基质细胞衍生因子受体在造血干/祖细胞宫内移植中的作用

目的探讨基质细胞衍生因子受体(CXCR4)在造血干/祖细胞(HSC)宫内移植归巢中的作用。方法分离人脐血CD34+细胞,用流式细胞仪检测SCF、IL-6处理前后细胞表面CXCR4(CD184)的表达及在Transwell板中的迁移率。在BALB/c胎鼠孕13～14d期间,经胎鼠腹腔注射经不同处理的CD34+细胞,胎鼠出生1个月后取骨髓,用流式细胞仪检测人CD45细胞。结果预处理后表达CD184的CD34+细胞的百分数由原来的9.58%±1.56%上升为19.32%±3.64%。CD34+/CXCR4high细胞迁移率显著增高,但迁移作用可以被antiCXCR4mAb和PTX明显抑制。SCF和IL-6预处理组胎鼠人CD45细胞阳性率显著高于其他组。抗CXCR4抗体或PTX预处理组人CD45细胞检出率显著降低。结论增加CD34+细胞CXCR4的表达有助于宫内移植HSC的归巢,HSC宫内移植归巢过程依赖CXCR4受体,SDF-1/CXCR4调节信号通过Gi蛋白进行跨膜传导。     

转FL、GM-CSF基因的人骨髓基质细胞促进脐血CD34+细胞体外扩增

研究转FL、GM-CSF基因的基质细胞对脐血CD34+细胞的扩增效应.将转FL、GM-CSF基因的入骨髓基质细胞系与脐血CD34+细胞共培养,观察细胞总数、CD34+细胞数、CFU-GM的变化情况.培养到第4周时,第(4)组(SCF+IL-3+IL-6+GM-CSF+FL)和第(8)组(HFCL/hGM-CSF+HFCL/hFL+SCF+IL-3+IL-6)的细胞总数增加到最大,分别扩增了717±24.47和709±63.63,第1周,第(5)组(HFCL+SCF+IL-3+IL-6)扩增了10.5±2.08倍,较第(8)组减少(P＜0.05).第1周时,CD34+细胞总数第(4)组和第(8)组分别扩增了8.44倍和11.5倍(P＜0.05),CD34+细胞百分率第(7)组(FCL/hFL+SCF+IL-3+II,-6)为50.2%,第(6)组(HFCL/hGM-CSF+SCF+IL-3+IL-6)为28.95%(P＜0.01).第2周,各组CFU-GM增加显著,以第(4)组和第(8)组增加最为明显,以后随扩增时间延长,造血细胞集落数、集落体积逐渐减少.表明转FL、GM-CSF基因的基质细胞,能有效的协同其他细胞因子对脐血CD34+细胞产生明显的扩增作用,能显著改变基质细胞造血功能.     

早期作用造血因子对人脐血CD34+细胞的体个扩增作用

为了观察早期作用造血细胞因子SCF、FL、IL-3、IL-6、TPO单独及联合应用,对脐血CD34+细胞的体外扩增作用.我们用吸附单克隆抗体-磁珠分离系统富集人脐血CD34+细胞,在体外液体培养体系中加入不同的细胞因子扩增4周,每周取样计数有核细胞总数及集落形成细胞(CFC)数.结果表明:用磁性细胞分离仪富集脐血CD34+细胞纯度为80%～87%;一些细胞因子有明显的协同效应,其联合应用的扩增作用显著高于单因子作用;SCF+FL存在下,IL-3是有效扩增有核细胞总数及CFC的关键因子;细胞因子SCF+FL+IL-3和SCF+FL+IL-3+IL-6组合对有核细胞总数及CFC均有良好的扩增效应,培养2周时对CFC的扩增倍数分别为38.3±4.4 和29.6±2.7倍,可满足成人移植及基因治疗等的需要.     

脐血红系祖细胞扩增的研究

脐血通过体外培养定向扩增为红系祖细胞及前体细胞作为新生红细胞血源有可行的实验室基础.红细胞生成涉及复杂过程,包括转录因子、生长因子、信号分子、红细胞相关蛋白.选择单个核细胞或CD34+为起始细胞对红系的区别不大,红系祖细胞CD71+CD36+CD34+CD117+CD48-CD123-.对CD34+造血干/祖细胞起作用有早期作用因子FL、TPO、SCF、IL-3、IL-6、SCF、IL-11,晚期作用因子如EPO、IGF-1、INS、TGFβ、Activin A.低氧促进造血祖细胞向红系定向,基质细胞对红系的扩增作用的影响不大.造血细胞向红系定向包括TAL1、LMO2、GATA-2转录因子参与;定向红系祖细胞分化包括NF-E2和EKLF转录因子.     

Ad-hOSM转基因饲养层细胞对脐血CD34~+造血干/祖细胞增殖及归巢能力的影响

目的:建立转人抑瘤素M(hOSM)基因腺病毒载体的饲养层细胞,观察转基因细胞对脐血CD34+造血干/祖细胞扩增的影响,比较扩增前、后造血干/祖细胞体外迁移能力的变化。方法:建立转hOSM基因腺病毒载体的饲养层细胞,并用RT-PCR法和ELISA法鉴定目的基因;采用免疫磁珠法分离脐带血CD34+造血干/祖细胞,流式细胞术(FCM)检测纯度;将CD34+造血干/祖细胞与饲养层细胞共培养,FCM检测各组增殖效果;扩增后的造血干/祖细胞用跨膜迁移实验(Transwell实验)检测自发迁移率和SDF-1诱导迁移率以鉴定体外扩增的造血干/祖细胞的归巢能力。结果:建立的转基因饲养层细胞均有绿色荧光,RT-PCR法和ELISA法证实有目的基因表达,免疫磁珠法分离的脐血CD34+造血干/祖细胞纯度可达(96.8±2.28)%,与Ad-hOSM转基因饲养层细胞共培养7 d后CD34+造血干/祖细胞可扩增15.73倍,表面黏附分子CXCR4和CD54表达量仍较高,培养后的细胞用Tran-swell板做体外迁移实验,与转基因饲养层细胞共培养的干细胞,其诱导迁移率为(40.68±1.35)%,明显高于对照组,可以较好的保持其归巢能力。结论:转hOSM基因腺病毒载体的饲养层细胞可有效扩增脐血CD34+造血干/祖细胞,延缓其分化,并且体外扩增后仍保持较高的归巢能力。     

基质细胞衍化因子-1促人内皮祖细胞迁移

目的 探讨基质细胞衍化因子-1对内皮祖细胞迁移的影响。方法 用流式细胞仪、RT-PCR、内皮功能试验鉴定内皮祖细胞，检测其CXCR4受体表达和迁移功能。结果 培养单个核细胞7d，CD34阳性率为36.3%±23.8%，CD133为19.7%±10.3%，双阳性率为18.6%±10.7%，表达KDR基因，＞90%的细胞吸收DiI-ac LDL和FITC-UEA-1。CXCR4表达率为74.8%，对照组、基质细胞衍化因子-1浓度为10、20和50μg/L时,细胞迁移数分别为3.5、7.4、24.9和28.0个。各组浓度的细胞迁移数均显著高于对照组（P＜0.01），20μg/L组显著高于10μg/L组、50μg/L组显著高于10μg/L组（P＜0.01）， 50μg/L组显著高于20μg/L组（P＜0.05）。结论 1.从外周血途径分离、培养和扩增获得内皮祖细胞，表达CXCR4受体；2.内皮祖细胞可在基质细胞衍化因子-1的趋化作用下迁移，且与其浓度呈正相关。     

CD34免疫亲合柱在脐血造血干/祖细胞分离与扩增中的应用

目的 :观察CD34免疫亲合柱对脐血造血干 祖细胞分离纯化的效果及纯化后CD34 细胞的增殖分化特性。方法 :采用CD34免疫亲合柱分离脐血单个核细胞 (MNC)中的CD34 细胞 ,流式细胞技术 (FACS)进行细胞表面标志测定。将分离前后的细胞加入造血生长因子进行液态扩增培养和多向祖细胞集落 (CFU GEMM)培养。结果 :经CD34免疫亲合柱分离后脐血中CD34 细胞为 49 6 2 %± 17 6 9% ,明显高于脐血MNC(1 17%± 0 6 8% ) ,细胞回收率为 5 4 38%± 11 91%。分离后CD34 细胞和脐血MNC经造血生长因子刺激培养 2 0d分别扩增 5 6 1 0 0倍和 44 44倍。培养至 12d时 ,免疫亲合柱分离组CD34 细胞阳性率为 5 3 38% ,对照组为 7 91%。分离组CFU GEMM产率明显高于对照组 (P <0 0 0 1)。结论 :CD34免疫亲合柱应用于脐血造血干 祖细胞的分离可充分富集CD34 细胞 ,且分离后的CD34 细胞具有明显的增殖效应和CFU GEMM形成能力。     

淋巴瘤患者外周血TCRVα24+Vβ11+自然杀伤T细胞体外活化特性研究

目的： 研究淋巴瘤患者外周血TCRVα24+Vβ11+自然杀伤T（NKT）细胞的数量以及体外活化后的功能状态，与正常人外周血NKT细胞的数量及功能状态进行比较。方法: 制备30例淋巴瘤患者和30例年龄及性别匹配的正常对照外周血单个核细胞（PBMNCs），以流式细胞术（FACS）检测TCRVα24+Vβ11+NKT细胞数量，以α-半乳糖神经酰胺（α-Galcer）及白细胞介素-2（IL-2）从PBMNCs中扩增活化NKT细胞，采用细胞内细胞因子流式细胞术检测手段，测定NKT细胞中胞内白细胞介素-4（IL-4）、干扰素-γ（IFN-γ）、肿瘤坏死因子-α（TNF-α）阳性细胞的比例。结果: 淋巴瘤患者与正常对照PBMNCs中TCRVα24+Vβ11+NKT细胞的细胞比率分别为0.17%±0.10%、0.28%±0.18%(P<0.05)。PBMNCs培养体系中加入α-Galcer及IL-2，将NKT细胞扩增活化7d后，淋巴瘤患者与正常对照的NKT细胞的扩增倍数分别为101.37±44.61、129.66±56.31(P<0.05)。扩增活化后，淋巴瘤患者与正常对照的NKT细胞中胞内细胞因子IFN-γ阳性细胞的比例分别为41.96%±15.06%、52.48%±18.85%(P<0.05)；TNF-α阳性细胞的比例分别为46.30%±16.03%、71.37%±17.28%(P<0.05)；IL-4阳性细胞的比例分别为36.19%±11.74%、33.12%±12.95%(P>0.05)。不同病理分型及分期的淋巴瘤患者之间上述各指标无显著差异。结论: 淋巴瘤患者外周血TCRVα24+Vβ11+NKT细胞数量较正常对照明显减少，经α-Galcer扩增活化后扩增倍数较正常对照降低，分泌细胞因子IFN-γ、TNF-α的功能较正常降低，此数量及功能的降低与淋巴瘤的分型及分期无关。但其仍保持有对α-Galcer刺激后的扩增活化反应能力。     

外周血内皮祖细胞的诱导培养

目的 探索外周血内皮祖细胞的诱导培养方法。方法 用密度梯度离心分离健康志愿者外周血单个核细胞,EGM-2培养基重悬并在纤连蛋白包被的培养板中进行诱导培养,动态观察贴壁细胞生长状况,免疫荧光技术鉴定内皮祖细胞特性,流式细胞术检测细胞周期分布及其相关表面标志CD34、CD133、CD31、VEGFR2和CD14。结果 贴壁细胞呈细长条状分布,整体形态和生长密度均以第9天最佳,约占外周血单个核细胞的4.62%~5.47%;细胞停留在G0/G1期,增殖指数仅为（1.20±0.18）％;细胞自第5天起即可同时吞噬乙酰化低密度脂蛋白和结合荆豆类凝集素,Ⅷ因子相关抗原于第9天始呈阳性;表面标志CD34、CD133、CD31、VEGFR2和CD14分别为0.19%±0.06%、1.67%±0.52%、61.56%±5.57%、70.29%±7.37%和89.31%±4.11%,共同指示诱导所得细胞属于正在分化的内皮祖细胞。结论 在特定条件下可直接从外周血单个核细胞中诱导培养出内皮祖细胞。     

用CD133免疫磁珠分离脐血内皮祖细胞的实验研究

目的：从脐血中分离、培养血管内皮祖细胞,研究内皮祖细胞的生长特性和诱导分化条件。 方法： 应用MACS磁球抗体标记法纯化脐血中的CD133+细胞，通过流式细胞仪、免疫细胞化学、免疫荧光等技术及形态学（光镜、电镜）观察研究内皮祖细胞；将细胞接种于添加（或未添加）VEGF、bFGF、干细胞因子（SCF）的含20％胎牛血清（FBS）的IMDM培养基中,观察内皮祖细胞的生长特性。 结果： 分离新鲜脐血所得CD133阳性细胞占单个核细胞的(1.41±1.14)%,经流式细胞仪鉴定CD133+细胞纯度为75%-85%；将分离细胞接种于纤维连接蛋白包被的24孔板内，培养1-2 h即有细胞贴壁，7-10 d可见贴壁细胞呈铺路石样排列；14 d后细胞出现小圆形、梭形等多样性变化，可见毛细血管管腔样结构，电镜观察可见胞浆内典型的Weibel-Palade小体；在VEGF、bFGF、SCF存在条件下,检测贴壁细胞培养14 d后细胞表面抗原表达情况：与培养开始时相比，祖细胞标志CD133和CD34阳性率呈明显下降趋势，分别由(77.0±3.3)%和(93.1±4.7)%降至(1.6±2.2)%和(37.4±4.9)%，P<0.05，内皮细胞特异性标志Flk-1表达明显增加，由(22.3±3.3)%增至(94.3±4.1)%，P<0.05，同时vWF抗原呈强阳性表达，阳性率为(77.9±3.3)%。 结论： 根据细胞表面特异性分子标志（CD133+/CD34+/Flk-1+）可以从脐血中分离出EPCs，EPCs可在体外一定的诱导因子作用下，培养7-10 d分化为成熟内皮细胞。     

Cytokine-induced expansion of human CD34+ stem/progenitor and CD34+CD41+ early megakaryocytic marrow cells cultured on normal osteoblasts

Thrombocytopenia remains a significant cause of morbidity in cancer patients undergoing allogeneic bone marrow transplantation (BMT), which consumes millions each year for frequent platelet transfusions. Using a novel culture system containing appropriate cytokine(s) on a layer of normal human osteoblasts, we investigated the expansion of early megakaryocytic progenitor cells while maintaining the number of CD34+ stem/progenitor marrow cells in an attempt to provide an effective solution for the problem of post-transplant thrombocytopenia. After seven days of culture, normal human osteoblasts alone without cytokines significantly increased the number of CD34+ and CD34+CD41+ marrow cells. Among the various cytokine combinations tested, both stem cell factor (SCF), interleukin 3 (IL-3)+IL-11 and SCF+IL-3+IL-11+thrombopoietin (TPO) emerged as the most effective in expanding early CD34+CD41+ megakaryocytic cells. Early CD34+CD41+ megakaryocytic cells have increased by 3.1- and 4.7-fold compared with day 7 control cultures, and by 62- and 94-fold, respectively, compared with day 0 input, respectively. Also, late CD41+ megakaryocytic cells have increased by 15.4- and 27.5-fold compared with day 7 control cultures in the presence of the same two combinations. In addition, the same cytokine combinations achieved 17.6- and 13.3-fold increases in the number of CD34+ marrow cells after the same seven days of culture on a layer of human osteoblasts. The combination (SCF+IL-3+IL-11+TPO) achieved the highest expansion of CD34+CD41+ early megakaryocytic cells from human marrow CD34+ cells reported so far in the literature. Recently, transplantation of SCF+IL-1+IL-3+TPO ex vivo expanded megakaryocytic progenitor cells as a supplement has been shown to accelerate platelet recovery by three to five days in mice. Therefore, the clinical use of the combination (SCF+IL-3+IL-11+TPO) for ex vivo expansion of CD34+ and megakaryocytic progenitor cells from a portion of the donor's marrow harvest is warranted in allogeneic BMT. Such a protocol would accelerate platelet recovery and shorten the period of hospitalization after allogeneic BMT. The present study has confirmed the role of human osteoblasts in supporting the proliferation and maintenance of human CD34+ stem/progenitor marrow cells. Given the facilitating role of osteoblasts shown previously in several allogeneic BMT studies in mice, it is possible to envisage a future role for donor osteoblasts in clinical BMT. Transplantation of the cultured donor osteoblasts together with the ex vivo expanded CD34+ marrow cells as a supplement might not only accelerate platelet recovery but also prevent acute graft-versus-host disease in allogeneic BMT. The present novel culture system should have useful clinical application in allogeneic BMT.     

HGF activates signal transduction from EPO receptor on human cord blood CD34+/CD45+ cells

Hepatocyte growth factor (HGF) is a multifunctional cytokine with early hematopoiesis-stimulatory activity. Here, we focus on its erythropoiesis-stimulatory effect on highly purified human hematopoietic progenitor cells (CD34+/CD45+ cells) derived from the cord blood. In immunoblot analyses, c-met protein (a receptor of HGF) was detected in the CD34+/CD45+ cells, although the expression levels were different among samples. The c-met expression was facilitated by incubation of the cells with stem cell factor (SCF) or interleukin 3 (IL-3), even if the expression level had been low. IL-6, G-CSF, or erythropoietin (EPO) did not show such a stimulatory effect on the c-met expression of the cells. When HGF was added to the CD34+/CD45+ cells in the presence of SCF, the numbers of CD36+/CD11b- cells (very early erythroid lineage cells) and BFU-E increased. EPO-dependent tyrosine phosphorylation of Stat 5 also increased, but the EPO receptor (EPO-R) expression remained unchanged in the CD34+/CD45+ cells treated with SCF + HGF. Our present study suggests that stimulation of the HGF/c-met signal is concomitant with induction of c-met protein by SCF. The subsequent enhancement of signal transduction via the activation of Stat 5 from the EPO-R plays a crucial role in the commitment of hematopoietic stem cells into erythroid lineage cells.     

Stem cells expressing homing receptors could be expanded from cryopreserved and unselected cord blood

We assessed the cytokine combinations that are best for ex vivo expansion of cord blood (CB) and the increment for cell numbers of nucleated cells, as well as stem cells expressing homing receptors, by an ex vivo expansion of cryopreserved and unselected CB. Frozen leukocyte concentrates (LC) from CB were thawed and cultured at a concentration of 1 x 10(5)/mL in media supplemented with a combination of SCF (20 ng/mL)+TPO (50 ng/mL)+FL (50 ng/mL)+/-IL-6 (20 ng/mL)+/-G-CSF (20 ng/mL). After culturing for 14 days, the expansion folds of cell numbers were as follows: TNC 22.3+/-7.8 approximately 26.3+/-4.9, CFU-GM 4.7+/-5.1 approximately 11.7+/-2.6, CD34+CD38- cell 214.0+/-251.9 approximately 464.1+/-566.1, CD34+CXCR4+ cell 4384.5+/-1664.7 approximately 7087.2+/-4669.3, CD34+VLA4+ cell 1444.3+/-1264.0 approximately 2074.9+/-1537.0, CD34+VLA5+ cell 86.2+/-50.9 approximately 113.2+/-57.1. These results revealed that the number of stem cells expressing homing receptors could be increased by an ex vivo expansion of cryopreserved and unselected CB using 3 cytokines (SCF, TPO, FL) only. Further in vivo studies regarding the engraftment after expansion of the nucleated cells, as well as the stem cells expressing homing receptors will be required.     

Interleukin 3 improves the ex vivo expansion of primitive human cord blood progenitor cells and maintains the engraftment potential of scid repopulating cells.

In umbilical cord blood (UCB) transplantation, the number of nucleated cells per kilogram is a major predictive and critical factor of hematopoietic recovery. Thus, ex vivo expansion of hematopoietic UCB progenitors could potentially accelerate engraftment. Whereas Flt-3 ligand (FL), stem cell factor (SCF), and thrombopoietin (TPO) are considered indispensable, the role of interleukin 3 (IL-3) is still controversial: it has been reported either to support or abrogate the reconstituting ability of stem cells. By adding IL-3 we aimed to enhance the amplification of early and committed progenitor cells without impairing the long-term engraftment of stem cells. Demonstrating a positive impact of IL-3 on the proliferation of all progenitor subsets, the amplification of CD34+ UCB cells was increased 20.9-fold +/- 5.4 (mean +/- standard error) in serum-free culture with FL, SCF, TPO, and IL-3 as opposed to 9.3-fold +/- 3.2 without IL-3 after 7 days. If IL-3 was included, primitive long-term culture-initiating cells and committed colony-forming cells were expanded 16.3-fold +/- 5.5 and 18.1-fold +/- 2.4, respectively, compared to 12.6-fold +/- 5.6 and 9.1-fold +/- 2.0 without IL-3. Analysis of cultured CD34+ UCB cells in sublethally irradiated nonobese diabetic/severe combined immunodeficient mice confirmed that cultured cells had preserved their repopulating potential. After 6 weeks, all mice showed multilineage engraftment with their bone marrow containing an average of 45% human CD45+ cells of the unmanipulated sample, 43% of cells after culture in the presence of IL-3, and 27% of cells after culture without IL-3. In combination with early acting cytokines, IL-3 therefore improves the ex vivo expansion of UCB stem and progenitor cells without impairing their engraftment potential.     

Expression and function of homing-essential molecules and enhanced in vivo homing ability of human peripheral blood-derived hematopoietic progenitor cells after stimulation with stem cell factor

Hematopoietic stem cell (HSC) homing from blood to bone marrow is a multistep process involving rolling, extravasation, migration, and finally adhesion in the correct microenvironment. With view to the hematopoietic recovery after clinical stem cell transplantation, we investigated the effect of stem cell factor (SCF) on the expression and the adhesive function of the alpha4beta1 and alpha5beta1 integrins very-late antigen (VLA)-4 and VLA-5 on peripheral blood-derived hematopoietic progenitor cells. After SCF stimulation, the expression of VLA-4 and VLA-5 on CD34+/c-kit+ cells obtained from healthy donors increased from 54% to 90% and from 3% to 82%, respectively. For patient-derived cells, the increase was 67% to 90% and 12% to 46%. The proportion of mononuclear cells adhering to the fibronectin fragment CH296 increased by stimulation with SCF from 14% to 23%. Accordingly, functional studies showed an approximate 30% increase of adherent long-term culture-initiating cell. The improvement of the homing abilities of SCF-stimulated HSC was confirmed by transplantation into sublethally irradiated nonobese diabetic-scid/scid mice. Six weeks after the transplantation, in eight of eight animals receiving human HSC with the addition of SCF, a profound multilineage hematopoietic engraftment was detected, whereas in the control group receiving only HSC, none of eight animals engrafted. Our data provide the first in vivo evidence that stimulation with cytokines improves the homing ability of transplanted human hematopoietic progenitor cells.     

Characterization of a lineage-negative stem-progenitor cell population optimized for ex vivo expansion and enriched for LTC-IC

Current hematopoietic stem cell transplantation protocols rely heavily upon CD34+ cells to estimate hematopoietic stem and progenitor cell (HSPC) yield. We and others previously reported CD133+ cells to represent a more primitive cell population than their CD34+ counterparts. However, both CD34+ and CD133+ cells still encompass cells at various stages of maturation, possibly impairing long-term marrow engraftment. Recent studies demonstrated that cells lacking CD34 and hematopoietic lineage markers have the potential of reconstituting long-term in vivo hematopoiesis. We report here an optimized, rapid negative-isolation method that depletes umbilical cord blood (UCB) mononucleated cells (MNC) from cells expressing hematopoietic markers (CD45, glycophorin-A, CD38, CD7, CD33, CD56, CD16, CD3, and CD2) and isolates a discrete lineage-negative (Lin-) cell population (0.10% +/- 0.02% MNC, n=12). This primitive Lin- cell population encompassed CD34+/- and CD133+/- HSPC and was also enriched for surface markers involved in HSPC migration, adhesion, and homing to the bone marrow (CD164, CD162, and CXCR4). Moreover, our depletion method resulted in Lin- cells being highly enriched for long-term culture-initiating cells when compared with both CD133+ cells and MNC. Furthermore, over 8 weeks in liquid culture stimulated by a cytokine cocktail optimized for HSPC expansion, TPOFLK (thrombopoietin 10 ng/ml, Flt3 ligand 50 ng/ml, c-Kit ligand 20 ng/ml) Lin- cells underwent slow proliferation but maintained/expanded more primitive HSPC than CD133+ cells. Therefore, our Lin- stem cell offers a promising alternative to current HSPC selection methods. Additionally, this work provides an optimized and well-characterized cell population for expansion of UCB for a wider therapeutic potential, including adult stem cell transplantation.     

Cytokine expansion culture of cord blood CD34+ cells induces marked and sustained changes in adhesion receptor and CXCR4 expressions

Recent studies have demonstrated defective bone marrow homing of hematopoietic stem cells after cytokine expansion culture. Adhesion receptors (ARs) are essential to the homing process, and it is possible that cytokine culture modulates AR expression. We studied changes in expression of very late antigen-4 (VLA-4), VLA-5, L-selectin, leukocyte function-associated antigen-1 (LFA-1), CD44, and the stromal cell-derived factor-1 (SDF-1) receptor, CXCR4, during cytokine culture of cord blood (CB) CD34(+) cells. Expression of ARs was studied by flow cytometry on CB CD34(+) cells in whole blood, after purification and during culture for up to 10 days. Cells were cultured with stem cell factor (SCF), thrombopoietin (TPO), Flt3-ligand (Flt3), and G-CSF. Results showed that 80% or more of uncultured CD34(+) cells were positive for VLA-4, L-selectin, LFA-1, CD44, and CXCR4 while 50% were positive for VLA-5. Purification of CD34(+) cells did not affect AR expression, but cytokines increased expression three- to nine-fold throughout the 10-day culture period. In contrast, expression of CXCR4 decreased. Expression changes of ARs and CXCR4 on CD34(+)/CD38(-) cells mirrored those of the total CD34(+) population. The results indicate that cytokine culture significantly increases AR expression on CB CD34(+) cells, which may be related to the decrease in homing of cytokine-cultured hematopoietic stem cells.     

Differential kinetics of primitive hematopoietic cells assayed in vitro and in vivo during serum-free suspension culture of CD34+ blood progenitor cells.

So far, blood progenitor cells (BPC) expanded ex vivo in the absence of stromal cells have not been demonstrated to reconstitute hematopoiesis in myeloablated patients. To characterize the fate of early hematopoietic progenitor cells during ex vivo expansion in suspension culture, human CD34(+)-enriched BPC were cultured in serum-free medium in the presence of FLT3 ligand (FL), stem cell factor (SCF) and interleukin 3 (IL-3). Both CD34 surface expression levels and the percentage of CD34+ cells were continuously downregulated during the culture period. We observed an expansion of colony-forming units granulocyte-macrophage (CFU-GM) and BFU-E beginning on day 3 of culture, reaching an approximate 2-log increase by days 5 to 7. Limiting dilution analysis of primitive in vitro clonogenic progenitors was performed through a week 6 cobblestone-area-forming cell (CAFC) assay, which has previously been shown to detect long-term bone marrow culture-initiating cells (LTC-IC). A maintenance or a slight (threefold) increase of week 6 CAFC/LTC-IC was found after one week of culture. To analyze the presence of BPC mediating in vivo engraftment, expanded CD34+ cells were transplanted into preirradiated NOD/SCID mice at various time points. Only CD34+ cells cultured for up to four days successfully engrafted murine bone marrow with human cells expressing myeloid or lymphoid progenitor phenotypes. In contrast, five- and seven-day expanded human BPC did not detectably engraft NOD/SCID mice. When FL, SCF and IL-3-supplemented cultures were performed for seven days on fibronectin-coated plastic, or when IL-3 was replaced by thrombopoietin, colony forming cells and LTC-IC reached levels similar to those of control cultures, yet no human cell engraftment was recorded in the mice. Also, culture in U-bottom microplates resulting in locally increased CD34+ cell density had no positive effect on engraftment. These results indicate that during ex vivo expansion of human CD34+ cells, CFC and LTC-IC numbers do not correlate with the potential to repopulate NOD/SCID mice. Our results suggest that ex vivo expanded BPC should be cultured for limited time periods only, in order to preserve bone-marrow-repopulating hematopoietic stem cells.     

Ex vivo expansion of megakaryocyte progenitor cells: cord blood versus mobilized peripheral blood

Thrombocytopenia is a problematic and potentially fatal occurrence after transplantation of cord blood stem cells. This problem may be alleviated by infusion of megakaryocyte progenitor cells. Here, we compared the ability of hematopoietic progenitor cells obtained from cord blood and expanded in culture to that of mobilized peripheral blood cells. The CD34(+) cells were plated for 10 days in presence of thrombopoietin (TPO) alone and combined with stem cell factor (SCF), Flt3-ligand (FL), interleukin-3 (IL-3), IL-6, and IL-11. Cells were analyzed for the CD41 and CD42b expression and for their ploidy status. Ex vivo produced platelets were enumerated. We show that (1) TPO alone was able to induce differentiation of CD34(+) cells into CD41(+) cells, with limited total leucocyte expansion; (2) the addition of SCF to TPO decreased significantly CD41(+) cell percentage in CB, but not in MPB; and (3) in CB, the addition of FL, IL-6, and IL-11 to TPO increased the leukocyte expansion with differentiation and terminal maturation into MK lineage. In these conditions, high numbers of immature CD34(+)CD41(+) MK progenitor cells were produced. Our results thereby demonstrate a different sensitivity of CB and MPB cells to SCF, with limited CB MK differentiation. This different sensitivity to SCF (produced constitutively by BM stromal cells) could explain the longer delay of platelet recovery after CB transplant. Nevertheless, in CB, the combination of TPO with FL, IL-6, and IL-11 allows generation of a suitable number of immature MK progenitor cells expressing both CD34 and CD41 antigens, which are supposed to be responsible for the platelet recovery after transplantation.