Timothy B. Campbell

Rapid mobilization of murine and human hematopoietic stem and progenitor cells with AMD3100, a CXCR4 antagonist

Improving approaches for hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC) mobilization is clinically important because increased numbers of these cells are needed for enhanced transplantation. Chemokine stromal cell derived factor-1 (also known as CXCL12) is believed to be involved in retention of HSCs and HPCs in bone marrow. AMD3100, a selective antagonist of CXCL12 that binds to its receptor, CXCR4, was evaluated in murine and human systems for mobilizing capacity, alone and in combination with granulocyte colony-stimulating factor (G-CSF). AMD3100 induced rapid mobilization of mouse and human HPCs and synergistically augmented G-CSF–induced mobilization of HPCs. AMD3100 also mobilized murine long-term repopulating (LTR) cells that engrafted primary and secondary lethally-irradiated mice, and human CD34+ cells that can repopulate nonobese diabetic-severe combined immunodeficiency (SCID) mice. AMD3100 synergized with G-CSF to mobilize murine LTR cells and human SCID repopulating cells (SRCs). Human CD34+ cells isolated after treatment with G-CSF plus AMD3100 expressed a phenotype that was characteristic of highly engrafting mouse HSCs. Synergy of AMD3100 and G-CSF in mobilization was due to enhanced numbers and perhaps other characteristics of the mobilized cells. These results support the hypothesis that the CXCL12-CXCR4 axis is involved in marrow retention of HSCs and HPCs, and demonstrate the clinical potential of AMD3100 for HSC mobilization.

Dipeptidylpeptidase 4 negatively regulates colony-stimulating factor activity and stress hematopoiesis

Enhancement of hematopoietic recovery after radiation, chemotherapy, or hematopoietic stem cell (HSC) transplantation is clinically relevant. Dipeptidylpeptidase (DPP4) cleaves a wide variety of substrates, including the chemokine stromal cell-derived factor-1 (SDF-1). In the course of experiments showing that inhibition of DPP4 enhances SDF-1–mediated progenitor cell survival, ex vivo cytokine expansion and replating frequency, we unexpectedly found that DPP4 has a more general role in regulating colony-stimulating factor (CSF) activity. DPP4 cleaved within the N-termini of the CSFs granulocyte-macrophage (GM)-CSF, G-CSF, interleukin-3 (IL-3) and erythropoietin and decreased their activity. Dpp4 knockout or DPP4 inhibition enhanced CSF activities both in vitro and in vivo. The reduced activity of DPP4-truncated versus full-length human GM-CSF was mechanistically linked to effects on receptor-binding affinity, induction of GM-CSF receptor oligomerization and signaling capacity. Hematopoiesis in mice after radiation or chemotherapy was enhanced in Dpp4−/− mice or mice receiving an orally active DPP4 inhibitor. DPP4 inhibition enhanced engraftment in mice without compromising HSC function, suggesting the potential clinical utility of this approach.

AMD3100 and CD26 Modulate Mobilization, Engraftment, and Survival of Hematopoietic Stem and Progenitor Cells Mediated by the SDF‐1/CXCL12‐CXCR4 Axis

Abstract:  The chemokine stromal cell‐derived factor‐1 (SDF‐1/CXCL12) and its receptor, CXCR4, are involved in a number of facets of the regulation of hematopoiesis at the level of hematopoietic stem (HSCs) and progenitor (HPCs) cells. Modulation of this ligand–receptor interaction may be of clinical utility. We now report that: (1) the CC chemokine, macrophage inflammatory protein‐1α (MIP‐1α/CCL3) synergizes with AMD3100 (an antagonist of the binding of SDF‐1/CXCL12 to CXCR4) to rapidly mobilize HPCs to the blood of mice; moreover, the combination of granulocyte colony‐stimulating factor (G‐CSF) with AMD3100 and MIP‐1α/CCL3, given in a specific sequence, mobilizes the greatest number of HPCs compared to any combination of two of these mobilizing agents; (2) pretreatment of recipient mice with Diprotin A, an inhibitor of CD26/Dipeptidylpeptidase IV (DPPIV), enhances the competitive HSCs repopulating capacity of untreated donor cells; (3) the survival‐enhancing effects of SDF‐1/CXCL12 on HPCs subjected in vitro to delayed addition of growth factors (GFs) are mediated in part through the cell cycle‐related proteins p21cip1/waf1 (as assessed using p21cip1/waf1−/− and +/+ mice) and Mad2 (using Mad2 +/− and +/+ mice); and (4) deletion of CD26/DPPIV on mouse bone marrow cells increases the survival‐enhancing effects of SDF‐1/CXCL12 on HPCs. These results demonstrate the means to increase the mobilization of HPCs, the engrafting capability of HSCs, and responsiveness of HPCs to the survival‐enhancing activity of SDF‐1/CXCL12, effects that may be of practical value.

Overexpression of Rheb2 enhances mouse hematopoietic progenitor cell growth while impairing stem cell repopulation.

Molecular mechanisms preserving hematopoietic stem cell (HSC) self-renewal by maintaining a balance between proliferation, differentiation, and other processes are not fully understood. Hyperactivation of the mammalian target of rapamycin (mTOR) pathway, causing sustained proliferative signals, can lead to exhaustion of HSC repopulating ability. We examined the role of the novel ras gene Rheb2, an activator of the mTOR kinase, in colony-forming ability, survival, and repopulation of immature mouse hematopoietic cells. In a cell line model of mouse hematopoietic progenitor cells (HPCs), we found enhanced proliferation and mTOR signaling in cells overexpressing Rheb2. In addition, overexpression of Rheb2 enhanced colony-forming ability and survival of primary mouse bone marrow HPCs. Expansion of phenotypic HSCs in vitro was enhanced by Rheb2 overexpression. Consistent with these findings, Rheb2 overexpression transiently expanded phenotypically defined immature hematopoietic cells after in vivo transplantation; however, these Rheb2-transduced cells were significantly impaired in overall repopulation of primary and secondary congenic transplantation recipients. Our findings suggest that HPCs and HSCs behave differently in response to growth-promoting signals stimulated by Rheb2. These results may have value in elucidating mechanisms controlling the balance between proliferation and repopulating ability, a finding of importance in clinical uses of HPCs/HSCs.

Ex vivo Rapamycin treatment of human cord blood CD34+ cells enhances their engraftment of NSG mice

Since cord blood (CB) has become a commonly used source of transplantable hematopoietic stem (HSC) and hematopoietic progenitor cells (HPC), there has been a need to overcome the limited HSC and HPC numbers available to transplant from a single CB, especially for adult recipients. Our laboratory previously demonstrated that Rheb2 overexpression significantly impaired the repopulating ability of HSC. Since overexpression of Rheb2 leads to increased signaling through mTOR, we examined the effect of the mTOR inhibitor rapamycin ex vivo on cytokine expanded CD34(+) CB cells for the engraftment of these cells in non-obese diabetic, severe combined immunodeficient, IL-2 receptor γ chain null (NSG) mice. We observed significant enhancement in engraftment of the CB treated ex vivo with cytokines in the presence of rapamycin prior to transplant, effects seen in primary as well as secondary transplants. These pre-clinical results suggest a positive role for rapamycin during ex vivo culture of CB SCID repopulating cells/HSC.

Identification of parameters required for efficient lentiviral vector transduction and engraftment of human cord blood CD34(+) NOD/SCID-repopulating cells.

OBJECTIVE Human cord blood (CB) is a potential source of hematopoietic stem cells (HSC) for gene therapy to treat patients with hematopoietic disorders. However, limited numbers of CB CD34(+) cells, low transduction efficiency with lentiviral vectors (LVs), and low engraftment efficiency of nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cells (SRC), a measure of HSC, are blocks to this procedure. To optimize culture and transduction conditions, we compared various lengths of time for prestimulation before transduction, transduction duration, and posttransduction cell culture. MATERIALS AND METHODS We used a LV to transduce human CB CD34(+) cells followed by engraftment into NOD/SCID mice. We evaluated the effects of prestimulation and transduction time and optimized ex vivo cell culture duration before transplantation. RESULTS We were able to achieve up to 40% transduction efficiency and up to 50% engraftment efficiency of SRC in CB CD34(+) cells when CB CD34(+) cells were either not prestimulated or prestimulated in 1% fetal bovine serum medium for 1 hour, followed by 5 hours transduction and 3 days culture in a cocktail of growth factors after transduction. No apparent functional changes of CB CD34(+) cells were noted under these conditions. CONCLUSION This gene-transduction/cell-expansion protocol is the first systematic study to optimize prestimulation time, transduction time, and, very importantly, ex vivo culture time after transduction, and may be of use for LV gene transduction in a gene therapy setting.

Modulating the Interaction of Stromal-cell-derived Factor-1/CXCL12 and its Receptor, CXCR4, for Enhanced Mobilisation, Homing and Engraftment of Haematopoietic Stem Cells

Normal blood cell production – haematopoiesis – is crucial for the maintenance of health.1 Haematopoiesis is initiated through rare populations of haematopoietic stem (HSC) and progenitor (HPC) cells that give rise to all blood-forming elements: HSCs/HPCs are found in the bone marrow of adults, where they are produced and nurtured. HSCs/HPCs are also found in high numbers in umbilical cord blood (CB) at birth, and circulate in the peripheral blood of adults – although in very low numbers. Numbers of HSCs/HPCs in adult blood can be enhanced by mobilising them out of the bone marrow into the circulation by agents such as granulocyte colony-stimulating factor (G-CSF). Because normal HSCs/HPCs can be used in a transplant setting to cure non-malignant and malignant blood-cell – as well as other non-blood-cell – disorders, knowledge of how HSC/HPC movement is regulated has clinical impact.