to lung pathology and death during respiratory poxvirus infection.

Excessive tumor necrosis factor (TNF) is known to cause significant pathology. Paradoxically, deficiency in TNF (TNF-/-) also caused substantial pathology during respiratory ectromelia virus (ECTV) infection, a surrogate model for smallpox. TNF-/- mice succumbed to fulminant disease whereas wild-type mice, and those engineered to express only transmembrane TNF (mTNF), fully recovered. TNF deficiency did not affect viral load or leukocyte recruitment but caused severe lung pathology and excessive production of the cytokines interleukin (IL)-6, IL-10, transforming growth factor beta (TGF-ß), and interferon gamma (IFN-γ). Short-term blockade of these cytokines significantly reduced lung pathology in TNF-/- mice concomitant with induction of protein inhibitor of activated STAT3 (PIAS3) and/or suppressor of cytokine signaling 3 (SOCS3), factors that inhibit STAT3 activation. Consequently, inhibition of STAT3 activation with an inhibitor reduced lung pathology. Long-term neutralization of IL-6 or TGF-ß protected TNF-/- mice from an otherwise lethal infection. Thus, mTNF alone is necessary and sufficient to regulate lung inflammation but it has no direct antiviral activity against ECTV. The data indicate that targeting specific cytokines or cytokine-signaling pathways to reduce or ameliorate lung inflammation during respiratory viral infections is possible but that the timing and duration of the interventive measure are critical.

Therapeutic Targeting of Inflammation and Virus Simultaneously Ameliorates Influenza Pneumonia and Protects from Morbidity and Mortality.

Influenza pneumonia is a severe complication caused by inflammation of the lungs following infection with seasonal and pandemic strains of influenza A virus (IAV), that can result in lung pathology, respiratory failure, and death. There is currently no treatment for severe disease and pneumonia caused by IAV. Antivirals are available but are only effective if treatment is initiated within 48 h of onset of symptoms. Influenza complications and mortality are often associated with high viral load and an excessive lung inflammatory cytokine response. Therefore, we simultaneously targeted the virus and inflammation. We used the antiviral oseltamivir and the anti-inflammatory drug etanercept to dampen TNF signaling after the onset of clinical signs to treat pneumonia in a mouse model of respiratory IAV infection. The combined treatment down-regulated the inflammatory cytokines TNF, IL-1ß, IL-6, and IL-12p40, and the chemokines CCL2, CCL5, and CXCL10. Consequently, combined treatment with oseltamivir and a signal transducer and activator of transcription 3 (STAT3) inhibitor effectively reduced clinical disease and lung pathology. Combined treatment using etanercept or STAT3 inhibitor and oseltamivir dampened an overlapping set of cytokines. Thus, combined therapy targeting a specific cytokine or cytokine signaling pathway and an antiviral drug provide an effective treatment strategy for ameliorating IAV pneumonia. This approach might apply to treating pneumonia caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Loss of Actin-Based Motility Impairs Ectromelia Virus Release In Vitro but Is Not Critical to Spread In Vivo.

Ectromelia virus (ECTV) is an orthopoxvirus and the causative agent of mousepox. Like other poxviruses such as variola virus (agent of smallpox), monkeypox virus and vaccinia virus (the live vaccine for smallpox), ECTV promotes actin-nucleation at the surface of infected cells during virus release. Homologs of the viral protein A36 mediate this function through phosphorylation of one or two tyrosine residues that ultimately recruit the cellular Arp2/3 actin-nucleating complex. A36 also functions in the intracellular trafficking of virus mediated by kinesin-1. Here, we describe the generation of a recombinant ECTV that is specifically disrupted in actin-based motility allowing us to examine the role of this transport step in vivo for the first time. We show that actin-based motility has a critical role in promoting the release of virus from infected cells in vitro but plays a minor role in virus spread in vivo. It is likely that loss of microtubule-dependent transport is a major factor for the attenuation observed when A36R is deleted.