Scientists have devised what they say is a reproducible and efficient virus-free method for reprogramming human lineage-committed cord blood myeloid progenitor cells into induced pluripotent stem cells (hIPSCs). The Johns Hopkins University-led team used electroporation to temporarily permeabilize the cells to plasmids encoding four reprogramming genes, SOX2, OCT4, KLF4, and MYC (the four Yamanaka factors). The transfected cells were then cultured in bone marrow stem cell-conditioned medium to provide the necessary soluble cues.
The achievement, by Elias Zambidis, M.D., and colleagues, follows on from experiments reported by the team last year in which a similar approach was used to transform adult blood cells into heart cells. Importantly, their work to transform cord blood progenitors into iPSCs resulted in up to a 50–60% reprogramming efficiency, compared with just a 0.5% maximum efficiency achieved using other methods.
Notably, the studies indicated that the technique is more effective on lineage-committed CD33+CD45+CD34– myeloid cells than it is on the more primitive hematopoietic stem progenitors, and necessitated both administration of the correct gene set and also presence of the right environmental factors. “The efficient conversion of mature myeloid populations into NANOG+TRA-1-81+ hiPSCs was mediated by synergies between hematopoietic growth factor (GF), stromal activation signals, and episomal Yamanaka factor expression,” they write in PLoS One.
Their analyses in addition suggested that efficient myeloid reprogramming was associated not just with activity of the endogenous Core factor (SOX2-OCT4-NANOG) gene network that initiates and maintains pluripotency, but rather with the expression of GF-activated transcriptional circuits that regulate plasticity in both hematopoietic progenitors and embryonic stem cells (ESC).
“To our knowledge, this study is the first to identify important synergies between hematopoietic regulatory circuits activated by GFs and extrinsic niche factors to efficiently direct the pluripotency induction of lineage-committed myeloid cells,” the investigators state. Their studies are described in a paper titled “Growth Factor-Activated Stem Cell Circuits and Stromal Signals Cooperatively Accelerate Non-Integrated iPSC Reprogramming of Human Myeloid Progenitors.”