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Comment on “Transplantation of undifferentiated murine embryonic stem cells in the heart: teratoma formation and immune response”

The recently published manuscript by Nussbaum et al. (1) describes teratoma formation and the generation of a host immune response following transplantation of undifferentiated murine embryonic stem cells into the heart. These are important findings, emphasizing the hurdles that need to be overcome before embryonic stem cell therapy can become a clinical reality. We thought it proper to remind the readership of The FASEB Journal of our study detailing undifferentiated embryonic stem cell transplantation into the heart published in 2005 (2). In this study, we presented evidence that undifferentiated embryonic stem cells transplanted into the heart both form teratomas and elicit an immune response by the host. We specifically classified the immune response by examining cellular infiltrates into the heart and presented proof of teratoma formation in both syngeneic and allogeneic recipients. We were somewhat surprised, then, that Dr. Nussbaum’s manuscript does not refer to this previously published work while presenting similar conclusions to those put forth by our study.