key: cord-315849-e16lln3f authors: Takayama, Kazuo title: In vitro and Animal Models for SARS-CoV-2 research date: 2020-05-30 journal: Trends Pharmacol Sci DOI: 10.1016/j.tips.2020.05.005 sha: doc_id: 315849 cord_uid: e16lln3f Abstract Basic research on SARS-CoV-2 is essential to understand its detailed pathophysiology and identify best drug targets. Models that can faithfully reproduce the viral life cycle and reproduce the pathology of COVID-19 are required. Here, we briefly review the cell lines, organoids, and animal models that are currently being used in COVID-19 research. In December 2019, pneumonia of an unknown etiology was confirmed in China [1] . The Chinese Center for Disease Control and Prevention (CCDC) identified a novel coronavirus infection as the cause of this pneumonia [2] . The World Health Organization (WHO) named the disease "2019-new coronavirus disease" (or i and the International Committee on Taxonomy of Viruses (ICTV) named the virus "severe acute respiratory syndrome coronavirus 2" (or SARS-CoV-2) ii . The WHO soon declared that COVID-19 was a fast-evolving pandemic iii . As of May, 26, 2020 , it is estimated that 5,406,282 people have been infected with COVID-19 and 343,562 people have died globally iii . Multiple clinical trials are currently underway for prevention or intervention in the disease progression [3] . In parallel, it is also equally essential to carry out basic research on SARS-CoV-2 to support the efficient development of therapeutic agents. For this, models that can faithfully reproduce the behavior of the virus and reproduce the pathology of COVID-19 are required. Here, we briefly review relevant cell lines, organoids, and animal model animals. An in vitro cell model for SARS-CoV-2 research is essential for understanding the viral life cycle, for amplifying and isolating the virus for further research and for preclinical evaluation of therapeutic molecules. This section lays out the cell lines used to replicate and isolate SARS-CoV-2, as well as organoids that can be used to examine the effects of SARS-CoV-2 infection on specific human tissues (Table 1A, Figure 1 ). In humans, airway epithelial cells highly express the putative SARS-CoV-2 entry receptor, angiotensin-converting enzyme 2 (ACE2) and transmembrane serine [12] . They reported that the viral RNA copies in the culture supernatants of these cells were >100 times higher than those of Vero E6 cells, suggesting that it would possible to isolate higher titer virus using TMPRSS2-overexpressing Vero E6 cells. Organoids are composed of multiple cell types and model the physiological conditions of human organs. Because organoids have the ability to self-replicate, they are also suitable models for large-scale screening in drug discovery and disease research [13] . Besides the lung damage caused by pneumonia, SARS-CoV-2 affects several organs like the kidney [14] , liver [15] , and the cardiovascular system [16] . Suzuki et al. and Han et al. generated human bronchial organoids [17] or human lung organoids [18] , respectively, for SARS-CoV-2 research. They showed that their organoids were permissive to the SARS-CoV-2 infection and could evaluate anti-viral effects of COVID-19 candidate therapeutic compounds including camostat [17] . Besides the lung damage caused by pneumonia, SARS-CoV-2 affects several organs like the kidney [14] , liver [15] , and the cardiovascular system [16] . Monteil infection and support replication [20] . Interestingly, virus infection impaired the bile acid transporting functions of cholangiocytes [20] . This effect might be the reason for Furthermore, it is expected that the intestine is another viral target organ [21] . Lamers The complex pathophysiology of the disease will only be understood by Figure 1 ). One of the works that set the pace for discovery of animal models was by Zhou et al. who conducted SARS-CoV-2 infection experiments using HeLa cells that expressed ACE2 proteins taken from multiple animal species from mice to humans [11] . Interestingly, SARS-CoV-2 could use all ACE2 proteins, except for mouse ACE2. Therefore, Bao et al. used transgenic mice that express human ACE2 [25] . The team found that such mice after SARS-CoV-2 infection, showed weight loss, virus replication in the lungs, and interstitial pneumonia [25] . In the search of alternative small animal models, molecular docking studies were performed on the binding between ACE2 of various mammals and the S protein of SARS-CoV-2, with the finding that the Syrian hamster might be suitable [26] . After infection, these hamsters show rapid breathing, weight loss, and alveolar damage with extensive apoptosis [26] . J o u r n a l P r e -p r o o f Figure 1 ) and help assess the advantages and disadvantages of each towards discovery of better models. J o u r n a l P r e -p r o o f manuscript. We also thank Dr. Eiri Ono (Kyoto University) for creating the figure. The author has no conflict of interests. Human ACE2 transgenic mice After SARS-CoV-2 infection, the mice show weight loss, virus replication in the lungs, and interstitial pneumonia. [25] Syrian hamster After SARS-CoV-2 infection, the hamsters show rapid breathing, weight loss, and diffuse alveolar damage with extensive apoptosis. [26] Ferrets After SARS-CoV-2 infection, acute bronchiolitis was observed in the lungs. [27] Cats After SARS-CoV-2 infection, intra-alveolar edema and congestion in the interalveolar septa were observed. Abnormal arrangement of the epithelium with loss of cilia and lymphocytic infiltration into the lamina propria were also observed. 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