Efficient Transplantation via Antibody-Based Clearance of Hematopoietic Stem Cell Niches

Institute of Stem Cell Biology and Regenerative Medicine, Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Science (Impact Factor: 33.61). 11/2007; 318(5854):1296-9. DOI: 10.1126/science.1149726
Source: PubMed


Upon intravenous transplantation, hematopoietic stem cells (HSCs) can home to specialized niches, yet most HSCs fail to engraft
unless recipients are subjected to toxic preconditioning. We provide evidence that, aside from immune barriers, donor HSC
engraftment is restricted by occupancy of appropriate niches by host HSCs. Administration of ACK2, an antibody that blocks
c-kit function, led to the transient removal of >98% of endogenous HSCs in immunodeficient mice. Subsequent transplantation
of these mice with donor HSCs led to chimerism levels of up to 90%. Extrapolation of these methods to humans may enable mild
but effective conditioning regimens for transplantation.

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Available from: Agnieszka Czechowicz, Nov 03, 2014
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    • "Using a highresolution fluorescence-based imaging platform (Guezguez et al., 2013), human-specific CD45 + CD34 + cells could be sensitively and accurately detected, paralleling our flow 2013), and in this study we extend these observations by reporting that LSC-enriched populations share an equivalent spatial and functional distribution in BM. Critically, we show that hematopoietic stem and progenitor cells (HSPCs) can rival leukemia-initiating cells (L-ICs) to populate vacant sites within the BM, which has been described to contain a limited number of saturable niches (Colvin et al., 2004; Czechowicz et al., 2007). We further demonstrate that in the context of established leukemic disease, it is necessary to dissociate leukemianiche interactions before HSC transplantation (HSCT), to achieve competitive healthy reconstitution at the expense of LSC self-renewal. "
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    ABSTRACT: Allogeneic hematopoietic stem cell (HSC) transplantation (HSCT) is currently the leading strategy to manage acute myeloid leukemia (AML). However, treatment-related morbidity limits the patient generalizability of HSCT use, and the survival of leukemic stem cells (LSCs) within protective areas of the bone marrow (BM) continues to lead to high relapse rates. Despite growing appreciation for the significance of the LSC microenvironment, it has remained unresolved whether LSCs preferentially situate within normal HSC niches or whether their niche requirements are more promiscuous. Here, we provide functional evidence that the spatial localization of phenotypically primitive human AML cells is restricted to niche elements shared with their normal counterparts, and that their intrinsic ability to initiate and retain occupancy of these niches can be rivaled by healthy hematopoietic stem and progenitor cells (HSPCs). When challenged in competitive BM repopulation assays, primary human leukemia-initiating cells (L-ICs) can be consistently outperformed by HSPCs for BM niche occupancy in a cell dose-dependent manner that ultimately compromises long-term L-IC renewal and subsequent leukemia-initiating capacity. The effectiveness of this approach could be demonstrated using cytokine-induced mobilization of established leukemia from the BM that facilitated the replacement of BM niches with transplanted HSPCs. These findings identify a functional vulnerability of primitive leukemia cells, and suggest that clinical development of these novel transplantation techniques should focus on the dissociation of L-IC-niche interactions to improve competitive replacement with healthy HSPCs during HSCT toward increased survival of patients.
    Preview · Article · Sep 2014 · Journal of Experimental Medicine
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    • "However its exact role has not been elucidated, and conflicting results have been reported. In another experiment, the functional blockade of c-kit with a neutralizing antibody was associated with HSC migration from the BM to the blood [62]. "
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    ABSTRACT: Following chemotherapy and/or the administration of growth factors, such as granulocyte-colony stimulated factor (G-CSF), hematopoietic stem cells (HSC) mobilize from bone marrow to peripheral blood. This review aims to systematically present the structure of the HSC "niche" and elucidate the mechanisms of their mobilization. However, this field is constantly evolving and new pathways and molecules have been shown to contribute to the mobilization process. Understanding the importance and the possible primary pathophysiologic role of each pathway is rather difficult, since they share various overlapping components. The primary initiating event for the mobilization of HSC is chemotherapy-induced endogenous G-CSF production or exogenous G-CSF administration. G-CSF induces proliferation and expansion of the myelomonocytic series, which leads to proteolytic enzyme activation. These enzymes result in disruption of various receptor-ligand bonds, which leads to the disanchorage of HSC from the bone marrow stroma. In everyday clinical practice, CXC chemokine receptor-4 (CXCR4) antagonists are now being used as mobilization agents in order to improve HSC collection. Furthermore, based on the proposed mechanisms of HSC mobilization, novel mobilizing agents have been developed and are currently evaluated in preclinical and clinical studies.
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    • "This model requires fully myeloablative busulfan conditioning combined with T cell co-receptor blockade of signal 1 for long-term graft acceptance. Having identified that higher syngeneic chimerism in C57BL/6 recipients was associated with an increased ratio of donor to recipient haematopoietic cells in BM initially after transplant, we then compared published methods for improving donor to recipient cell number in the BM niche including ACK2 [27], G-CSF [28] or high cell dose [7], against further costimulatory blockade of signal 2 [5], all in combination with RIC and signal 1 blockade in our CBA-C57BL/6 transplant model. Despite early engraftment with G-CSF or high cell doses, costimulatory blockade was the only factor that could permit the use of NMC in combination with signal 1 blockade in this stringent mouse model of transplantation. "
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    ABSTRACT: Non-myeloablative allogeneic haematopoietic stem cell transplantation (HSCT) is rarely achievable clinically, except where donor cells have selective advantages. Murine non-myeloablative conditioning regimens have limited clinical success, partly through use of clinically unachievable cell doses or strain combinations permitting allograft acceptance using immunosuppression alone. We found that reducing busulfan conditioning in murine syngeneic HSCT, increases bone marrow (BM):blood SDF-1 ratio and total donor cells homing to BM, but reduces the proportion of donor cells engrafting. Despite this, syngeneic engraftment is achievable with non-myeloablative busulfan (25 mg/kg) and higher cell doses induce increased chimerism. Therefore we investigated regimens promoting initial donor cell engraftment in the major histocompatibility complex barrier mismatched CBA to C57BL/6 allo-transplant model. This requires full myeloablation and immunosuppression with non-depleting anti-CD4/CD8 blocking antibodies to achieve engraftment of low cell doses, and rejects with reduced intensity conditioning (≤75 mg/kg busulfan). We compared increased antibody treatment, G-CSF, niche disruption and high cell dose, using reduced intensity busulfan and CD4/8 blockade in this model. Most treatments increased initial donor engraftment, but only addition of co-stimulatory blockade permitted long-term engraftment with reduced intensity or non-myeloablative conditioning, suggesting that signal 1 and 2 T-cell blockade is more important than early BM niche engraftment for transplant success.
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