Overall, it remains unclear whether the varying results reflect the differing features of each approach, including differences in the host (age), in the MSCs (source, number, route of administration), and in the virus-specific inflammatory patterns. Infection of the administered MSCs by the viruses, particularly the avian influenza viruses, might explain the lack of effectiveness observed in some in vivo studies, but MSC infection after their administration in vivo has not yet been investigated. In order to bypass the impact of viruses on MSCs, extracellular vesicles might be an option for further studies. Clearly, further pre-clinical studies must be done to evaluate the infectiveness of MSCs by coronaviruses and the impact of MSCs in coronavirus-induced lung injury models.