Positive effect of human ESC conditioned medium on somatic cell reprogramming

Induced pluripotent stem cells (iPSC), created by reprogramming of somatic cells into embryonic-like state are the latest developments in stem-cell research. These cells have a great potential in research and medicine, however the full exploitation of these cells is hampered by several issues such as derivation efficiency, heterogeneity and safety. Here we describe a simple method to enhance generation of fully reprogrammed human iPSCs from dermal fibroblasts. We have shown that the addition of culture medium that has been previously conditioned by human embryonic stem cells (hESC-CM) at the final stage of reprogramming procedure (≥3rd week) improves the efficiency of somatic cell reprogramming, possibly by promoting the transition of pre-iPSC colonies to a fully reprogrammed state. This approach may offer an alternative to the epigenetic modulators and chemicals method in the generation of safer and more efficient iPSCs. Introduction Several pieces of research including the cloning of Dolly the sheep (Wilmut et al., 1997), put to rest for once and for all a long believed dogma that the cellular patterning of cells during the mammalian embryogenesis is irreversible. This break-through was accomplished due to iPSC technology, a method by which any somatic cell type may be reprogrammed in vitro to a pluripotent-like state by the introduction of specific transcription factors and subsequent culture under ESC-like conditions. Cells generated in such way, referred to as induced pluripotent stem cells (iPSCs), have been proven to be similar to embryonic stem cells in terms of morphology, gene expression and differentiation abilities. Such characteristics have raised hopes for the generation of patient specific iPSCs for biomedical research and clinical applications. Though, before any personalized stem cell-based therapies can be considered, a number of limitations needs to be addressed. The risk of potential mutagenesis due to the genomic insertion of exogenous reprogramming factors has been partially overcomed in recent years by replacing integrating retro- and lentiviruses with transiently transgene-expressing carriers (such as inducible/excisable vectors, adenoviruses), however the slow kinetics coupled with very low efficiency (≤0.01%) (Takahashi et al., 2007, Yu et al., 2007) and heterogeneous nature of emerging iPSC colonies are still significant handicaps for iPSC technology. As part of the undergoing effort to solve these problems we found that hESC-culture medium conditioned with hESC (hESC-CM) improves the efficiency of somatic cell reprogramming possibly by promoting the transition of pre-iPSC colonies to a fully reprogrammed state.