SDF-1/CXCR4信号通路在造血干细胞归巢中作用的研究进展

造血干细胞移植(HSCT)是治疗白血病、淋巴瘤、再生障碍性贫血等恶性血液病的一种有效治疗手段.但是,HSCT后造血功能的恢复与归巢至骨髓造血微环境中的造血干细胞(HSC)数目有关.HSCT输注入受者体内的HSC不会立刻发挥作用,而是先经历一系列复杂的过程归巢至骨髓造血微环境后,才能继续增殖并分化为相应的效应细胞发挥作用.其中,供者HSC与众多细胞及细胞因子间的相互作用是决定HSC归巢、增殖及分化的关键因素.基质细胞衍生因子(SDF)-1及其唯一的受体CXC趋化因子受体(CXCR)4所构成的SDF-1/CXCR4信号通路,可能在HSC归巢中发挥重要作用.为了更深入地研究HSC归巢的具体过程和SDF-1/CXCR4信号通路在该过程中发挥的作用,现对SDF-1、CXCR4的结构、作用机制,以及SDF1/CXCR4信号通路在HSC归巢中作用的研究进展进行综述.     

SDF-1/CXCR4介导骨髓干细胞归巢至损伤肝脏的研究进展

基质细胞衍生因子一1（SDF一1）与其受体CXCR4结合,所介导的骨髓干细胞迁移归巢在多种组织器官损伤后的再生修复中发挥重要作用。研究表明,在肝损伤及肝细胞再生的过程中,干细胞起着重要的作用,而骨髓干细胞是肝细胞的重要的肝外来源。SDF一1及其受体CXCR4组成的功能轴在骨髓干细胞迁移方面的研究进展,为治疗肝损伤提供了新的方向。本文主要对SDF1／CXCR4轴体系统的生物学特性及其在骨髓干细胞归巢至损伤肝脏的作用进行综述。     

以SDF-1/CXCR4轴为靶点治疗发性骨髓瘤的研究进展

早期研究发现,由基质细胞衍生因子-1(SDF1,亦被称为CXCL12)与其受体CXCR4结合形成的SDF-1/CXCR4轴在干细胞归巢、迁移中起主要作用.近期研究发现,抑制SDF1/CXCR4轴在多发性骨髓瘤、淋巴瘤和急性白血病等造血系统肿瘤中有潜在治疗价值.笔者将以SDF 1/CXCR4轴为靶点治疗多发性骨髓瘤的研究进展进行综述.     

胎儿骨髓源Flk1＋间充质干细胞的归巢机制

背景：间充质干细胞移植后是否成功,依赖于经静脉输注后能否定居于靶器官并长期存活,这个过程被称为归巢。然而,调节和控制间充质干细胞归巢的分子机制目前尚不十分清楚。目的：探讨胎儿骨髓源Flk1＋间充质干细胞向骨髓归巢的机制,观察基质细胞衍生生长因子1及其受体CXCR4对干细胞归巢效率的影响,摸索提高其归巢和长期植入效率的方法。设计、时间及地点：细胞学体内实验,于2005—09／2006-07在中国医学科学院、中国协和医科大学组织工程中心完成。材料：Flk1＋骨髓间充质干细胞来源于流产胎儿,由天津医科大学第二附属医院妇产科提供。6-8周龄NOD／SCID小鼠购自中国医学科学院实验动物研究所。方法：采用流式细胞仪、实时定量PCR等方法检测特定细胞因子刺激前后Flk1＋间充质干细胞CXCR4表达和体外迁移能力的变化。NOD／SCID小鼠预先经全身亚致死量照射后,从尾静脉输入经或未经细胞因子刺激的Flk1＋间充质干细胞,对照组注射等体积生理盐水。移植后24h,应用流式细胞仪分析骨髓中供体细胞的含量,或在移植后定期从小鼠的尾静脉取血,分析外周血中白细胞、红细胞及血小板的数量变化。移植后6个月,实时定量PCR法检测小鼠骨髓中的人特异性DNA含量,了解人源细胞的植入情况。结果：Flk1＋间充质干细胞的胞浆中有CXCR4表达,在适当细胞因子刺激下,能够在短时间内被诱导至细胞表面表达。通过24h短时间细胞因子刺激,不仅能够上凋细胞表面及内部的CXCR4,而且可以增加细胞在体外沿基质细胞衍生生长因子1浓度梯度迁移的活性,促进细胞植入经亚致死量照射的NOD／SCID小鼠体内后向骨髓的归巢及长期存活,同时也加快了受体小鼠的造血恢复;用CXCR4中和抗体处理的Flk1＋间充质干细胞,则明显减少其移植后在受体小鼠中的归巢和植入。结论：基质细胞衍生生长因子1及其受体CXCR4在Flk1＋间充质干细胞迁移和归巢中发挥着重要作用,增加细胞表面CXCR4的表达,有助于促进Flk1＋间充质干细胞向骨髓归巢和加快受体造血恢复。     

胎儿骨髓源FIk1+间充质干细胞的归巢机制

背景:间充质干细胞移植后是否成功,依赖于经静脉输沣后能否定居于靶器官并长期存活,这个过程被称为归巢.然而,调节和控制间充质干细胞归巢的分子机制目前尚不十分清楚.目的:探讨胎儿骨髓源FIk1+间充质干细胞向骨髓归巢的机制,观察基质细胞衍生生长因子1及其受体CXCR4对干细胞归巢效率的影响,摸索提高其归巢和长期植入效率的方法.设计、时间及地点:细胞学体内实验,于2005-09/2006-07在中国医学科学院、中国协和医科大学组织工程中心完成.材料:FIk1+骨髓间充质干细胞来源于流产胎儿,由天津医科大学第二附属医院妇产科提供.6～8周龄NOD/SCID小鼠购自中国医学科学院实验动物研究所.方法:采用流式细胞仪、实时定量PCR等方法检测特定细胞因子刺激前后FIk1+间充质干细胞CXCR4表达和体外迁移能力的变化.NOD/SCID小鼠预先经全身亚致死量照射后,从尾静脉输入经或未经细胞因子刺激的FIk1+间充质干细胞,对照组注射等体积生理盐水.移植后24 h,应用流式细胞仪分析骨髓中供体细胞的含量,或在移植后定期从小鼠的尾静脉取血,分析外周血中白细胞、红细胞及血小板的数量变化.移植后6个月,实时定量PCR法检测小鼠骨髓中的人特异性DNA含量,了解人源细胞的植入情况.结果:FIk1+间充质干细胞的胞浆中有CXCR4表达,在适当细胞因子刺激下,能够在短时间内被诱导至细胞表面表达.通过24 h短时间细胞因子刺激,不仅能够上调细胞表面及内部的CXCR4,而且可以增加细胞在体外沿基质细胞衍生生长因子1浓度梯度迁移的活性,促进细胞植入经亚致死量照射的NOD/SCID小鼠体内后向骨髓的归巢及长期存活,同时也加快了受体小鼠的造血恢复;用CXCR4巾和抗体处理的FIk1+间充质干细胞,则明显减少其移植后在受体小鼠中的归巢和植入.结论:基质细胞衍生生长因子1及其受体CXCR4在FIk1+间充质干细胞迁移和归巢中发挥着重要作用,增加细胞表面CXCR4的表达,有助于促进FIk1+间充质干细胞向骨髓归巢和加快受体造血恢复.     

白血病微环境的靶向药物趋化因子受体CXCR4拮抗剂作用机制的研究

造血来源的肿瘤细胞表达趋化因子受体CXCR4,是一种7次跨膜G蛋白耦联受体。组成骨髓微环境的基质细胞分泌基质细胞衍生因子SDF-1/CXCL12,是CXCR4的配体。CXCR4的活化可诱导白血病细胞向骨髓微环境的归巢,白血病细胞表达的CXCL12与骨髓基质细胞紧密相连并且提     

以SDF-1/CXCR4为靶点治疗血液肿瘤的研究进展

基质细胞衍生因子-1(SDF-1)是一种主要由骨髓基质细胞合成释放的趋化因子,属CXC亚家族成员。SDF1与其表达于正常造血干/祖细胞和多种血液肿瘤细胞表面的受体CXCR4特异性结合及相互作用,在造血调控及血液肿瘤转归中具有重要作用。本文就以SDF1/CXCR4为靶点治疗血液系统肿瘤的有关研究进展作一综述。     

SDF—1、CXCR4在造血系统中的表达生物学功能研究

趋化因子是血液学基因与临床研究的一个热点,近年来对趋化因子在造血干／祖细胞动员和归巢以及白血病细胞播散中的作用研究发现,基质细胞衍生因子（stromal cell-derived factor 1,SDF-1）及其受体CXCR4在这些生理和病理过程中发挥关键的作用。本文就SDF－1／CXCR4趋化因子及受体的基本结构和造血系统中的表达及其与干祖细胞、白血病细胞的作用进行综述。     

SDF—1／CXCR—4在造血干细胞归巢中的作用

造血干细胞向骨髓内归巢是影响造血干细胞移植是否成功的一个重要因素。在干细胞归巢环节中，近年来新发现的基质细胞源性细胞因子-1（stromal cell derived factor-1,SDF-1)及其受体CX-CR-4（SDF-1/CXCR-4）系统起着重要的作用。本文就该因子系统的结构。表达以及对造血干细胞的趋化作用及其下游信号传导综述。     

慢病毒载体介导的CXCR4基因过表达对骨髓间充质干细胞归巢影响

目的:研究小鼠CXCR4基因过表达对小鼠骨髓间充质干细胞(mesenchymal stem cell, MSC)体内归巢特性的影响。方法:利用慢病毒载体介导小鼠MSC过表达CXCR4基因,建立过表达CXCR4的MSC。将BALB/c小鼠分为单纯照射组(TBI组):受鼠接受全身照射(total body irradiation, TBI)后输注生理盐水;受鼠TBI后经鼠尾静脉输注EGFP空载体转导的MSC 5×10~5空载体对照组(EGFP-MSC)和受鼠TBI后经鼠尾静脉输注同时携带EGFP和CXCR 4基因的MSC 5×10~5过表达CXCR4组(CXCR4-MSC)3组,每组动物10只。冰冻切片观察MSC在受鼠体内重要脏器的分布,应用流式细胞术检测MSC归巢至受鼠体内骨髓及脾脏效率,酶联免疫吸附法(enzyme-linked immunosorbent assay, ELISA)检测受鼠外周血和骨髓中基质细胞衍生因子1(stromal cell derived factor-1, SDF-1)水平。结果:冰冻切片结果显示,过表达CXCR 4可明显提高MSC归巢至肺脏、肝脏和脾脏的效率;流式细胞术测定过表达CXCR4的MSC归巢至脾脏和骨髓数量明显高于EGFP对照组(P 0.05);ELISA结果显示照射24小时后小鼠外周血及骨髓中SDF-1水平明显升高,并且SDF-升高水平与过表达CXCR4的MSC归巢效率存在相关性。结论:利用慢病毒载体介导的过表达CXCR4基因可促进小鼠骨髓间充质干细胞归巢。     

Enhanced recruitment and hematopoietic reconstitution of bone marrow‐derived mesenchymal stem cells in bone marrow failure by the SDF‐1/CXCR4

Aplastic anemia (AA) is a bone marrow failure disease. It is difficult to treat AA, and in addition, relapses are common because of its complex disease pathogenesis. Allogeneic bone marrow‐derived mesenchymal stem cells (BMSCs) infusion is an effective and safe treatment option for the AA patients. However, it found that BMSCs infusion in AA patients is less than 30% effective. Therefore, the key to improve the efficacy of BMSCs treatment in these patients is to enhance their homing efficiency to the target sites. Studies have shown that stromal cell‐derived factor‐1 (SDF‐1)/CXC chemokine receptor 4 (CXCR4) axis plays an important role in promoting BMSCs homing. In this study, human BMSCs were transduced with lentivirus stably expressing CXCR4‐BMSCs. Transduced BMSCs resemble normal BMSCs in many ways. Migration ability of CXCR4‐BMSCs toward SDF‐1 was increased because of the overexpression of CXCR4. In the mice with bone marrow failure, the migration and colonization ability of CXCR4‐BMSCs to the bone marrow was significantly improved as seen by IVIS imaging and FACS. The SDF‐1 level in the bone marrow failure mice was significantly higher than in the normal mice. Thus, from our study, it is clear that after CXCR4‐BMSCs were infused into mice with bone marrow failure, SDF‐1 interacted with CXCR4 receptor, leading cells to migrate and colonize to bone marrow. Because of the high SDF‐1 expression in mouse bone marrow and CXCR4 receptor expression in cells, BMSCs homing was increased.     

A Small-molecule Inhibitor Directed against the Chemokine Receptor CXCR4 Prevents its Use as an HIV-1 Coreceptor

The chemokine receptor CXCR4 is the major coreceptor used for cellular entry by T cell– tropic human immunodeficiency virus (HIV)-1 strains, whereas CCR5 is used by macrophage (M)-tropic strains. Here we show that a small-molecule inhibitor, ALX40-4C, inhibits HIV-1 envelope (Env)-mediated membrane fusion and viral entry directly at the level of coreceptor use. ALX40-4C inhibited HIV-1 use of the coreceptor CXCR4 by T- and dual-tropic HIV-1 strains, whereas use of CCR5 by M- and dual-tropic strains was not inhibited. Dual-tropic viruses capable of using both CXCR4 and CCR5 were inhibited by ALX40-4C only when cells expressed CXCR4 alone. ALX40-4C blocked stromal-derived factor (SDF)-1α–mediated activation of CXCR4 and binding of the monoclonal antibody 12G5 to cells expressing CXCR4. Overlap of the ALX40-4C binding site with that of 12G5 and SDF implicates direct blocking of Env interactions, rather than downregulation of receptor, as the mechanism of inhibition. Thus, ALX40-4C represents a small-molecule inhibitor of HIV-1 infection that acts directly against a chemokine receptor at the level of Env-mediated membrane fusion.     

CXCR4 is required for the quiescence of primitive hematopoietic cells

The quiescence of hematopoietic stem cells (HSCs) is critical for preserving a lifelong steady pool of HSCs to sustain the highly regenerative hematopoietic system. It is thought that specialized niches in which HSCs reside control the balance between HSC quiescence and self-renewal, yet little is known about the extrinsic signals provided by the niche and how these niche signals regulate such a balance. We report that CXCL12 produced by bone marrow (BM) stromal cells is not only the major chemoattractant for HSCs but also a regulatory factor that controls the quiescence of primitive hematopoietic cells. Addition of CXCL12 into the culture inhibits entry of primitive hematopoietic cells into the cell cycle, and inactivation of its receptor CXCR4 in HSCs causes excessive HSC proliferation. Notably, the hyperproliferative Cxcr4(-/-) HSCs are able to maintain a stable stem cell compartment and sustain hematopoiesis. Thus, we propose that CXCR4/CXCL12 signaling is essential to confine HSCs in the proper niche and controls their proliferation.     

抑制SDF-1活性对人急性髓性白血病HL-60细胞系增殖的影响

本研究通过观察抑制SDF-1活性对HL-60细胞增殖活性的影响，探讨趋化因子SDF-1在维持HL-60细胞生存能力中的作用。培养骨髓基质细胞，并与HL-60细胞共培养，采用SDF-1受体CXCR4单克隆抗体阻断SDF-1生物活性后，用MTT法检测HL-60细胞活力、用流式细胞术观察HL-60细胞增殖周期变化、检测细胞膜表面CXCR4表达，同时检测CXCR4单克隆抗体应用前后HL-60细胞内钙离子浓度变化。结果显示，抗CXCR4单克隆抗体可下调HL-60细胞膜表面CXCR4的表达，同时处于G0／G1期的细胞增多，处于S期的细胞减少，而白血病细胞存活率下调，细胞内钙离子浓度降低。结论：抑制SDF-1活性可在一定程度上抑制白血病细胞的增殖。     

狼疮肾炎患者外周血中趋化因子受体CXCR4及其配体SDF—1α的表达研究

目的探讨趋化因子受体CXCR4及其配体基质细胞衍生因子-1（SDF-1）在狼疮肾炎（LN）外周血中的表达水平及意义。方法用流式细胞术分别检测健康对照组、LN患者组、非肾损害系统性红斑狼疮（SLE）患者组的外周血中CD3＋CD4＋T淋巴细胞、CD5＋CD8＋T淋巴细胞表面CxCR4的表达,采用双抗体夹心ABC—ELISA法检测以上各组血清SDF-1α浓度水平。结果健康对照组外周血中CD3＋CD4＋T淋巴细胞、CD3＋CD8＋T淋巴细胞表面CXCR4表达及SDF-1α表达水平均明显低于狼疮肾炎组和非肾损害SLE组,而非肾损害SLE患者组外周血中CD3＋CD4＋T淋巴细胞、CD5＋CD8＋T淋巴细胞表面CXCR4表达及SDF-1α表达水平也均明显低于LN组。结论SLE患者发病与CXCR4／SDF-1α高表达有关,LN患者发病与CXCR4／SDF—1α高表达有密切关系,提示CXCRd／SDF-1α可能在LN的发病中起重要作用。     

Differential response of platelets to chemokines: RANTES non-competitively inhibits stimulatory effect of SDF-1α

Summary. Background: Among the chemokines related to CXC and CC receptor groups and released from platelets, leukocytes and endothelial cells, SDF‐1, TARC and MDC have been found to be platelet agonists. Platelets do not contain SDF‐1α. In contrast, RANTES is constitutively present in platelet α‐granules and released upon platelet activation. Objectives: To study a possible role of RANTES as a modulator of SDF‐1α effect on platelets, in relation to CXCR4 and various CC receptors. Methods: CXCR‐4 (CXCL12) receptor expression and platelet activation were evaluated by flow cytometry, platelet deposition was studied by cone and plate(let) analyzer, and platelet aggregation by turbidometric aggregometry. Results: Flow cytometry studies revealed similar expression of CXCR‐4, the specific receptor of SDF‐1α on intact, inactivated, and activated platelets. Preincubation of platelets with RANTES affected neither CXCR‐4 expression, nor SDF‐1α binding to the platelet membrane. In the presence of fibrinogen, SDF‐1α activated gel‐filtered platelets. RANTES did not activate platelets, but substantially (by 70%) inhibited SDF‐1α‐induced fibrinogen binding. Similarly, RANTES abrogated the promoting effect of SDF‐1α on whole blood platelet adhesion to endothelial cell monolayer under venous flow conditions. In platelet‐rich plasma, RANTES moderately inhibited SDF‐1α‐induced platelet aggregation, while it did not affect aggregation induced by thrombin‐receptor activation peptide, adenosine diphosphate, or phorbol 12‐myristate 13‐acetate. A synergistic inhibitory effect of RANTES and prostaglandin E₁ used at subthreshold concentrations, on SDF‐1α‐induced aggregation and SDF‐1α‐induced fibrinogen binding to platelets was observed, which may suggest involvement of RANTES in a cAMP‐dependent signal transduction pathway. Conclusions: RANTES non‐competitively inhibits activation of platelets by SDF‐1α, and thus may play a regulatory role in platelet response to inflammation.     

Chemokine requirements for B cell entry to lymph nodes and Peyer's patches

B cell entry to lymph nodes and Peyer's patches depends on chemokine receptor signaling, but the principal chemokine involved has not been defined. Here we show that the homing of CXCR4-/- B cells is suppressed in CCL19 (ELC)- and CCL21 (SLC)-deficient paucity of lymph node T cells mice, but not in wild-type mice. We also find that CXCR4 can contribute to T cell homing. Using intravital microscopy, we find that B cell adhesion to high endothelial venules (HEVs) is disrupted when CCR7 and CXCR4 are predesensitized. In Peyer's patches, B cell entry is dependent on CXCR5 in addition to CCR7/CXCR4. CXCL12 (SDF1) is displayed broadly on HEVs, whereas CXCL13 (BLC) is found selectively on Peyer's patch follicular HEVs. These findings establish the principal chemokine and chemokine receptor requirements for B cell entry to lymph nodes and Peyer's patches.     

Intrakines—Evidence for a Trans-Cellular Mechanism of Action

Human CXCR4 is the receptor for the CXC chemokine SDF-1α and also acts as a coreceptor for T lymphotropic HIV-1 strains. Blocking the surface expression of this receptor via an intrakine approach has recently been shown to efficiently prevent HIV-1 infection of T cells. The CXC-chemokine gene is fused to an endoplasmic reticulum retention signal (KDEL) that retains the newly synthesized chemokine and its receptor within the cell, where both are subsequently degraded. We constructed MoMuLV-based vectors containing the SDF–KDEL construct driven by the “MND” long terminal repeat, using eGFP as a marker gene (MND-SDF-KDEL-IRES-eGFP) and a control vector (MND-X-IRES-eGFP). CEM human T lymphoblastic leukemia cells were transduced with the intrakine vector or the control vector. We detected a marked downregulation of CXCR4 expression in the cells transduced with the intrakine vectors as opposed to the cells transduced with the control vector. However, the eGFP-negative fraction of the cells transduced with the intrakine vector displayed the same CXCR4 downregulation as the eGFP-positive fraction, suggesting an effect in trans. The possibility of this being due to eGFP being silenced while SDF–KDEL was still expressed was excluded by Southern and Northern blot analyses. Upon cultivating the control cells with supernatant of the cells transduced with the intrakine vector, we observed a downregulation of CXCR4 expression on the control cells. Experiments using rhSDF-1α showed downregulation by the supernatant to be comparable to that achieved by the exogenous addition of 30 ng/ml SDF-1α. To assess the bioactivity of the secreted substance in the supernatant, a chemotaxis assay was performed. The transmigration observed was, once again, within the range of that achieved by the addition of 30 ng/ml SDF-1α. We conclude that the intrakine SDF–KDEL, apart from acting within the cell, is also in part secreted and causes the downregulation of the receptor by acting like a secreted chemokine.     

MMP-2 mediates mesenchymal stem cell tropism towards medulloblastoma tumors

Matrix metalloproteinases (MMPs) are a family of proteinases known to have a role in cell migration. In the present study, we evaluated the role of MMP-2 on tropism of human umbilical cord blood-derived stem cells (hUCBSCs) in a human medulloblastoma tumor model. Consequences of MMP-2 inhibition on stem cell tropism towards medulloblastoma were studied in terms of stem cell migration by using cell culture inserts, transwell chamber assay, western blotting for MMP-2 and migratory molecules, and immunohistochemistry. Conditioned medium from Daoy/D283 cells infected with adenoviral vector encoding MMP-2 small interfering RNA (siRNA) (Ad-MMP-2 si)-reduced stem cell migration as compared with conditioned medium from mock and scrambled vector (Ad-SV) infected cells. In addition, MMP-2 inhibition in the tumor cells decreased the expression of stromal cell-derived factor 1 (SDF1) in the tumor-conditioned medium, which results in impaired SDF1/CXCR4 signaling leading to decreased stem cell tropism towards the tumor cells. We further show that MMP-2 inhibition in the tumor cells repressed stem cell tropism towards medulloblastoma tumors in vivo. In summary, we conclude that hUCBSCs can integrate into human medulloblastoma after local delivery and that MMP-2 expression by the tumor cells mediates this response through the SDF1/CXCR4 axis.     

CD34+ cell responsiveness to stromal cell-derived factor-1alpha underlies rate of engraftment after peripheral blood stem cell transplantation

BACKGROUND: Stromal cell–derived factor (SDF)‐1, a chemokine produced in the bone marrow (BM), is essential for the homing of hematopoietic stem/progenitor cells (HSPCs) to the BM after transplantation. This study examines whether there is a correlation between the in vitro chemotaxis of CD34+ HSPC toward an SDF‐1 gradient and in vivo hematopoietic engraftment. STUDY DESIGN AND METHODS: Thirty‐five patients underwent granulocyte–colony‐stimulating factor HSPC collection and autologous transplant with a median dose of 7.7 (range, 3.9‐41.5) × 10⁶ CD34+ cells per kg body weight. The chemotactic index (CI) of CD34+ cells isolated from leukapheresis products collected from these patients was calculated as the ratio of the percentages of cells migrating toward an SDF‐1 gradient to cells migrating to media alone. Expression of the SDF‐1 receptor CXCR4 on CD34+ cells was measured by flow cytometry. RESULTS: Spontaneous cell migration (range, 3.1 ± 0.6 to 26.5 ± 7.7%) and SDF‐1–directed chemotaxis (11.1 ± 0.7 to 54.9 ± 8.3%) of CD34+ cells did not correlate with time to neutrophil engraftment, which occurred at a median of 10 days (range, 8‐16 days). Nonparametric tests showed a negative correlation (r = ?0.434) between CI and CD34+ cell dose such that neutrophil recovery occurred within the same period in patients transplanted with a lower dose of CD34+ cells but having a high CI as in those transplanted with a higher dose of CD34+ cells but having a low CI. Moreover, CI correlated (r = 0.8) with surface CXCR4 expression on CD34+ cells. CONCLUSION: In patients transplanted with a relatively lower CD34+ cell dose who achieved fast engraftment, a higher responsiveness to SDF‐1 and high CI could have compensated for the lower cell dose. However, to apply the CI as a prognostic factor of the rate of engraftment requires validation in a larger number of patients.