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 Authors: Xiaoqing Zhang et al. 2020 

Journal/ Pre-PrintStem Cell & Developmental Cell Biology (Preprint in review) 

Tags: Stem cells, Therapeutics, Molecular biology 

Research Highlights

1. The recombinant fusion protein of human ACE2 extracellular region (hACE21-740-Fc) binds spike protein and inhibits pseudotyped SARS-CoV-2 viral entry into ACE2+ Hek-293 cells. scFv-IL6R-Fc inhibits IL6 induced proliferation in TF-1 cells. 

2. Fc fused protein (hACE21-740-Fc) can trigger antibody-dependent cell-mediated (ADCC) cytotoxicity and complement-dependent cytotoxicity (CDC) response of spike positive Raji cells 

3. Authors suggest MSCs are a suitable vector for delivering the bioactive fusion proteins hACE2-Fc and IL6R-Fc, with the cells preferentially localizing to the lungs and other organs. 


Using stably transfected MSCs, a combinatorial approach was introduced to inhibit viral entry of SARS-CoV-2 into cells with recombinant hACE21-740-hFc, while minimising the cytokine storm effect via scFv-IL6R-Fc and simultaneously guide NK cells specifically to target infected cells. Expression of scFv-IL6R-Fc and hACE21-740-hFc by MSCs in the serum remained detectable after two weeks. MSCs were preferentially found in the lungs. ACE2 Fc-fusion protein (hACE21-740-hFc) inhibited viral entry of a pseudotyped version of SARS-CoV-2 into ACE2+ HEK-293 cells. ACE2 Fc fusion protein triggered an ADCC and CDC response preferentially in Spike+ Raji cells. IL6 induced TF-1 cell proliferation was blocked by MSC secreted scFv-IL6R-Fc, comparable to the effect of an FDA-approved anti-IL6 therapy (Tocilizumab). 

Impact for SARS-CoV2/COVID19 research efforts  

Treatment of SARS-CoV2/COVID19 positive individuals 

In vitro and mouse study demonstrating the possibility of transfected MSC-derived human ACE2 fusion protein as a treatment to inhibit viral entry in COVID-19 patients combined with scFv-IL6R-Fc to protect against cytokine storm.  

Study Type 

In vitro study 

In vivo study (transfected MSCs in mouse) 

Strengths and limitations of the paper 

Novelty: Although recombinant ACE-2 based therapeutic approach has been suggested previously.    

Combinatorial therapeutic approach is novel using MSCs to produce fusion proteins against viral entry in the desired area and simultaneously coping with inflammation.  

Standing in the field:The strategies combined in this transfected MSC approach have been suggested previously, but this study introduces the possibility of combining inhibition of viral entry via rACE2-Fc, induction of ADCC and CDC response by rACE2, and targeting of IL-6 via rIL6R-Fc together via targeted MSCs. 

Other methods of the same approach e.g. anti-IL6 therapy are currently being tested in COVID-19 patients. 

Appropriate statistics:Two-tailed unpaired Student’s t-test for all comparisons used. 

Statistical comparison of multiple groups should use ANOVA and/or correct for multiple comparisons. 

Viral model usedPseudotyped SARS-CoV-2 virus in Spike+ and in ACE2+ HEK-293 cells. 

TranslatabilityMore a potential future therapy, with the initial proof of concept. 

The fusion protein produced is demonstrated in vitro on pseudotyped virus; this should be confirmed on SARS-CoV-2 for efficacy before translation. 

They did not demonstrate efficacy of viral blockage in vivo; they only showed the protein is present in serum after MSC infusion. 

Regulatory hurdles of MSC therapy, of which you cannot control the dose or production after infusion. 

Main limitations: They did not demonstrate efficacy of transfected MSCs or fusion protein in vivo. 

Viral inhibition was demonstrated on pseudotyped version of virus, not SARS-CoV-2 itself. 

Source of MSCs not specified in paper. 

MSC localisation to organs was detected by qPCR rather than by visualisation. 

All experiments on fusion protein efficacy were performed on cell lines, not specific to the disease context. 

They do not show clinical efficacy, or efficacy in the disease setting (e.g. any beneficial effect of the ADCC or CDC in COVID-19).