Osteogenic Differentiation of Human Periodontal Ligament Stromal Cells Influences Their Immunosuppressive Potential toward Allogenic CD4⁺ T Cells

The differentiation ability of human periodontal ligament mesenchymal stromal cells (hPDL-MSCs) in vivo is limited; therefore, some studies considered strategies involving their pre-differentiation in vitro. However, it is not known how the differentiation of hPDL-MSCs influences their immunomodulatory properties. This study investigated how osteogenic differentiation of hPDL-MSCs affects their ability to suppress CD4(+) T-lymphocyte proliferation. hPDL-MSCs were cultured for 21 days in osteogenic differentiation or standard culture media. Allogeneic CD4(+) T lymphocytes were co-cultured with undifferentiated and differentiated cells in the presence or absence of interferon (IFN)-gamma, interleukin (IL)-1 beta or tumor necrosis factor (TNF)-alpha, and their proliferation and apoptosis were measured. Additionally, the effects of these cytokines on the expression of immunomodulatory or pro-inflammatory factors were investigated. Our data show that osteogenic differentiation of hPDL-MSCs reduced their ability to suppress the proliferation of CD4(+) T lymphocytes in the presence of IFN-gamma and enhanced this ability in the presence of IL-1 beta. These changes were accompanied by a slightly decreased proportion of apoptotic CD4(+) in the presence of IFN-gamma. The osteogenic differentiation was accompanied by decreases and increases in the activity of indoleamine-2,3-dioxygenase in the presence of IFN-gamma and IL-1 beta, respectively. The basal production of interleukin-8 by hPDL-MSCs was substantially increased upon osteogenic differentiation. In conclusion, this study suggests that pre-differentiation strategies in vitro may impact the immunomodulatory properties of hPDL-MSCs and subsequently affect their therapeutic effectiveness in vivo. These findings provide important insights for the development of MSC-based therapies.