Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can induce mild to life-threatening symptoms. Especially individuals over 60 years of age or with underlying comorbidities, including heart or lung disease and diabetes, or immunocompromised patients are at a higher risk. Fatal multiorgan damage in coronavirus disease 2019 (COVID-19) patients can be attributed to an interleukin-6 (IL-6)-dominated cytokine storm. Consequently, IL-6 receptor (IL-6R) monoclonal antibody treatment for severe COVID-19 cases has been approved for therapy. High concentrations of soluble IL-6R (sIL-6R) were found in COVID-19 intensive care unit patients, suggesting the involvement of IL-6 trans-signaling in disease pathology. Here, in analogy to bispecific antibodies (bsAbs), we developed the first bispecific IL-6 trans-signaling inhibitor, c19s130Fc, which blocks viral infection and IL-6 trans-signaling. c19s130Fc is a designer protein of the IL-6 trans-signaling inhibitor cs130 fused to a single-domain nanobody directed against the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. c19s130Fc binds with high affinity to IL-6:sIL-6R complexes as well as the spike protein of SARS-CoV-2, as shown by surface plasmon resonance. Using cell-based assays, we demonstrate that c19s130Fc blocks IL-6 trans-signaling-induced proliferation and STAT3 phosphorylation in Ba/F3-gp130 cells as well as SARS-CoV-2 infection and STAT3 phosphorylation in Vero cells. Taken together, c19s130Fc represents a new class of bispecific inhibitors consisting of a soluble cytokine receptor fused to antiviral nanobodies and principally demonstrates the multifunctionalization of trans-signaling inhibitors. IMPORTANCE The availability of effective SARS-CoV-2 vaccines is a large step forward in managing the pandemic situation. In addition, therapeutic options, e.g., monoclonal antibodies to prevent viral cell entry and anti-inflammatory therapies, including glucocorticoid treatment, are currently developed or in clinical use to treat already infected patients. Here, we report a novel dual-specificity inhibitor to simultaneously target SARS-CoV-2 infection and virus-induced hyperinflammation. This was achieved by fusing an inhibitor of viral cell entry with a molecule blocking IL-6, a key mediator of SARS-CoV-2-induced hyperinflammation. Through this dual action, this molecule may have the potential to efficiently ameliorate symptoms of COVID-19 in infected individuals.

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