key: cord-0700658-ekpe9t70 authors: Oroojalian, Fatemeh; Haghbin, Ali; Baradaran, Behzad; Hemat, Nima; Shahbazi, Mohammad-Ali; Baghi, Hossein Bannazadeh; Mokhtarzadeh, Ahad; Hamblin, Michael R. title: Novel insights into the treatment of SARS-CoV-2 infection: An overview of current clinical trials date: 2020-09-28 journal: Int J Biol Macromol DOI: 10.1016/j.ijbiomac.2020.09.204 sha: a976e1f88546245ea53b4e716f6a86ac8d1bb8b0 doc_id: 700658 cord_uid: ekpe9t70 The emergence of the global pandemic caused by the novel SARS-CoV-2 virus has motivated scientists to find a definitive treatment or a vaccine against it in the shortest possible time. Current efforts towards this goal remain fruitless without a full understanding of the behavior of the virus and its adaptor proteins. This review provides an overview of the biological properties, functional mechanisms, and molecular components of SARS-CoV-2, along with investigational therapeutic and preventive approaches for this virus. Since the proteolytic cleavage of the S protein is critical for virus penetration into cells, a set of drugs, such as chloroquine, hydroxychloroquine, camostat mesylate have been tested in clinical trials to suppress this event. In addition to angiotensin-converting enzyme 2, the role of CD147 in the viral entrance has also been proposed. Mepolizumab has shown to be effective in blocking the virus's cellular entrance. Antiviral drugs, such as remdesivir, ritonavir, oseltamivir, darunavir, lopinavir, zanamivir, peramivir, and oseltamivir, have also been tested as treatments for COVID-19. Regarding preventive vaccines, the whole virus, vectors, nucleic acids, and structural subunits have been suggested for vaccine development. Mesenchymal stem cells and natural killer cells could also be used against SARS-CoV-2. All the above-mentioned strategies, as well as the role of nanomedicine for the diagnosis and treatment of SARS-CoV-2 infection, have been discussed in this review. The harm wreaked by infectious agents, particularly viruses, among the world's population has a very long history and has periodically challenged human life every few years. Viral infections (especially respiratory viruses) have accounted for a large proportion of epidemics and pandemics to date. Discovering an effective vaccine and implementing a correct vaccination program has led many of these viruses to be eradicated or at least severely restricted. Following the outbreak of any widespread viral disease, studies from around the world should be initiated to undertake the design of an effective vaccine. One of the most important viral families, which have always been a major concern for researchers in vaccine design, is the Coronoviridae family. Viruses of this family can periodically infect humans, causing mainly severe respiratory syndromes, ranging from Severe Acute Respiratory During a viral infection, and especially a coronavirus infection, not only is there an innate immune response, but the adaptive immune response is also activated in the host. Cytotoxic T lymphocytes mostly function during cellular immunity to eliminate the virally infected cells. The S proteins of SARS-CoV have two HLA-A2-restricted T cell epitopes that can activate T cells responses in SARS-positive patients [19] . Surprisingly, lymphopenia has been observed during SARS-CoV infection, and this reduction was more pronounced in CD4+ T cells compared to CD8+ T cells [20] . It has been demonstrated that an IgG against the N protein of SARS-CoV is the first antibody produced after primary infection [21] . However, antibodies against the S protein have been reported to have neutralization effects on SARS-CoV virions [22] . These antibodies could also trigger the phagocytosis of infected-cells by Ms, leading to an elevated level of proinflammatory cytokines and chemokines, and subsequent tissue injury due to excessive inflammation [23] . An understanding of SARS-CoV-2 cell entry mechanisms will facilitate the design of effective therapeutics that could target this critical step in the viral life cycle. The host cell membrane is essential to prevent infection, acting as a barrier between the viral particle and the intracellular site of viral replication [25] . Although not a guarantee of successful infection, the binding and passage of the virus through the cell membrane barrier is a critical step in the life cycle of a virus [26] , especially for coronaviruses. Coronavirus entry into a host cell is a dynamic, multi-step cascade process. These viruses access target cells by binding to cell surface receptors, followed by membrane fusion mediated by a multifunctional fusion protein [27, 28] . Although there is evidence implicating cellular endocytic pathways for entry of viruses into host cells, the exact mechanisms of entry for many viruses, including coronaviruses, have yet to be fully characterized [29] . Identification of the host cell receptors, the structural binding mechanism, and the virus trafficking pathway will support the development of therapeutic agents against SARS-CoV-2. In the classical pathway, viruses enter host cells via endocytosis, following binding to cell surface receptors. Viruses can physically penetrate cells by endocytic cellular uptake in a process usually referred to as receptor-mediated endocytosis [30] . Angiotensin-converting enzyme 2 (ACE2) is a critical type 1 integral membrane protein, which is expressed in most human and some animal tissues. ACE2 is highly expressed in the endothelium, the lungs, and the heart [31] . When this cell surface protein was discovered three decades ago, neither of the research groups involved could have appreciated the large number of distinct functions this receptor plays in biology, from viral infection to cardiovascular regulation [32] . ACE2 is the first known host receptor for SARS-CoV-2 [33] , and it was found that SARS-CoV-2 does not use other host cell membrane proteins, such as dipeptidyl peptidase 4 (DP IV, CD26) or Their results showed that was little evidence of genetic variations supporting the existence of susceptibility or resistance in diverse populations. East Asian populations had much higher frequencies in the eQTL allele variants, which may govern different responses to SARS-CoV-2 in different populations [35] . In addition to ACE2, Wang et al. reported that SARS-CoV-2 could enter target cells through a novel interaction of the viral proteins with CD147 [36] . CD147, also known as basigin or extracellular matrix metalloproteinase inducer (EMMPRIN), is expressed in a variety of human cells. CD147 regulates extracellular matrix remodeling during many critical biological processes, including cancer, inflammatory disease, and wound healing [37] . It could be the case that some SARS-CoV-2 receptor variants and expression levels in different patients may be associated with more severe forms of the infection. Increased viremia (level of viruses in the bloodstream and other bodily fluids) leads to higher severity of infection [38] . During viremia, the human circulatory system facilitates the transport of viruses throughout the entire body. Coronavirus viremia mainly appears one week after the onset of symptoms. Viremia then decreases gradually over a week, becoming undetectable in the bodily fluid samples of convalescent patients [39] . ACE2 is widely expressed in other tissues and cell types, such as cardiomyocytes, cardiofibroblasts, and coronary endothelial cells [40] . CD147, in a similar manner to ACE2, is expressed in many different epithelial, neuronal, lymphoid, and myeloid cell types [41] . Over-expression of Host cell entry of SARS-CoV can proceed via two distinct routes; in the absence of SARS-S-activating protease, the virus is internalized via the binding of SARS-S to ACE2 on the surface of host cells. Within the endosomes, the SARS-S is then cleaved and activated by cathepsin L, a pH-dependent cysteine protease. The SARS-S may also be activated by TMPRSS2 on the membrane surface of host cells when this protease is expressed along with ACE2 allowing the fusion of two membranes (i.e., host and the virus) and viral entrance. b) The role of class I transmembrane proteins expressed on the surface of SARS-CoV-2 in promoting membrane fusion. Conformational changes of these proteins before and after fusion have been shown. c) The conformation of the viral S2 protein has also been indicated in vitro (left) and in vivo (right). Abbreviations: FP, fusion peptide; HR-N, heptad repeat region N; HR-C, heptad repeat region C; IC, intracellular tail; SARS-CoV-2, severe acute respiratory syndrome coronavirus; TM, transmembrane anchor. SARS-CoV-2 entry into cells is a critical step of its life cycle that can be used as a target for treatment. Antiviral molecules that inhibit the host cell entry of coronaviruses have been reported. For example, Adedeji et al. identified compounds that could inhibit coronavirus cell entry through different mechanisms. The first identified inhibitor of SARS-CoV-2 cellular entry was SSAA09E2 (N-[[4-(4-methylpiperazin-1-yl)phenyl]methyl]-1,2-oxazole-5carboxamide) that acted through prevention of the ACE2-RBD interaction. SSAA09E1 [(Z)-1-thiophen-2-ylethylideneamino]thiourea, was the second identified compound, which inhibited cathepsin L, and SSAA09E3, [N-(9,10-dioxo-9,10-dihydroanthracen-2yl)benzamide], suppressed the fusion of the viral particles with the target cells [65] . For human coronaviruses, some other peptides have been reported to inhibit host cell entry through different mechanisms. For instance, Struck et al. demonstrated that a hexapeptide that bound to the ACE2 receptor, could block viral infection of host cells [66] . As mentioned, SARS-CoV-2 uses specific receptors, ACE2, and CD147, which are expressed on human airway epithelial cells and lung parenchyma. Compounds that act as angiotensin receptor blockers have been in clinical use since 1995, and are known to be effective antihypertensive agents with excellent tolerability profiles [67] . Many anti-ACE agents that can inhibit the renin-angiotensin system, such as losartan, rifampin, fluconazole, candesartan RdRp ( Figure 5 ). Remdesivir is an adenosine analog pro-drug with a broad-spectrum antiviral activity that has been shown to inhibit the replication of a wide array of RNA viruses [78, 79] . For instance, remdesivir was in clinical trials for the treatment of male Ebola virus disease survivors [80, 81] . Remdesivir is presently in clinical trials for the COVID-19 outbreak (Table 2) , and in one completed clinical trial showed promising antiviral activity against SARS-CoV-2 infection. Although the FDA has approved only a few antiviral combination treatments for a relatively small number of viral diseases, several combinations of antiviral agents with activity against SARS-CoV-2 are currently being assessed ( Table 2) . Among the clinical trials in progress, some are testing antiviral agents, such as lopinavir plus ritonavir, as the most common drug combination. Overall, among the new antiviral trials that were commenced in 2020, remdesivir has attracted the most attention for the treatment of SARS-CoV-2. Azithromycin is a 15-membered macrolide antibiotic, that is distinguished from other macrolides by its extensive and rapid penetration into biological compartments, accompanied by an acceptable serum half-life and a prolonged concentration in tissue [82] . Azithromycin has been effective in vitro against Ebola and Zika viruses [83] [84] [85] , and some other viral infections of the lower and upper respiratory tracts [86] . Gautret whom immunosuppressive drugs may actually be more effective ( Figure 6 ). None of these potential drugs (either alone or in combinations) can be considered definitive treatments without passing extensive and well-designed clinical trials, which are fortunately underway. In recent studies, it has been stated that dexamethasone, a corticosteroid that has been effective in treating autoimmune diseases (e.g. multiple sclerosis, rheumatoid arthritis) as well as inflammatory and hepatic disorders and cancer, may be effective in reducing mortality in patients with COVID-19 infection [88, 89] . In fact, this corticosteroid was the first medication that brought hope for saving the lives of J o u r n a l P r e -p r o o f Journal Pre-proof Several preclinical and clinical trials are now underway testing candidate vaccines against SARS-CoV-2. Vaccination against infectious diseases can be a powerful tool for preventing potential outbreaks of epidemic diseases before they become public health problems [92] . Vaccine strategies are considered as a critical component of SARS-CoV-2 prevention, especially since therapeutic agents are unavailable or ineffective, and that rapid clinical deterioration may limit the effectiveness of any treatment options. We describe below the different platforms of SARS-CoV-2 vaccines based on the WHO landscape and clinical trials. Interestingly, children appear to suffer from a much less severe form of the SARS-CoV-2 infection. This may be related to differences in innate immunity evident at a young age, as applies to the use of vaccines such as Bacille Calmette-Guerin (BCG) [104, 105] . Various strategies have been tried by researches for this purpose. Using alive attenuated virus is one of the options. Alongside this, there are ongoing efforts to develop viral-vector and recombinant protein-based vaccines to deliver viral antigens such as spike (S) protein to antigen-presenting cells. Nucleic acid-based vaccines (viral DNA and mRNA) have also been tried. Because the viral S protein is critical for the entrance of the virus into target cells, this protein has been under attention as an optimal candidate for developing vaccines. To be efficient, a vaccine must be able to trigger the production of adequate anti-virus antibodies. Simultaneously, it should possess a low risk of complications, such as unwanted immune reactions. One potentially threatening phenomenon to be avoided is known as antibodydependent enhancement (ADE), which can result in exaggerated uptake of viral particles. Furthermore, unprotective Th2 responses, which lead to allergic inflammatory reactions, should be kept minimal following vaccination. A whole-virus vaccine is based on a physically or chemically inactivated virion, which is the entity that causes the entire disease. The inactivated whole-virus approach offers several advantages, including a good safety profile, cost-effective production, high productivity, and no need for genetic modification [95, 106] . An inactivated SARS-CoV vaccine is probably the easiest and most practical for developing a coronavirus vaccine by analogy with available vaccines, including rabies and polio vaccines [107] . Whole vaccines may be more reactogenic to confer protective immunity against coronaviruses [108] . One investigation used an inactivated coronavirus (performed with formaldehyde after preparation in Vero cells) that was intramuscularly injected into rhesus monkeys to promote protective immunity. After three weeks, this vaccine preferentially induced Th1-type inflammatory responses, in addition to other beneficial cellular immune responses [107] . Moreover, a live-attenuated virus vaccine is generated by a variety of techniques to significantly reduce the virulence of a virus while retaining its immunogenicity. Compared with inactivated whole-virus vaccines, live-attenuated virus vaccines can stimulate an adaptive long-term immune response. However, higher immunogenicity is usually associated with a lower safety profile [109, 110] . So far, one inactivated virus and five live attenuated whole-virus vaccines, prepared by different developers, have progressed into human pre-clinical trials. Potential whole-virus vaccine candidates against SAR-CoV-2 are summarized in Table 4 . responses [111] . Replicating and non-replicating forms of viral vectors that are available include adenoviruses and poxviruses [112] . Zhao et al. found that immunization with a nucleocapsid (N) protein-based vaccine protected mice from this coronavirus through activation of CD 4+ T IFN-γ-and cell-dependent immunity [113] . Furthermore, the modified viral vector Ankara was modified to encode the MERS-CoV S protein, and induced CD 8+ T cell responses and neutralizing antibodies in pre-clinical studies [114] . The third type of viral vector-based vaccines is adenoviruses, and immunization of mice with a vector expressing S/N proteins led to the production of antibodies [115] . In addition, both Ad5-and Ad41-MERS-CoV S vaccines were shown to induce immune responses in mice [116] . Table 4 . Several nucleic acid-based vaccines for coronavirus have been reported to date. Nucleic acidbased vaccines combine the positive attributes of both subunit vaccines and live-attenuated vaccines, and there has been substantial research into this type of vaccine for diverse diseases, over the last three decades [118] . These vaccines involve direct immunization through the delivery of DNA or RNA sequences encoding the antigen, and have as their main advantages, their purity and the simplicity by which this type of vaccine can be produced [119, 120] . In addition, nucleic acid-based vaccines can be manufactured rapidly on a large scale and are relatively low-cost [95, 121] . Furthermore, the use of these vaccines that combine the benefits of subunit and inactivated vaccines has been a critical advance [122] . The enhanced humoral and cellular immune response against SARS-CoV were elicited by a DNA-based vaccine encoding S protein, or the S1 fragment. This vaccine induced T-cell responses, as well as neutralizing antibodies [115] . Similarly, a nucleic acid-based vaccine encoding the S protein or the shorter S1 fragment, was developed for MERS-CoV. pVax1 TM is a nucleic acid-based vaccine against MERS-CoV, that encodes the S protein plus an IgE leader sequence and a codon to promote expression and mRNA export [123] . Another nucleic acid-based vaccine encoding a full-length S protein against MERS-CoV strain England1, used intramuscular administration and induced neutralizing antibodies in rhesus monkeys [124] . human studies [125] . Some potential nucleic acid vaccine candidates against SAR-CoV-2 are summarized in Table 5 . These vaccines are produced using recombinant or synthetic virus subunits. The viral nucleocapsid (N), spike (S) or envelope (E) subunits are obtained through proteolysis or chemical hydrolysis to prepare the subunit vaccines. By using one viral protein subunit, this type of vaccine activates an immune response without inducing the production of antibodies against unrelated antigens [110] . Although these vaccine platforms have the highest safety profile among all other platforms, they have been considered to be weakly immunogenic [126] . Subunit vaccines are of great interest in the treatment and prevention of coronavirus diseases. Several subunit vaccines have been introduced against coronavirus targeting the S glycoprotein. Of note, the full-length S protein or its fragments, including RBD, NTD, S1 subunit, and S2 subunit, can be used as immunogens for the development of these vaccines Journal Pre-proof against coronaviruses [127] . For example, a polypeptide of the SARS-CoV S glycoprotein has been successfully expressed in baculovirus vectors [128] . The recombinant protein was purified and infused into mice using Ribi or saponin as an adjuvant, and induced higher antibody titers and better protection against SARS-CoV [129] . Modified Ankara virus vaccines were developed to express the full length S protein [130] . RBD in the S1 subunit comprises the critical neutralizing fragment of MERS-CoV S protein without the nonneutralizing immunodominant domain. This type of subunit vaccine is limited to producing RBD-dependent immune responses, and these vaccines are unable to induce harmful nonspecific antibodies [95, 124, 131] . A sequence engineered RBD-based vaccine allowed the production of three-fold greater neutralizing antibody titers [132, 133] . The N protein may provide an ideal target for the development of vaccines against coronavirus. Of note, the N protein cannot elicit antibodies to block the interaction of the virus with host cells and subsequently neutralize viral infection. Nevertheless, it may still induce cellular immune responses and specific antibodies [134, 135] . M protein is a major structural protein, which could serve as a potential target for the development of subunit vaccines. In fact, SARS-CoV M subunits have high immunogenicity and can trigger high-titer antibody responses [136] . Several subunit vaccines against SAR-CoV-2 have progressed into human pre-clinical trials. Potential subunit vaccine candidates against SAR-CoV-2 are summarized in Table 6 . Immunotherapy potentially overcomes one problem of SARS-CoV-2 treatment. Various host factors in the human immune system are responsible for SARS-CoV-2 progression or regression. Immunotherapy is defined as a therapeutic intervention that targets or manipulates these immune system factors [139] . . This so-called "cytokine storm" can initiate inflammation-induced lung injury and cause viral sepsis, which leads to acute respiratory distress syndrome (ARDS), respiratory failure, pneumonitis, organ failure, and potentially death [117] . Furthermore, severe cases of SARS-CoV-2 tend to have lower lymphocyte counts, higher leukocyte counts, and an altered neutrophil-lymphocyte-ratio, as well as smaller percentages of eosinophils, basophils, and monocytes. In contrast, the number of both helper T cells and suppressor T cells is significantly decreased in severe cases. However, the percentage of memory helper T cells is reduced, and that of naive helper T cells is increased in severe patients. These patients also have lower levels of regulatory T cells and more noticeable lung damage in acute cases [142] . These immune responses could be modified by drugs, cytokines, monoclonal antibodies, antisera, vitamins and minerals, transplantation, and immunization. It may be possible to treat SARS-CoV-2 patients using convalescent plasma obtained from recovered patients, and this approach is being considered for several emerging virus outbreaks. A meta-analysis of studies using convalescent plasma for managing severe acute respiratory infections suggests that the appropriate use of these products results in reduced mortality risk [143] . Convalescent plasma was used for treating SARS-CoV patients with potentially promising results. However, in the absence of suitable clinical trials, the results Journal Pre-proof remain controversial [144] . In addition, Zhao et al. published results showed the therapeutic and prophylactic efficacy of camel serum-containing MERS-CoV neutralizing antibodies in reducing weight loss, viral load, and improving pulmonary function in MERS patients [145] . Recently, in a preliminary non-controlled case series of 5 severe patients, the administration of convalescent plasma collected from patients who had recovered from SARS-CoV-2 containing antibodies was followed by an improved clinical outcome [146] . Table 7 . Adding interferon-γ to an interferon-I, as a synergistic combination therapy, might maximize the benefits [151] . There are currently several interferons employed in clinical settings that could provide a therapy for SARS-CoV-2. Furthermore, nitric oxide (NO) is a selective pulmonary vasodilator and holds promise as an anti-inflammatory agent [152] . NO is a critical cellular signaling molecule synthesized by nitric oxide synthase (NOS). In the pulmonary airways, NOS is present in a variety of cells, including neurons, macrophages, airway epithelial cells, and vascular endothelial cells. NOS activity is critical to mediate smooth muscle relaxation, neurotransmission, mucin secretion, and is also a well-known mediator in the cellular response to microbial infection [153] . increased the likelihood of acute kidney injury [155] . Several clinical trials are underway to determine whether inhaled NO can improve oxygenation in SARS-CoV-2 patients (Table 6 ). In addition, it was proposed that treatment with statins, a multifunctional class of drugs with several potential applications, could inhibit MyD88 signaling and NF-κB response. This could inhibit inflammatory responses that would lead to ameliorated disease progression in COVID19 patients. There is evidence that down-regulation of NF-κB signaling could increase survival in mouse models of SARS-CoV infection [156, 157] . A number of immunotherapies that have been proposed as a treatment for SARS-CoV-2 are currently undergoing clinical trials (Table 6 ). Melatonin is a neurohormone produced by the pineal gland. This molecule has many beneficial activities, including immunomodulatory, anti-inflammatory, antioxidant properties within the body [158, 159] . Because of these functions, some researchers have proposed this agent could be a therapeutic option for treating viral infections and respiratory diseases, including ARDS and acute lung injury (ALI) [160] . The mechanisms of action of melatonin (which has an excellent safety profile) include, at least in part, reducing anxiety, improving sleep, and modulating vascular permeability, which may be useful in improving prognosis of SARS-CoV-2 patients [161] . . Journal Pre-proof Non-specific recognition by innate immune receptors (e.g., RNA sensors, TLR7/8, RIG-I/MDA-5, and NLRP3 inflammasome) seems to be the first effect of the virus within alveolar epithelial cells. The main transcription factors involved in the induction of inflammatory mediators (e.g., IL-1β, IL-6, and type I IFNs) are NF-κB and IRF3/7. The antiviral activity of type I IFNs is augmented by many ISGs such as RNAse L. Cell-based immunity is based on macrophages, B cells, and T cells, which directly eliminate viral particles. However, hyper-inflammation resulting from an unbalanced action of the immune system could exacerbate COVID-19 outcomes. signaling pathway [163] . MSCs are also capable of fighting microbial agents by activating tryptophan metabolism by increasing indoleamine 2,3-dioxygenase activity [164] . They are known to support the survival and function of neutrophils and macrophages. This activity is mediated by transforming the macrophage phenotype to the anti-inflammatory (type 2) from the pro-inflammatory (type 1). MSCs mediate many processes, including secretion of growth factors that target vascular cells, hepatocytes, neurons, and other cells, altering the balance of anti/proapoptotic genes, changing mitochondrial biology, and microvesicle transfer [165] . MSCs can trigger antiapoptotic proteins both in vivo (animal models of renal, cerebral, and cardiac injuries) and also in vitro. On the other hand, MSCs can promote autophagy, another form of programmed cell death, through the phosphoinositide 3-kinase/protein kinase B signaling pathway. This function, along with another phenomenon known as mitophagy (i.e., selective degradation of mitochondria), has been shown to be important for MSCs to carry out their protective role against oxidative damage to the lungs. Xu et al. reported the pathological characteristics of a biopsy sample obtained at autopsy from a SARS-CoV-2 patient with severe ARDS [166] . Unfortunately, age-related loss of the capacity of the lung tissue to self-repair may explain the progressive age-related mortality reported in older J o u r n a l P r e -p r o o f Journal Pre-proof Treatment of pulmonary infectious diseases using nanoparticles has recently attracted significant attention [194, 195] . Small molecule drugs have disadvantages such as lack of targeting to lungs, difficulties with stability during storage and administration, and considerable expense [196, 197] . Upon reaching the lungs, drugs may be enzymatically degraded by pulmonary enzymes. In addition, the pulmonary airways is a mucus-covered epithelial bed, which can act as a barrier preventing the penetration of drugs into the lungs [198] . However, therapeutic nanoparticles may act as an alternative delivery platform to the lungs, depending on physiological parameters (respiratory rate and lung volume) and the pathophysiological state (disease nature). Considering the particle size, the target tissue, and respiratory rate, various mechanisms can be employed to deliver therapeutic agents into the lungs. In the pulmonary alveoli, the clearance rate of particles is mainly determined by the size [199] . Furthermore, vaccines must be equipped with efficient molecules (i.e., new generation composite vaccines) to potentiate their immunogenic and adjuvant activities [200] . To address some of these issues, nano-delivery platforms could provide a viable option as they are designed to allow protection against biological degradation, better stability, and higher efficiency (synergistic effects) [201, 202] , to improve the effectiveness of therapeutic agents [203] . Therefore, nanoparticles (NPs) are being investigated as carriers for targeting drugs to treat a variety of pulmonary infectious diseases. protein, using a heterologous prime-boost immunization strategy. They used a recombinant adenovirus serotype 5 to conjugate the antigens to the NPs. The vaccines were proved to be able to activate Th1/Th2 lymphocytes in an appropriate ratio [206] . In another study, Roh et al. used a combination of SARS-CoV N protein inhibitors and NP-based RNA oligonucleotides to develop a vaccine against the virus. By applying RNA oligonucleotide conjugated to QDs on a biochip, they showed that the SARS-CoV N protein was effectively suppressed by (-)-catechin gallate and (-)-gallocatechin gallate through a dose-dependent attenuation of its binding affinity [207] . Biosensors are used to detect and quantify biological responses and are now widely used in medical diagnostic procedures as point-of-care instruments [208, 209] . Biosensor-based systems are effective, simple, reliable, and relatively inexpensive platforms that can be used in clinical settings. Using these systems, the sensitivity and reproducibility of clinical analysis can be maximized [210, 211] . Nanobiosensors were first applied to detect antibody mimicking proteins Because NPs-based vaccines can effectively trigger the humoral immune response and act as a versatile antigen-presenting system, they can be effectively used to increase immunity against the viruses that cause acute respiratory syndromes [215] . Vaccines that have been developed using mRNAs benefit from advantages, such as mimicking natural infection and triggering a more potent immune response. In addition, there is a possibility to incorporate multiple mRNAs into a single vaccine. The SARS-CoV-2 S protein (140 kDa) is a peptide with 1273 residues [216] , and its respective mRNA has been employed to develop an effective vaccine. In this approach, liquid NPs and chemical modification were used to stabilize an injectable form of the SARS-CoV-2 infections. We further discussed the complex cellular interactions responsible for SARS-CoV-2 cell entry and replication, as well as drugs that can target these pathways. Vaccine platforms, passive immunotherapy, and cell-based therapies were also covered. Currently in use or investigational agents for SARS-CoV-2 target either the virus or host-derived molecules (e.g., interferons, glucocorticoids). The combination of lopinavir and ritonavir might treat the specific virus, and SARS-CoV-2 receptor inhibitors may be helpful in reducing lung cell viral entry and improve lung function in COVID19 patients. Some patients infected with SARS-CoV-2 were significantly improved after treatment with the lopinavir in combination with ritonavir. However, other case reports showed that treatment with lopinavir and ritonavir did not significantly alleviate SARS-CoV-2 related pneumonia [218] . Although there were no reports of acute respiratory failure in these patients, it is questionable whether this was solely related to the antiviral drugs or not [69] . Regardless, lopinavir plus ritonavir is still considered a viable treatment for SARS-CoV-2 infection. Cell entry-based therapeutics, such as chloroquine, hydroxychloroquine, anti-ACE2, and anti-CD147 antibodies could also guide us towards the discovery of new treatments for SARS-CoV-2 infection. These therapeutic modalities could also be useful to reveal the fundamental pathways of SARS-CoV-2 replication. There is also interest in testing whether immunotherapy or biological therapies, such as convalescent plasma and hyperimmune globulin, containing antibodies isolated from blood In conclusion, despite many studies in humans, there is not yet an optimal treatment for SARS-CoV-2 infection. Detailed laboratory studies and further clinical trials will be required to establish evidence-based treatment for patients with SARS-CoV-2 as well as ARDS. MRH declares the following potential conflicts of interest. Scientific Advisory Boards: History and recent advances in coronavirus discovery Human coronaviruses: insights into environmental resistance and its influence on the development of new antiseptic strategies Human coronaviruses: what do they cause? Commentary: Middle East respiratory syndrome coronavirus (MERS-CoV): announcement of the Coronavirus Study Group of the International, The species Severe acute respiratory syndrome-related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2 Coronavirus disease 2019 (COVID-19): Situation Report-76 Continuous and discontinuous RNA synthesis in coronaviruses Receptor recognition and cross-species infections of SARS coronavirus Molecular evolution of the SARS coronavirus during the course of the SARS epidemic in China SARS-CoV-2: an Emerging Coronavirus that Causes a Global Threat Coronavirus infections and immune responses Immunopathogenesis of coronavirus infections: implications for SARS National Research Project for SARS, The involvement of natural killer cells in the pathogenesis of severe acute respiratory syndrome Mechanisms of host defense following severe acute respiratory syndrome-coronavirus (SARS-CoV) pulmonary infection of mice Plasma proteome of severe acute respiratory syndrome analyzed by twodimensional gel electrophoresis and mass spectrometry Inhibition of beta interferon induction by severe acute respiratory syndrome coronavirus suggests a twostep model for activation of interferon regulatory factor 3 SARS-coronavirus replication in human peripheral monocytes/macrophages Chemokine up-regulation in sars-coronavirus-infected, monocyte-derived human dendritic cells T-cell epitopes in severe acute respiratory syndrome (SARS) coronavirus spike protein elicit a specific T-cell immune response in patients who recover from SARS Haematological manifestations in patients with severe acute respiratory syndrome: retrospective analysis Chronological evolution of IgM, IgA, IgG and neutralisation antibodies after infection with SARS-associated coronavirus Contributions of the structural proteins of severe acute respiratory syndrome coronavirus to protective immunity Prior infection and passive transfer of neutralizing antibody prevent replication of severe acute respiratory syndrome coronavirus in the respiratory tract of mice Molecular immune pathogenesis and diagnosis of COVID-19 Flavivirus Receptors: Diversity, Identity, and Cell Entry Targeting viral entry as a strategy for broad-spectrum antivirals Host cell entry of Middle East respiratory syndrome coronavirus after two-step, furin-mediated activation of the spike protein Structures and mechanisms of viral membrane fusion proteins: multiple variations on a common theme Mechanisms of viral entry: sneaking in the front door Dynamics of virus-receptor interactions in virus binding, signaling, and endocytosis Angiotensin-converting enzyme 2 is a key modulator of the renin-angiotensin system in cardiovascular and renal disease Angiotensin-converting enzyme 2: the first decade A pneumonia outbreak associated with a new coronavirus of probable bat origin Structural basis for the recognition of the SARS-CoV-2 by full-length human ACE2 Comparative genetic analysis of the novel coronavirus (2019-nCoV/SARS-CoV-2) receptor ACE2 in different populations SARS-CoV-2 invades host cells via a novel route: CD147-spike protein Role of CD147 (EMMPRIN/basigin) in Tissue Remodeling Characterization of Pathogenic Sepsis Etiologies and Patient Profiles: A Novel Approach to Triage and Treatment Antibody response and viraemia during the course of severe acute respiratory syndrome (SARS)-associated coronavirus infection Role of the ACE2/Angiotensin 1-7 Axis of the Renin-Angiotensin System in Heart Failure How, with whom and when: an overview of CD147-mediated regulatory networks influencing matrix metalloproteinase activity Structure, Function, and Evolution of Coronavirus Spike Proteins Evolution of the novel coronavirus from the ongoing Wuhan outbreak and modeling of its spike protein for risk of human transmission Structure of SARS coronavirus spike receptor-binding domain complexed with receptor Composition and divergence of coronavirus spike proteins and host ACE2 receptors predict potential intermediate hosts of SARS-CoV-2 Structure analysis of the receptor binding of 2019-nCoV Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation Stabilized coronavirus spikes are resistant to conformational changes induced by receptor recognition or proteolysis ACE2 X-ray structures reveal a large hinge-bending motion important for inhibitor binding and catalysis The SARS-CoV S glycoprotein: expression and functional characterization A potential role for integrins in host cell entry by SARS-CoV-2 Mechanisms of host receptor adaptation by severe acute respiratory syndrome coronavirus Receptor recognition by novel coronavirus from Wuhan: An analysis based on decade-long structural studies of SARS Principles of Virus Uncoating: Cues and the Snooker Ball Mechanisms of coronavirus cell entry mediated by the viral spike protein Structure of mouse coronavirus spike protein complexed with receptor reveals mechanism for viral entry Ready, set, fuse! The coronavirus spike protein and acquisition of fusion competence A comparative review of viral entry and attachment during large and giant dsDNA virus infections Tetraspanins: Architects of Viral Entry and Exit Platforms Host cell proteases: Critical determinants of coronavirus tropism and pathogenesis Host cell proteases: Critical determinants of coronavirus tropism and pathogenesis SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically Proven Protease Inhibitor Evidence that TMPRSS2 activates the severe acute respiratory syndrome coronavirus spike protein for membrane fusion and reduces viral control by the humoral immune response Inhibitors of cathepsin L prevent severe acute respiratory syndrome coronavirus entry Novel Inhibitors of SARS-CoV Entry acting by Three Distinct Mechanisms A hexapeptide of the receptor-binding domain of SARS corona virus spike protein blocks viral entry into host cells via the human receptor ACE2 The comparative efficacy and safety of the angiotensin receptor blockers in the management of hypertension and other cardiovascular diseases Angiotensin receptor blockers as tentative SARS-CoV-2 therapeutics Letter to the Editor: Case of the Index Patient Who Caused Tertiary Transmission of Coronavirus Disease 2019 in Korea: the Application of Lopinavir/Ritonavir for the Treatment of COVID-19 Pneumonia Monitored by Quantitative RT-PCR A Trial of Lopinavir-Ritonavir in Adults Hospitalized with Severe Covid-19 Lopinavir/ritonavir combination therapy amongst symptomatic coronavirus disease 2019 patients in India: Protocol for restricted public health emergency use Case of the Index Patient Who Caused Tertiary Transmission of COVID-19 Infection in Korea: the Application of Lopinavir/Ritonavir for the Treatment of COVID-19 Infected Pneumonia Monitored by Quantitative RT-PCR The mechanisms of sudden-onset type adverse reactions to oseltamivir The origin, transmission and clinical therapies on coronavirus disease 2019 (COVID-19) outbreak -an update on the status The potential chemical structure of anti-SARS-CoV-2 RNA-dependent RNA polymerase Therapeutic options for the 2019 novel coronavirus (2019-nCoV) New Nucleoside Analogues for the Treatment of Hemorrhagic Fever Virus Infections Middle East respiratory syndrome coronavirus: another zoonotic betacoronavirus causing SARS-like disease Middle East Respiratory Syndrome SARS-like WIV1-CoV poised for human emergence Coronavirus Susceptibility to the Antiviral Remdesivir (GS-5734) Is Mediated by the Viral Polymerase and the Proofreading Exoribonuclease Azithromycin induces anti-viral effects in cultured bronchial epithelial cells from COPD patients Zika virus cell tropism in the developing human brain and inhibition by azithromycin Azithromycin Inhibits the Replication of Zika Virus Evaluation of Ebola Virus Inhibitors for Drug Repurposing Early Administration of Azithromycin and Prevention of Severe Lower Respiratory Tract Illnesses in Preschool Children With a History of Such Illnesses: A Randomized Clinical Trial Hydroxychloroquine and azithromycin as a treatment of COVID-19: results of an open-label non-randomized clinical trial Dexamethasone for COVID-19? Not so fast Dexamethasone in severe COVID-19 infection: A case series Dexamethasone nanomedicines for COVID-19 Nanomedicines for inflammatory arthritis: head-to-head comparison of glucocorticoid-containing polymers, micelles, and liposomes Estimating the cost of vaccine development against epidemic infectious diseases: a cost minimisation study From SARS to COVID-19: A previously unknown SARS-related coronavirus (SARS-CoV-2) of pandemic potential infecting humans -Call for a One Health approach Timely development of vaccines against SARS-CoV-2 Recent Advances in the Vaccine Development Against Middle East Respiratory Syndrome-Coronavirus Bacterial Outer Membrane Vesicles (OMVs)-based Dual Vaccine for Influenza A H1N1 Virus and MERS-CoV, Vaccines (Basel) Middle East Respiratory Syndrome Vaccine Candidates: Cautious Optimism From SARS to MERS, Thrusting Coronaviruses into the Spotlight Detection of antibodies against SARS-CoV-2 in patients with COVID-19 How will country-based mitigation measures influence the course of the COVID-19 epidemic? Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic The COVID-19 vaccine development landscape A severe acute respiratory syndrome coronavirus that lacks the E gene is attenuated in vitro and in vivo SARS-CoV-2 infection in children: Transmission dynamics and clinical characteristics Innate and Adaptive Immune Memory: an Evolutionary Continuum in the Host's Response to Pathogens Whole-Inactivated and Virus-Like Particle Vaccine Strategies for Chikungunya Virus Immunogenicity, safety, and protective efficacy of an inactivated SARS-associated coronavirus vaccine in rhesus monkeys Comparative evaluation of two severe acute respiratory syndrome (SARS) vaccine candidates in mice challenged with SARS coronavirus Extended Preclinical Safety, Efficacy and Stability Testing of a Live-attenuated Chikungunya Vaccine Candidate Recent Progress in Vaccine Development Against Chikungunya Virus Developments in Viral Vector-Based Vaccines Replicating and non-replicating viral vectors for vaccine development Airway Memory CD4(+) T Cells Mediate Protective Immunity against Emerging Respiratory Coronaviruses Middle East respiratory syndrome coronavirus spike protein delivered by modified vaccinia virus Ankara efficiently induces virus-neutralizing antibodies Vaccines to prevent severe acute respiratory syndrome coronavirus-induced disease Adenoviral expression of a truncated S1 subunit of SARS-CoV spike protein results in specific humoral immune responses against SARS-CoV in rats Immune responses in COVID-19 and potential vaccines: Lessons learned from SARS and MERS epidemic Chapter Seven -Self-Amplifying mRNA Vaccines Recent advances on HIV DNA vaccines development: Stepwise improvements to clinical trials Comparison of DNA and mRNA vaccines against cancer mRNA vaccines -a new era in vaccinology Development of nucleic acid vaccines: Use of selfamplifying RNA in lipid nanoparticles A synthetic consensus anti-Spike protein DNA vaccine induces protective immunity against Middle East Respiratory Syndrome Coronavirus in non-human primates Evaluation of candidate vaccine approaches for MERS-CoV COVID-19 infection: origin, transmission, and characteristics of human coronaviruses Vaccines for the prevention against the threat of MERS-CoV Subunit Vaccines Against Emerging Pathogenic Human Coronaviruses Neutralizing antibody and protective immunity to SARS coronavirus infection of mice induced by a soluble recombinant polypeptide containing an N-terminal segment of the spike glycoprotein Prior Infection and Passive Transfer of Neutralizing Antibody Prevent Replication of Severe Acute Respiratory Syndrome Coronavirus in the Respiratory Tract of Mice Severe acute respiratory syndrome coronavirus spike protein expressed by attenuated vaccinia virus protectively immunizes mice Middle East respiratory syndrome: Current status and future prospects for vaccine development Vaccines for emerging infectious diseases: Lessons from MERS coronavirus and Zika virus Introduction of neutralizing immunogenicity index to the rational design of MERS coronavirus subunit vaccines Immunological characterizations of the nucleocapsid protein based SARS vaccine candidates Boosted expression of the SARS-CoV nucleocapsid protein in tobacco and its immunogenicity in mice Identification of immunodominant epitopes on the membrane protein of the severe acute respiratory syndrome-associated coronavirus Human coronaviruses: a review of virus-host interactions Severe acute respiratory syndrome coronavirus viroporin 3a activates the NLRP3 inflammasome Harnessing the immune system to improve cancer therapy Plasma inflammatory cytokines and chemokines in severe acute respiratory syndrome Clinical features of patients infected with 2019 novel coronavirus in Clinical infectious diseases : an official publication of the Infectious Diseases Society of America The Effectiveness of Convalescent Plasma and Hyperimmune Immunoglobulin for the Treatment of Severe Acute Respiratory Infections of Viral Etiology: A Systematic Review and Exploratory Meta-analysis SARS: Systematic Review of Treatment Effects Passive Immunotherapy With Dromedary Immune Serum In An Experimental Animal Model For MERS Coronavirus Infection Treatment of 5 Critically Ill Patients With COVID-19 With Convalescent Plasma T-cell immunity of SARS-CoV: Implications for vaccine development against MERS-CoV Effect of treatment with inosine pranobex in acute respiratory viral infections in children Human-Leukocyte Antigen Class I Cw 1502 and Class II DR 0301 Genotypes Are Associated with Resistance to Severe Acute Respiratory Syndrome (SARS) Infection Perspectives on monoclonal antibody therapy as potential therapeutic intervention for Coronavirus disease-19 (COVID-19) Therapeutic Approaches for COVID-19 Based on the Dynamics of Interferon-mediated Immune Responses Distinguishing the Effects of Inhaled Nitric Oxide and Lung Recruitment in Pediatric Acute Respiratory Distress Syndrome: Scope for Further Improvement Antimicrobial reactive oxygen and nitrogen species: Concepts and controversies Inhaled Nitric Oxide Therapy Fails to Improve Outcome in Experimental Severe Influenza Statins may decrease the Fatality Rate of MERS Infection Inhibition of NF-kappaB-mediated inflammation in severe acute respiratory syndrome coronavirus-infected mice increases survival Role of Melatonin in the Regulation of Pain Effects of AANAT overexpression on the inflammatory responses and autophagy activity in the cellular and transgenic animal levels Treatment of ebola and other infectious diseases: melatonin "goes viral COVID-19: Melatonin as a potential adjuvant treatment In Vivo Effects of Mesenchymal Stromal Cells in Two Patients With Severe Acute Respiratory Distress Syndrome Antibacterial effect of mesenchymal stem cells against Escherichia coli is mediated by secretion of beta-defensin-2 via toll-like receptor 4 signalling Human bone marrow stromal cells inhibit allogeneic T-cell responses by indoleamine 2, 3-dioxygenase-mediated tryptophan degradation Network analysis of transcriptional responses induced by mesenchymal stem cell treatment of experimental sepsis Pathological findings of COVID-19 associated with acute respiratory distress syndrome, The Lancet Respiratory Medicine Human mesenchymal stromal cells reduce influenza A H5N1-associated acute lung injury in vitro and in vivo The acute respiratory distress syndrome Personalized pharmacological therapy for ARDS: a light at the end of the tunnel Prone Positioning in Severe Acute Respiratory Distress Syndrome Therapeutic Potential and Mechanisms of Action of Mesenchymal Stromal Cells for Acute Respiratory Distress Syndrome Xenogeneic human umbilical cordderived mesenchymal stem cells reduce mortality in rats with acute respiratory distress syndrome complicated by sepsis Advance on human umbilical cord mesenchymal stem cells for treatment of ALI in severe burns Human umbilical cord mesenchymal stem cells reduce fibrosis of bleomycin-induced lung injury Therapeutic Effects of Human Umbilical Cord-Derived Mesenchymal Stem Cells in Acute Lung Injury Mice Effects of human umbilical cord blood mononuclear cells on respiratory system mechanics in a murine model of neonatal lung injury Transplantation of Menstrual Blood-Derived Mesenchymal Stem Cells Promotes the Repair of LPS-Induced Acute Lung Injury The Promise of Mesenchymal Stem Cell Therapy for Acute Respiratory Distress Syndrome Ratio of angiopoietin-2 to angiopoietin-1 as a predictor of mortality in acute lung injury patients Genetically modified mesenchymal stromal cells in cancer therapy Keratinocyte Growth Factor Gene Delivery via Mesenchymal Stem Cells Protects against Lipopolysaccharide-Induced Acute Lung Injury in Mice Use of Genetically Modified Mesenchymal Stem Cells to Treat Neurodegenerative Diseases Mesenchymal Stem Cells Reconditioned in Their Own Serum Exhibit Augmented Therapeutic Properties in the Setting of Acute Respiratory Distress Syndrome Overexpression of IL-10 Enhances the Efficacy of Human Umbilical-Cord-Derived Mesenchymal Stromal Cells in E. coli Pneumosepsis Kynurenic acid, an IDO metabolite, controls TSG-6-mediated immunosuppression of human mesenchymal stem cells Human Mesenchymal Stem (Stromal) Cells Promote the Resolution of Acute Lung Injury in Part through Lipoxin A4 Mesenchymal stem cells enhance survival and bacterial clearance in murine Escherichia coli pneumonia Antibacterial effect of mesenchymal stem cells against Escherichia coli is mediated by secretion of beta-defensin-2 via toll like receptor 4 signaling Therapeutic potential of products derived from mesenchymal stem/stromal cells in pulmonary disease Mesenchymal stem cells-derived extracellular vesicles in acute respiratory distress syndrome: a review of current literature and potential future treatment options Mesenchymal Stem (Stromal) Cells for Treatment of ARDS: A Phase 1 Clinical Trial, The Lancet Potential therapeutic agents against COVID-19: What we know so far Transplantation of ACE2 -Mesenchymal Stem Cells Improves the Outcome of Patients with COVID-19 Pneumonia Recent advances in nanotechnology-based drug delivery systems for the kidney Synthesis and evaluation of injectable thermosensitive penta-block copolymer hydrogel (PNIPAAm-PCL-PEG-PCL-PNIPAAm) and star-shaped poly (CL─ CO─ LA)-b-PEG for wound healing applications Nanotechnology and medicine -The upside and the downside Applications of Nanoparticle Systems in Drug Delivery Technology Right or Left: The Role of Nanoparticles in Pulmonary Diseases Medical nanoparticles for next generation drug delivery to the lungs Nanoparticle Vaccines Against Infectious Diseases Synthetic and biological vesicular nanocarriers designed for gene delivery Recent advances in codelivery systems based on polymeric nanoparticle for cancer treatment, Artificial Cells Nanomedicine for Infectious Disease Applications: Innovation towards Broad-Spectrum Treatment of Viral Infections Purified coronavirus Spike protein nanoparticles induce coronavirus neutralizing antibodies in mice MERS-CoV spike nanoparticles protect mice from MERS-CoV infection Heterologous prime-boost vaccination with adenoviral vector and protein nanoparticles induces both Th1 and Th2 responses against Middle East respiratory syndrome coronavirus A facile inhibitor screening of SARS coronavirus N protein using nanoparticle-based RNA oligonucleotide Nanomaterial-based biosensors for detection of pathogenic virus An innovative immunosensor for ultrasensitive detection of breast cancer specific carbohydrate (CA 15-3) in unprocessed human plasma and MCF-7 breast cancer cell lysates using gold nanospear electrochemically assembled onto thiolated graphene quantum dots Recent trends in rapid detection of influenza infections by bio and nanobiosensor Graphene quantum dot as an electrically conductive material toward low potential detection: A new platform for interface science Label-Free, Electrical Detection of the SARS Virus N-Protein with Nanowire Biosensors Utilizing Antibody Mimics as Capture Probes Multiplex Paper-Based Colorimetric DNA Sensor Using Pyrrolidinyl Peptide Nucleic Acid-Induced AgNPs Aggregation for Detecting MERS-CoV, MTB, and HPV Oligonucleotides Development of Label-Free Colorimetric Assay for MERS-CoV Using Gold Nanoparticles Peptide nanoparticles as novel immunogens: design and analysis of a prototypic severe acute respiratory syndrome vaccine Progress and Prospects on Vaccine Development against SARS-CoV-2, Vaccines (Basel) Research and Development on Therapeutic Agents and Vaccines for COVID-19 and Related Human Coronavirus Diseases The First Case of 2019 Novel Coronavirus Pneumonia Imported into Korea from Wuhan, China: Implication for Infection Prevention and Control Measures The Authors are grateful for financial supports from the Immunology Research Center, Tabriz