Efficacy of mesenchymal stromal cells and cellular products in improvement of symptoms for COVID‐19 and similar lung diseases

Abstract At the end of 2019, respiratory coronavirus diseases 2019 (COVID‐19) appeared and spread rapidly in the world. Besides several mutations, the outcome of this pandemic was the death up to 15% of hospitalized patients. Mesenchymal stromal cell therapy as a therapeutic strategy seemed successful in treatment of several diseases. Not only mesenchymal stromal cells of several tissues, but also their secreted extracellular vesicles and even secretome indicated beneficial therapeutic function. All of these three options were studied for treatment of COVID‐19 as well as those respiratory diseases that have similar symptom. Fortunately, most of the outcomes were promising and optimistic. In this paper, we review in‐vivo and clinical studies which have been used different sources of mesenchymal stromal cell, secreted extracellular vesicles, and secretome to improve and treat symptoms of COVID‐19 and similar lung diseases.

MSCs as multipotent cells are known for self-renewing and differentiating into adipogenic, osteogenic, and chondrogenic lineages (Taghavi-Farahabadi et al., 2020). MSCs can be found in connective tissue and organ stroma, including adipose tissue, bone marrow, umbilical cord blood, Wharton's jelly placenta, dental pulp, menstrual blood, periodontal ligament, amniotic and other tissues (Atluri et al., 2020;Gentile & Sterodimas, 2020;Wang, 2020). In 1995, MSCs were used as a cellular pharmaceutical agent in human cases (Lazarus et al., 1995) and up to now, they do not indicated adverse events in systemic administration (Poulos, 2018;Rajarshi et al., 2020). It has reported that the most prevailing source in recent clinical trials were adult bone marrow mesenchymal stromal cells (BM-MSC), adipose tissue derived mesenchymal stromal cells (AT-MSC), umbilical cord tissue mesenchymal stromal cells (UC-MSC) and placental cells respectively (Galipeau & Sensébé, 2018).
MSCs could secrete some antimicrobial molecules which could reduce feeling pain (Rogers et al., 2020). In-vitro studies showed low expression of major histocompatibility complex-I (MHC-I) and no expression of MHC II or costimulatory molecules B7-1, CD40, or B7-2 in MSCs which leads to the immune-evasively (Rogers et al., 2020).
It is proved that human MSCs shows heterogeneity in the quality, so their products depend on the donor, isolation procedure, and culture methods (Lukomska et al., 2019). The Food and Drug Administration (FDA) standards should be considered in labs that are the source of stromal cells (Atluri et al., 2020). The isolation source of MSC affects the gene expression like genes that are related to cell adhesion molecules (Shotorbani et al., 2017), HLA molecules (Rogers et al., 2020)), transcription factors, differentiation potential (Gebler et al., 2012), as well as functional differences. Therefore, Yen et al. (2020) suggested that "not all MSCs are equal." In this paper, we aim to review and compare different sources of MSC and MSC secreted extracellular vesicles (MSC-EVs) in clinical and preclinical treatment of Coronavirus disease and its related lung diseases with similar symptoms.

| COVID-19 pathology, and immune response in a glance
Since December 2019, novel COVID-19 initiated from China and after a few months, many people all over the world were contaminated (Öztürk et al., 2020). SARS-CoV-2 as one of the coronaviridae could induce respiratory diseases. Following infection, to kill the virus, immune system become over-activated and caused cytokine storm (secretion of large volumes of inflammatory cytokines) that could lead to organ damage, air exchange dysfunction, edema, acute respiratory distress syndrome (ARDS), acute cardiac injury, pulmonary damage induced by ARDS, secondary infection and even death (Atluri et al., 2020;Taghavi-Farahabadi et al., 2020). | 2169 loss of lung function, and even death. It seems that suppression of cytokine storm as a reason of ARDS that leads to death, may reduce the inflammation and lung damage (Taghavi-Farahabadi et al., 2020).

SARS-CoV
Immune responses to the body once COVID-19 virus contagiously affected the new patient to kill the virus and inhibit the advancement to difficult stages, demands the primary start of a specific adaptive immune response (Rao et al., 2020). There are diverse complicated mechanisms are involved in ARDS, targeting a single pathway or mediator as a therapeutic approach which cannot be beneficial enough. Consequently, targeting different aspects of immunepathogenesis and related damages seems to be essential (Taghavi-Farahabadi et al., 2020). In the following parts, MSC administration in COVID-19 and its related lung diseases will discuss to compare outcomes of different MSC sources to realize whether there is any relation between cell source and successful ideal strategy or not.

| MSCs and secreted extracellular vesicles
Comparing BM-MSCs to AT-MSCs and AT-MSCs, not only indicates lower expression of HLA-I (Rogers et al., 2020) but also, shows higher quantity of cells (Gentile & Sterodimas, 2020;Kawecki et al., 2018) with better in vitro proliferation (Kawecki et al., 2018). Furthermore, AT-MSC potency could be preserved with the age of the donor, unlike BM-MSCs (Rogers et al., 2020). Additionally, UC-MSC population especially Wharton jelly (as one of the wealthy origins) is higher than BM-MSCs (Atluri et al., 2020). Other advantageous of UC-MSCs are higher plasticity, probably more potency, faster doubling times, and being scalable (that will be important in the great population of COVID-19 cases) with the noninvasive obtaining process (Atluri et al., 2020). Menstrual blood derived MSCs (men-MSCs) of young healthy women proliferated twice faster than BM-MSCs. Men-MSCs express markers of MSCs and some embryonic markers like Nanog and SSEA-4. Different studies showed the differentiation potential of Men-MSCs into bone, adipose, cartilage, neural, cardiac, and hepatic cells (Khoury et al., 2014). Widespread advancement were applied to explain the immune characteristics of MSCs and immune effects of Men-MSCs which required further investigations (Khoury et al., 2014). AT-, BM-and UC-MSCs could inhibit B cell, T cell, and natural killer (NK) cell-mediated immune response through inhibiting acquisition of lymphoblast features, triggering, and altering the protein expression with an critical role in immune response, but AT-MSCs do it in earlier phase and higher than UC-or BM-MSCs (Ribeiro et al., 2013). Notwithstanding the similarities some differences between MSCs were found, therefore, selecting the suitable MSC source for therapeutic or experimental plans became more important (Ribeiro et al., 2013).
For instance, the mortality in preclinical studies of acute lung injury models, UC-and BM-MSCs seemed more effective than AT-MSCs (Yen et al., 2020).
Published evidence demonstrated the interesting events of the paracrine release of MSC-EVs that contain various regulatory microRNAs (miRNAs), messenger RNAs (mRNAs), bioactive proteins, organelles, such as mitochondria, and some other compounds with the regulatory role.
Interestingly, these MVs and exosomes could be used rather than direct cell substitution (Abraham & Krasnodembskaya, 2020;Lukomska et al., 2019). MSC-EVs are similar to MSCs not only in round shape, but also in mesenchymal marker expression and lacked the expression of swine leukocyte antigens I and II (Khatri et al., 2018). Secreted MSC exosomes showed both typical markers of the exosome surface (including CD81 and CD9) and some adhesion molecules of MSC membrane (like CD73, CD44, and CD29) (Yu et al., 2014). It was shown that secretion of microparticles (that are enriched for pre-miRNA by MSCs) could facilitate miRNA-mediated intercellular communication (Chen et al., 2010).
The most general way for exosome isolation is ultracentrifugation that gives highly enriched exosomes. This method usually used in combination with sucrose cushions or sucrose density gradients. The centrifugal forces remove larger particles and cells and finally exosomes would precipitated (Yu et al., 2014). It was reported that this method could cause the isolation of heterogeneous MVs, such as smaller exosomes (Monsel et al., 2015). High-performance liquid chromatography is another method that was used rarely due to the complexity. It includes two filtration steps, low-gravity centrifugation, purification (by exclusion chromatography), and final centrifugation step. Also, exosome could be isolated using ultrafiltration based on the size. Comparing to ultracentrifugation, this method requires less time and does not demand specific devices. Furthermore, nowadays several kits for exosome isolation are produced by various companies. It was reported that storing exosomes at 37°C or 4°C may led to size reduction after some days, while at −20°C they can be stored for a long time without any change in the size and therefore, storage situation seems to be an important issue (Yu et al., 2014).

| MSC and MSC-EVs in lung diseases especially in COVID-19
Orleans et al. thought that although BM-MSC injection is useful in some diseases, such as spine and joint, but they would not likely be ideal for coronavirus treatment which is a serious systemic illness (Atluri et al., 2020). On the other hand, in a retrospective study was reported that cautious MSCs therapy could be a hopeful treatment of severe COVID-19 (particularly in patients with coronary heart disease or metabolic acidosis it should be done cautiously) (Chen, Shan, et al., 2020). Several cell-based therapies have been done for issues such as pulmonary diseases (Atluri et al., 2020;Behnke et al., 2020;Iyer et al., 2009). It was reported that the intravenous (IV), the intra-alveolar, and inhalation route are efficient for cell delivery. Homing of MSCs happens in damaged organs. Survival can be reduced due to some other injuries in patients with acute lung injury, IV delivered MSCs which could cause better systemic treatment in the lung and other organs (Chrzanowski et al., 2020;Matthay et al., 2010). Also, after IV administration of MSCs, early observation indicated that highest amount of cell were present in the lungs, liver and spleen (Leibacher & Henschler, 2016). Also, improvement of myocardial infarction by IV administration in mice was reported by Lee et al. They believed that it can be due to embolized lung cell activation that leads to the secretion of Anti-inflammatory Protein TSG-6 ( . MSC accumulation in the lung is the result of IV administration and was followed by secretion of several paracrine factors Shetty, 2020). Improvement of lung function, counteracting of fibrosis, and protecting epithelial cells of alveolar are notable effects of these factors (Shetty, 2020). Also pulmonary settlement of MSCs by IV administration could lessen over activation of the immune system and support tissue regeneration by improving microenvironment of the lung.
IV administration of MSCs in COVID-19 patients especially in aged people with severe pneumonia considers as an effective and safe treatment (Esquivel et al., 2020;Leng et al., 2020;Shetty, 2020). In a pilot, clinical study MSC-exosomes were administered via the inhalation route.
Comparing IV injection, inhalation administration prevents exosome aggregation in the injured microcirculation (Chrzanowski et al., 2020). Although, IV route is the most common way but it was suggested that choosing the route of administration should consider the patient's circumstances. On the other hand, it was proposed that the inhalation route for chronic lung disease is a more direct method with a lower incidence of unfavorable results. Beside this for using the inhaled route for treatment of COVID-19 patient's hospital environment must be properly managed (Chrzanowski et al., 2020).
Signaling molecules of damaged tissue and their receptors on the MSCs helps the MSC homing process (Squillaro et al., 2016). Although, MSC become disappear in 24-48 h, they can persist for a longer time in inflamed or damaged lungs (Khoury et al., 2020). Additionally, they could preserve the vascular endothelial and alveolar epithelial barrier function in ARDS animal models . It was shown that using MSC cause promising outcomes in ARDS treatment (Taghavi-Farahabadi et al., 2020). The ability of MSCs to suppressing those immune responses that are exaggerated in tissue repair or regeneration, called immunemodulatory. Therefore, it was suggested that in the absence of inflammatory responses, MSCs have the potential to manage severe symptoms of COVID-19 infection in patients and reduce lung injury (Rao et al., 2020;Taghavi-Farahabadi et al., 2020). Latterly Wilson et al. showed that treatment of (nine) patients with ARDS by allogeneic MSC does not cause pre-specified adverse effects, such as cardiac arrhythmia, hypoxemia, and ventricular tachycardia Wilson et al., 2015).
In an excessive immune response, MSCs secrete various soluble agents including angiogenic growth factors (Khoury et al., 2020), antimicrobial peptides (Khoury et al., 2020;Krasnodembskaya et al., 2010), EVs (Khoury et al., 2020), transforming growth factor (TGF), Nitric oxide (NO), soluble IL-6, indoleamine 2 3-dioxygenase (IDO) HLA-G5, and beta Prostaglandin E2 (PGE2) (Rao et al., 2020). These agents reduce genesis of interleukin 17 and interferon-γ. Basically, these could prevent the cytotoxic CD8+ cell activation through diminishing direct damage to the lung parenchyma (Rao et al., 2020). Also, PGE2 pathways decreased maturity and activity of dendritic cells (DCs) therefore, IL-10 and TNF-α reduced (anti-inflammatory effect). This could activate Treg cells and additional enhancement in IL-10 production. NK cells could be suppressed via the excretion of these soluble agents as well as contactmediated communication with MSCs. On the other hand, MSCs could enhance mobilization and reduce the chemotaxis of neutrophils (Rao et al., 2020). IV transplanted MSCs could reach the lungs speedily (Wang, 2020). Unfortunately, in a recent report, it has claimed that the outcome of IV injection of MSCs is nonuniform differentiation and embolise in the lungs that may lead to epithelial damage (Poulos, 2018). In other study, IV infusion of MSC therapy introduced safe and efficient for COVID-19 pneumonia, even in aged patients with severe pneumonia (Shetty, 2020).

Rajarshi et al. reported anti-inflammatory and immune-modulatory of
MSCs in clinical studies related to respiratory diseases (Rajarshi et al., 2020).
Lately, not only other cell types, but also MSC-EVs or conditioned media (CM) have been investigating largely for COVID-19 treatment in China (Khoury et al., 2020). Therapeutic effects of MSC-EV was indicated in animal models of lung injury, such as viral pneumonia (Khatri et al., 2018), severe bacterial pneumonia (Monsel et al., 2015), and hyperoxia (Braun et al., 2018;Porzionato et al., 2019;Willis et al., 2018). Also, in the murine model of lung disease, reduced lung weight gain following per- anti-inflammatory phenotypic polarization, DCs maturation, proliferation, and differentiation inhibition in B lymphocytes, and improving the recruitment of Treg cells, such as CD4+CD25+FoxP3+ T lymphocytes and CD8+CD28− T lymphocytes (Wang, 2020).
Additioanlly, MSCs not only arrest cell division of NK cells, B cells, and DCs but also affect some other functions of immune cells.
These effects include maturation and antibody secretion of B cells, cytotoxicity, and cytokine secretion of T and NK cells, maturation, activation, and antigen presentation of DCs (Uccelli et al., 2007).

| Lung regeneration
MSCs could inhibit lung cell apoptosis and encourage them to regenerate especially alveolar cell II. Providing some growth factors such as vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF).
Angiopoietin-1 secretion by MSCs could restore the permeability of epithelial protein Taghavi-Farahabadi et al., 2020). In a model of lung fibrosis, it was shown that MSC administration could decrease both collagen deposition and inflammation (Uccelli et al., 2007). Micro-vesicle transferring of MSCs improve macrophage phagocytosis capacity (Taghavi-Farahabadi et al., 2020).
Additionally, evidence showed that MSC-based treatments could inhibit collagen accumulation and alveolar collapse .

| Antiviral activity
Some studies reported about antiviral activity of MSCs (Yang et al., 2015). Yang et al. infected MSCs by gamma herpes virus. MSCs sense virus DNA through cGAS and then initiate the STING-TBK1 signaling pathway to restricting replication. This pathway generates IFN-γ and also is responsible for the antiviral function of MSCs in the IFN-γ independent manner (Taghavi-Farahabadi et al., 2020;Yang et al., 2015). Furthermore, some other investigation demonstrated that IDO expression of MSCs may be responsible for the antiviral behavior too (Taghavi-Farahabadi et al., 2020). Meisel et al. showed that IDO-positive MSCs triggered by inflammatory cytokines act as antimicrobial effectors against pathogens like viruses (Meisel et al., 2004;Taghavi-Farahabadi et al., 2020). On the other hand, Meisel et al. reported that IDO expression of MSCs could be stimulate by FN-γ and also could reduce the HSV-1 and CMV replication (Meisel et al., 2011;Taghavi-Farahabadi et al., 2020).
Also, viral resistance of MSCs was reported previously (Khoury et al., 2020) and another study demonstrated that MSC won't be infected by Covid-19. As MSCs are ACE2 negative initially and therefore, during the follow-up they did not differentiate or shift to ACE2 positive (Metcalfe, 2020). DCs and CD4+ T cells, and increasing IL-10 ( Leng et al., 2020;Metcalfe, 2020;Qu et al., 2020). The source of the cells was not reported in this study. According to a systematic review, UC-MSCs and BM-MSCs showed further decreasing in mortality than AD-MSCs in in-vivo acute lung injury models (Leng et al., 2020). Also, ventilation-induced lung injury could be recovered by paracrine mechanism of intra-tracheal (IT) and IV MSC administration too (Curley et al., 2013).
Effect of MSC administration on mice shows salubrious effect on reduction of sepsis-related morbidity and mortality. They assumed that immune-modulatory effect may be carried out by paracrine mechanisms. Unfortunately, tissue source of MSCs was not mentioned in this study (Mei et al., 2010). In following parts, MSCs administering for lung diseases with similar symptoms to COVID-19 are classified and discussed by origin.

| AT-MSC
Gentile et al. thought that AT-MSCs may be the most important representative of MSCs (Gentile & Sterodimas, 2020). In 2014, allogeneic AT-MSCs therapies reported as a feasible and safe approach for ARDS treatment (Zheng et al., 2014). In an in-vivo study, it was shown that AT-MSCs can inhibit the nuclear factor-κB signaling pathway, reduce pulmonary inflammation, decreasing pulmonary proinflammatory factor expression and also, reverse the pulmonary fibrosis process of induced by amiodarone (Wang, 2020). Also, they decrease ventricular systolic pressure, smooth muscle cell proliferation, lung tissue collagen fiber content, CD68+ macrophages, Bcl-2, and interleukin-6 in pulmonary arterial hypertension. However, plasma VEGF and procaspase-3 enhanced.
Furthermore, the pulmonary artery may cause dampening of the endothelial-mesenchymal transition (de Mendonça et al., 2017). Another investigation showed that immune-modulatory effect of AT-MSC on DC differentiation is more than BM-MSCs (Rogers et al., 2020). It was shown that this is due to secretion of KGF. KGF influences the permeability of lung endothelial and epithelial to enhance the potential of alveolar epithelium to remove edema fluid of alveolar Matthay et al., 2010   | 2175 act as emboli in the mice lung and secreted TSG-6 that is a powerful anti-inflammatory factor TNF-α-induced protein 6. This finding proved the therapeutic role of hBM-MSCs for related diseases . Anti-inflammatory and reduced collagen deposition in mice challenged with BLM were reported in BM-MSCs too (Ortiz et al., 2003). Mobilization of BM-MSCs may be the general modulatory mechanism of acute inflammatory response. MSCs could moderate cytokine secretion of endotoxin injured lungs not only by humoral factor but also by operations that need direct contact of lung cells and stem cells (Xu et al., 2007). Xu et al. in 2008, showed the efficiency of MSC-based Ang1 gene therapy acute lung injury treatment in mice (Xu et al., 2008).
Animal studies on pig and rodent using systemic BM-MSC in influenza viruses (H5N1 and H7N9) could develop the dysregulated alveolar fluid clearance and protein permeability (Chan et al., 2016;Khoury et al., 2020). IV administration of murine BM-MSCs in young immunocompetent mice model of avian influenza virus (H9N2)-induced lung injury showed decreasing in lung edema, mortality and lung damage, enhancement in gas exchanging, as well as amount of anti-inflammatory mediators but no reduction was seen in lung virus titration (Khoury et al., 2020;Li et al., 2016).
Investigating Non-immunosuppressed C57BL6 mice received BM-MSC through the IT route to appraise the efficacy of MSC on lung injury. Higher Survival, lowered histologic lung injury, decreased pulmonary edema, pro-inflammatory cytokines, and enhanced anti-inflammatory cytokines were reported (Gupta et al., 2007;Matthay et al., 2010).
It was reported that mostly used MSC source for clinical trials for immune or inflammatory lung ailments is bone marrow (32.4%) (Yen et al., 2020).

| UC-MSC
Ease of isolation and culture, low immunogenicity, notable immunemodulatory, and tissue repair activities, makes them an ideal choice for allogenic transfer therapy (Liang et al., 2020). After BM-MSCs (32.4%), UC-MSCs (29.4%) are the most common used source in clinical trials for immune or inflammatory lung diseases. In contrast, in clinical trials for COVID-19, Umbilical cord is the most used source (32.3%) (Yen et al., 2020). Another recently published paper reported that 65% of MSCs used for COVID-19 clinical trials were UC-MSCs (Smith et al., 2020). This different can be related to the time of report and number of studies up to those days.
In A/H5N1-associated acute lung damage, hUC-MSCs showed a protective role. Whether the administration of hUC-MSCs could lead to better clinical improvement or not was investigated, related results summarized in Table 1 (Shu et al., 2020).
A case report paper demonstrated using allogeneic hUC-MSC for a critically affected COVID-19 patient (3 days apart). Level of T cell become normal and the patient was not required a ventilator anymore and could walk and noticeable side effects were not seen (Liang et al., 2020;Metcalfe, 2020).

| Menstrual-blood-derived MSCs (men-MSCs)
The potential of source, painless noninvasive procedure, low immunogenicity, high proliferation capacity and free of ethical concerns make menstrual-blood derived MSCs a suitable choice (Chen, Qu & Cheng, Chen, et al., 2019;Chen, Yu, et al., 2020;Khoury et al., 2014;Tang et al., 2020). Chen used Men-MSCs for H7N9-induced ARDS. Men-MSCs transplantation notably enhances survival in preclinical and clinical investigations. In the five- year follow-up period, no adverse was observed. In their opinion, the pathological characteristics of SARS-CoV-2-associated ARDS look similar to that of H7N9-induced ARDS and MSC-based treatment potentially could be an alternative for COVID-19 treatment .
Men-MSCs could decrease inflammatory impact to defend cytokine storm in COVID-19 patients. As an underlying mechanism, it was suggested that for the prevention of myofibroblasts activity, MSCs inhibited epithelia cell apoptosis and decrease inflammatory factor secretion. MSC therapy of COVID-19 patients and especially those with ARDS or subsequent pulmonary fibrosis seems beneficial .

| Potential of MSC exosome and secretome in lung diseases and COVID-19
As discussed previously, MSCs could secrete several paracrine factors that have ability to adjust endothelial and epithelial permeability, reduce inflammation, improve tissue repair, and restrain bacterial growth (Lee et al., 2011). These paracrine molecules and EVs play important role in the protective effect of stem cells. Protective effect of MSC-EV in ARDS was indicated by different studies (Guglielmetti et al., 2020;Wu et al., 2018).
MSC-EVs could be secrete from several sources such as adipose tissue, bone marrow, peripheral blood, amniotic fluid, umbilical cord, placenta, gingival tissues, and periodontal ligament (O'Driscoll, 2020). MSC-EVs consist of various growth factors and cytokines, such as HGF, TGF-β1, IL-6, and IL-10 (Burrello et al., 2016) and could transfer some molecules such as proteins, miRNA, and mRNA. Released exosomes from the endosomal compartment are known as being an integral element of the intercellular microenvironment.
Limited antigenic components on the surface of MSC-EVs make it a nonimmunogenic option (Biancone et al., 2012).
Taghavi et al. suggested MSCs-derived exosomes as another option. They could utilize for the same immuno-modulatory effect.
The advantage is that there is no difficulty with cell maintenance and injection, ease access, phospholipid nature, and proper size. Their structure not only allows them to integrate the cell membrane but also preserves the contents of the exosomes from degradation (Taghavi-Farahabadi et al., 2020). MSC-EVs lead to comparable results and also more efficient than MSCs in bettering inflammation and damage in a range of in vivo lung damage models (Khoury et al., 2020). It is thought that EV therapy could be an alternative treatment to whole cell-based therapy (Chrzanowski et al., 2020). In systemic administration, EVs may be lost or not reach the airways and lungs, so intranasal or inhalation delivery suggested as more attractive ways. Lack of self-replicate in EVs, enhance their safety to avoid uncontrolled cell division (O'Driscoll, 2020). Generally, MSC-EVs-based therapies reported as efficient, quick, safe (Lanyu & Feilong, 2019), cost effective way with higher chance of long-term storage, lower oncogenic and mutagenic risk, easier transportation, and better resistance to damage by microenvironment of adverse disease for treatment of lung injury and COVID-19. Possibility of long-term storage is a critical option for developing countries to use the therapy without needing sumptuous GMP manufacturing equipment (Askenase, 2020;Chrzanowski et al., 2020). Also, they could be more precisely standardized per dose and duration of biologic action, compared to the difficult variability of live MSC (Askenase, 2020). It was reported that not only MSC exosomes could be freeze-dried (on-site administration without refrigeration) but also could be freeze-thawed (without toxic cryo-preservatives) for months to years (Askenase, 2020;El Baradie et al., 2020).
It was approved that MSC-exosomes could facilitate oxygen exchange via enhancing of anti-inflammatory mediators which could decrease lung injury intensity by enhancing alveolar epithelium permeability (Gupta et al., 2020;Worthington & Hagood, 2020). Inhalation administration of MSC-exosomes could prevent exosome aggregation as reported in a pilot, clinical study (NCT04276987) (Chrzanowski et al., 2020). Step1, viruses are present in patient's lung and could infected others by dispersing of the virus particles (as an example by cough), then these particles enter into the body of healthy man (2), viruses bind to ACE2 receptor in cells of the respiratory system (3), symptoms could be different between patients from tolerable condition to intolerable states which the patient needs to be hospitalizing. These patients can make other people sick (4). MSC-based therapies include MSCs, MSC-EVs, and MSC-secretome (5) that are from four main sources including, adipose, bone marrow, menstrual blood, and umbilical cord (6). (7) Results show the potential of these treatments in COVID-19 recovery. (8) The recovered body could be infected and receive viruses again. EV, extracellular vesicle [Color figure can be viewed at wileyonlinelibrary.com] inflammation and mortality of septic mouse models. All aspects of exosomes on treatment of COVID-19 or its related symptoms is discuses on reference: (Kadriyan et al., 2020,). EVs interestingly not only can be useful for treatment but also could predict the severity of COVID-19 (Fujita et al., 2020;Inal, 2020;Rosell et al., 2020).
Khatri et al. studied the effect of MSC-EVs on lung epithelial cells. They found out MSC-EVs not only transported the miRNAs, mRNAs and decrease the apoptosis but also inhibited the replication of influenza virus in cells. Furthermore they utilized a pig model infected by the influenza virus for in vivo study. Their outcomes confirmed that using MSC-EVs result in reduction of virus replication, production of proinflammatory cytokines and finally lowered lung injury (Khatri et al., 2018;Taghavi-Farahabadi et al., 2020). Also, Song et al. improved immuno-modulatory effects of MSCs by pretreatment with IL-1β. They suggested that this is due to the existence of exosomes that carry the miR-146a to the cells (Song et al., 2017;Taghavi-Farahabadi et al., 2020).
Papers indicated an inhibitory role in apoptosis of lung epithelial cells and replication of influenza virus (Khatri et al., 2018), attenuation of pulmonary inflammation, and increased airway hyperreactivity (BM) (Cruz et al., 2015). It was reported that exosomic vaccines including Spike proteins of SARS-CoV cause highly neutralization of antibodies (Basiri et al., 2020;Kuate et al., 2007). This shows the potential of an exosome-based vaccine for COVID-19.
Also as an adjunct or alternative, using ACE2+-small MSC-EVs considered as a inhibition therapy to reduce infection development (Inal, 2020 anti-inflammatory of MSC-EVs is effective in more than one model of lung disease (Cruz et al., 2015).
BM-MSC derived exosome therapy during hyperoxia indicated proangiogenic and anti-inflammatory effects to preserve the lung from hyperoxia-induced lung and BPD associated heart disease (Braun et al., 2018). Using hBM-MSC-EVs in a pulmonary fibrosis model that induced by bleomycin, showed that EVs could elevate anti-inflammatory and immuno-modulatory monocyte phenotype (Mansouri et al., 2019).
In a prospective cohort study, secreted exosomes (ExoFlo) of allogeneic BM-MSCs were used through IV route for severe COVID-19 treatment. Improvement of the clinical situation, neutrophil count, and oxygenation was observed after one treatment.
Number of lymphopenia and lymphocytes increased and also reduced acute phase reactants were detected.   1.16 | The secretome as "cell-free" therapy Different stresses such as acidosis, hypoxia, thermal stress, oxidative stress, and cytotoxic drugs could enhance vesicle liberation in cells.
MSC secretome as paracrine factors of several bioactive molecules in therapeutic employment become interesting investigation (Khoury et al., 2014;Matthay et al., 2010). Using freeze-drying technology to produce the powder of MSC secretome could be another treatment approach (Pourjabbar et al., 2020). It has previously proved that MSC secretome is a beneficial approach for pulmonary injuries of murine models. Deffune et al. suggested this approach for COVID-19 patients in critical conditions (Deffune et al., 2020).
In BPD, MSC secretome similar to MSCs could modulate neonatal lung injury and also, maintain distal lung structure during period of lung development. Authors suggested that various issues need more investigation to find out more about CM that affect cells, or how exogenously applied MSCs act during hyperoxia (although endogenous MSC quantity in the blood and lung decrease due to hyperoxia, yet administration of a low amount of MSC could inhibit lung damage notwithstanding incessant exposure to hyperoxia) (Abman & Matthay, 2009).
The administration of secretome could have some issues, such as tumorigenicity, costs, immune incompatibility, and waiting for cell expansion which can be solved by using secretome. It has suggested that homeostasis, niche, and the physiological situation may affect the secretome signature (Khoury et al., 2014). In a perspective paper, MSC secretome offered as a new therapeutic strategy for COVID-19 pneumonia. This is due to its extensive pharmacological impacts, such as immunomodulatory, proangiogenic, anti-inflammatory, regenerative, and anti-fibrotic properties (Bari et al., 2020).
Nevertheless there was not difference in other angiogenic factors, such as EGF, HGF, and VEGF (Khoury et al., 2014).

| LIFNano
In viral pneumonia, presence of leukemia inhibitory factor (LIF) to opposing the cytokine storm in the lung is necessary. MSC-based LIF is not very cost-effective, therefore, "LIFNano" as engineered stem cells showed 1000 times increase in potency. In vivo, results showed that it can be effective in the case of COVID-19 pneumonia (Metcalfe, 2020 management. Due to the generation of proinflammatory TNF-α and IL-6 which could be inhibited by LXA4, PGE2, and their precursors (dihomo-gamma-linolenic acid, arachidonic acid, and gammalinolenic acid), they look useful for cytokine storm, immune checkpoint inhibitory therapy, ARDS, and sepsis (Das, 2020).

| CONCLUSION
In the treatment of COVID-19 patients, those approaches are a priority that could successful in related lung diseases such as ARDS, ALI, influenza and etc. In this article, cell-based treatments and reports including various sources of MSC, MSC-EVs, and other cellular products which were administrated for lung diseases especially coronavirus were reviewed. It is useful to gather repeated beneficial suggestions and experiments to get the ideal method and approach to improve symptoms and cure COVID-19 patients.
Nearly all outcomes approved the beneficial effects of several sources of MSCs and their products. Although some products, such as secretome and EVs could be effective as well as MSCs. In fact, additional studies, such as cohort required to validate this therapeutic intervention further

CONFLICT OF INTERESTS
The authors declare no competing interests.