Allogeneic chondrogenically differentiated human mesenchymal stromal cells do not induce immunogenic responses from T lymphocytes in vitro

Background aims. In regenerative medicine, the use of allogeneic cells could enable the development of "off the shelf" therapies for patients with critical size bone defects, reducing limitations observed with the use of autologous cells, such as cost and time to treat the patient. The idea of the use of allogeneic bone marrow mesenchymal stromal cells (BMSCs) has been of interest in tissue engineering studies. However, little is known about the properties of these cells upon differentiation. Chondrogenically differentiated BMSCs have already been shown to form endochondral bone in immunodeficient and immunocompetent animals. The success of this bone formation is dependent on the host's endogenous cells. This study investigates the interactions between allogeneic chondrogenically differentiated human bone marrow mesenchymal stromal cell (hBMSC) pellets and T lymphocytes in vitro. Methods. Non-chondrogenic (-transforming growth factor (TGF)beta 3) and chondrogenic hBMSC (+TGF beta 3) pellets were directly co-cultured with unstimulated and CD3/CD28-stimulated peripheral blood mononuclear cells (PBMCs) for 7 days. hBMSC pellets from the co-culture were either fixed for histological analysis or quantitative real time polymerase chain reaction (qRT-PCR). PBMCs were harvested for flow cytometry. Results. Flow cytometic analysis revealed that chondrogenically differentiated hBMSC pellets did not alter the number or proliferation of CD4+, CD8+T cells or FoxP3+ T regulatory cells (CD4+CD25+CD127-). Chondrogenic hBMSC pellets did not induce immunogenic responses in unstimulated PBMCs. Infiltrating CD3T cells were found in the matrix of hBMSC pellets. Furthermore, qRT-PCR demonstrated low levels of T-cell activation genes (CD25, CD69, PRF1 and GZMB) in addition to low gene expression levels of the pro-inflammatory gene tumor necrosis factor alpha (TNF alpha) in chondrogenically differentiated hBMSC pellets cultured with unstimulated PBMCs in comparison with non-chondrogenic hBMSC pellets. Conclusions. Collectively the results of this study demonstrate that allogeneic chondrogenically differentiated hBMSC pellets are nonimmunogenic and do not induce the activation of destructive T-cell responses in vitro.