Adult human cells maintain a 'memory' when reprogrammed into a stem cell-like state, US scientists have found. The finding suggests the resulting iPS cells are not yet a viable alternative to human embryonic stem cells (ES cells) for modelling or treating disease.
The researchers from the Salk Institute in California found human iPS cells retained DNA methylation patterns - a type of epigenetic marker left on DNA - from their parent adult cells. The lead author of the study, Dr Joseph Ecker, said: 'they look fairly similar [to ES cells], but if you zoom in you find different signatures of what an iPS cell is'. Common among the five iPS cell lines the team examined were hotspots of failed reprogramming. There was also significant variability in reprogramming between iPS cell lines.
The findings agree with work last year by Dr George Daley and colleagues comparing mouse iPS and ES cells. However, the mouse study found the methylation differences between iPS and ES cells could be erased, which the latest study discovered wasn't the case for human cells.
iPS cells are considered an attractive alternative to ES cells as they do not require the destruction of human embryos. 'Embryonic stem cells are considered the gold standard for pluripotency, so we need to know whether - and if so, how - iPS cells differ from ES cells', Dr Ecker said. Dr Ecker and his colleagues hope identifying defect hotspots will spur the development of new techniques that can generate iPS cells more closely resembling ES cells.