In the last decade, the secreting activity of mesenchymal stem/stromal cells (MSCs) has been widely investigated, due to its possible therapeutic role. In fact, MSCs release extracellular vesicles (EVs) containing relevant biomolecules such as mRNAs, microRNAs, bioactive lipids, and signaling receptors, able to restore physiological conditions where regenerative or anti-inflammatory actions are needed. An actual advantage would come from the therapeutic use of EVs with respect to MSCs, avoiding the possible immune rejection, the lung entrapment, improving the safety, and allowing the crossing of biological barriers. A number of concerns still have to be solved regarding the mechanisms determining the beneficial effect of MSC-EVs, the possible alteration of their properties as a consequence of the isolation/purification methods, and/or the best approach for a large-scale production for clinical use. Most of the preclinical studies have been successful, reporting for MSC-EVs a protecting role in acute kidney injury following ischemia reperfusion, a potent anti-inflammatory and anti-fibrotic effects by reducing disease associated inflammation and fibrosis in lung and liver, and the modulation of both innate and adaptive immune responses in graft versus host disease (GVHD) as well as autoimmune diseases. However, the translation of MSC-EVs to the clinical stage is still at the initial phase. Herein, we discuss the therapeutic potential of an acellular product such as MSC derived EVs (MSC-EVs) in acute and chronic pathologies.

Mesenchymal stromal cells (MSCs) have been proposed as a new therapeutic strategy to treat congenital and acquired respiratory system diseases. We describe a case report of an 18-month-old male patient with progressive chronic respiratory failure, associated with mutations of the surfactant protein C gene (SFTPC) due to c.289G > T variant p.Gly97Ser (rs927644577) and c.176A > G variant (p.His59Arg), submitted to repeated intravenous infusions of allogeneic bone marrow (BM) MSCs. The clinical condition of the patient was monitored. Immunologic studies before and during MSC treatment were performed. No adverse events related to the MSC infusions were recorded. Throughout the MSC treatment period, the patient showed a growth recovery. Starting the second infusion, the patient experienced an improvement in his respiratory condition, with progressive adaptation to mechanical ventilation. After the third infusion, five hours/die of spontaneous breathing was shown, and after infusion IV, spontaneous ventilation for 24/24 h was recorded. A gradual decrease of lymphocytes and cell subpopulations was observed. No variations in the in vitro T cell response to PHA were determined by MSC treatment as well as for the in vitro B cell response. A decrease in IFN-γ, TNF-α, and IL-10 levels was also detected. Even though we cannot exclude an improvement of pulmonary function due to the physiological maturation, the well-known action of MSCs in the repair of lung tissue, together with the sequence of events observed in our patient, may support the therapeutic role of MSCs in this clinical condition. However, further investigations are necessary to confirm the result and long-term follow-up will be mandatory to confirm the benefits on the pulmonary condition.

In December 2019 in China, after a pneumonia outbreak of unknown etiology, a new RNA virus has been identified and called Sars-CoV-2. Sars-CoV-2 induced severe respiratory infections, with global and rapid epidemic diffusion, designated coronavirus disease 2019 (Covid-19). Sars-CoV-2 infection can lead to severe complications, such as acute respiratory distress syndrome (ARDS) with progression to pulmonary fibrosis. Recent clinical studies described that in patients with severe Covid-19, MSC infusions, promote regenerative and reparative effects with anti-inflammatory and anti-fibrotic action. MSCs do not express ACE2 and TMPRSS2, the two main human receptors for host-pathogen interaction, and are not permissive to in vitro Sars-CoV-2 infection, making them suitable for clinical application. The aim of our study was to evaluate the safety and efficacy of MSCs as cellular therapy in ARDS secondary to Sars-CoV-2 in patients undergoing mechanical ventilation, in order to prevent pulmonary fibrosis. MSCs for infusions are thawed at 2x106/ml cellular concentration. The intravenous infusion protocol consists of two doses of third party allogenic MSCs at 1x106/Kg, 15 day apart. From April 2020, six adult patients median age 65 years, median body weight 80 Kg, in mechanical ventilation for ARDS secondary to Sars-CoV-2 infection have been treated. Early or late adverse events were not recorded. Four out six patients showed a significant gas exchange improvement with extubation within seven days from the first infusion. Our results underline the safety and efficacy of MSC infusions for ARDS patients in mechanical ventilation, supporting the need of a phase I/II clinical trial.

Mesenchymal stromal cells (MSCs) are adult multipotent stem cells that, for their immunomodulatory and reparative/anti-inflammatory properties, are a promising tool in cell therapy. For the treatment of patients, MSCs are in vitro stimulated to proliferate in a non-physiological condition and this situation could lead MSCs to malignant transformation. The clinical application of MSCs requires that the biosafety of these cells must be investigated. The cellular senescence is a crucial mechanism that prevents the growth of cells at risk for neoplastic transformation. The aim of this study was to investigate the capacity of healthy donor bone marrow derived MSCs to enter the senescence phase by evaluating the β-galactosidase activity. We tested 131 MSC batches after long-term in vitro culture, resulting positive for β-gal staining and showing a branched shape morphology typical of senescent cells. They displayed a progressive decline in proliferative capacity and none of them bypassed the senescence. In conclusions, our data indicate that MSCs are not inclined towards spontaneous neoplastic transformation. We believe that the control of MSC capacity to enter senescence is fundamental for quality and safety, considering the relevant interest in the MSC clinical applications.