Xenografts of Pediatric Acute Lymphoblastic Leukemia Retain the Gene Expression Pattern From the Diagnostic Material They Originated From Over Serial Passages.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1629-1629
Author(s):  
Manon Queudeville ◽  
Elena Vendramini ◽  
Marco Giordan ◽  
Sarah M. Eckhoff ◽  
Giuseppe Basso ◽  
...  
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Expression Profiles ◽  
Lymphoblastic Leukemia ◽  
Gene Expression Profiles ◽  
Leukemia Cells ◽  
Diagnostic Samples ◽  
Xenotransplantation Model

Abstract Abstract 1629 Poster Board I-655 Primary childhood acute lymphoblastic leukemia (ALL) samples are very difficult to culture in vitro and the currently available cell lines only poorly reflect the heterogeneous nature of the primary disease. Many groups therefore use mouse xenotransplantation models not only for in vivo testing but also as a means to amplify the number of leukemia cells to be used for various analysis. It remains unclear as to what extent the xenografted samples recapitulate their respective primary leukemia. It has been suggested for example that transplantation may result in the selection of a specific clone present only to a small amount in the primary diagnostic sample. We used a NOD/SCID xenotransplantation model and injected leukemia cells isolated from fresh primary diagnostic material of 4 pediatric ALL patients [2 pre-B-ALL, 1 pro-B-ALL (MLL/AF4}, 1 cortical T-ALL] intravenously into the lateral tail vein of unconditioned mice. As soon as the mice presented clinical signs of leukemia, leukemia cells were isolated from bone marrow and spleen. Isolated leukemia cells were retransplanted into secondary and tertiary recipients. RNA was isolated from diagnostic material and serial xenograft passages and gene expression profiles were obtained using a human whole genome array (Affymetrix U133 2.0). Simultaneously, immunophenotypic analysis via multicolor surface and cytoplasmatic staining by flow cytometry was performed for the diagnostic samples and respective serial xenograft passages. In an unsupervised clustering analysis the diagnostic sample of each patient clustered together with the 3 derived xenograft samples, although the 3 xenograft samples clustered stronger to each other than to their respective diagnostic sample. Comparison of the 4 diagnostic samples vs. all xenograft samples resulted in a gene list of 270 genes upregulated at diagnosis and 8 genes upregulated in the xenograft passages (Wilcoxon, p< .05). The high number of genes upregulated at diagnosis is most likely due to contamination of primary patient samples with normal peripheral blood and/or bone marrow cells as 15% of genes are attributed to myeloid cells, 7% to erythroid cells, 7% to lymphoid cells, 32% to bone marrow in general as well as to innate immunity, chemokines, immunoglobulins. The remaining genes can not be attributed to a specific hematopoetic cell lineage and are not known to be related to leukemia or cancer in general. Accordingly, there are no statistically significant differences between the primary, secondary and tertiary xenograft passages. The immunophenotype analysis are also in accordance with these findings, as the diagnostic blast population retains its immunophenotypic appearance during serial transplantation, whereas the contaminating CD45-positive non- leukemic cells disappear after the first xenograft passage. The few genes upregulated in xenograft samples compared to diagnosis are mainly involved in cell cycle regulation, protein translation and apoptosis resistance. Some of the identified genes have already been described in connection with cancer subtypes, their upregulation therefore being indicative of a high proliferative state in general and could argue towards a more aggressive potential of the engrafted leukemia cells but alternatively could also simply be due to the fact that the xenograft samples are pure leukemic blasts and are not contaminated with up to 15% of non-cycling healthy bone marrow cells as in the diagnostic samples. We conclude that the gene expression profiles generated from xenografted leukemias are very similar to those of their respective primary leukemia and moreover remain stable over serial retransplantation passages as we observed no statistically significant differences between the primary, secondary and tertiary xenografts. The differentially expressed genes between diagnosis and primary xenotransplant are most likely to be due to contaminating healthy cells in the diagnostic samples. Hence, the NOD/SCID-xenotransplantation model recapitulates the primary human leukemia in the mouse and is therefore an appropriate tool for in vivo and ex vivo studies of pediatric acute leukemia. Disclosures No relevant conflicts of interest to declare.

Identification of Gene Expression Profiles in Acute Lymphoblastic Leukemia Cells That Discriminate Intracellular Thioguanine Nucleotide Accumulation in ALL Cells after In Vivo Treatment with Mercaptopurine.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 453-453
Author(s):  
Gianluigi Zaza ◽  
Meyling Cheok ◽  
Wenjian Yang ◽  
Pei Deqing ◽  
Cheng Cheng ◽  
...  
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
Expression Profiles ◽  
Lymphoblastic Leukemia ◽  
Gene Expression Profiles ◽  
Post Treatment ◽  
Leukemia Cells ◽  
True Positive

Abstract Thioguanine nucleotides (TGN) are considered the principal active metabolites exerting the antileukemic effects of mercaptopurine (MP). Numerous clinical studies have reported substantial inter-patient variability in intracellular TGN concentrations during continuation therapy of acute lymphoblastic leukemia (ALL). To identify genes whose expression is related to the intracellular accumulation of TGN in leukemia cells after in vivo treatment with MP alone (MP) or in combination with MTX (MP+MTX), we used oligonucleotide microarrays (Affymetrixâ HG-U95Av2) to analyze the expression of approximately 9,670 genes in bone marrow leukemic blasts obtained at diagnosis from 82 children with ALL. TGN levels were determined in bone marrow aspirates of these patients 20 hours after mercaptopurine infusion (1 g/m2 I.V). Because, as previously reported, patients treated with MP alone achieved higher levels of intracellular TGN compared to those treated with the combination, we used Spearman’s rank correlation to identify genes associated with TGN levels separately for the 33 patients treated with MP alone and the 49 with the combination (MP: median TGN: 2.46 pmol/5x106 cells, range: 0.01–19.98; and MTX+MP: median TGN: 0.55 pmol/5x106 cells, range: 0.005–3.31). Hierarchical clustering using these selected probe sets clearly separated the 33 patients treated with MP alone into two major groups according to TGN concentration (< 2.46 and > 2.46 pmol/5x106 cells; n=60 genes) and two major branches were also found for patients treated with the combination (< 0.55 and > 0.55 pmol/5x106 cells; n=75 genes). Interestingly, there was no overlap between the two sets of genes, indicating that different genes influence the accumulation of TGN when this drug is given alone or in combination with MTX. The association between gene expression profiles and TGN levels determined by leave-one-out cross-validation using support vector machine (SVM) based on Spearman correlation, was rho=0.60 (p<0.001) for MP alone and rho=0.65 (p<0.001) for MTX+MP, with false discovery rate (FDR) computed using Storey’s q-value (MP: 50% true positive, MTX+MP: 70% true positive respectively). Genes highly associated with the post-treatment TGN level in ALL patients treated with MP alone encode transporters, enzymes involved in the MP metabolic pathway and cell proliferation. Genes associated with post-treatment levels of TGN after combined therapy have been implicated in protein and ATP biosynthesis. Together, these in vivo data provide new insights into the basis of inter-patient differences in TGN accumulation in ALL cells, revealing significant differences between treatment with MP alone or in combination with MTX.

Gene Expression Profiling of Murine HOXB4-Transduced HSCs Shows Multiple Counter-Regulatory Signals That May Control HSC Pool Size

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2361-2361
Author(s):  
Hui Yu ◽  
Sheng Zhou ◽  
Geoffrey A. Neale ◽  
Brian P. Sorrentino
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Expression Profiles ◽  
Gene Expression Profiles ◽  
Expression Array ◽  
Self Renewal ◽  
Time Points ◽  
Time Point

Abstract Abstract 2361 HOXB4 is a homeobox transcription factor that can induce hematopoietic stem cell (HSC) expansion both in vivo and in vitro. An interesting feature of HOXB4-induced HSC expansion is that HSC numbers do not exceed normal levels in vivo due to an unexplained physiological capping mechanism. To gain further insight into HOXB4 regulatory signals, we transplanted mice with bone marrow cells that had been transduced with a MSCV-HOXB4-ires-YFP vector and analyzed gene expression profiles in HSC-enriched populations 20 weeks after transplant, a time point at which HSC numbers have expanded to normal levels but no longer increasing beyond physiologic levels. We used Affymetrix arrays to analyze gene expression profiles in bone marrow cells sorted for a Lin−Sca-1+c-Kit+ (LSK), YFP+ phenotype. Using ANOVA, we identified1985 probe sets with >2 fold difference in expression (FDR<, 0.1) relative to a control vector-transduced LSK cells. A cohort of genes was identified that were known positive regulators of HSC self-renewal and proliferation. Hemgn, which we identified in a previous screen as a positive regulator of expansion and a direct transcriptional target of HOXB4, was 3.5 fold up-regulated in HOXB4 transduced LSKs. Other genes known to be important for HSCs survival, self-renewal and differentiation were upregulated to significant levels including N-myc, Meis1, Hoxa9, Hoxa10 and GATA2. Microarray data for selected genes was validated by quantitative real-time PCR on HOXB4 transduced CD34low LSK cells, a highly purified HSC population, obtained from another set of transplanted mice at the 20 week time point. In contrast, other gene expression changes were noted that would potentially limit or decrease stem cell numbers. PRDM16, a set domain transcription factor critical for HSC maintenance and associated with clonal hematopoietic expansions when inadvertently activated as a result of retroviral insertion, was dramatically down-regulated on the expression array and 7.6 fold decreased in the real time PCR assay of CD34low LSK cells. TFG-beta signaling is a well defined inhibitor HSC proliferation and utilize Smad proteins as downstream effectors. Expression of Smad1 and Smad7 were significantly upregulated on the LSK expression array and 8.1 and 3.5 fold up-regulated by qPCR in CD34low LSK cells. Another potential counter-regulatory signal was down regulation of Bcl3 mRNA, a potential anti-apoptotic effector in HSCs. We hypothesize that the HOXB4 expansion program involves activation of genes that lead to increased HSC numbers with later activation of counter-regulatory signals that limit expansion to physiologic numbers of HSCs in vivo. We are now examining how this program changes at various time points after transplantation and hypothesize the capping limits are set at relatively later time points during reconstitution. We also are studying the functional effects of these gene expression changes, and in particular, whether enforced expression of HOXB4 and PRMD16 will result in uncontrolled HSC proliferation and/or leukemia. Disclosures: No relevant conflicts of interest to declare.

Changing Gene Expression Patterns during Early Treatment of B-Precursor Acute Lymphoblastic Leukemia May Be Predictive of Relapse.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 232-232 ◽  
Author(s):  
Valerie de Haas ◽  
Rob Dee ◽  
Goedele Cheroutre ◽  
Henk van den Berg ◽  
Huib Caron ◽  
...  
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Acute Lymphoblastic Leukemia ◽  
Cell Lines ◽  
Expression Profiles ◽  
Lymphoblastic Leukemia ◽  
Gene Expression Profiles ◽  
Expression Level ◽  
Leukemic Cells ◽  
Diagnostic Samples

Abstract Treatment of pediatric ALL is based on the concept of tailoring the intensity of treatment to a patients risk. Clinical studies have shown that it is possible to stratify patients according to the levels of minimal residual disease after induction therapy and early during further treatment, since it has been demonstrated that the MRD level is the best predictive level for disease outcome. More recently, it has been shown that gene expression profiles of leukemic cells at diagnosis might be correlated with outcome. In previous studies we reported that slow responding subclones represent the clones causative for a leukemic relapse in oligoclonal disease. Based on these results, we hypothesized that the gene expression profile of the slow responding subclones present after the first weeks of chemotherapy might be more predictive than the profiles of all leukemic cells at diagnosis. Twenty-four genes were selected; most signalling molecules, transcription factors and functions relevant for oncogenesis, drug resistance and metastasis. Selection of genes was based on the presently available data on prognostic cDNA microarry studies of cytogenetically defined subgroups of childhood ALL. In particular, we analyzed results of recently published studies that compared gene expression levels between diagnosis and relapse in B-precusor acute lymphoblastic leukemia. (Staal, 2003 and Beesley, 2005). Gene sequences were obtained from public databases. Genes were tested on different leukemic cell lines. For all cell lines differences in gene expression level were demonstrated. The same panel of genes was tested on diagnostic samples of 16 ALL patients, subsequently followed by investigation of paired diagnosis - day 15 - relapse samples of 3 relapsed ALL patients. Leukemic material was obtained from cryopreserved bone marrow samples. All leukemic cells were purified by MACS purification based on markers expressed on the tumour, i.e. CD34, CD19 and CD10. RNA extraction and cDNA synthesis was performed according to the TRIZOL protocol. Expression levels were determined in a SYBR Green based real-time PCR assay. We were able to show different gene expression profiles in the 16 tested diagnostic samples. For the paired samples from relapsed B-precursor ALL patients, the expression level of several genes at day 15 was different (ΔCT&gt;1) in regard to diagnosis. Moreover, the changed expression at day 15 was comparable to the expression level of this gene at relapse. We conclude that indeed we were able to demonstrate that some of the genes have a changing pattern of expression during early therapy (day15), a pattern which is comparable to the pattern of gene expression at relapse and which is different from the pattern at diagnosis. We also demonstrated that purification of the bone marrow samples is necessary to be certain that the gene expression shown is relevant for the leukemic cells and not contaminated by other cells, i.e. T-cells. Figure Figure

Rearranged Infant Acute Lymphoblastic Leukemia.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1913-1913 ◽  
Author(s):  
Ronald W. Stam ◽  
Monique L. Den Boer ◽  
Pauline Schneider ◽  
Jasper de Boer ◽  
Jill Hagelstein ◽  
...  
Keyword(s):  
Gene Expression ◽  
Acute Lymphoblastic Leukemia ◽  
Expression Profiles ◽  
Lymphoblastic Leukemia ◽  
Gene Expression Profiles ◽  
Glucocorticoid Resistance ◽  
Glucocorticoid Treatment ◽  
Pediatric All

Abstract MLL rearranged Acute Lymphoblastic Leukemia (ALL) represents an unfavorable and difficult to treat type of leukemia that often is highly resistant to glucocorticoids like prednisone and dexamethasone. As the response to prednisone largely determines the clinical outcome of pediatric ALL patients, overcoming resistance to these drugs may be an important step towards improved prognosis. Here we compared gene expression profiles between prednisone-resistant and prednisone-sensitive pediatric ALL patients to obtain gene expression signatures associated with prednisone resistance for both childhood (&gt;1 year of age) and MLL rearranged infant (&lt;1 year of age) ALL. Merging both signatures in search for overlapping genes associated with prednisone resistance in both patient groups we, found that elevated expression of MCL-1 (an anti-apoptotic member of the BCL-2 protein family) appeared to be characteristic for both prednisone-resistant ALL samples. To validate this observation, we determined MCL-1 expression using quantitative RT-PCR in a cohort of MLL rearranged infant ALL samples (n=23), and confirm that high-level MCL-1 expression significantly confers glucocorticoid resistance both in vitro and in vivo. Finally, down-regulation of MCL-1 in prednisone resistant MLL rearranged ALL cells by RNA interference (RNAi) markedly sensitized these cells to prednisone. Therefore we conclude that MCL-1 plays an important role in glucocorticoid resistance and that MCL- 1 suppressing agents co-administered during glucocorticoid treatment may be beneficial especially for MLL rearranged infant ALL patients.

Specific Promoter CpG Island Methylation Patterns Identify Different Subgroups of MLL - Rearranged Infant Acute Lymphoblastic Leukemia, and Define Clinical Outcome

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 596-596 ◽  
Author(s):  
Dominique Jpm Stumpel ◽  
Pauline Schneider ◽  
Eddy HJ van Roon ◽  
Judith M Boer ◽  
Renee X Menezes ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Bone Marrow ◽  
Cpg Island ◽  
Expression Profiles ◽  
Lymphoblastic Leukemia ◽  
Gene Expression Profiles ◽  
Relapse Free Survival ◽  
Free Survival ◽  
Methylation Patterns

Abstract At present, long-term survival rates in childhood acute lymphoblastic leukemia (ALL) easily exceed 80%. However, the prognosis for infants (&lt;1 year) with ALL barely reaches 50%. Infant ALL is characterized by chromosomal translocations involving the Mixed Lineage Leukemia (MLL) gene that occur in about 80% of the cases. The most frequent MLL translocations in infant ALL include t(4;11), t(11;19) and t(9;11). In about 20% of the infant ALL cases no MLL rearrangements are observed. Recent gene-expression profiling characterized MLL-rearranged ALL as a unique type of leukemia, that is genetically clearly separable from other ALL subtypes. As epigenetic modifications affect gene-expression, we hypothesized that the specific gene-expression profiles associated with MLL-rearranged ALL may well be driven by epigenetic changes. The best-studied epigenetic event in hematological malignancies constitutes the transcriptional silencing of (tumor suppressor) genes by promoter CpG island hypermethylation. To explore the DNA methylation patterns underlying MLL-rearranged infant ALL, we applied Differential Methylation Hybridization (DMH) using both 9k (Huang, 2002) and 244k CpG island microarrays (Agilent) on primary infant ALL samples carrying t(4;11) (n=21), t(11;19) (n=17), t(9;11) (n=6) or wild-type MLL genes (n=13). The resulting DNA methylation patterns were compared with the patterns found in healthy pediatric bone marrow samples (n=8). In addition, relapse material from three infants with MLL-rearranged ALL was included and compared with the corresponding patient sample obtained at diagnosis. Both CpG island microarray platforms demonstrate that t(4;11) and t(11;19) characterize extensively hypermethylated leukemias, whereas t(9;11)-positive and translocation-negative infant ALL epigenetically resemble normal bone marrow. When the CpG array data (Agilent) were compared with available gene expression profiles (Affymetrix), we found that 95% of the genes from the top 100 of genes most significantly hypermethylated in t(4;11)- or t(11;19)-positive infant ALL were indeed down-regulated. Using the t(4;11)-positive cell line models SEMK2 and RS4;11, we demonstrate that the majority of these hypermethylated genes could be demethylated by the demethylating agent zebularine. Among t(4;11)- and t(11;19)-positive infant ALL samples, two subgroups could be identified displaying either more or less pronounced methylation patterns. Heavy methylation appeared to be associated with a significantly reduced relapse-free survival (p=0.03). Encouraged by these data, we analyzed relapse samples from t(4;11)- and t(11;19)-positive infant ALL patients, and found that these samples were even more extensively hypermethylated than the corresponding initial infant ALL samples. We here present, for the first time to our knowledge, a global view of the methylome in infant patients with MLL-rearranged ALL. We demonstrate that severe promoter CpG hypermethylation is present in t(4;11)- and t(11;19)-positive infant ALL. Of main therapeutic interest is our finding that the degree of DNA methylation among t(4;11)- and t(11;19)-positive infant ALL patients is related to relapse-free survival. Therefore, MLL-rearranged infant ALL patients with heavily methylated leukemias in particular should be considered candidates for therapies including inhibitors of DNA methylation in order to reverse the malignant phenotypes of these leukemias, and improve prognosis. Since MLL-rearranged infant ALL patients are even more hypermethylated at relapse, inhibition of aberrant DNA methylation might also be of vital importance at this stage of disease. Based on these data, we propose to initiate clinical trials using demethylating agents for patients with relapsed MLL- rearranged infant ALL. Meanwhile, we are investigating the in vitro cytotoxicity of various demethylating agents in our laboratory to pave the way for future clinical trials.

Adjuvant CD49d Blockade Eradicates Chemoresistant ALL

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 869-869 ◽  
Author(s):  
Yao-Te Hsieh ◽  
Eugene Park ◽  
Enzi Jiang ◽  
Katrin Dauber ◽  
Doreen Chudziak ◽  
...  
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Flow Cytometry ◽  
Bone Marrow Cells ◽  
Normal Karyotype ◽  
Leukemia Cells ◽  
Drug Resistant ◽  
Murine Leukemia

Abstract Abstract 869 Despite the recent advances in chemotherapy for acute lymphoblastic leukemia (ALL), drug resistance resulting in relapse and long-term side effects of current treatments warrant new treatment modalities. Integrin α4β1 (VLA4/ITGA4/CD49d) mediates adhesion of hematopoietic cells onto bone marrow cells and has been implicated in cell adhesion-mediated drug resistance of leukemia cells. Gene expression analyses indicate that VLA4 is upregulated in B-lineage Acute Lymphocytic Leukemia (ALL). Therefore, we hypothesize that VLA4 might be a potential target for treatment of drug resistant ALL To test our hypothesis, we determined the effect of VLA4 inhibition on engraftment of primary pre-B ALLs using a humanized CD49d antibody, Tysabri, as a single agent in our NOD/SCID xenograft model of primary pre-B ALL. Tysabri is known to mobilize normal hematopoietic progenitor cells into the circulation. It blocks binding of VLA-4 to its counter receptors VCAM-1 and osteopontin and we have shown previously in a small pilot study that adjuvant administration with chemotherapy sensitizes one drug resistant primary ALL in vivo to drug treatment. In this study, we injected primary ALL cells from eight different donors into NOD/SCID mice. The samples encompass various cytogenetic aberrations (BCR-ABL, E2A-PBX, MLL-AF, normal karyotype). Cells were luciferase-transduced for in vivo cell tracking and pretreated in vitro with either Tysabri (n=3 per leukemia, n=24 total) or human Ig as a control (n=3 per leukemia, n=24 total). Recipients of Tysabri treated leukemias showed significantly prolonged median survival time (BCR-ABL: MST=112days, E2A-PBX: MST=83days, MLL-AF4: MST=51days; Normal karyotype: MST=48days) compared to control groups (BCR-ABL: MST=84days, E2A-PBX: MST=54days, MLL-AF4: MST=35days; Normal: MST=39days) (p<0.05). Therefore, engraftment of leukemia was significantly delayed in the Tysabri-treated groups as determined by bioluminescent imaging (p<0.05) and survival analysis (p<0.05). Next, we injected two luciferase-labeled pre-B ALLs (US7R, RS4;11) into NOD/SCID mice, which were then treated intraperitoneally with saline (US7R: n=4; RS4;11: n=3), Tysabri (US7R: n=4; RS4;11: n=3), VDL (Vincristine, Dexamethasone and L-Asparaginase) (US7R: n=9; RS4;11: n=5), or VDL+Tysabri (US7R: n=9; RS4;11: n=5), for 4 weeks. Tysabri-treated groups showed prolonged survival time (US7R: MST=52days; RS4;11: MST=83) compared with saline-treated groups (US7R: MST=38days; RS4;11: MST=60 days) (p=0.007). VDL-only treated animals died rapidly (US7R: MST=74days; RS4;11: MST=109 days), however, the animals treated with the combination VDL+ Tysabri, survived disease-free until the end of follow-up (US7R: MST=151days; RS4;11: MST=141 days) (p<0.0001). The sacrificed animals showed absence of human CD45 in spleen, liver, bone marrow and lung by immunohistochemistry and flow cytometry indicating eradication of recalcitrant leukemia cells. We have also shown in vivo using an immunocompetent mouse model that VLA4 ablation does not result in dose-limiting toxicity to normal hematopoietic cells after VDL or 5-FU treatment. To understand further the role of VLA4 deletion in ALL, we established a model of murine leukemia using bone marrow cells from VLA4 floxed mice, retrovirally transformed with BCR-ABL1 p210 and cmyc. Subsequent to leukemic outgrowth, cells were transduced with either Empty GFP control, or Cre-GFP vector to delete VLA4. Knockout of VLA4 in transduced cells was detected by PCR on genomic DNA and by flow cytometry (Empty GFP control: 97% CD49+; Cre-GFP vector: 0.8% CD49+). Upon in vitro culturing of the cells 4-fold more VLA4 deleted cells were found in the supernatant compared to the control cells (p<0.05) determined by Trypan blue exclusion counts of dead cells, indicating that CD49d in murine leukemia is required for cell adhesion. Further functional studies addressing engraftment and gene expression upon induced VLA4 deletion are ongoing. Taken together, our data demonstrate that CD49d-blockade with adjuvant chemotherapy can eradicate chemotherapy-resistant leukemia. Further studies are warranted to understand and evaluate preclinically adjuvant inhibition of integrins to overcome relapse of leukemia. Disclosures: No relevant conflicts of interest to declare.

Nfi Genes Are Novel Regulators Of Murine Hematopoietic Stem- and Progenitor Cell Survival

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 735-735
Author(s):  
Per Holmfeldt ◽  
Pardieck Jennifer ◽  
Shannon McKinney-Freeman
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
Gene Family ◽  
Peripheral Blood ◽  
Fetal Liver ◽  
Expression Profiles ◽  
Gene Expression Profiles ◽  
Hematopoietic Stem ◽  
Post Transplant

Abstract Hematopoietic stem cells (HSCs) are responsible for life-long maintenance of hematopoiesis. HSC transplantation represents one of the most heavily exploited cell based therapies, routinely used to treat a myriad of life threating disorders, such as leukemia and bone marrow failure. Identifying the molecular pathways that regulate HSC engraftment is crucial to further improving outcomes in patients that rely on HSC transplantation as a curative therapy. By examining the global gene expression profiles of highly purified HSC (Lineage-Sca-1+c-Kit+CD150+CD48-), we recently identified the following members of the Nfi gene family of transcription factors as highly expressed by HSC (McKinney-Freeman et al., Cell Stem Cell, 2012): Nfix, Nfia, and Nfic. These data suggest that Nfi genes may play a novel role in regulating HSC function. To test this hypothesis, HSCs were enriched from adult bone marrow (Lineage-, c-kit+, Sca-1+ (LSK) cells) and then transduced, individually, with lentiviruses carrying shRNAs targeting each Nfi gene. Twenty-four hours post-transduction, cells were injected into lethally irradiated mice along with untransduced bone marrow LSK competitor cells congenic at the CD45 allele. The peripheral blood of recipient mice was then analyzed periodically over 16 weeks for engraftment of the Nfi-depleted cells. Although shRNA mediated knockdown of Nfi gene expression had no effect on the in vitro cell growth or viability of LSK cells, Nfi-depleted HSCs displayed a significant loss of short- and long-term in vivo hematopoietic repopulating activity. This was true for Nfia-, Nfic-, and Nfix-deficient HSC. While Nfia and Nfic are only expressed by bone marrow HSC, Nfix is highly expressed by both bone marrow and fetal liver HSC. When Nfix was depleted by shRNAs from LSK cells purified from E14.5 fetal liver, a similar loss in competitive repopulating potential was seen. Lineage analysis of peripheral blood of recipients showed no significant differences in the distribution of the major blood lineages derived from LSK cells transduced with Nfi-specific shRNAs compared to controls. When the bone marrow of recipients transplanted with Nfix- depleted cells was examined 4 and 16 weeks post-transplant, a general loss of all hematopoietic stem- and progenitor compartments examined was seen relative to control. Thus, the observed decrease in repopulating activity occurs at the level of HSCs and multipotent progenitors. To confirm an essential role for an Nfi gene family member in the regulation of HSC engraftment post-transplant, LSK cells were purified from Nfix fl/fl mice, transduced with lentiviral Cre recombinase and subsequently introduced into lethally irradiated recipients alongside congenic competitor cells. Like LSK transduced with Nfix-specific shRNAs, Nfix-/- LSK cells failed to repopulate the peripheral blood of recipient mice as efficiently as control and similar trends were detected in all stem- and progenitor cell populations examined. Time-course experiments immediately following transplantation revealed that Nfix-depleted LSK cells establish themselves in the marrow of recipient mice as efficiently as control at 5 days post-transplant, but thereafter exhausted rapidly. Examination 10 days post-transplant revealed a 5-fold increase in apoptosis specifically in the LSK compartment, but not in its differentiated progeny, in recipients transplanted with Nfix-depleted LSK cells compared to control. The increase in apoptosis was not associated with any apparent change in the cell cycle status of the LSK cells. These data suggest that Nfi genes are necessary for the survival of HSC post-transplantation. In an effort to identify the molecular pathways regulated by Nfi genes in HSC, we acquired the global gene expression profiles of Nfix-depleted HSC. In agreement with our observation that Nfix-deficient HSC displays elevated levels of apoptosis following transplantation in vivo, we observed a significant decrease in multiple genes known to be important for HSC survival, such as Erg, Mecom and Mpl, in Nfix-depleted HSC. In summary, we have for the first time established a role for the Nfi gene family in HSC biology, as evident by a decrease in bone marrow repopulating activity in Nfi-depleted HSCs. By dissecting the precise role of Nfi genes in HSC biology, we will glean insights that could improve our understanding of graft failure in clinical bone marrow transplantations. Disclosures: No relevant conflicts of interest to declare.

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