Constraining the Pluripotent Fate of Human Embryonic Stem Cells for Tissue Engineering and Cell Therapy – The Turning Point of Cell-Based Regenerative Medicine

Abstract

To date, the lack of a clinically-suitable source of engraftable human stem/progenitor cells with adequate neurogenic potential has been the major setback in developing safe and effective cell-based therapies for regenerating the damaged or lost CNS structure and circuitry in a wide range of neurological disorders. Similarly, the lack of a clinically-suitable human cardiomyocyte source with adequate myocardium regenerative potential has been the major setback in regenerating the damaged human heart. Given the limited capacity of the CNS and heart for self-repair, there is a large unmet healthcare need to develop stem cell therapies to provide optimal regeneration and reconstruction treatment options to restore normal tissues and function. Derivation of human embryonic stem cells (hESCs) provides a powerful in vitro model system to investigate molecular controls in human embryogenesis as well as an unlimited source to generate the diversity of human somatic cell types for regenerative medicine. However, realizing the developmental and therapeutic potential of hESC derivatives has been hindered by the inefficiency and instability of generating clinically-relevant functional cells from pluripotent cells through conventional uncontrollable and incomplete multi-lineage differentiation. Recent advances and breakthroughs in hESC research have overcome some major obstacles in bringing hESC therapy derivatives towards clinical applications, including establishing defined culture systems for de novo derivation and maintenance of clinical-grade pluripotent hESCs and lineage-specific differentiation of pluripotent hESCs by small molecule induction. Retinoic acid was identified as sufficient to induce the specification of neuroectoderm direct from the pluripotent state of hESCs and trigger a cascade of neuronal lineage-specific progression to human neuronal progenitors and neurons of the developing CNS in high efficiency, purity, and neuronal lineage specificity by promoting nuclear translocation of the neuronal specific transcription factor Nurr-1. Similarly, nicotinamide was rendered sufficient to induce the specification of cardiomesoderm direct from the pluripotent state of hESCs by promoting the expression of the earliest cardiac-specific transcription factor Csx/Nkx2.5 and triggering progression to cardiac precursors and beating cardiomyocytes with high efficiency. This technology breakthrough enables direct conversion of pluripotent hESCs into a large supply of high purity neuronal cells or heart muscle cells with adequate capacity to regenerate CNS neurons and contractile heart muscles for developing safe and effective stem cell therapies. Transforming pluripotent hESCs into fate-restricted therapy derivatives dramatically increases the clinical efficacy of graft-dependent repair and safety of hESC-derived cellular products. Such milestone advances and medical innovations in hESC research allow generation of a large supply of clinical-grade hESC therapy derivatives targeting for major health problems, bringing cell-ba...

The Designation of Human Cardiac Stem Cell Therapy Products for Human Trials

“…Derivation of human embryonic stem cells (hESCs) from the in vitro fertilization (IVF) leftover embryos has brought a new era of cellular medicine for the heart [1][2][3][4][5][6][7]. The intrinsic ability of a hESC to both unlimited self-renew and differentiate into cardiac tissue elements makes it a practically inexhaustible source of replacement cells for the damaged heart.…”

“…The intrinsic ability of a hESC to both unlimited self-renew and differentiate into cardiac tissue elements makes it a practically inexhaustible source of replacement cells for the damaged heart. The hESC cardiac cell therapy derivatives are emerging as a new type of pharmacologic agent of cellular entity in cell-based regenerative medicine because they have direct pharmacologic utility and capacity for human myocardial tissue reconstitution and contractile function restoration that the conventional compound drug of molecular entity lacks [1][2][3][4][5][6][7]. Although a vast sum of government and private funding has been spent on looking for adult alternates, such as reprogramming and trans-differentiation of fibroblasts or mature tissues, so far, only human cardiac stem/precursor/ progenitor cells derived from embryo-originated hESCs have shown such cellular pharmacologic utility and capacity adequate for myocardium regeneration in pharmaceutical development of stem cell therapy for the damaged heart [1][2][3][4][5][6][7].…”

“…In the adult heart, the mature contracting cardiac muscle cells, known as cardiomyocytes, are terminally differentiated and unable to regenerate. There is no evidence that adult stem/ precursor/progenitor cells derived from mature tissues, such as bone marrow, cord blood, umbilical cord, mesenchymal stem cells, patients' heart tissue, placenta, or fat tissue, are able to give rise to the contractile heart muscle cells following transplantation into the heart [1][2][3][4][5][6][7]. To date, the lack of a suitable human cardiomyocyte source with adequate myocardium regenerative potential has been the major setback in regenerating the damaged human heart, either by endogenous cells or by cellbased transplantation or cardiac tissue engineering [1][2][3][4][5][6][7].…”

“…There is no evidence that adult stem/ precursor/progenitor cells derived from mature tissues, such as bone marrow, cord blood, umbilical cord, mesenchymal stem cells, patients' heart tissue, placenta, or fat tissue, are able to give rise to the contractile heart muscle cells following transplantation into the heart [1][2][3][4][5][6][7]. To date, the lack of a suitable human cardiomyocyte source with adequate myocardium regenerative potential has been the major setback in regenerating the damaged human heart, either by endogenous cells or by cellbased transplantation or cardiac tissue engineering [1][2][3][4][5][6][7]. Despite numerous reports about cell populations expressing stem/ precursor/progenitor cell markers identified in the adult hearts, the minuscule quantities and growing evidences indicating that they are not genuine heart cells and that they give rise predominantly to non-functional smooth muscle cells rather than issues for commercial and therapeutic uses: 1) such human stem cells or their cardiac progenies or derivatives must be able to be manufactured in a commercial scale; 2) such human stem cells and their cardiac progenies or derivatives must be able to retain their normality or stability for a long term; and 3) such human stem cells must to be able to differentiate or generate a sufficient number of contractile cardiomyocytes for repair.…”

“…Only a very small fraction of pluripotent hESCs differentiate into cardiomyocytes through spontaneous multi-lineage germ-layer induction in culture [1]. Although such hESC-derived immature cardiomyocytes can be enriched to attenuate the progression of heart failure in acute myocardial infarction model, the grafts generated by cell transplantation have been small and insufficient to restore heart function or to alter adverse remodeling of chronic infarcted models following transplantation [1][2][3][4][5][6][7]. Functional enhancement in preclinical animal models by such hESC-derived cardiomyocytes through conventional multi-lineage germ-layer induction has been limited to mid-term at most, equivalent to perhaps a few months in humans, and there is no evidence that the underlying mechanism depends on the contractile properties of the transplanted human cells [1][2][3][4][5][6][7].…”