Adipose tissue-derived stem cells show both immunogenic and immunosuppressive properties after chondrogenic differentiation

Background aims. The chondrogenic differentiation potential of mesenchymal stromal cells (MSC), as well as their immunosuppressive properties, have been studied extensively. So far, only a few studies have addressed the question of whether MSC still retain their immunosuppressive qualities after transdifferentiation. In particular, the expression of immunogenic markers, such as human leukocyte antigen (HLA)-DR, after differentiation has never been investigated. Methods. Chondrogenic transdifferentiation was induced in human adipose tissue-derived stem cell (ADSC) pellet cultures derived from 10 different patients, using 10 ng/mL transforming growth factor (TGF)-beta beta 3. Samples were harvested over a time--course of 28 days and analyzed by immunohistochemistry and reverse transcription (RT)--polymerase chain reaction (PCR). The cytokine levels in the supernatants of the samples were measured semi-quantitatively by dot-blots and quantitatively by enzyme-linked immunosorbant assays (ELISA). Results. Undifferentiated ADSC were negative for chondrogenic markers, as well as HLA-ABC and HLA-DR epitopes in immunofluorescence. In contrast, TGF-beta beta 3-induced pellet cultures showed both expression of chondrogenic differentiation markers, such as transcription factor 9 (Sox 9), collagen type IIa and aggrecan, and an up-regulation of HLA-DR, beginning at day 7 after induction. Interferon-gamma gamma (INF-gamma gamma) is known to up-regulate HLA-DR. Therefore we measured INF-gamma gamma levels in the supernatants of TGF-beta beta 3-induced pellets and, indeed, INF-gamma gamma was up-regulated during chondrogenesis in ADSC pellet cultures. However, both undifferentiated and TGF-beta beta 3-induced ADSC also showed expression of immunosuppressive HLA-G and interleukin (IL)-10 up-regulation. Conclusions. These results suggest that the immunogenicity of adult stem cell-derived tissue should be tested in animal models before clinical trials for allogeneic engineered tissue are considered.