A novel role of CD73-IFNγ signalling axis in human mesenchymal stromal cell mediated inflammatory macrophage...

Immunomodulation is the predominant mechanism via which Mesenchymal stromal cells (MSCs) mediate their therapeutic benefits. However, inconsistent success in numerous clinical trials warrants a better understating of the molecular mechanisms regulating their immunomodulatory properties. CD73, an ecto-5'-nucleotidase is abundantly expressed by MSCs, however its precise role in regulating their immunomodulatory properties is still elusive. The present study explored the role of CD73 in Interferon-gamma (IFNγ) sensing and in turn their ability to suppress "inflammatory" M1 macrophages.

CD73 knockdown MSCs (CD73-KDN) were initially assessed for expression of immunoregulatory molecules and IFNγ sensing ability by analysing expression of IFNγ signalling downstream targets such as pSTAT-1, Interferon-Stimulated Genes (ISG) and Indoleamine 2,3-dioxygnease (IDO), a prototypic IFNγ-induced immunomodulator. Next CD73-KDN MSCs were co-cultured with inflammatory M1 macrophages and evaluated for their ability to suppress them. To delineate the contributory role of CD73 and IFNγ signalling downstream target IDO, they were overexpressed independently in CD73-KDN MSCs and re-evaluated for their ability to suppress M1 macrophages.

CD73-KDN MSCs exhibited reduced expression of immunoregulatory molecules and were refractory to IFNγ signalling as indicated by attenuated expression of pSTAT-1, Interferon-Stimulated Genes (ISG) and Indoleamine 2,3-dioxygnease (IDO) upon IFNγ exposure. Since sensing of inflammation is critical for MSC mediated immunomodulation, CD73-KDN MSCs were functionally evaluated for their ability to immune-modulate "inflammatory" M1 macrophages wherein they failed to suppress M1 macrophages. Interestingly, ectopic expression of either CD73 or IFNγ signalling target IDO1 in CD73-KDN MSCs restored their ability to suppress M1 macrophages, establishing the importance of CD73-IFNγ signalling axis in MSC-mediated inflammatory macrophage suppression.

The present study uncovers the unexplored role of CD73-IFNγ axis in MSC-mediated M1 macrophage suppression. MSC-educated macrophages are the actual immune-modulators at MSC transplant sites, thus CD73 can serve as a key immune-potency marker for benchmarking therapeutically relevant MSCs.