Human cord blood reprogrammed into embryonic‐like stem cells

Abstract

Embryonic stem (ES) cell therapies are often promoted as the optimal stem cell source for regenerative medicine applications. Although the first clinical trail involving hES progenitors has been approved, ES cell applications are currently limited by ethical, political and regulatory hurdles. In addition, the use of hES cell‐derived progenitors has been fraught with difficulties associated with immunological incompatibility, due in part to the increase in expression of major histocompatibility complex molecules during differentiation of hES cells. Induced pluripotent stem (iPS) cells could solve both the ethical problem of human embryo use and the immunological rejection problem. Patient‐specific iPSC have been hailed as an enormous development for regenerative medicine since transplantation of the differentiated progeny of these individual iPSC should not be subject to immune rejection when transplanted back into a patient. However, in many instances, a ready to use approach could be desirable, such as for cell therapy of acute conditions or when the patient’s somatic cells are altered as a consequence of a chronic disease or ageing. An alternative could be the generation of healthy iPSC lines with a wide genetic variety rather than specific‐patient iPSC, which will enable broader immune histocompatibility. However, this is not presently feasible as many thousand of hiPS‐cell lines would be required to ensure sufficient diversity. Cord blood (CB) stem cells could represent a new source of cells for the generation of clinically sound iPSC in an allogenic setting. For example, a bank of CB‐iPSC derived from selected donors homozygous for common human leukocyte antigen (HLA) haplotypes, could significantly reduce the number of CB‐iPSC lines needed to provide a perfect HLA match for a large percentage of the population. We have recently reported that the overexpression of only two transcription factors, OCT4 and SOX2, are sufficient to reprogram CB CD133+ cells faster than fibroblasts and keratinocytes. CB‐iPSC showed a differential potential similar to human embryonic stem cells in vitro and in vivo . Following specific in vitro differentiation protocols, CB‐iPSC gave rise also to specialized cell types such as rhythmically beating cardiomyocytes and dopaminergic neurons. The generation of CB‐iPSC lines from thawed CB units, that had been stored frozen for more than 8 years, has excluded the possibility that the standard cryopreservation protocol could affect the reprogramming process. In addition, we have demonstrated that CB cells were properly reprogrammed into pluripotent stem cells from both the expression and the epigenetic point of view. However, a number of technical issues need to be resolved before the iPS technology can be used in a clinical setting. These include the establishment of efficient reprogramming strategies that do not result in genetically modified cells as well as the development of robust protocols for differentiating iPSC to self‐renewing stem cells and lineage‐committed cells. Ultimately, these methods must be adapted to the generation of iPSC under good manufacturing practice conditions.