Normal and leukemic human stem cells assayed in SCID mice

How can we establish animal models of HIV-associated lymphoma?

Human immunodeficiency virus (HIV) infection is strongly associated with a heightened incidence of lymphomas. To mirror the natural course of human HIV infection, animal models have been developed. These models serve as valuable tools to investigate disease pathobiology, assess antiretroviral and immunomodulatory drugs, explore viral reservoirs, and develop eradication strategies. However, there are currently no validated in vivo models of HIV-associated lymphoma (HAL), hampering progress in this crucial domain, and scant attention has been given to developing animal models dedicated to studying HAL, despite their pivotal role in advancing knowledge. This review provides a comprehensive overview of the existing animal models of HAL, which may enhance our understanding of the underlying pathogenesis and approaches for malignancies linked to HIV infection.

Challenges in Cell Fate Acquisition to Scid-Repopulating Activity from Hemogenic Endothelium of hiPSCs Derived from AML Patients Using Forced Transcription Factor Expression

The generation of human hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) represents a major goal in regenerative medicine and is believed would follow principles of early development. HSCs arise from a type of endothelial cell called a “hemogenic endothelium” (HE), and human HSCs are experimentally detected by transplantation into SCID or other immune-deficient mouse recipients, termed SCID-Repopulating Cells (SRC). Recently, SRCs were detected by forced expression of seven transcription factors (TF) (ERG, HOXA5, HOXA9, HOXA10, LCOR, RUNX1, and SPI1) in hPSC-derived HE, suggesting these factors are deficient in hPSC differentiation to HEs required to generate HSCs. Here we derived PECAM-1-, Flk-1-, and VE-cadherin-positive endothelial cells that also lack CD45 expression (PFV^CD45−) which are solely responsible for hematopoietic output from iPSC lines reprogrammed from AML patients. Using HEs derived from AML patient iPSCs devoid of somatic leukemic aberrations, we sought to generate putative SRCs by the forced expression of 7TFs to model autologous HSC transplantation. The expression of 7TFs in hPSC-derived HE cells from an enhanced hematopoietic progenitor capacity was present in vitro, but failed to acquire SRC activity in vivo. Our findings emphasize the benefits of forced TF expression, along with the continued challenges in developing HSCs for autologous-based therapies from hPSC sources.

Cancer stem cells in breast and prostate: Fact or fiction?

Since the introduction of the cancer stem cell (CSC) hypothesis, accumulating evidence shows that most cancers present stem-like niches. However, therapies aimed at targeting this niche have not been as successful as expected. New evidence regarding CSCs hierarchy, similarities with normal tissue stem cells and cell plasticity might be key in understanding their role in cancer biology and how to efficiently eliminate them. In this Chapter, we discuss what is known in breast and prostate CSCs from their initial discoveries to the current therapeutic efforts in the field. Future challenges towards better CSC identification and isolation strategies will be key to shed light into how CSCs could accurately be targeted in combination to traditional therapies to ultimately prolong patient survival.

CLT030, a leukemic stem cell-targeting CLL1 antibody-drug conjugate for treatment of acute myeloid leukemia

The current standard of care for acute myeloid leukemia (AML) is largely ineffective with very high relapse rates and low survival rates, mostly due to the inability to eliminate a rare population of leukemic stem cells (LSCs) that initiate tumor growth and are resistant to standard chemotherapy. RNA-sequencing analysis on isolated LSCs confirmed C-type lectin domain family 12 member A (CLL1, also known as CLEC12A) to be highly expressed on LSCs but not on normal hematopoietic stem cells (HSCs) or other healthy organ tissues. Expression of CLL1 was consistent across different types of AML. We developed CLT030 (CLL1-ADC), an antibody-drug conjugate (ADC) based on a humanized anti-CLL1 antibody with 2 engineered cysteine residues linked covalently via a cleavable linker to a highly potent DNA-binding payload, thus resulting in a site-specific and homogenous ADC product. The ADC is designed to be stable in the bloodstream and to release its DNA-binding payload only after the ADC binds to CLL1-expressing tumor cells, is internalized, and the linker is cleaved in the lysosomal compartment. CLL1-ADC inhibits in vitro LSC colony formation and demonstrates robust in vivo efficacy in AML cell tumor models and tumor growth inhibition in the AML patient-derived xenograft model. CLL1-ADC demonstrated a reduced effect on differentiation of healthy normal human CD34⁺ cells to various lineages as observed in an in vitro colony formation assay and in an in vivo xenotransplantation model as compared with CD33-ADC. These results demonstrate that CLL1-ADC could be an effective ADC therapeutic for the treatment of AML.

Pituitary adenomas, stem cells, and cancer stem cells: what's new?

PURPOSE

To clarify the existence of pituitary stem cells (SCs) both in the embryonic and the postnatal gland and the role for SCs in pituitary adenomas.

METHODS

This work, which does not address the pathogenesis of pituitary adenomas, reviews the latest research findings and discoveries on SCs in pituitary and cancer SCs (CSCs) in pituitary adenomas and discusses the involvement of the EMT.

RESULTS

Several groups using different approaches and techniques have demonstrated the existence of SCs and CSCs and as they are major players in pituitary adenoma onset.

CONCLUSIONS

As in other benign and malignant tumors, the hypothesis that CSCs play a pivotal role in pituitary adenoma onset has been confirmed as well as the existence of a link between the epithelial-to-mesenchymal transition (EMT) process and CSC formation in epithelial tumors.

A revised road map for the commitment of human cord blood CD34-negative hematopoietic stem cells

We previously identified CD34-negative (CD34-) severe combined immunodeficiency (SCID)-repopulating cells as primitive hematopoietic stem cells (HSCs) in human cord blood. In this study, we develop a prospective ultra-high-resolution purification method by applying two positive markers, CD133 and GPI-80. Using this method, we succeed in purifying single long-term repopulating CD34- HSCs with self-renewing capability residing at the apex of the human HSC hierarchy from cord blood, as evidenced by a single-cell-initiated serial transplantation analysis. The gene expression profiles of individual CD34+ and CD34- HSCs and a global gene expression analysis demonstrate the unique molecular signature of CD34- HSCs. We find that the purified CD34- HSCs show a potent megakaryocyte/erythrocyte differentiation potential in vitro and in vivo. Megakaryocyte/erythrocyte progenitors may thus be generated directly via a bypass route from the CD34- HSCs. Based on these data, we propose a revised road map for the commitment of human CD34- HSCs in cord blood.

Catching moving targets: cancer stem cell hierarchies, therapy-resistance & considerations for clinical intervention

It is widely believed that targeting the tumour-initiating cancer stem cell (CSC) component of malignancy has great therapeutic potential, particularly in therapy-resistant disease. However, despite concerted efforts, CSC-targeting strategies have not been efficiently translated to the clinic. This is partly due to our incomplete understanding of the mechanisms underlying CSC therapy-resistance. In particular, the relationship between therapy-resistance and the organisation of CSCs as Stem-Progenitor-Differentiated cell hierarchies has not been widely studied. In this review we argue that modern clinical strategies should appreciate that the CSC hierarchy is a dynamic target that contains sensitive and resistant components and expresses a collection of therapy-resisting mechanisms. We propose that the CSC hierarchy at primary presentation changes in response to clinical intervention, resulting in a recurrent malignancy that should be targeted differently. As such, addressing the hierarchical organisation of CSCs into our bench-side theory should expedite translation of CSC-targeting to bed-side practice. In conclusion, we discuss strategies through which we can catch these moving clinical targets to specifically compromise therapy-resistant disease.

Prospectively Isolated Human Bone Marrow Cell-Derived MSCs Support Primitive Human CD34-Negative Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are maintained in a specialized bone marrow (BM) niche, which consists of osteoblasts, endothelial cells, and a variety of mesenchymal stem/stromal cells (MSCs). However, precisely what types of MSCs support human HSCs in the BM remain to be elucidated because of their heterogeneity. In this study, we succeeded in prospectively isolating/establishing three types of MSCs from human BM-derived lineage- and CD45-negative cells, according to their cell surface expression of CD271 and stage-specific embryonic antigen (SSEA)-4. Among them, the MSCs established from the Lineage(-) CD45(-) CD271(+) SSEA-4(+) fraction (DP MSC) could differentiate into osteoblasts and chondrocytes, but they lacked adipogenic differentiation potential. The DP MSCs expressed significantly higher levels of well-characterized HSC-supportive genes, including IGF-2, Wnt3a, Jagged1, TGFβ3, nestin, CXCL12, and Foxc1, compared with other MSCs. Interestingly, these osteo-chondrogenic DP MSCs possessed the ability to support cord blood-derived primitive human CD34-negative severe combined immunodeficiency-repopulating cells. The HSC-supportive actions of DP MSCs were partially carried out by soluble factors, including IGF-2, Wnt3a, and Jagged1. Moreover, contact between DP MSCs and CD34-positive (CD34(+) ) as well as CD34-negative (CD34(-) ) HSCs was important for the support/maintenance of the CD34(+/-) HSCs in vitro. These data suggest that DP MSCs might play an important role in the maintenance of human primitive HSCs in the BM niche. Therefore, the establishment of DP MSCs provides a new tool for the elucidation of the human HSC/niche interaction in vitro as well as in vivo.

Directed T-cell therapies for leukemia and lymphoma after hematopoietic stem cell transplant: beyond chimeric antigen receptors

This review focuses on the recent advances utilizing adoptive T-cell immunotherapies for patients after hematopoietic stem cell transplant using T cells after autologous transplant to treat the highest risk patients. The particular emphasis is the use of T cells to treat leukemias and lymphomas with gene transfer and nongene transfer approaches to direct specificity to tumor associated antigens. In this review, we will highlight how these novel therapeutics can be successfully used to prevent or treat high-risk patients who relapse after hematopoietic stem cell transplant.

Cytotoxic T lymphocytes for leukemia and lymphoma

This chapter focuses on the recent advances in adoptive T-cell immunotherapies, not only for patients after hematopoietic stem cell transplantation, but also in the autologous setting using T cells early in the disease process for the treatment of the highest-risk patients with leukemias and lymphomas. The particular emphasis is to highlight the role of T-cell therapies for hematologic malignancies using a non-gene-transfer approach to direct specificity, including the clinical use of T-cell therapies for EBV-associated lymphomas and strategies for targeting nonviral lymphoma- and leukemia-associated antigens.

Interplay of Stem Cell Characteristics, EMT, and Microtentacles in Circulating Breast Tumor Cells

Metastasis, not the primary tumor, is responsible for the majority of breast cancer-related deaths. Emerging evidence indicates that breast cancer stem cells (CSCs) and the epithelial-to-mesenchymal transition (EMT) cooperate to produce circulating tumor cells (CTCs) that are highly competent for metastasis. CTCs with both CSC and EMT characteristics have recently been identified in the bloodstream of patients with metastatic disease. Breast CSCs have elevated tumorigenicity required for metastatic outgrowth, while EMT may promote CSC character and endows breast cancer cells with enhanced invasive and migratory potential. Both CSCs and EMT are associated with a more flexible cytoskeleton and with anoikis-resistance, which help breast carcinoma cells survive in circulation. Suspended breast carcinoma cells produce tubulin-based extensions of the plasma membrane, termed microtentacles (McTNs), which aid in reattachment. CSC and EMT-associated upregulation of intermediate filament vimentin and increased detyrosination of α-tubulin promote the formation of McTNs. The combined advantages of CSCs and EMT and their associated cytoskeletal alterations increase metastatic efficiency, but understanding the biology of these CTCs also presents new therapeutic targets to reduce metastasis.

PI3K/Akt and Stat3 signaling regulated by PTEN control of the cancer stem cell population, proliferation and senescence in a glioblastoma cell line

Malignant gliomas are the most common primary brain tumor in adults. A number of genes have been implicated in glioblastoma including mutation and deletion of PTEN. PTEN is a regulator of PI3K-mediated Akt signaling pathways and has been recognized as a therapeutic target in glioblastoma. To achieve potent therapeutic inhibition of the PI3K-Akt pathway in glioblastoma, it is essential to understand the interplay between the regulators of its activation. Here, ectopic expression of PTEN in the U-87MG human glioblastoma-astrocytoma cell line is shown to result in the depletion of glioblastoma stem cells (GSCs) and to cause growth retardation and senescence. These effects are likely to be associated with PTEN-mediated cooperative perturbation of Akt and Stat3 signals. Using an in vivo rat model of glioblastoma, we showed that PTEN-overexpressing U-87MG cells failed to induce tumor formation, while untreated U-87MG cells did so. Furthermore, cells expressing the phosphorylated form of Stat3 were completely absent from the brain of rats implanted with PTEN-overexpressing U-87MG cells. Based on these results, PTEN appears to function as a crucial inhibitor of GSCs and as an inducer of senescence, suggesting that functional enhancement of the PTEN pathway will be useful to provide a therapeutic strategy for targeting glioblastoma.

In vivo generation of transplantable human hematopoietic cells from induced pluripotent stem cells

Lineage-restricted cells can be reprogrammed to a pluripotent state known as induced pluripotent stem (iPS) cells through overexpression of 4 transcription factors. iPS cells are similar to human embryonic stem (hES) cells and have the same ability to generate all the cells of the human body, including blood cells. However, this process is extremely inefficient and to date has been unsuccessful at differentiating iPS into hematopoietic stem cells (HSCs). We hypothesized that iPS cells, injected into NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ immunocompromised (NSG) mice could give rise to hematopoietic stem/progenitor cells (HSPCs) during teratoma formation. Here, we report a novel in vivo system in which human iPS cells differentiate within teratomas to derive functional myeloid and lymphoid cells. Similarly, HSPCs can be isolated from teratoma parenchyma and reconstitute a human immune system when transplanted into immunodeficient mice. Our data provide evidence that in vivo generation of patient customized cells is feasible, providing materials that could be useful for transplantation, human antibody generation, and drug screening applications.

Contribution of GATA1 dysfunction to multi-step leukemogenesis

In mammals, hematopoietic homeostasis is maintained by a fine-tuned balance among the self-renewal, proliferation, differentiation and survival of hematopoietic stem cells and their progenies. Each process is also supported by the delicate balance of the expression of multiple genes specific to each process. GATA1 is a transcription factor that comprehensively regulates the genes that are important for the development of erythroid and megakaryocytic cells. Accumulating evidence supports the notion that defects in GATA1 function are intimately linked to hematopoietic disorders. In particular, the somatic mutation of the GATA1 gene, which leads to the production of N-terminally truncated GATA1, contributes to the genesis of transient myeloproliferative disorder and acute megakaryoblastic leukemia in infants with Down syndrome. Similarly, a mutation in the GATA1 regulatory region that reduces GATA1 expression is involved in the onset of erythroid leukemia in mice. In both cases, the accumulation of immature progenitor cells caused by GATA1 dysregulation underlies the pathogenesis of the leukemia. This review provides a summary of multi-step leukemogenesis with a focus on GATA1 dysfunction.

Human embryonic stem cell-derived hematopoietic cells maintain core epigenetic machinery of the polycomb group/Trithorax Group complexes distinctly from functional adult hematopoietic stem cells

Hematopoietic cells derived from human embryonic stem cells (hESCs) have a number of potential utilities, including the modeling of hematological disorders in vitro, whereas the use for cell replacement therapies has proved to be a loftier goal. This is due to the failure of differentiated hematopoietic cells, derived from human pluripotent stem cells (hPSCs), to functionally recapitulate the in vivo properties of bona fide adult hematopoietic stem/progenitor cells (HSPCs). To better understand the limitations of differentiation programming at the molecular level, we have utilized differential gene expression analysis of highly purified cells that are enriched for hematopoietic repopulating activity across embryonic, fetal, and adult human samples, including in vivo explants of human HSPCs 8-weeks post-transplantation. We reveal that hESC-derived hematopoietic progenitor cells (eHPCs) fail to express critical transcription factors which are known to govern self-renewal and myeloid/lymphoid development and instead retain the expression of Polycomb Group (PcG) and Trithorax Group (TrxG) factors which are more prevalent in embryonic cell types that include EZH1 and ASH1L, respectively. These molecular profiles indicate that the differential expression of the core epigenetic machinery comprising PcGs/TrxGs in eHPCs may serve as previously unexplored molecular targets that direct hematopoietic differentiation of PSCs toward functional HSPCs in humans.

Recent updates on the role of microRNAs in prostate cancer

MicroRNAs (miRNAs) are short non-coding RNAs that are involved in several important biological processes through regulation of genes post-transcriptionally. Carcinogenesis is one of the key biological processes where miRNAs play important role in the regulation of genes. The miRNAs elicit their effects by binding to the 3' untranslated region (3'UTR) of their target mRNAs, leading to the inhibition of translation or the degradation of the mRNA, depending on the degree of complementary base pairing. To-date more than 1,000 miRNAs are postulated to exist, although the field is moving rapidly. Currently, miRNAs are becoming the center of interest in a number of research areas, particularly in oncology, as documented by exponential growth in publications in the last decade. These studies have shown that miRNAs are deregulated in a wide variety of human cancers. Thus, it is reasonable to ask the question whether further understanding on the role of miRNAs could be useful for diagnosis, prognosis and predicting therapeutic response for prostate cancer (PCa). Therefore, in this review article, we will discuss the potential roles of different miRNAs in PCa in order to provide up-to-date information, which is expected to stimulate further research in the field for realizing the benefit of miRNA-targeted therapeutic approach for the treatment of metastatic castrate resistant prostate cancer (mCRPC) in the near future because there is no curative treatment for mCRPC at the moment.

[Tumor stem cell research - basis and challenge for diagnosis and therapy]

Biological features of tumor cells relevant to progression, metastasis, and prognosis in cancer patients have been investigated for many years. During the past few years, the concept of tumor stem cells has gained widespread acceptance. The cancer stem cell (CSC) model is based on the observation that continuous growth of tumors depends on a small population of immature neoplastic cells with unlimited proliferative potential. In contrast to these CSC, more mature clonal cells in the same neoplasm undergo apoptosis and die after a variable number of cell divisions. The self-renewal capacity of CSC plays a central role in this scenario and enables permanent tumor cell repopulation in vivo in patients as well as in experimental animals, e.g., immunodeficient mice. Based on the stem cell concept, it is clear that the success of an anti-neoplastic approach depends on efficient targeting and elimination of CSC. An important aspect of CSC is their intrinsic resistance against conventional drugs. Therefore, a major focus in current research is molecular targets and their expression in CSC, with the goal to use targeted drugs for CSC elimination. It is the hope for the future that therapeutic approaches involving CSC-targeting concepts will lead to sustained remission and thus improvement of prognosis in leukemia and cancer patients.

Regulation of breast cancer stem cell activity by signaling through the Notch4 receptor

Notch receptor signaling pathways play an important role not only in normal breast development but also in breast cancer development and progression. We assessed the role of Notch receptors in stem cell activity in breast cancer cell lines and nine primary human tumor samples. Stem cells were enriched by selection of anoikis-resistant cells or cells expressing the membrane phenotype ESA(+)/CD44(+)/CD24(low). Using these breast cancer stem cell populations, we compared the activation status of Notch receptors with the status in luminally differentiated cells, and we evaluated the consequences of pathway inhibition in vitro and in vivo. We found that Notch4 signaling activity was 8-fold higher in stem cell-enriched cell populations compared with differentiated cells, whereas Notch1 signaling activity was 4-fold lower in the stem cell-enriched cell populations. Pharmacologic or genetic inhibition of Notch1 or Notch4 reduced stem cell activity in vitro and reduced tumor formation in vivo, but Notch4 inhibition produced a more robust effect with a complete inhibition of tumor initiation observed. Our findings suggest that Notch4-targeted therapies will be more effective than targeting Notch1 in suppressing breast cancer recurrence, as it is initiated by breast cancer stem cells.

MicroRNA regulation of cancer stem cells and therapeutic implications

MicroRNAs (miRNAs) are a class of endogenous non-protein-coding RNAs that function as important regulatory molecules by negatively regulating gene and protein expression via the RNA interference (RNAi) machinery. MiRNAs have been implicated to control a variety of cellular, physiological, and developmental processes. Aberrant expressions of miRNAs are connected to human diseases such as cancer. Cancer stem cells are a small subpopulation of cells identified in a variety of tumors that are capable of self-renewal and differentiation. Dysregulation of stem cell self-renewal is a likely requirement for the initiation and formation of cancer. Furthermore, cancer stem cells are a very likely cause of resistance to current cancer treatments, as well as relapse in cancer patients. Understanding the biology and pathways involved with cancer stem cells offers great promise for developing better cancer therapies, and might one day even provide a cure for cancer. Emerging evidence demonstrates that miRNAs are involved in cancer stem cell dysregulation. Recent studies also suggest that miRNAs play a critical role in carcinogenesis and oncogenesis by regulating cell proliferation and apoptosis as oncogenes or tumor suppressors, respectively. Therefore, molecularly targeted miRNA therapy could be a powerful tool to correct the cancer stem cell dysregulation.

Biscoclaurine alkaloid cepharanthine inhibits the growth of primary effusion lymphoma in vitro and in vivo and induces apoptosis via suppression of the NF-kappaB pathway

Primary effusion lymphoma (PEL) is a unique and recently identified non-Hodgkin's lymphoma that was originally identified in patients with AIDS. PEL is caused by the Kaposi sarcoma-associated herpes virus (KSHV/HHV-8) and shows a peculiar presentation involving liquid growth in the serous body cavity and a poor prognosis. As the nuclear factor (NF)-kappaB pathway is activated in PEL and plays a central role in oncogenesis, we examined the effect of a biscoclaurine alkaloid, cepharanthine (CEP) on PEL derived cell lines (BCBL-1, TY-1 and RM-P1), in vitro and in vivo. An methylthiotetrazole assay revealed that the cell proliferation of PEL cell lines was significantly suppressed by the addition of CEP (1-10 microg/ml). CEP also inhibited NF-kappaB activation and induced apoptotic cell death in PEL cell lines. We established a PEL animal model by intraperitoneal injection of BCBL-1, which led to the development of ascites and diffuse infiltration of organs, without obvious solid lymphoma formation, which resembles the diffuse nature of human PEL. Intraperitoneal administration of CEP inhibited ascites formation and diffuse infiltration of BCBL-1 without significant systemic toxicity in this model. These results indicate that NF-kappaB could be an ideal molecular target for treating PEL and that CEP is quite useful as a unique therapeutic agent for PEL.

Oct4, a novel marker for human gastric cancer

BACKGROUND AND OBJECTIVE

Octamer-4 (Oct4), a transcription factor involved in regulating human embryonic stem cells (ESCs), may play a role in tumorigenesis. Since little is known about the efficacy of Oct4 as a potential biomarker for gastric cancer (GC), we investigated its expression in GC tissues and its relationship to various clinicopathological parameters.

METHODS

Primary tumor tissues and matching, adjacent non-cancerous tissues were obtained from 62 GC patients, and Oct4 expression was examined by reverse transcription-PCR (RT-PCR) and real-time PCR. Twenty biopsy specimens of atrophic gastritis and gastric ulcer individually were collected as control. To detect Oct4 expression in the paired GC and non-cancerous tissues at the protein level, Western blotting and immunohistochemistry (IHC) were employed. Correlation analyses were conducted to assess the relationship between Oct4 expression and clinicopathological parameters.

RESULTS

Oct4 expression levels were higher in GC tissues compared to matching, adjacent non-cancerous tissues, atrophic gastritis and gastric ulcer tissues. Additionally, Oct4 expression in GC tumors correlated with their differentiation status, but not with patient age or gender, tumor size, TNM stage, depth of invasion, or the presence of lymph node metastasis.

CONCLUSIONS

Oct4 may be a potential biomarker for the initiation, progression, and differentiation of human GC.

Stem cells of GATA1-related leukemia undergo pernicious changes after 5-fluorouracil treatment

OBJECTIVE

Transcription factor GATA1 plays a critical role in erythropoiesis through the integrated regulation of cell proliferation, differentiation, and apoptosis. In Gata1.05 gene knockdown mice, Gata1 expression deteriorates to 5% of wild-type allelic expression, a level insufficient for supporting normal erythropoiesis and one that leads to accumulation of erythroid progenitors that are readily transformed into erythroblastic leukemia. Serial engraftment of leukemic cells into primary or subsequent nude mice reconstituted complete leukemic phenotype in recipient. To delineate characteristics of leukemic stem cells (LSCs), we analyzed LSCs of Gata1.05 leukemia, which have a potential to reestablish leukemia in mice.

MATERIALS AND METHODS

Leukemic cells isolated from the first recipient mice of Gata1.05 leukemia cells were divided into two fractions using Hoechst dye. Fractionated cells were transplanted into second recipient, or analyzed gene expression profiles and cell-cycle status. Consequences of 5-fluorouracil (5-FU) treatment on leukemic cells in vivo were studied.

RESULTS

LSCs were enriched in the Hoechst dye-excluded side population (SP), and leukemic cells in the SP population (LSP cells) were morphologically and immunophenotypically indistinguishable from other leukemic cells. However, expression of hematopoietic stem cell (HSC)-related genes was upregulated in the LSP cells. In cell-cycle analyses, LSP cells were quiescent like HSCs, but reentry into the cell cycle was stimulated by 5-FU treatment. Nonetheless, 5-FU treatment established a point of newly adjusted equilibrium in the LSP cells and the cells never recovered to their previous quiescent state.

CONCLUSION

Based on this observation, distinct self-renewal regulatory mechanisms in LSCs may be considered as one of the causes of worsening of the features of leukemia after injury and relapse.

Stem cell concepts renew cancer research

Although uncontrolled proliferation is a distinguishing property of a tumor as a whole, the individual cells that make up the tumor exhibit considerable variation in many properties, including morphology, proliferation kinetics, and the ability to initiate tumor growth in transplant assays. Understanding the molecular and cellular basis of this heterogeneity has important implications in the design of therapeutic strategies. The mechanistic basis of tumor heterogeneity has been uncertain; however, there is now strong evidence that cancer is a cellular hierarchy with cancer stem cells at the apex. This review provides a historical overview of the influence of hematology on the development of stem cell concepts and their linkage to cancer.

Humanized mouse models to study the human haematopoietic stem cell compartment

The ideal way to assess hematopoietic stem cells is to observe their growth in the endogenous microenvironment where they would receive the appropriate signals. With colonies of inbred mice, it is possible to myeloablate recipients and transplant hematopoietic cells from genetically similar mice and observe the growth of primitive hematopoietic cells in their endogenous environment for a significant proportion (10 months) of an organisms lifespan (29 months average). It is not possible to perform these experiments in humans, but xenotransplantation mouse models provide the closest paradigm for the human hematopoietic environment at the present time.

Preclinical ex vivo expansion of peripheral blood CD34+ selected cells from cancer patients mobilized with combination chemotherapy and granulocyte colony-stimulating factor

BACKGROUND AND OBJECTIVES

Ex vivo peripheral blood progenitor cell (PBPC) expansion has been proposed as a strategy to increase the number of haematopoietic progenitors available for cell transplantation. We have expanded CD34+ cells from PBPCs obtained from four patients with haematological malignancies and one patient with an Ewing's sarcoma.

MATERIALS AND METHODS

Cells were expanded in the Dideco 'Pluricell system'. After 12 days in culture, we evaluated cell phenotype, total nucleated cells, CD34+ fold increase, cell apoptosis and colony assay of expanded cells. Cell engraftment has been evaluated by transplanting two groups of irradiated non-obese diabetic/severe combined immunodeficient (NOD-SCID) mice with expanded and non-expanded cell populations.

RESULTS

Total nucleated cells and CD34+ cells increased 59.5 and 4.0 times, respectively. The expanded cells were mainly constituted of myeloid and megakaryocytic cells. A significant increase in the number of colony-forming unit-granulocyte macrophage (CFU-GM) was observed in the CFU assay. Ten mice transplanted with expanded cells showed a best overall survival (80%) compared to 10 mice transplanted with non-expanded cells (20%). Human CD45+ cells were detected by flow cytometry and polymerase chain reaction in bone marrow and spleen of transplanted animals. The relative low engraftment level obtained with the expanded cells suggests a loss of SCID repopulating cells maybe due to cell differentiation during expansion.

CONCLUSIONS

We have demonstrated the feasibility of the ex vivo expansion of mobilized PBPCs from cancer patients, evidencing a clonal expansion of CFUs and the ability of the expanded cells to engraft the bone marrow and spleen of immunosuppressed mice. The differentiation of the CD34+ stem cell compartment could be further minimized by ameliorating the expansion conditions.

NF-kappa B-mediated adaptive resistance to ionizing radiation

Ionizing radiation (IR) began to be a powerful medical modality soon after Wilhelm Röntgen's discovery of X-rays in 1895. Today, more than 50% of cancer patients receive radiotherapy at some time during the course of their disease. Recent technical developments have significantly increased the precision of dose delivery to the target tumor, making radiotherapy more efficient in cancer treatment. However, tumor cells have been shown to acquire a radioresistance that has been linked to increased recurrence and failure in many patients. The exact mechanisms by which tumor cells develop an adaptive resistance to therapeutic fractional irradiation are unknown, although low-dose IR has been well defined for radioadaptive protection of normal cells. This review will address the radioadaptive response, emphasizing recent studies of molecular-level reactions. A prosurvival signaling network initiated by the transcription factor NF-kappa B, DNA-damage sensor ATM, oncoprotein HER-2, cell cyclin elements (cyclin B1), and mitochondrial functions in radioadaptive resistance is discussed. Further elucidation of the key elements in this prosurvival network may generate novel targets for resensitizing the radioresistant tumor cells.

Cancer, stem cells, and oncolytic viruses

Cells with stem cell-like attributes, such as self-renewal and pluripotency, have been isolated from hematological malignancies and from several solid tumor types. Tumor-initiating cells, also referred to as cancer stem cells, are thought to be responsible for the initiation and growth of tumors. Like their normal counterparts, putative cancer stem cells show remarkable resistance to radiation and chemotherapy. Their capacity for surviving apparently curative treatment can result in tumor relapse. Novel approaches that target tumor-initiating cells in addition to differentiated malignant cells, which constitute the bulk of the tumor, are required for improved survival of patients with metastatic tumors. Oncolytic viruses enter cells through infection and may therefore be resistant to defense mechanisms exhibited by cancer stem cells. Oncolytic adenoviruses can be engineered to attack tumor stem cells, recognized by linage-specific cell surface markers, dysfunctional stem cell-signaling pathways, or upregulated oncogenic genes. Normal stem cells may possess innate resistance to adenoviruses, as most humans have sustained numerous infections with various wild-type serotypes. This review focuses on current literature in support of cancer stem cells and discusses the possibility of using oncolytic virotherapy for killing these tumor-initiating cells.

[Stem cell therapy. Biology of hematopoietic stem cells]

In recent years much progress has been made in the understanding of the biology of hematopoietic stem cells (HSC) and their involvement in normal blood cell development. Using immunophenotyping it is possible, to enrich HSC, however, so far we are not able to positively select HSC. For the identification, characterization and quantification of HSC it is necessary to use functional assay systems, such as xenotransplantation models. HSC from bone marrow, peripheral blood and in some cases also cord blood have been used for years in transplantation settings especially in patients with leukemia. A better understanding of the mechanisms underlying stem cell regulation as well as stem cell self renewal would have clinical implications e. g. for clinical transplantation strategies. A number of hematological diseases such as chronic myeloid leukemia originates from a malignant transformed HSC. A better understanding of the biology of normal as well as malignant HSC is therefore crucial not only for a better understanding of the disease, but also for the development of strategies aiming at the discrimination of normal and malignant stem cell candidates and the development of therapies targeting the leukemic stem cell.

Effect of hepatocyte growth factor on long term hematopoiesis of human progenitor cells in transgenic-sever combined immunodeficiency mice

Hepatocyte growth factor (HGF), which was originally isolated as a liver generating factor, enhances hematopoiesis. To study the effect of HGF on hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs), we generated severe combined immunodeficiency (SCID) mice producing human (h) HGF and/or stem cell factor (SCF) by transferring the relevant genes to fertilized eggs, and then transplanted hematopoietic progenitors from human cord blood into the transgenic (Tg) SCID mice. Six months after transplantation, a significantly larger number of human cells were found in the Tg SCID mice than in non-Tg controls. Characteristically, the recipient SCID mice producing h HGF (HGF-SCID) had a significantly increased number of h CD41+ cells, whereas the SCF-SCID recipients had more CD11b+ cells. Significantly large numbers of CD34+ progenitors were found in the SCID mice transferred with both h HGF and h SCF genes (HGF/SCF-SCID) when compared with HGF-SCID or SCF-SCID mice. These results imply that HGF supports the differentiation of progenitors in megakaryocyte lineage, whereas SCF supports that in myeloid lineage. The results also imply that HGF acts on HSCs/HPCs as a synergistic proliferative factor combined with SCF. We have demonstrated the advantage of the human cytokine-producing animal in the maintenance of human HSCs.

Isolation and characterization of hematopoietic progenitor cells in canine bone marrow

For ultimate diagnoses of canine leukemia or malignant lymphoma, we sought to isolate hematopoietic progenitor cells (HPCs) from canine bone marrow (BM) using physiological phenotypes. Canine BM cells were separated by equilibrium discontinued density centrifugation, and HPCs, detected by in vitro colony formation, were significantly enriched in the relatively low density (LD) fraction. In flow cytometry, many CD34 or MHC class II expressing cells were detected in the LD fraction, but these were not significantly enriched. When the LD cells were separated, using a cell-sorting method, into cells with high affinity of wheat germ agglutinin (WGAhigh) and cells with WGAlow, almost all multipotent HPCs (MHPCs) and HPCs committed to myeloid lineage were found in the WGAhigh population. When the WGAhigh population was further stained for rhodamin 123, almost all MHPCs were included in the dull population (Rhlow), but not in the bright one (Rhhigh). Morphologically, most Rhlow cells were round, blastic cells containing a large nucleus with nucleoli and narrow cytoplasm. Based on these results, we suggest that all of the MHPCs in canine BM show the Rhlow WGAhigh LD phenotype, and may contain hematopoietic stem cells, which are the primitive HPCs.

TA-p63-gamma regulates expression of DeltaN-p63 in a manner that is sensitive to p53

Genetic analysis indicates that TP63 is required for establishment and preservation of self-renewing progenitors within the basal layer of several epithelial structures, however, the specific contributions of transactivating (TA-p63) and dominant-negative (DeltaN-p63) isoforms remain largely undefined. Recent studies have suggested a model in which TA-p63 plays an important role in the establishment of progenitor populations in which expression of DeltaN-p63 contributes to the preservation of self-renewing capacity. Our previous studies indicate that DeltaN-p63 is a transcriptional target of p53, however, the absence of overt epithelial deficiencies in p53-/- mice and reports of increased expression of DeltaN-p63 in p53-/- mice suggest p53-independent mechanisms also contribute to expression of DeltaN-p63. Here, we present data indicating that, prolonged loss of p53 leads to the activation of a p53-independent mechanism for transcriptional regulation of DeltaN-p63. This p53-independent mechanism is sensitive to ectopic p53 but not to a p53 mutant that lacks the transactivation domain. We further show that in cells in which p53 is expressed TA-p63-gamma protein is destabilized in a manner that is p53 dependent and sensitive to pharmacologic inhibition of the 26S proteosome. Consistent with this observation, we demonstrate that loss of p53 leads to the stabilization of TA-p63-gamma that is reversible by ectopic p53. Finally, we present evidence that disruption of TA-p63-gamma expression leads to decreased expression of DeltaN-p63 and that overexpression of TA-p63-gamma was sufficient to enhance the activity of the DeltaN-p63 promoter. Taken together, our studies indicate that TA-p63-gamma is capable of activating expression of DeltaN-p63 and that this mechanism may account for p53-independent expression of DeltaN-p63.

Stem cells and cancer

The cell of origin of cancer has been a strongly debated topic through out the history of cancer research. This review provides a historic framework and a synopsis of how the theories of cancer initiation and progression evolved from early times to the present day. We present the concept of a cancer stem cell, and review for you the literature supporting the existence of cancer stem cells in addition to a brief discussion on our own work supporting a bone marrow-derived source for the cancer stem cell, as well as cells of the cancer stroma.

Recent translational research: stem cells as the roots of breast cancer

Common phenotypes of cancer and stem cells suggest that breast cancers arise from stem cells. Breast epithelial cells with stem cell phenotypes have been shown to be more susceptible to immortalization and neoplastic transformation. Breast tumor stem cells with CD44⁺/CD24^-/lowLineage^- markers have been isolated. The role of these cells in tumor progression and clinical outcome is not clear. The relationship between breast stem cell and tumor stem cell may be elucidated by further studies of carcinogenesis of nonadherent mammosphere cells with stem cell features and by derivation of CD44⁺/CD24^-/low cells from an adherent breast epithelial stem cell type.

Experimental Models to Study Development and Function of the Human Immune System In Vivo

The study of development and function of the immune system in vivo has made intensive use of animal models, but performing such work in humans is difficult for experimental, practical, and ethical reasons. Confronted with this scientific challenge, several pioneering groups have developed in the late 1980s mouse models of human immune system development. Although these experimental approaches were proven successful and useful, they were suffering from limitations due to xenograft transplantation barriers. By reviewing the characteristics of the successive models over the last 20 years, it becomes apparent that screening of potentially interesting mouse strains and usage of combinations of genetic deficiencies has led to major advances. This is particularly true for human T cell development in the murine thymus. This review will focus on these advances and the potential future improvements that remain to be accomplished.

Chronic Myelogenous Leukemia: From Molecular Biology to Clinical Aspects and Novel Targeted Therapies

The critical causative event in chronic myelogenous leukemia (CML) is the fusion of the head of the bcr gene with the body of the abl gene, named bcr/abl gene. This chimeric BCR/ABL molecule transforms primary myeloid cells to leukemic cells and induces a CML-like disease in mice. The mouse CML model expressing the BCR/ABL molecule has provided important new insights into the molecular pathophysiology of CML and has directly answered many questions regarding this disease. Furthermore, numerous clinical studies have demonstrated a correlation between leukemic clinical features and the position of the breakpoint in the BCR gene of the chimeric BCR/ABL gene. Understanding of the molecular pathogenesis of CML has led to the development of several novel therapies. The BCR/ABL molecule is unique oncogeneiety, having ABL tyrosine kinase activity, making it an ideal target for drug development. Subsequent clinical studies now realize the hypothesis that selective inhibition of the abl tyrosine kinase activity using imatinib mesylate might be useful for the treatment of CML. This article reviews the history of BCR/ABL molecular biology, including the CML model mouse, clinical molecular studies and the recent findings of imatinib mesylate and more potent tyrosine kinase inhibitors developed for the treatment of CML.

Evaluation of ex vivo expansion and engraftment in NOD-SCID mice of umbilical cord blood CD34+ cells using the DIDECO "Pluricell System"

The Dideco "Pluricell System" is a commercially available closed device composed of an expansion chamber and a kit of certified reagents that allow haematopoietic stem cell expansion. We have expanded seven umbilical cord blood (UCB) samples following the manufacturer's instructions; two groups of irradiated NOD-SCID mice have been transplanted with expanded and nonexpanded cells from the same UCB, and bone marrow was analysed for the presence of human cells. Average UCB volume was 61.6+/-8.8 ml; mean nucleated cell content was 1090.5+/-189.9 x 10(6). Percentage and number of CD34+ cells were 0.37+/-0.13% and 3.9+/-1.2 x 10(6). After separation, CD34+ cell purity was 82+/-11%. Mean number of inoculated cells was 760 000; mean NC and CD34+ fold expansion at 12 days was 230.4+/-91.5 and 21.0+/-11.9. Both groups of mice showed successful engraftment: the percentage of human cells was higher in the group receiving expanded cells (3.4+/-2.01%) compared to the group receiving nonexpanded cells (1.5+/-0.66%) (P<0.00018, Mann-Whitney test). The cell population obtained after 12 days expansion consisted mainly of myeloid and megakaryocytic progenitors. The CD34+ antigen reached the maximum expression level at day 12 (7.5+/-2.0%). Analysis of lineage-markers for human myelomonocytic, megakaryocytic, B, T, CD34 and erythroid cells, gave evidence that all the lineages were represented in the marrow of transplanted mice.

Normal and leukaemic stem cells

The blood-related cancer leukaemias were the first diseases where human cancer stem cells, or leukaemic stem cells (LSC), were isolated. The haematopoietic system is one of the best tissues for investigating cancer stem cells, because the developmental hierarchy of normal blood formation is well defined. Leukaemias can now be viewed as aberrant haematopoietic processes initiated by rare LSC that have maintained or reacquired the capacity for indefinite proliferation through accumulated mutations and/or epigenetic changes. Yet, despite their critical importance, much remains to be learned about the developmental origin of LSC and the mechanisms responsible for their emergence in the course of the disease. This report will review our current knowledge on normal and LSC development and examine the impact of these discoveries may have clinically and in our understanding of the leukaemogenic process.

Animal models of acute myelogenous leukaemia - development, application and future perspectives

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

Hierarchical and Ontogenic Positions Serve to Define the Molecular Basis of Human Hematopoietic Stem Cell Behavior

The molecular basis governing functional behavior of human hematopoietic stem cells (HSCs) is largely unknown. Here, using in vitro and in vivo assays, we isolate and define progenitors versus repopulating HSCs from multiple stages of human development for global gene expression profiling. Accounting for both the hierarchical relationship between repopulating cells and their progenitors, and the enhanced HSC function unique to early stages of ontogeny, the human homologs of Hairy Enhancer of Split-1 (HES-1) and Hepatocyte Leukemia Factor (HLF) were identified as candidate regulators of HSCs. Transgenic human hematopoietic cells expressing HES-1 or HLF demonstrated enhanced in vivo reconstitution ability that correlated to increased cycling frequency and inhibition of apoptosis, respectively. Our report identifies regulatory factors involved in HSC function that elicit their effect through independent systems, suggesting that a unique orchestration of pathways fundamental to all human cells is capable of controlling stem cell behavior.

Mammary stem cells, self-renewal pathways, and carcinogenesis

The mammary gland epithelial components are thought to arise from stem cells that undergo both self-renewal and differentiation. Self-renewal has been shown to be regulated by the Hedgehog, Notch, and Wnt pathways and the transcription factor B lymphoma Mo-MLV insertion region 1 (Bmi-1). We review data about the existence of stem cells in the mammary gland and the pathways regulating the self-renewal of these cells. We present evidence that deregulation of the self-renewal in stem cells/progenitors might be a key event in mammary carcinogenesis. If 'tumor stem cells' are inherently resistant to current therapies, targeting stem cell self-renewal pathways might provide a novel approach for breast cancer treatment.

Smad7 alters cell fate decisions of human hematopoietic repopulating cells

Intracellular Smad proteins mediate signal transduction of the transforming growth factor-β (TGF-β) superfamily that play pleiotropic roles in hematopoietic development, suggesting that intracellular Smad proteins may play key roles in hematopoietic regulation. Although inhibitory Smad7, which negatively regulates TGF-β signaling, has been implicated in the development of mature hematopoietic cells, a role for Smad7 in regulating more primitive hematopoietic cells has yet to be examined. Here, Smad7 was overexpressed in primary human severe combined immunodeficient (SCID) repopulating cells (SRCs), representing a common myeloid/lymphoid precursor cell with the functional capacity to repopulate the bone marrow of nonobese diabetic (NOD)/SCID recipient mice. Retroviral transduction of Smad7 into human umbilical cord blood (CB)-SRCs caused a shift from lymphoid dominant engraftment toward increased myeloid contribution, and increased the myeloid-committed clonogenic progenitor frequency in reconstituted mice. Neither myeloid nor B-lymphoid lineage developmental stages were compromised by Smad7 overexpression, suggesting Smad7 regulates cell fate commitment decisions of myeloid/lymphoid precursors by augmenting myeloid differentiation at the expense of lymphoid commitment. In addition, global gene expression analysis using microarray was used to identify potential target genes regulated by Smad7 in primitive hematopoietic cells that may control this process. Our study demonstrates a novel and unexpected role for Smad7 in modulating the cell fate decisions of primary multipotent human repopulating cells and establishes a role for Smad7 in the development of primitive human hematopoietic cells.

Inhibitory Anti-FLT3 Antibodies Are Capable of Mediating Antibody-Dependent Cell-Mediated Cytotoxicity and Reducing Engraftment of Acute Myelogenous Leukemia Blasts in Nonobese Diabetic/Severe Combined Immunodeficient Mice

Aberrant FLT3 expression and/or mutation plays a significant role in leukemogenesis. This has prompted the development of selective small molecule tyrosine kinase inhibitors against FLT3. However, like most tyrosine kinase inhibitors, those against FLT3 are not completely specific and at the doses required to completely inhibit target, significant toxicities may occur. In addition, tyrosine kinase inhibitors for other kinases have been shown to select for cells that become resistant. To overcome some of these limitations we developed two fully human phage display monoclonal antibodies against FLT3 (IMC-EB10 and IMC-NC7). These antibodies inhibited ligand-mediated activation of wild-type FLT3 and constitutively activated mutant FLT3 and in most cell types affected downstream STAT5, AKT, and mitogen-activated protein kinase activation. In addition to interfering with FLT3 signaling, IMC-EB10 and, to a significantly lesser extent, IMC-NC7 initiated antibody-dependent cell-mediated cytotoxicity on FLT3-expressing cells. When IMC-EB10 was used in vivo to treat nonobese diabetic/severe combined immunodeficient mice given injections of primary FLT3/ITD acute myelogenous leukemia samples or myeloid cell lines with FLT3 expression, it significantly decreased engraftment of leukemic cells and increased survival, respectively. In contrast, IMC-EB10 treatment did not reduce engraftment of normal human CD34+ cord blood cells nor did it show any significant inhibition of normal murine hematopoiesis. Thus, these types of antibodies have the potential to be safe and effective new therapeutic agents for acute myelogenous leukemia and possibly other FLT3-expressing malignancies.

Mechanisms controlling pathogenesis and survival of leukemic stem cells

Stem cells are an integral component of normal mammalian physiology and have been intensively studied in many systems. Intriguingly, substantial evidence indicates that stem cells also play an important role in the initiation and pathogenesis of at least some cancers. In particular, myeloid leukemias have been extensively characterized with regard to stem and progenitor cell involvement. Thus, as a focal point for both scientific and therapeutic endeavors, leukemic stem cells (LSC) represent a critical area of investigation. LSC appear to retain many characteristics of normal hematopoietic stem cells (HSC) as evidenced by a hierarchical developmental pattern, a mostly quiescent cell cycle profile, and an immunophenotype very similar to HSC. Consequently, defining unique properties of LSC remains a high priority in order to elucidate the molecular mechanisms driving stem cell transformation, and for developing therapeutic strategies that specifically target the LSC population. In this review, we discuss emerging concepts in the field and describe how various molecular and cellular characteristics of leukemia cells might be exploited as a means to preferentially ablate malignant stem cells.