Multipotent Mesenchymal Stromal Cells: Possible Culprits in Solid Tumors?
Table 1
Overview on cell types that are present within the tumor microenvironment (based on [7, 59]).
Cell type
Function and contribution to the tumor microenvironment
Factors which contribute to the function
Neutrophil granulocytes
(i) Remodelling of extracellular matrix (ii) Promotion of tumor growth, angiogenesis, and metastasis
(i) MMP (ii) VEGF, TGF-β
T cells
(i) Functionally compromised in the tumor microenvironment (ii) Immunosuppression
IL-10, TGF-β
NK cells
Tumor cell lysis (often immature NK cells infiltrating the tumor)
(Reduced) NKp44/NKp33 expression in tumors
Dendritic cells
Skewed towards immunosuppression (induce regulatory T cells)
TGF-β, IL-10
Tumor associated macrophages
(i) Functionally compromised in the tumor microenvironment (ii) Mostly polarized towards the M2 phenotype (iii) Inhibition of immune cell proliferation
IL-4 (induces M2 phenotype)
Mesenchymal cells/tumor associated fibroblasts
(i) Secretion of tumor growth promoting factors (ii) Remodelling of extracellular matrix
(i) TGF-β, HGF, VEGF (ii) MMP
Endothelial cells/blood vessels
(i) Secretion of VEGF (ii) Formation of new blood vessels
VEGF, PDGF-α
Tumor cells
(i) Immunosuppression (ii) ECM remodeling (iii) Cross-talk with TAF/MSCs and induction
