Effect of Aging and 5-Fluorouracil Treatment on Bone Marrow Stem Cell Dynamics

Industrialized GMP Production of CD34+ Cells (ProtheraCytes®) at Clinical Scale for Treatment of Ischemic Cardiac Diseases Is Feasible and Safe

Regenerative medicine now needs to pass a crucial turning point, from academic research to the market. Several sources/types of cells have been experimented with, more or less successfully. CD34⁺ cells have demonstrated multipotent or even pluripotent capacities, making them good candidates for regenerative medicine, particularly for treating heart diseases. Strongly encouraged by the results we achieved in a pilot study using CD34⁺ stem cells in patients with poor-prognosis acute myocardial infarcts (AMIs), we soon began the development of an industrialized platform making use of a closed automated device (StemXpand^®) and a disposable kit (StemPack^®) for the large-scale expansion of CD34⁺ cells with reproducible good manufacturing practice (GMP). This scalable platform can produce expanded CD34⁺ cells (ProtheraCytes^®) of sufficient quality that, interestingly, express early markers of the cardiac and endothelial pathways and early cardiac-mesoderm markers. They also contain CD34⁺ pluripotent cells characterized as very small embryonic-like stem cells (VSELs), capable of differentiating under appropriate stimuli into different tissue lineages, including endothelial and cardiomyocytic ones.

Very small embryonic-like stem cells (VSELs) regenerate whereas mesenchymal stromal cells (MSCs) rejuvenate diseased reproductive tissues

Compared to embryonic and induced pluripotent stem cells, mesenchymal stem/stromal cells (MSCs) have made their presence felt with good therapeutic promise and safety profile. Transplanting MSCs has successfully helped to reverse infertility and resulted in live births in animal models and also in humans. But the underlying mechanism for their therapeutic potential is not yet clear. MSCs are not pluripotent and hence lack plasticity to differentiate into multiple adult cell types. They rather act as 'paracrine providers' to the tissue-resident stem cells since similar beneficial effects are also observed when their secretome (microvesicles or exosomes) is transplanted. Cytokines, growth factors, signaling lipids, mRNAs, and miRNAs secreted by MSCs enables tissue-resident stem cells to undergo differentiation into specific cell types. Tissue-resident stem cells include pluripotent, very small embryonic-like stem cells (VSELs) and progenitors [spermatogonial (SSCs), ovarian (OSCs) and endometrial (EnSCs) stem cells in testes, ovary and uterus respectively] which function in a subtle manner to maintain life-long tissue homeostasis and regenerate damaged (non-functional) reproductive tissues by differentiating into sperm, oocytes and endometrial epithelial cells respectively. Similar to restoring spermatogenesis, primordial follicles numbers are increased upon transplanting MSCs. Published literature suggests that MSCs do not differentiate into epithelial cells in the endometrium. Nuclear OCT-4 positive VSELs and cytoplasmic OCT-4, AXIN2 and KERATIN-19 positive epithelial progenitors have a greater role during endometrial regeneration. We propose, transplantation of MSCs simply provides growth factors/cytokines essential for the tissue-resident stem/progenitor cells to undergo differentiation into sperm, eggs and endometrial epithelial cells in the reproductive tissues.

Lead in Synergism With IFNγ Acts on Bone Marrow-Resident Macrophages to Increase the Quiescence of Hematopoietic Stem Cells

Lead (Pb) is a highly toxic heavy metal that broadly exists in our living environment. Although Pb has been shown to influence the development of immune cells, to date, the impact of Pb on hematopoietic stem cells (HSCs) in the bone marrow (BM) remains unknown. As people are ubiquitously exposed to Pb and HSC are essential for human health, understanding the impact of Pb on HSC is significant for public health. In this study, we found that wild-type B6 mice treated with 1250 ppm Pb, but not 125 ppm Pb via drinking water for 8 weeks had increased quiescence of HSC in the BM. Functional analyses demonstrated that wild-type mice treated with 1250 ppm Pb had increased potential for HSC to repopulate the immune system and engraft to the niche in the BM under a competitive chimeric microenvironment of lethally irradiated recipients. Moreover, we found that Pb-increased quiescence of HSC critically relied on a synergetic action of Pb and interferon γ (IFNγ) on BM-resident macrophages (BM-MΦ), but not a direct action of Pb on HSC. Specifically, in steady state, BM-MΦ promoted HSC proliferation; and upon Pb treatment, IFNγ was induced in the BM, and thereafter Pb in synergism with IFNγ acted on BM-MΦ to cause BM-MΦ to become suppressive for HSC proliferation, thus leading to increased quiescence of HSC. Our study suggests that Pb increased the quiescence of HSC via a synergetic action of Pb and IFNγ on BM-MΦ, which was previously unrecognized toxicity of Pb.