Immunogenicity of Induced Pluripotent Stem Cells

Induced pluripotent stem (iPS) cells, which are produced by reprogramming fully differentiated adult cells back to an embryonic-like state by expression of specific genes, have important therapeutic potential. As iPS cells are derived entirely from the patient, one hoped-for advantage of using them in therapy is that there should be no immune rejection. Now it seems this might not be the case. In experiments in which iPS cells were reprogrammed using a retroviral or non-integrative episomal approach and then transplanted into mice, teratoma cells derived from the iPS cells were rejected by the immune system, even in syngeneic recipients. This finding suggests that altered gene expression in some cells differentiated from iPS cells can induce T-cell-dependent immune responses. The authors suggest that the immunogenicity of therapeutically valuable cells derived from patient-specific iPS cells should be evaluated before they are used in any clinical applications. Induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells with defined factors, hold great promise for regenerative medicine as the renewable source of autologous cells1,2,3,4,5. Whereas it has been generally assumed that these autologous cells should be immune-tolerated by the recipient from whom the iPSCs are derived, their immunogenicity has not been vigorously examined. We show here that, whereas embryonic stem cells (ESCs) derived from inbred C57BL/6 (B6) mice can efficiently form teratomas in B6 mice without any evident immune rejection, the allogeneic ESCs from 129/SvJ mice fail to form teratomas in B6 mice due to rapid rejection by recipients. B6 mouse embryonic fibroblasts (MEFs) were reprogrammed into iPSCs by either retroviral approach (ViPSCs) or a novel episomal approach (EiPSCs) that causes no genomic integration. In contrast to B6 ESCs, teratomas formed by B6 ViPSCs were mostly immune-rejected by B6 recipients. In addition, the majority of teratomas formed by B6 EiPSCs were immunogenic in B6 mice with T cell infiltration, and apparent tissue damage and regression were observed in a small fraction of teratomas. Global gene expression analysis of teratomas formed by B6 ESCs and EiPSCs revealed a number of genes frequently overexpressed in teratomas derived from EiPSCs, and several such gene products were shown to contribute directly to the immunogenicity of the B6 EiPSC-derived cells in B6 mice. These findings indicate that, in contrast to derivatives of ESCs, abnormal gene expression in some cells differentiated from iPSCs can induce T-cell-dependent immune response in syngeneic recipients. Therefore, the immunogenicity of therapeutically valuable cells derived from patient-specific iPSCs should be evaluated before any clinic application of these autologous cells into the patients.