Updated publication reference for PubMed record(s): 30785213. Mesenchymal stromal cells (MSCs) with regenerative and immunomodulatory potential are being investigated as a potential therapeutic tool for cartilage lesions. MSCs express a wide variety of bioactive molecules including cytokines, trophic factors, and proteases, which act in a paracrine fashion to modulate the tissue microenvironment. Yet, little is known about the divergence of these signalling molecules between MSCs populations from adult or young tissues. This makes it challenging to decide the optimal source of MSCs for a specific clinical application. In this study, we investigated cell secretomes from cultured human stromal cells harvested from Hoffa’s fat pad (HFPSCs), synovial membrane (SMSCs), umbilical cord (UCSCs) and cartilage (ACs) by quantitative LC-MS/MS proteomics. We also performed multiplex protein arrays and functional assays to compare the constitutive immunomodulatory capabilities of different MSCs. Proteins involved in extracellular matrix degradation and inflammation such as MMPs, IL-17, and complement factors were significantly downregulated in UCSCs compared to other cell types. Additionally, we found enhanced expression of TGF-β1 and PGE2 in UCSCs supernatants. UCSCs were superior in inhibiting peripheral blood mononuclear cells proliferation, migration and TNF-α and IFN-γ secretion compared to ACs, HFPSCs and SMSCs. Although all cell types could repress HLA-DR surface expression and cytokine release by activated macrophages, only UCSCs significantly blocked IL-6 and IL-12 production. Our data demonstrate that stromal cells from umbilical cords display superior anti-inflammatory and immunosuppressive properties than stromal cells from adult tissues. This Allogeneic cell source could potentially be considered as an adjuvant therapy for articular cartilage repair.