Respiratory Syncytial Virus-Infected Mesenchymal Stem Cells Regulate Immunity via Interferon Beta and Indoleamine-2,3-Dioxygenase

Abstract

Respiratory syncytial virus (RSV) has been reported to infect human mesenchymal stem cells (MSCs) but the consequences are poorly understood. MSCs are present in nearly every organ including the nasal mucosa and the lung and play a role in regulating immune responses and mediating tissue repair. We sought to determine whether RSV infection of MSCs enhances their immune regulatory functions and contributes to RSV-associated lung disease. RSV was shown to replicate in human MSCs by fluorescence microscopy, plaque assay, and expression of RSV transcripts. RSV-infected MSCs showed differentially altered expression of cytokines and chemokines such as IL-1β, IL6, IL-8 and SDF-1 compared to epithelial cells. Notably, RSV-infected MSCs exhibited significantly increased expression of IFN-β (~100-fold) and indoleamine-2,3-dioxygenase (IDO) (~70-fold) than in mock-infected MSCs. IDO was identified in cytosolic protein of infected cells by Western blots and enzymatic activity was detected by tryptophan catabolism assay. Treatment of PBMCs with culture supernatants from RSV-infected MSCs reduced their proliferation in a dose dependent manner. This effect on PBMC activation was reversed by treatment of MSCs with the IDO inhibitors 1-methyltryptophan and vitamin K3 during RSV infection, a result we confirmed by CRISPR/Cas9-mediated knockout of IDO in MSCs. Neutralizing IFN-β prevented IDO expression and activity. Treatment of MSCs with an endosomal TLR inhibitor, as well as a specific inhibitor of the TLR3/dsRNA complex, prevented IFN-β and IDO expression. Together, these results suggest that RSV infection of MSCs alters their immune regulatory function by upregulating IFN-β and IDO, affecting immune cell proliferation, which may account for the lack of protective RSV immunity and for chronicity of RSV-associated lung diseases such as asthma and COPD.

Current status of cell-based therapies for respiratory virus infections: applicability to COVID-19

“…This can occur rapidly following exposure of uninfected MSCs [23] and virus-infected MSCs may thus not be functionally effective at stopping virus replication and lung inflammation. [24][25][26][27]. BM-MSCs express influenza virus alpha-2,3 and alpha-2,6 sialic acid receptors on their cell surfaces and can support replication of both avian H1N1 and H9N5 influenza strains.…”

“…[26] The respiratory syncytial virus (RSV) can also infect MSCs modifying immune cell proliferation and activity. [27] As such, depending on the virus type and the level of expression or percentage of MSCs expressing the virus receptor, MSCs may get infected if infused into a patient with an ongoing respiratory virus infection. How this would affect potential beneficial effects remains to be determined.…”

Contribution of IDO to human respiratory syncytial virus infection

“…It has been suggested that the inhibition of IDO activity may improve the immune response against some viral pathogens . Inactivation of IDO can reverse the immunosuppressive effects induced by its activity.…”

Gene editing as a promising approach for respiratory diseases

“…They found that the loss of Grhl2 inhibited HBE cells to differentiate into multiciliated cells, and organoid morphogenesis and reduced the mRNA level of both Notch and ciliogenesis genes, indicating that the Grhl2 plays an important role in epithelial morphogenesis and differentiation of the airway epithelium. Cheung et al used CRISPR/Cas9 to knock out the indoleamine-2,3-dioxygenase ( IDO ) gene in human mesenchymal stem cells (MSC) 78. They found that the proliferation of peripheral blood mononuclear cells treated with conditioned media from infected IDO -knockout MSCs was reduced compared with the control MSCs.…”