In Vivo Modulation of Mitochondrial Activity Determines HSC Engraftment and Post-Transplant Survival in Mice

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 213-213
Author(s):  
Nicola Vannini ◽  
Olaia M. Naveiras ◽  
Vasco Campos ◽  
Eija Pirinen ◽  
Riekelt Houtkooper ◽  
...  

Abstract Abstract 213 Cellular metabolism is emerging as a potential fate determinant in cancer and stem cell biology, constituting a crucial regulator of the hematopoietic stem cell (HSC) pool [1–4]. The extremely low oxygen tension in the HSC microenvironment of the adult bone marrow forces HSCs into a low metabolic profile that is thought to enable their maintenance by protecting them from reactive oxygen species (ROS). Although HSC quiescence has for long been associated with low mitochondrial activity, as testified by the low rhodamine stain that marks primitive HSCs, we hypothesized that mitochondrial activation could be an HSC fate determinant in its own right. We thus set to investigate the implications of pharmacologically modulating mitochondrial activity during bone marrow transplantation, and have found that forcing mitochondrial activation in the post-transplant period dramatically increases survival. Specifically, we examined the mitochondrial content and activation profile of each murine hematopoietic stem and progenitor compartment. Long-term-HSCs (LT-HSC, Lin-cKit+Sca1+ (LKS) CD150+CD34-), short-term-HSCs (ST-HSC, LKS+150+34+), multipotent progenitors (MPPs, LKS+150-) and committed progenitors (PROG, Lin-cKit+Sca1-) display distinct mitochondrial profiles, with both mitochondrial content and activity increasing with differentiation. Indeed, we found that overall function of the hematopoietic progenitor and stem cell compartment can be resolved by mitochondrial activity alone, as illustrated by the fact that low mitochondrial activity LKS cells (TMRM low) can provide efficient long-term engraftment, while high mitochondrial activity LKS cells (TMRM high) cannot engraft in lethally irradiated mice. Moreover, low mitochondrial activity can equally predict efficiency of engraftment within the LT-HSC and ST-HSC compartments, opening the field to a novel method of discriminating a population of transitioning ST-HSCs that retain long-term engraftment capacity. Based on previous experience that a high-fat bone marrow microenvironment depletes short-term hematopoietic progenitors while conserving their long-term counterparts [5], we set to measure HSC mitochondrial activation in high-fat diet fed mice, known to decrease metabolic rate on a per cell basis through excess insulin/IGF-1 production. Congruently, we found lower mitochondrial activation as assessed by flow cytometry and RT-PCR analysis as well as a depletion of the short-term progenitor compartment in high fat versus control chow diet fed mice. We then tested the effects of a mitochondrial activator known to counteract the negative effects of high fat diet. We first analyzed the in vitro effect on HSC cell cycle kinetics, where no significant change in proliferation or division time was found. However, HSCs responded to the mitochondrial activator by increasing asynchrony, a behavior that is thought to directly correlate with asymmetric division [6]. As opposed to high-fat diet fed mice, mice fed with the mitochondrial activator showed an increase in ST-HSCs, while all the other hematopoietic compartments were comparable to mice fed on control diet. Given the dependency on short-term progenitors to rapidly reconstitute hematopoiesis following bone marrow transplantation, we tested the effect of pharmacological mitochondrial activation on the recovery of mice transplanted with a limiting HSC dose. Survival 3 weeks post-transplant was 80% in the treated group compared to 0% in the control group, as predicted by faster recovery of platelet and neutrophil counts. In conclusion, we have found that mitochondrial activation regulates the long-term to short-term HSC transition, unraveling mitochondrial modulation as a valuable drug target for post-transplant therapy. Identification of molecular pathways accountable for the metabolically mediated fate switch is currently ongoing. Disclosures: No relevant conflicts of interest to declare.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 361-361 ◽  
Author(s):  
Laura A. Paganessi ◽  
Stephanie A. Gregory ◽  
Henry C. Fung ◽  
Kent W. Christopherson

Abstract A firm understanding of the biology of hematopoietic stem and progenitor cell (HSC/ HPC) trafficking is believed to be critical for the development of methodologies to improve transplant efficiency and subsequently immune reconstitution during hematopoietic stem cell transplantation in the clinical setting. Through the use of CD26 inhibitors and CD26 deficient mice (CD26−/−), we have previously generated data in mice suggesting that suppression of CD26/DPPIV (dipeptidylpeptidase IV) enzymatic activity on the transplant donor cell population can be utilized as a method of increasing transplant efficiency (Christopherson, KW 2nd, et al, Science 2004. 305:1000–3). However, the clinical importance of the transplant recipient should not to be overlooked given the potential importance of the bone marrow microenvironment in regulating the transplant process. We therefore investigated here whether inhibition or loss of CD26 activity in recipient mice would have an effect on transplant efficiency utilizing an in vivo congenic mouse model of transplantation. The short-term homing and long-term engraftment of BoyJ donor cells (expressing CD45.1+) into lethally irradiated control C57BL/6, CD26 inhibitor (Diprotin A) treated C57BL/6, or CD26−/− mice (expressing CD45.2+) was monitored by flow cytometric analysis of the bone marrow and peripheral blood at 24 hours and 6 months post-transplant respectively. Twenty-four hours post-transplant of 20×106 BoyJ mononuclear cells, we observed 8.85±0.58%, 10.69±1.01%, and 12.45±1.33% donor derived Sca-1+lin− cells in the bone marrow of recipient mice for control, Diprotin A treated, and CD26−/− recipient mice respectively. As compared to control mice, this represents a 20.8% increase (p=0.01) with CD26 inhibitor treatment and a 40.7% increase (p£0.05) resulting from the use of a CD26−/− recipient in short-term homing (N=5 mice per group). Six months post-transplant of 1×105 BoyJ mononuclear cells, we observed 39.90± 4.38%, 70.22± 3.72%, and 92.51± 1.04% donor contribution to hematopoiesis in the peripheral blood of control, Diprotin A treated, and CD26−/− recipient mice respectively. This represents a 76.0% increase (p£0.01) with CD26 inhibitor treatment and a 131.9% increase (p£0.01) as a result of the CD26−/− recipient in long-term engraftment as compared to control recipient mice (N=14 mice per group). These results provide pre-clinical evidence of the importance of CD26 expression within the transplant recipient with regard to regulating hematopoietic stem cell homing and engraftment. Our results also support the potential use of CD26 inhibitors to treat transplant patients during hematopoietic stem cell transplantation as a method of improving transplant efficiency. Lastly, our use of inhibitor treated C57BL/6 and CD26−/− recipient mice, which are also on a C57BL/6 background, in conjunction with a congenic model of transplantation provides a accurate and convenient model system for the in vivo testing of the efficacy of existing and new CD26 inhibitors in transplant recipients.


Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 33-33 ◽  
Author(s):  
Shiri Gur Cohen ◽  
Tomer Itkin ◽  
Sagarika Chakrabarty ◽  
Claudine Graf ◽  
Orit Kollet ◽  
...  

Abstract Bone marrow (BM) homing and lodgment of long-term repopulating hematopoietic stem cells (LT-HSCs) is an active and essential first step in clinical stem cell transplantation. EPCR is expressed by murine BM LT-HSCs endowed with the highest repopulation potential and its ligand, activated protein C (aPC), has anticoagulant and anti-sepsis effects in EPCR+/PAR1+ endothelial cells. We recently found that signaling cascades, traditionally viewed as coagulation and inflammation related, also independently control EPCR+ LT-HSC BM retention and recruitment to the blood via distinct PAR1 mediated pathways. EPCR/PAR1 signaling retains LT-HSCs in the BM by restricting nitric oxide (NO) production and Cdc42 activity, promoting VLA4 affinity and adhesion. Conversely, thrombin/PAR1 signaling overcome EPCR+ LT-HSC BM retention by initiating NO production, leading to TACE-‎mediated EPCR shedding, CXCR4 and PAR1 upregulation and parallel CXCL12 secretion by PAR1+ BM stromal cells, enhancing stem cell migration and mobilization. Since EPCR shedding is essential for BM LT-HSC recruitment, we tested EPCR role in LT-HSC BM homing. EPCR+ LT-HSC exhibited reduced in vitro migration towards CXCL12 and enhanced CXCL12-dependent adhesion to fibronectin. Unexpectedly, transplanted EPCR+ LT-HSCs preferentially homed ‎to the host BM, while immature progenitors were equally distributed between the BM and spleen. Specificity of BM homing was further confirmed by EPCR neutralizing antibody treatment, which blocks binding to aPC, leading to attenuated EPCR+ LT-HSC homing to the BM but not to the spleen. Importantly, short term aPC pretreatment inhibited NO production and dramatically increased EPCR+ LT-HSC BM homing. Since EPCR navigates LT-HSC to the BM, we studied the role of EPCR signaling in LT-HSC BM repopulation. Mimicking EPCR signaling by in vivo NO inhibition induced preferential expansion of blood and bone-forming stem cells and gave rise to higher donor type EPCR+ LT-HSCs in competitive repopulation assays. Similarly, repeated treatment with aPC expanded BM EPCR+ stem cells and increased competitive LT-repopulation. Importantly, loss of EPCR function reduced HSC long-term repopulation ability while maintaining their short-term repopulation activity. BM HSCs obtained from Procrlow mice, expressing markedly reduced surface EPCR, failed to compete with normal stem cells in competitive long-term repopulation assays. Consistent with inferior HSC BM repopulation, Procrlow mice exhibited reduced numbers of BM LT-HSC with reduced adhesion capacity. Additionally, these mice displayed increased HSC frequencies in the blood circulation and the spleen, which were pharmacologically corrected by inhibiting NO generation with L-NAME treatment. BM retention is essential for quiescent HSC protection from chemotherapy. Mice treated with NO donor SNAP, or with blocking EPCR antibody as well as Fr2-/-mice lacking PAR1 expression, were more susceptible to hematological failure and mortality induced by 5-FU treatment compared to control mice. Together, these results indicate a functional aPC/EPCR/PAR1 signaling pathway, regulating EPCR+ LT-HSC BM homing, adhesion and long-term repopulation potential. The thrombin-thrombomodulin (TM) complex converts protein C to its activated form aPC, facilitating high affinity binding to its receptor EPCR. To further address the preferential homing of EPCR+ LT-HSCs to the BM, we found that TM is exclusively expressed by a unique BM endothelial cell (BMEC) subpopulation, but not in the spleen. Moreover, EPCR+ LT-HSCs were found adjacent to TM+/aPC+ BMECs, imposing their adhesion and retention. Interestingly, similar to BMECs, BM EPCR+ LT-HSC also express surface TM, implying the possibility of autocrine aPC generation. Herein we define EPCR as a guidance molecule, navigating slow migrating LT-HSC in the blood flow specifically to TM+ BMEC supporting niches, maintaining NOlow stem cell retention, long-term blood production and protection from myelotoxic insult. Conversely, thrombin/PAR1 signaling oppositely increase NO generation and EPCR shedding allowing increased CXCR4-dependent LT-HSC migration and mobilization. Harnessing EPCR signaling may improve clinical stem cell transplantation, increasing LT-HSC specific BM homing and repopulation by aPC pretreatment, as well as potentially to overcome malignant stem cell chemotherapy resistance. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 5117-5117
Author(s):  
Valentina Giai ◽  
Elona Saraci ◽  
Eleonora Marzanati ◽  
Christian Scharenberg ◽  
Monica De Stefanis ◽  
...  

Abstract BACKGROUND: In the recent years, numerous studies based on multicolor flowcytometry have analyzed the different subpopulations of bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) (Manz MG et al, PNAS 2002; Majeti R et al, Cell Stem Cell 2007): the common myeloid progenitors (CMPs: Lin-CD34+CD38+CD45RA-CD123+), the granulocyte-macrophage progenitors (GMPs: Lin-CD34+CD38+CD45RA+CD123+) and the megakaryocyte-erythroid progenitors (MEPs: Lin-CD34+CD38+CD45RA-CD123-) constitute the progenitor compartment, while the hematopoietic stem cells (HSCs: Lin-CD34+CD38- CD45RA-CD90+), the multipotent progenitors (MPPs: Lin-CD34+CD38- CD45RA-CD90-) and the lymphoid-myeloid multipotent progenitors (LMPPs: Lin-CD34+CD38- CD45RA+CD90-) represent the more immature HSPCs. In animal models, the progenitor compartment includes short-term repopulating cells, leading to the hematological recovery in the first 5 weeks after transplantation, whereas the stem cell compartment comprehends the long-term repopulation cells, responsible for the long-term hematological recovery. However, very little is known about the different subpopulations of HSPCs among peripheral blood (PB) CD34+ in basal state and after mobilization for harvest and transplantation. Our study was conducted to analyze PB CD34+ cells from healthy volunteers and from hematological patients during CD34+ cells mobilization. Our main aim was to understand if the proportions of different HSPCs among PB CD34+ cells were similar to those found in BM and whether the mobilizing regimens employed in chemo treated patients differently affected CD34+ cells subfractions in PB. METHODS: multicolor flowcytometry was used to analyze CD34+ cells from 4 BM samples and 9 PB samples from healthy volunteers and 32 PB samples from hematological patients prior CD34+ cells harvesting. RESULTS: Percentages of CD34+ cells subpopulations were different in basal PB compared to the BM: indeed, CMPs, GMPs and MEPs constituted respectively 27.6% ± 9.5, 23.8% ± 7.2 and 27.6% ± 16.2 of BM CD34+ cells and 47.8% ± 9.5, 10.3% ± 6.9 and 16.1% ± 7.6 of the total PB CD34+ cells. HSCs constituted 2.1% of BM and 1.5% of PB CD34+ cells. The differences between BM and circulating CMPs and GMPs were significant (p<0.005 and p<0.01). No differences in subpopulations proportions were shown comparing G-CSF mobilized and basal PB CD34+ cells. Interestingly, the 2 patients mobilized with AMD3100 (the inhibitory molecule for CXCR4) showed a higher percentage of GMPs (33.8% and 37.8% versus the average 16.3% ± 9.8 in G-CSF mobilized samples) and a lower fraction of CMPs (29.5% and 41.6% versus the average 58% ± 12 in G-CSF mobilized samples). In order to understand this result, we looked then at the CXCR4 mean fluorescence intensity among the progenitor subsets: GMPs showed significantly higher levels of this molecule compared to CMPs and MEPs. Regarding the mobilizing chemotherapy regimens, CMPs percentages were higher (61.1% versus 49.1%, p: 0.038) and GMPs’ were significantly lower (11.1% versus 27.6%, p<0.0001) in cyclophosphamide treated patients, compared to patients mobilized with other chemotherapy regimens. The percentage of HSCs did not significantly differ among bone marrow, unmobilized and mobilized PB CD34+ cells. Therefore, since an average collection of mobilized PB cells contains approximately one log more CD34+ cells than a BM harvest, a similarly higher amount of HSC are infused with mobilized CD34+ cell transplantation. A linear positive correlation between the number of mobilized CD34+ cells and the number of mobilized CMPs, GMPs, and MEPs was observed indicating that the proportions of different HSPCs did not significantly change among high- and low-mobilizers. There were no correlations between the number of mobilized subpopulations and leucocytes, hemoglobin and platelets levels. CONCLUSIONS: Our data displayed the heterogeneity of HSPC compartment between PB and BM. Many factors could contribute to this variegated scenario. These mechanisms comprehension can help us to choose the most suitable chemotherapy and cytokine administrations in order to improve clinical outcomes as infections complications, length of aplasia and transfusion requirements during an hematopoietic stem cell transplantation. Disclosures Palumbo: Bristol-Myers Squibb: Consultancy, Honoraria; Genmab A/S: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen-Cilag: Consultancy, Honoraria; Millennium Pharmaceuticals, Inc.: Consultancy, Honoraria; Onyx Pharmaceuticals: Consultancy, Honoraria; Array BioPharma: Honoraria; Amgen: Consultancy, Honoraria; Sanofi: Honoraria. Boccadoro:Celgene: Honoraria; Janssen: Honoraria; Onyx: Honoraria.


Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 821-821 ◽  
Author(s):  
Marina Cavazzana-Calvo ◽  
Nathalie Cartier ◽  
Salima Hacein-Bey Abina ◽  
Gabor Veres ◽  
Manfred Schmidt ◽  
...  

Abstract We report preliminary results in 3 children with cerebral X-linked adrenoleukodystrophy (ALD) who received in September 2006, January 2007 and June 2008 lentiviral vector transduced autologous hematopoietic stem cell (HSC). We have previously demonstrated that cerebral demyelination associated with cerebral ALD can be stopped or reversed within 12–18 months by allogeneic HSC transplantation. The long term beneficial effects of HCT transplantation in ALD are due to the progressive turn-over of brain macrophages (microglia) derived from bone-marrow cells. For the current HSC gene therapy procedure, we used mobilized peripheral blood CD34+ cells that were transduced ex vivo for 18 hours with a non-replicative HIV1-derived lentiviral vector (CG1711 hALD) at MOI25 and expressing the ALD cDNA under the control of the MND (myeloproliferative sarcoma virus enhancer, negative control region deleted, dl587rev primer binding site substituted) promoter, and in the presence of 4 human recombinant cytokines (Il- 3, Stem Cell Factor [SCF], Flt3-ligand and Megakaryocyte Growth and Differentiation Factor [MGDF]) and CH-296 retronectine. Transduced cells were frozen to perform the required (RCL) safety tests. After thawing and prior to reinjection, 50%, 30% and 40% of transduced CD34+ cells expressed the ALD protein with a mean of 0.7, 0.6 and 0.65 copies of integrated provirus per cell. Transduced CD34+ cells were infused to ALD patients after a conditioning regimen including full doses of cyclophosphamide and busulfan. Hematopoietic recovery occured at day 13–15 post-transplant and the procedure was uneventful. In patient P1 and P2, the percentage of lymphocytes and monocytes expressing the ALD protein declined from day 60 to 6 months after gene therapy (GT) and remained stable up to 16 months post-GT. In P1, 9 to 13% of CD14+, CD3+, CD19+ and CD15+ cells expressed ALD protein 16 months post-transplant. In P2 and at the same time-point after transplant, 10 to 18% of CD14+, CD3+, CD19+ and CD15+ cells expressed ALD protein. ALD protein was expressed in 18–20% of bone marrow CD34+ cells from patients P1 and P2, 12 months post-transplant. In patient P3, 20 to 23% of CD3+, CD14+ and CD15+ cells expressed ALD protein 2 months after transplant. Tests assessing vector-derived RCL and vector mobilization were negative up to the last followups in the 3 patients. Integration of the vector was polyclonal and studies of integration sites arein progress. At 16 months post-transplant, HSC gene therapy resulted in neurological effects comparable with allogeneic HSC transplantation in patient P1 and P2. These results support that: ex-vivo HSC gene therapy using HIV1-derived lentiviral vector is not associated with the emergence of RCL and vector mobilization; a high percentage of hematopoietic progenitors were transduced expressing ALD protein in long term; no early evidence of selective advantage of the transduced ALD cells nor clonal expansion were observed. (This clinical trial is sponsored by Institut National de la Santé et de la Recherche Médicale and was conducted in part under a R&D collaboration with Cell Genesys, Inc., South San Francisco, CA)


Blood ◽  
2018 ◽  
Vol 132 (7) ◽  
pp. 735-749 ◽  
Author(s):  
Simranpreet Kaur ◽  
Liza J. Raggatt ◽  
Susan M. Millard ◽  
Andy C. Wu ◽  
Lena Batoon ◽  
...  

Key Points Recipient macrophages persist in hematopoietic tissues and self-repopulate via in situ proliferation after syngeneic transplantation. Targeted depletion of recipient CD169+ macrophages after transplant impaired long-term bone marrow engraftment of hematopoietic stem cells.


Blood ◽  
2015 ◽  
Vol 125 (17) ◽  
pp. 2678-2688 ◽  
Author(s):  
Marisa Bowers ◽  
Bin Zhang ◽  
Yinwei Ho ◽  
Puneet Agarwal ◽  
Ching-Cheng Chen ◽  
...  

Key Points Bone marrow OB ablation leads to reduced quiescence, long-term engraftment, and self-renewal capacity of hematopoietic stem cells. Significantly accelerated leukemia development and reduced survival are seen in transgenic BCR-ABL mice following OB ablation.


Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2193-2193
Author(s):  
Munir Shahjahan ◽  
Jorge Alamo ◽  
Sergio Giralt ◽  
Michelle Detry ◽  
Mark Munsell ◽  
...  

Abstract Allogeneic HSCT has the potential to cure patients with AML or MDS, but is associated with significant morbidity and complications that can affect the QOL of survivors. We examined QOL of AML/MDS patients surviving 2 years or more in remission after allo HSCT, including physical, psychosocial and functional well being. OBJECTIVES: We seek to describe QOL of long-term survivors (LTS) with AML/MDS and to compare QOL as a function of age at transplant. METHODS: Long-term survivorship was defined as survival in remission beyond 2 years from HSCT; 2 years was chosen given the stabilization of the failure rate on the 3rd year after HSCT. There were 544 adult AML/MDS patients treated with allogeneic HSCT between January 1976 and September 2001. Of these, 129 (24%) were in remission for at least 2 years and were eligible for the study. QOL was assessed using the standardized Functional Assessment of Cancer Therapy-BMT (FACT-BMT) questionnaire that measures multidimensional QOL concepts and consists of 5 subscales measuring physical (PWB), functional (FWB), social/family (SFWB), and emotional well being (EWB), including satisfaction with the doctor-patient relationship (RWD) (McQuellon et al., Bone Marrow Transplant, 1997). There was an additional concern (AC) subscale that asked questions related to job, appetite, body appearance, tiredness, interest in sexual activity etc. FACT-BMT allowed for responses to have values ranging from 0 (not at all) to 4 (very much). Specified QOL questions were recorded so that higher score reflected a higher QOL in the reported dimension. The questionnaire was mailed, and delivery could be confirmed for 121 patients out of whom 82 (68%) responded. Demographic and clinical characteristics were collected from patient charts and clinical database. RESULTS: Median age at transplant was 38.44 years (range 18.54–68.08). Median time from HSCT to receipt of questionnaire was 4.53 years. Gender: 47 males and 35 females. Diagnosis: AML (n=70) and MDS (n=12). Conditioning regimens were of reduced intensity in 29 cases and myeloablative in 53 cases. Stem cell source: bone marrow (n=52), and peripheral blood (n=30). GVHD prophylaxis: tacrolimus based in 61 cases and cyclosporine based in 18 cases; none in 2 cases. Disease status at HSCT: complete remission (n=40), relapsed (n= 37) and untreated disease (n=5). Median follow-up time was 4.53 years (range 2.0–21.1 yrs). There were no significant differences in QOL scores between the older and younger patients (above and below the median age at transplant) in the PWB, SFWB, EWB, FWB and RWD subscales. In the AC subscale, however, older patients had higher QOL scores than younger patients (mean score 37.97 vs. 33.25, p=0.005). When we compared non-myeloablative (NMA) vs. myeloablative (MA) regimens, there were no significant differences in mean QOL scores in all but the AC subscale where NMA group did better (39.00 vs. 33.34, p=0.001). Acute graft versus host disease (aGVHD) did not impact long-term QOL but lack of chronic GVHD was associated with better QOL score in the PWB, EWB, FWB and AC subscales (PWB: 25.04 vs. 20.62, p=0.005; EWB: 21.77 vs. 18.98, p=0.003; FWB: 22.91 vs. 18.00, p=0.008; and AC: 40.00 vs. 34.28, p=0.002). CONCLUSIONS: Among LTS with AML/MDS, older age did not affect QOL at a median of 4.5 yrs post HSCT.


Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2846-2846
Author(s):  
M. Kozik ◽  
J. Banks ◽  
L. Fanning ◽  
M. Finney ◽  
Y. Huang ◽  
...  

Abstract Cytokine-based expansion of umbilical cord blood (UCB) in vitro prior to infusion has been pursued in an attempt to overcome the limited cellular content of a single UCB unit. Thus far, these attempts have not shown improvement in kinetics of donor-derived hematopoietic recovery. Our studies have incorporated UCB expanded over a feeder-layer of human mesenchymal stem cells (huMSC), known to inhibit the differentiation of hematopoietic stem cells (HSC) observed in expansion with cytokines alone. Expansion conditions included: UCB expanded over a huMSC monolayer with the addition of cytokines (IL-3, IL-6, G-CSF, SCF, FLT-3L, EPO) and UCB expanded in the same cytokines alone. Day 12 culture readouts included: viable cell counts, 4-color flow analysis, and rates of human engraftment in NOD/SCID mice. In the current study the fold expansion was 6.4 fold in the huMSC + cytokines condition and 7 fold in the cytokines alone condition. Flow cytometry surface marker analysis proportions (absolute numbers) were notable for higher proportions and numbers of early HSC expressing CD133 in cultures incorporating huMSC stromal layer: Unexpanded MSC+ cytokines Cytokines CD34 0.68 (.068M) 0.74 (3.63M) 1.94 (5.39M) CD133 5.69 (.569M) 2.56 (12.54M) 0.74 (2.06M) CD3 49.6 (4.96M) 2.2 (10.78M) 0.42 (1.17M) CD56 17.4 (1.74M) 2.71 (13.28M) 1.06 (2.95M) CD69 0.80 (7.28M) 7.28 (35.67M) 24.4 (67.8M) UCB graft T and NK populations were maintained in huMSC culture conditions and the observed difference in CD69 expression supports the hypothesis that huMSC may have an inhibitory effect on T cell activation during UCB ex vivo expansion. To assess the human engraftment potential of the cultures, cells from each culture condition were injected by tail vein into NOD/SCID mice (no CD34 selection was performed). Mice receiving unexpanded UCB received 10M mononuclear cells each. Mice receiving culture expanded cells received cell doses in proportion to the fold expansion over the number of cells at the initiation of the cultures. Engraftment was assessed by the percentage of human CD45+ (≥0.4%) cells found within the bone marrow of mice at seven weeks post infusion. Mice were injected as follows: 7 mice with unexpanded UCB (2 of which died within a month of transplant), 7 mice with UCB expanded in huMSC + cytokines, and 3 mice with UCB expanded in cytokines alone. Flow analysis of mouse bone marrow cells revealed average CD45+ percentages of 1.79% for mice injected with unexpanded UCB, 2.66% for mice injected with cytokine alone cells, and 5.94% for mice injected with huMSC + cytokine cells. Human cell subset analysis was performed for CD3, CD19, and CD56 content. The percentages of gated CD45+ co-expressing CD3+ were 10.3% in the unexpanded UCB, 16.6% in the cytokine alone condition and 10.4% in the huMSC + cytokine condition. Cells co-expressing CD19+ were 7.86% in the unexpanded UCB, 8.31% in the huMSC + cytokine condition and dropped to 1.43% in the cytokine alone condition. Gated CD45+ cells co-expressing CD56+ were 16.4% in the unexpanded UCB, 8.8% in the huMSC + cytokines condition, and dropped to 2.6% in the cytokines alone condition. In conclusion, UCB expanded short-term in cytokines demonstrates maintenance of earlier HSC phenotype and improved human engraftment in NOD/SCID in cultures incorporating a huMSC monolayer platform.


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