key: cord-0691713-cqeulecp authors: Cossarizza, Andrea; De Biasi, Sara; Guaraldi, Giovanni; Girardis, Massimo; Mussini, Cristina title: SARS‐CoV‐2, the Virus that Causes COVID‐19: Cytometry and the New Challenge for Global Health date: 2020-03-18 journal: Cytometry A DOI: 10.1002/cyto.a.24002 sha: 6551ec75977c216566539d2c552d52e96a8c833e doc_id: 691713 cord_uid: cqeulecp nan The community of cytometrists and scientists has already been heavily touched by this epidemic, not just because of the threat to our health. Indeed, the meeting "CYTO Asia," which should have been held in Shanghai in early September 2020, has been postponed to 2021. Similarly, in different parts of the world, a relevant number of scientific and nonscientific meetings are now being canceled. Moreover, several prestigious research centers and universities are prohibiting their members and employees not only from traveling to "dangerous" countries but also from participating in any sort of domestic or international meeting, for 60 days at least. Several countries have adopted similar decisions at the government level. Many viruses have existed in their natural reservoirs for a very long time without causing relevant problems to humans. However, in the last decades, there has been an increased spillover of viruses from natural hosts (like the bat) to intermediate hosts (like market civets and dromedary camels) and then to humans, likely because of human activities, including modern agricultural practices and urbanization. Coronaviruses are broadly distributed in humans and in other mammals, and there are at least seven viruses that have been able to pass from animals to humans, crossing the species barriers and infecting humans (7) . Some of them are, however, relatively innocuous and cause the common cold, while those quoted here below are extremely dangerous for human health as they are highly pathogenic, able to be readily transmitted from human to human, and able to spread to multiple continents in a very short time. Thus, to cope with this epidemic, and to substantially contribute to the fight against SARS-CoV-2, we have to learn the lesson derived from two recent outbreaks caused by two other highly pathogenic coronaviruses. The first was due to the SARS-CoV, which started creating victims in Foshan, China, in November 2002, before being recognized a few months later in Hanoi, Vietnam, by the Italian doctor Carlo Urbani (who died of this disease) (8) . SARS affected 17 countries and, during an epidemic of a few months, caused 774 deaths of 8,096 laboratory-confirmed cases (9). The second was due to the Middle East respiratory syndrome (MERS)-CoV that, in 2012, was first described in a man in Saudi Arabia (10) . MERS has been found in 27 countries and is still present in many of them because of the continuing introduction from dromedary camels. Until last November 2019, MERS has caused 858 deaths of 2,494 laboratoryconfirmed cases (11). The present epidemic due to SARS-CoV-2 has a much higher number of cases. As of the middle of March, there are over 100,000 confirmed cases all over the world, with over 3,500 deaths (for a continuous update, see https://gisanddata.maps.arcgis.com/apps/opsdashboard/index. html#/bda7594740fd40299423467b48e9ecf6 (12)). Several studies have described the biological and immunological features of the previous coronavirus epidemics, and obviously, most researchers have used flow cytometry to describe the changes in T and B lymphocytes, as well as the role of inflammatory cells in the immunopathogenesis of the disease (reviewed in Ref. (13) ). Currently, very limited information is available on the host innate immune status of SARS-CoV-2-infected patients and regard the description of increased total neutrophils, reduced total lymphocytes, and increased serum levels of IL-6 and of C-reactive protein, which suggest a strong inflammatory response. This is indeed evidenced by reports detecting abnormally high plasma levels of innate cytokines such as IP-10, MCP-1, MIP-1A, and TNFα or of high levels of proinflammatory cytokines (including IL-2, IL-7, IL-10, G-CSF, IP-10, MCP-1, MIP-1A, and TNFα). Furthermore, mortality is higher in patients with elevated levels of IL-6 (14) . The overall picture is similar to what happens during SARS and MERS and underlines the fact that leukocyte alterations and a cytokine storm that initiates a viral sepsis could be important in the pathogenesis of Covid-19. Unfortunately, to the best of our knowledge, as of middle of March 2020 no data have been published on the specific cellular immune response to SARS-CoV-2. The first data on changes in lymphocyte populations in patients severely affected by Covid-19 indicate a low T cells count, an increase in naïve helper T cells and a decrease in memory helper T cells (15) . Thus, the immunopathogenesis of this disease is still largely unknown. However, several groups, including ours, are now investigating different molecular, cellular and immunological aspects. Confirming this previous report (15), Figure 1 shows our most recent data, related to the distribution of different subpopulations of peripheral blood CD4+ and CD8+ T cells from four aged patients in the symptomatic phase of the infection. There are several crucial clinical questions that urgently await an answer and that require strong and highly dedicated work by a community such as ours that certainly remembers the terrific contribution that has been made and is still given to the fight against HIV/AIDS (17). Thus, to begin: why do some patients get infected but do not develop any disease, while others die from the infection? Which are the protective factors, and which are the biomarkers that clinicians could use to predict, and eventually modify, the course of the disease? Assuming that the scant, available data are reliable, why do children seem to develop a milder form of Covid-19, similar to what was described in the case of SARS? Can the immaturity of the immune system protect against immunemediated damages that could occur during Covid-19? Which assays are useful to monitor the efficacy of an antiviral therapy? How can we help in developing a vaccine? Needless to say, using adequate approaches, models, and methodologies (18) , the starting point will likely be a deep characterization of the immune system in patients with different stage of the disease in order to understand, among others: 1. The role of different components of innate immunity, such as monocytes, macrophages, dendritic cells, NK cells, and different innate lymphocytes, and their ability in controlling the early phases of the infection. 2. The production and utilization of cytokines, chemokines, and their receptors, which are crucial in the initial cytokine storm. 3. The kinetics of the humoral response and production of antibodies against the virus including those with neutralizing activity. NAIVE NAIVE,CD38+ TREG NAIVE,DR+ CM CM,CD38+ CM,PD1+ TM TREG EM,DR+ EM ACTIVATED EM EM,PD1+,CD57+ EMRA,PD1+,CD57+ CD45RA CD28 CCR7 PD1 CD27 CD57 CD127 CD25 CD95 CD38 HLA- 4. The importance of different types of B and plasma cells, considering the problems related to short-and longterm memory. 5. The role of T-cell immunity, with the identification of eventual gross changes in CD4+ and CD8+ T cell populations that could have a prognostic meaning. 6. The specific T-cell response to different viral epitopes, which could allow a better characterization of the most antigenic parts of the viral proteins. 7. The importance of regulatory T-cells in modulating the response and controlling, or favoring, immunoactivation and suppression Clearly, this is only a very partial list of the possible contributions that we can offer to the fight against SARS-CoV-2, but it is full of gaps that need to be filled as soon as possible. Our community has all the technical skills, scientific capabilities, and strength to help in significantly improving the knowledge of the main molecular and cellular aspects of this new infection and to help in developing a cure, based on drugs or, even better, innovative vaccines, with no fear of the SARS-CoV-2 threat. Genomic characterisation and epidemiology of 2019 novel coronavirus: Implications for virus origins and receptor binding Clinical features of patients infected with 2019 novel coronavirus in Wuhan Early transmission dynamics in Wuhan, China, of novel coronavirusinfected pneumonia First case of 2019 novel coronavirus in the United States Transmission of 2019-nCoV infection from an asymptomatic contact in Germany Origin and evolution of pathogenic coronaviruses Newly discovered coronavirus as the primary cause of severe acute respiratory syndrome Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia An interactive web-based dashboard to track COVID-19 in real time Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic Clinical predictors of mortality due to COVID-19 based on an analysis of data of 150 patients from Wuhan, China. Intensive Care Med Dysregulation of immune response in patients with COVID-19 in Wuhan, China CATALYST: Cytometry dATa anALYSis Tools Cytometry, immunology, and HIV infection: Three decades of strong interactions Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition) We kindly acknowledge Dr. Leonardo Beretta, (Beckman Coulter, Milan, Italy) for his continuous support.