Mariano Di Trapani

Comparative Study of Immune Regulatory Properties of Stem Cells Derived from Different Tissues.

Allogeneic stem cell (SC)-based therapy is a promising tool for the treatment of a range of human degenerative and inflammatory diseases. Many reports highlighted the immune modulatory properties of some SC types, such as mesenchymal stromal cells (MSCs), but a comparative study with SCs of different origin, to assess whether immune regulation is a general SC property, is still lacking. To this aim, we applied highly standardized methods employed for MSC characterization to compare the immunological properties of bone marrow-MSCs, olfactory ectomesenchymal SCs, leptomeningeal SCs, and three different c-Kit-positive SC types, that is, amniotic fluid SCs, cardiac SCs, and lung SCs. We found that all the analyzed human SCs share a common pattern of immunological features, in terms of expression of activation markers ICAM-1, VCAM-1, HLA-ABC, and HLA-DR, modulatory activity toward purified T, B, and NK cells, lower immunogenicity of inflammatory-primed SCs as compared to resting SCs, and indoleamine-2,3-dioxygenase-activation as molecular inhibitory pathways, with some SC type-related peculiarities. Moreover, the SC types analyzed exert an anti-apoptotic effect toward not-activated immune effector cells (IECs). In addition, we found that the inhibitory behavior is not a constitutive property of SCs, but is acquired as a consequence of IEC activation, as previously described for MSCs. Thus, immune regulation is a general property of SCs and the characterization of this phenomenon may be useful for a proper therapeutic use of SCs.

Differential and transferable modulatory effects of mesenchymal stromal cell-derived extracellular vesicles on T, B and NK cell functions.

Mesenchymal stromal cells (MSCs) are multipotent cells, immunomodulatory stem cells that are currently used for regenerative medicine and treatment of a number of inflammatory diseases, thanks to their ability to significantly influence tissue microenvironments through the secretion of large variety of soluble factors. Recently, several groups have reported the presence of extracellular vesicles (EVs) within MSC secretoma, showing their beneficial effect in different animal models of disease. Here, we used a standardized methodological approach to dissect the immunomodulatory effects exerted by MSC-derived EVs on unfractionated peripheral blood mononuclear cells and purified T, B and NK cells. We describe here for the first time: i. direct correlation between the degree of EV-mediated immunosuppression and EV uptake by immune effector cells, a phenomenon further amplified following MSC priming with inflammatory cytokines; ii. induction in resting MSCs of immunosuppressive properties towards T cell proliferation through EVs obtained from primed MSCs, without any direct inhibitory effect towards T cell division. Our conclusion is that the use of reproducible and validated assays is not only useful to characterize the mechanisms of action of MSC-derived EVs, but is also capable of justifying EV potential use as alternative cell-free therapy for the treatment of human inflammatory diseases.

Notch signalling drives bone marrow stromal cell-mediated chemoresistance in acute myeloid leukemia

Both preclinical and clinical investigations suggest that Notch signalling is critical for the development of many cancers and for their response to chemotherapy. We previously showed that Notch inhibition abrogates stromal-induced chemoresistance in lymphoid neoplasms. However, the role of Notch in acute myeloid leukemia (AML) and its contribution to the crosstalk between leukemia cells and bone marrow stromal cells remain controversial. Thus, we evaluated the role of the Notch pathway in the proliferation, survival and chemoresistance of AML cells in co-culture with bone marrow mesenchymal stromal cells expanded from both healthy donors (hBM-MSCs) and AML patients (hBM-MSCs*). As compared to hBM-MSCs, hBM-MSCs* showed higher level of Notch1, Jagged1 as well as the main Notch target gene HES1. Notably, hBM-MSCs* induced expression and activation of Notch signalling in AML cells, supporting AML proliferation and being more efficientin inducing AML chemoresistance than hBM-MSCs*. Pharmacological inhibition of Notch using combinations of Notch receptor-blocking antibodies or gamma-secretase inhibitors (GSIs), in presence of chemotherapeutic agents, significant lowered the supportive effect of hBM-MSCs and hBM-MSCs* towards AML cells, by activating apoptotic cascade and reducing protein level of STAT3, AKT and NF-κB. These results suggest that Notch signalling inhibition, by overcoming the stromal-mediated promotion of chemoresistance,may represent a potential therapeutic targetnot only for lymphoid neoplasms, but also for AML.

Role of Wnt/β-Catenin Signalling in Acute Myeloid Leukemia (AML) Cell Response to Chemotherapy

Although drug-induced thrombotic microangiopathy (TMA) is commonly reported, evidence for a causal association is uncommonly documented. In this issue of Blood, Kavanagh et al use multiple methods to clearly establish a causal association of type I interferon with TMA.1