Abstract
Transplantation of hematopoietic stem cells (HSCs) is a well-established therapeutic approach for numerous disorders. HSCs are typically derived from bone marrow or peripheral blood after cytokine-induced mobilization. Umbilical cord blood (CB) represents an appealing alternative HSC source, but the small amounts of the individual CB units have limited its applications. The availability of strategies for safe ex vivo expansion of CB-derived HSCs (CB-HSCs) may allow to extend the use of these cells in adult patients and to avoid the risk of insufficient engraftment or delayed hematopoietic recovery.Here we describe a system for the ex vivo expansion of CB-HSCs based on their transient exposure to a recombinant TAT-BMI-1 chimeric protein. BMI-1 belongs to the Polycomb family of epigenetic modifiers and is recognized as a central regulator of HSC self-renewal. Recombinant TAT-BMI-1 produced in bacteria was able to enter the target cells via the HIV TAT-derived protein transduction peptide covalently attached to BMI-1, and conserved its biological activity. Treatment of CB-CD34+ cells for 3 days with repeated addition of 10 nM purified TAT-BMI-1 significantly enhanced total cell expansion as well as that of primitive hematopoietic progenitors in culture. Importantly, TAT-BMI-1-treated CB-CD34+ cells displayed a consistently higher rate of multi-lineage long-term repopulating activity in primary and secondary xenotransplants in immunocompromised mice. Thus, recombinant TAT-BMI-1 may represent a novel, effective reagent for ex vivo expansion of CB-HSC for therapeutic purposes.
Highlights
Hematopoietic stem cells (HSCs) are unquestionably the best-characterized somatic stem cells, and their transplant is routinely employed in clinical practice
The fusion protein was produced in bacteria, purified as detailed below, and used to stimulate umbilical cord blood-derived CD34+ growing in the presence of cytokines that induce their proliferation (Figure 1B)
In Drosophila, PRC1 is composed of five core subunits, designated Polycomb (Pc), Polyhomeotic (Ph), Posterior sex combs (Psc), Sex Comb on Midleg (Scm) and Sex combs extra (Sce/Ring)
Summary
Hematopoietic stem cells (HSCs) are unquestionably the best-characterized somatic stem cells, and their transplant is routinely employed in clinical practice. Bone marrow (BM) initially represented the sole source of HSCs for transplantation, but in more recent years umbilical cord blood (CB), as well as peripheral blood of donors treated with cytokines that induce egress of HSCs from the www.impactjournals.com/oncotarget bone marrow (mPB), have been recognized as convenient alternative sources of stem cells [3, 4]. In this regard, cord blood is attractive owing to the availability of massive collections of cryopreserved samples and to the relative abundance of stem cells with extensive self-renewal potential. While improvements of engraftment and longer overall and leukemia-free survival were reported [8], only one of the two units is typically observed to provide long-term hematopoiesis (single unit dominance)
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