Therapeutic implications of human umbilical cord derived mesenchymal stromal cells in acute lung injury associated with Influenza A/H5N1 infection

Abstract

Highly pathogenic avian influenza viruses can cause severe forms of acute lung injury (ALI) in humans, where pulmonary flooding compromises gaseous exchange ultimately ending in respiratory failure. To date, there are no effective treatments available for ALI. Therapeutic benefits of mesenchymal stromal cells derived from bone marrow (BM-MSCs) in influenza induced ALI models have been widely demonstrated mainly through immunomodulation and secretory soluble factors that restore the damaged alveolar epithelium. However, clinical application is impractical and limited by declining efficacy with increase in donor age. MSCs derived from human umbilical cord (UC-MSCs) have less limitations and are of particular interest due to superior immunomodulatory capacities and growth factor secretion, which may translate into greater therapeutic effects in ALI.

This project aims to investigate the therapeutic efficacy of UC-MSCs and its constituents in highly pathogenic avian influenza H5N1 human in vitro and mouse in vivo models of ALI. BM-MSCs were also included in the in vitro experiments to compare and elucidate mechanistic differences between the two MSC types.

UC-MSCs restored two major mechanisms of pulmonary edema formation; alveolar fluid clearance (AFC) and alveolar protein permeability (APP) of H5N1-infected primary human alveolar epithelial cells (AECs) more effectively than BM-MSCs. In addition, UC-MSCs exerted greater effects on epithelial ion channel expression, suppression of pro-inflammatory cytokines and chemokines, up-regulation of anti-inflammatory cytokines of AECs. Next, UC-MSCs were applied in a young mouse model of highly pathogenic avian influenza infection. Despite UC-MSCs showing promising results and outperforming BM-MSCs in many aspects of the in vitro model, UC-MSCs only marginally improved survival and body weight of H5N1-infected mice compared with fibroblast treatment.

Conditioned UC-MSC medium recapitulated effects of its parent MSC on impaired AFC and APP of H5N1-infected primary human AECs, and performed better than conditioned BM-MSC medium. Exosomes were also successfully isolated from UC-MSCs and applied to the in vitro model where they were found to be as effective as UC-MSCs themselves. Analysis of conditioned MSC medium and results from mechanistic studies showed that the greater efficacy of UC-MSCs can be partly attributed to greater secretion of angiopoietin-1 (Ang-1) and hepatocyte growth factor (HGF). Recombinant Ang-1 or HGF restored AFC and APP and exerted greater effects together, but to a lesser degree than UC-MSCs, strongly suggesting involvement of other key soluble factors. This was also shown with Ang-1 or HGF silenced UC-MSCs. In summary, data presented here suggest that UC-MSCs confer functional advantages over conventional BM-MSCs and hold great potential towards the treatment of influenza-induced ALI. The major findings of this project forms the preliminary basis of future preclinical and clinical studies involving UC-MSCs, conditioned UC-MSC medium or its key soluble factors, and UC-MSC derived exosomes as potential therapeutic products for severe human influenza disease.