Modeling COVID-19 with Human Pluripotent Stem Cell-Derived Cells Reveals Synergistic Effects of Anti-inflammatory Macrophages with ACE2 Inhibition Against SARS-CoV-2 (preprint)

Dysfunctional immune responses contribute critically to the progression of Coronavirus Disease-2019 (COVID-19) from mild to severe stages including fatality, with pro-inflammatory macrophages as one of the main mediators of lung hyper-inflammation. Therefore, there is an urgent need to better understand the interactions among SARS-CoV-2 permissive cells, macrophage, and the SARS-CoV-2 virus, thereby offering important insights into new therapeutic strategies.  Here, we used directed differentiation of human pluripotent stem cells (hPSCs) to establish a lung and macrophage co-culture system and model the host-pathogen interaction and immune response caused by SARS-CoV-2 infection. Among the hPSC-derived lung cells, alveolar type II and ciliated cells are the major cell populations expressing the viral receptor ACE2 and co-effector TMPRSS2, and both were highly permissive to viral infection. We found that alternatively polarized macrophages (M2) and classically polarized macrophages (M1) had similar inhibitory effects on SARS-CoV-2 infection. However, only M1 macrophages significantly up-regulated inflammatory factors including IL-6 and IL-18, inhibiting growth and enhancing apoptosis of lung cells. Inhibiting viral entry into target cells using an ACE2 blocking antibody enhanced the activity of M2 macrophages, resulting in nearly complete clearance of virus and protection of lung cells. These results suggest a potential therapeutic strategy, in that by blocking viral entrance to target cells while boosting anti-inflammatory action of macrophages at an early stage of infection, M2 macrophages can eliminate SARS-CoV-2, while sparing lung cells and suppressing the dysfunctional hyper-inflammatory response mediated by M1 macrophages.    

Immunodepletion with Hypoxemia: A Potential High Risk Subtype of Coronavirus Disease 2019 (preprint)

Background The outbreak of COVID-2019 is becoming a global public health emergency. Although its basic clinical features have been reported, the dynamic characteristics of immune system in COVID-2019 patients, especially those critical patients with refractory hypoxemia, are not yet well understood. We aim to describe the dynamic characteristics of immune system in 3 critical patients with refractory hypoxemia, and discuss the relationship between hypoxemia severity and immune cell levels, and the changes of gut microbes of COVID-2019 patient. Methods This is a retrospective study from 3 patients with 2019-nCoV infection admitted to Renmin Hospital of Wuhan University, a COVID-2019 designated hospital in Wuhan, from January 31 to February 6, 2020. All patients were diagnosed and classified based on the Diagnosis and Treatment of New Coronavirus Pneumonia (6th edition) published by the National Health Commission of China4. We recorded the epidemiological history, demographic features, clinical characteristics, symptoms and signs, treatment and clinical outcome in detail. Blood samples were collected and we determined the expression levels of immune cells (CD3+ T cells, CD4+ T cells, CD8+ T cells, CD19+ B cells, and CD16+56+ NK cells) in different time points. Nanopore Targeted Sequencing was used to determine the alterations of gut microbiota homeostasis. Results Apart from the clinical features described previously4, we found that four patients had decreased immune cells and refractory hypoxemia during the hospitalization, and the severity of hypoxemia was strongly correlated to the expression levels of immune cells. Additionally, we found that the proportion of probiotics was significantly reduced, such as Bifidobacterium, Lactobacillus, and Eubacterium, and the proportion of conditioned pathogenic bacteria was significantly increased, such as Corynebacterium of Actinobacteria and Ruthenibacterium of Firmicutes. Notably, all patients died. Conclusions We discussed the dynamic characteristics of host immune system and the imbalance of gut microbiota in 3 critical patients with COVID-2019. Hypoxemia severity was closely related with host immune cell levels, and the vicious circle between immune disorder and gut microbiota imbalance may be a high risk of fatal pneumonia. To the best of our knowledge, this is the first study which revealing that immunodepletion with refractory hypoxemia is a potential high risk subtype of COVID-2019 and the vicious circle between immune disorder and gut dysbiosis may be a high risk of fatal pneumonia.