Although the exact mechanism of pathogenesis in COVID-19 is not fully understood, cytokine storm following viral infection plays an important role in the initiation and progression of disease. SARS-CoV-2 infection induces over-activation of the immune system and massive production of inflammatory cytokines. Therefore, it is necessary to develop new strategies to modulate inflammatory responses [1]. Despite many efforts to improve therapeutic protocols for COVID-19, there is no specific approved treatment or preventable vaccine for this disease [2, 3]. However, intensive research has been conducted to both prevent and treat COVID-19. This commentary is an update for our recent paper in “Journal of Molecular Medicine, June 2020” and highlights the recent achievements in terms of preventive and therapeutic approaches in COVID-19 [4].

Development of SARS-CoV-2 preventive vaccines

  • mRNA-1273 (Moderna TX, Inc.) is an mRNA vaccine that is composed of synthetic mRNA expressing the prefusion-stabilized SARS-CoV-2 spike trimer (mRNA-1273) [5, 6]. The efficacy and immunogenicity of Moderna vaccine investigated in a phase III clinical trial (NCT04470427). Moderna has announced its primary efficacy analysis (95%) and recently applied to the FDA (USA) for emergency use authorization.

  • ChAdOx1 nCOV-19 is another vaccine under evaluation in phase II/III clinical trials. This vaccine has been developed by Oxford University and produced due to the technology in which an adeno-viral vector encodes SARS-CoV-2 S protein (NCT04400838) [7]. The pre-clinical investigations showed that ChAdOx1 nCOV-19 was immunogenic in vaccinated mice and rhesus macaques and triggered robust humoral and cell-mediated responses [8]. Its safety and immunogenicity were evaluated in a phase II/III trial in a prime-boost regimen in young and old adults. In 14 days after receiving the boost dose, > 99% of participants had neutralizing antibodies [9].

  • BNT162b2 is a COVID-19 RNA vaccine candidate that has been announced by BioNTech/Pfizer. This vaccine encodes the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Data from a phase III clinical trial showed vaccine efficiency over 95% [12, 13].

  • CoronaVac is inactivated SARS-CoV-2 manufactured by Sinovac Life Sciences (Beijing, China). Its safety, tolerability, and immunogenicity have been approved in healthy adults aged 18–59 years in a phase I/II clinical trial [14]; and now it is under investigation in a phase III clinical trial (NCT04582344).

  • Gam-COVID-Vac (Sputnik V) is a combined vector vaccine that consists of recombinant adenovirus type 26 (rAd26) and type 5 (rAd5) vectors. They carry the spike glycoprotein gene. Gam-COVID-Vac has been developed by Gamaleya National Research Center for Epidemiology and Microbiology (Moscow, Russia) [15]. Its safety and immunogenicity was approved in two formulations in a phase I/II clinical trial [15]. And now, the safety and efficiency of this vaccine is under assessment in a phase III clinical trial (NCT04530396).

  • Using Ad5 vector to carry the spike glycoprotein gene, CanSino Biologics Inc. (China) has developed a recombinant novel coronavirus vaccine which safety and efficiency has been being evaluated in a phase III clinical trial (NCT04526990).

The progress in vaccine development is critically discussed in the following recently published reviews in detail [10, 11].

SARS-CoV-2 therapeutic approaches

In our recently published paper entitled “Novel therapeutic approaches for treatment of COVID-19,” we grouped novel therapies into passive immunotherapy, cell-based therapies (including immune cell and non-immune cell therapies), monoclonal antibodies, and anti-viral drugs.

Searching terms “COVID-19” and “treatment” using https://clinicaltrials.gov/ resulted in more than 2200 clinical trials (October 29, 2020). Among these clinical trials, over 200 studies were related to cell-based therapies. They included mesenchymal stromal cell (MSC) therapies and adoptive T cell and natural killer (NK) cell therapies. Other studies applied monoclonal antibodies and nano-medicine to treat COVID-19 patients (Table 1) (Figs. 1 and 2).

Table 1 SARS-CoV-2 therapeutic approaches
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Fig. 1
figure 1

Overview of molecular- and cellular-based treatments

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Fig. 2
figure 2

Comparative analysis of therapeutic approaches to treat COVID-19

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Mesenchymal stromal cells in COVID-19 treatment

  • Due to the immunomodulatory effects of MSCs [16, 17], clinical trials using MSCs from various sources including the umbilical cord, adipose tissue, and bone marrow have been registered for the treatment of acute respiratory distress syndrome (ARDS) caused by COVID-19 (NCT04341610, NCT04366063). Primary results showed that this strategy was safe and effective. The MSC therapy improved lung function, downregulated inflammatory cytokines, increased anti-inflammatory ones, and decreased mortality rate [18,19,20]. MSCs exert their anti-inflammatory properties through direct cell-cell contact, paracrine effects, and their extracellular vesicles such as exosomes [21, 22]. It seems that application of MSCs and their exosomes could be a promising approach for the management of respiratory complications in COVID-19.

Adoptive T cells in COVID-19 treatment

  • Some studies reported lymphopenia and functional exhaustion due to the over-activation of the immune system during infection [23]. COVID-19 specific T and TCD8+ cells play an important role in the virus clearance by producing inflammatory cytokines and their cytotoxicity effects [24]. Moreover, virus-specific memory T cells were isolated from the serum of the recovered patients [25,26,27]. Based on this evidence, recent clinical trials designed and used the adoptive T cells in severe COVID-19 patients. Using this treatment protocol, HLA-matched T cells from fully recovered patients were transfused into newly infected individuals. This approach may help patients who are at the risk of requiring mechanical ventilation (NCT04457726, NCT04401410, and NCT04406064).

Exosomes derived from adoptive T cells in COVID-19 treatment

  • In addition, another clinical trial used COVID-19-specific T cell-derived exosomes (CSTC-Exo) for the treatment of early infected patients in order to boost the IFN-γ production. Compared to the cells, CSTC-Exo does not need HLA-matching, and their administration route is an aerosol inhalation (NCT04389385). If it meets the endpoints, it could be a suitable alternative as an off-the-shelf product.

  • Since regulatory T cells (Treg) are known as major anti-inflammatory T cell subsets, Treg cell therapy may be a novel regenerative and anti-inflammatory treatment strategy for COVID-19. Infusion of cord blood-derived Treg cells (CK0802) may improve the ARDS symptoms in these patients (NCT04468971). RAPA-501-ALLO is a hybrid Treg/Th2 off-the-shelf reprogrammed Treg cell product produced by the healthy donors. RAPA-501-ALLO could have a dual advantage by modulating Th1 and Th17 subpopulations and inhibiting the massive production of inflammatory cytokines, as well as regenerating the damaged alveolar tissues [28]. This product may be a useful therapeutic option for the treatment of severe COVID-19 (NCT04482699).

NK cells in COVID-19 treatment

  • NK cells are an essential part of the innate immune system and play an important role in mediating virus-induced immune responses. So, interventional therapies using NK cells have been developed for the COVID-19 treatment. Recently, the adoptive transfer of allogenic NK cells has been developed to boost the antiviral immune responses and clearance of the infected cells in COVID-19 patients (NCT04344548, NCT04280224). NKG2D-ACE2 CAR-NK is an off-the-shelf product that has been investigated in a phase I/II clinical trial (NCT04324996). These cells simultaneously target ACE2 (the main receptor for SARS-CoV-2) [29] and NKG2D on the infected cells and removed them. Therefore, they could inhibit the SARS-CoV-2 infection through ACE2 blockade.

Monoclonal antibodies in COVID-19 treatment

  • It has been shown that monoclonal antibodies could be a promising treatment approach for COVID-19. Monoclonal antibodies against inflammatory cytokines such as anti-IL-1 receptor, IL-6 antagonist, anti-TNF-α, anti-GM-CSF, anti-IFN-γ, and C5a inhibitor have been studied in different clinical trials. Over 60 clinical trials have been registered to evaluate the treatment efficiency of Tocilizumab and Olokizumab (anti-IL-6 mAbs) [30,31,32,33]. The published studies showed that Tocilizumab (anti-IL-6 mAb) could improve the outcomes in COVID-19 patients and inhibit a cytokine storm [34]. Anakinra (IL-1ra) [35, 36] also showed beneficial effects for the treatment of COVID-19 patients and could decrease the mechanical ventilation need. Moreover, REGN-COV2 has been developed and consists of two neutralizing antibodies (REGN10987 + REGN10933) targeting SARS-CoV-2 spike protein [37, 38].

Nano-medicine in COVID-19 treatment

  • Using nano-medicine including aerosol inhalations of therapeutic agents attracts lots of attention. Recent studies have investigated the efficiency and safety of the MSC-derived exosome (NCT04491240, NCT04276987) and interferon beta inhalation (NCT04385095).

Now, most of the mentioned studies are ongoing. The growing number of clinical trials in this field could provide more validated designs and higher quality data. In this context, the increase in international collaborations to provide larger number of patients will be helpful to obtain more definite results [39]. Identifying the exact mechanisms of the COVID-19 immunopathogenesis will ensure the development of more effective therapies.