RESUMO
PURPOSE: Due to their unique capacity to self-renew and for multiple differentiation, stem cells are considered potent candidates for cell replacement therapy in many devastating diseases. However, studies on immune rejection, which is a major problem facing successful stem cell therapy, are rare. Thus, we examined MHC expression of human stem cells and effects of IFN-gamma on the MHC class I expression of the cells in order to determine whether human stem cells might be rejected after transplantation. METHODS: The MHC antigen expressions of human embryonic neural stem cell line (HB1.F3) and human breast epithelial stem cell line (M13SV1) were examined by RT-PCR and FACS. The effects of varying concentrations of IFN-gamma and of varying incubation times with IFN-gamma on the expression of MHC class I antigens in these stem cell lines were also examined by FACS. RESULTS: The results show low expression levels of MHC class I antigens on surfaces of these cells. A dramatic induction of MHC class I expression was observed when the cells were treated with IFN-gamma. Maximal induction of MHC class I antigen expression in HB1.F3 and M13SV1 cells was observed at above the concentrations of 20 ng/mL and 5 ng/mL of IFN-gamma 48 h after treatment, respectively. Elevated MHC class I levels in HB1.F3 and M13SV1 cells were sustained for 48 h and 72 h after withdrawing IFN-gamma, respectively. CONCLUSION: These results suggest that human stem cells express high levels of MHC class I antigens, and thus may be rejected on transplantation unless they are modified. Therefore, in addition to studies on stem cell differentiation, studies on overcoming the immunological barriers to stem cell transplantation are prerequisite for successful clinical application of stem cell therapy.