Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Mesenchymal stem cells (MSCs) from the mouse bone marrow show differential expression of interferon regulatory factors IRF-1 and IRF-2

BACKGROUND

Interferon regulatory factors (IRF-1 and IRF-2) are transcription factors widely implicated in various cellular processes, including regulation of inflammatory responses to pathogens, cell proliferation, oncogenesis, differentiation, autophagy, and apoptosis.

METHODS

We have studied the expression of IRF-1, IRF-2 mRNAs by RT-PCR, cellular localization of the proteins by immunofluorescence, and expression of mRNAs of genes regulated by IRF-1, IRF-2 by RT-PCR in mouse bone marrow cells (BMCs) and mesenchymal stem cells (MSCs).

RESULTS

Higher level of IRF-1 mRNA was observed in BMCs and MSCs compared to that of IRF-2. Similarly, differential expression of IRF-1 and IRF-2 proteins was observed in BMCs and MSCs. IRF-1 was predominantly localized in the cytoplasm, whereas IRF-2 was localized in the nuclei of BMCs. MSCs showed nucleo-cytoplasmic distribution of IRF-1 and nuclear localization of IRF-2. Constitutive expression of IRF-1 and IRF-2 target genes: monocyte chemoattractant protein-1 (MCP-1), vascular cell adhesion molecule-1 (VCAM-1), cyclooxygenase-2 (COX-2), matrix metalloproteinase-9 (MMP-9), and caspase-1 was observed in both BMCs and MSCs. MSCs showed constitutive expression of the pluripotency-associated factors, Oct3/4 and Sox-2. Lipopolysaccharide (LPS)-treatment of MSCs induced prominent cellular localization of IRF-1 and IRF-2.

CONCLUSIONS

Our results suggest that IRF-1 and IRF-2 exhibit differential expression of their mRNAs and subcellular localization of the proteins in BMCs and MSCs. These cells also show differential levels of constitutive expression of IRF-1 and IRF-2 target genes. This may regulate immune-responsive properties of BMCs and MSCs through IRF-1, IRF-2-dependent gene expression and protein-protein interaction. Regulating IRF-1 and IRF-2 may be helpful for immunomodulatory functions of MSCs for cell therapy and regenerative medicine.

Engagement of Mesenchymal Stromal Cells in the Remodeling of the Bone Marrow Microenvironment in Hematological Cancers

Mesenchymal stromal cells (MSCs) are a subset of heterogeneous, non-hematopoietic fibroblast-like cells which play important roles in tissue repair, inflammation, and immune modulation. MSCs residing in the bone marrow microenvironment (BMME) functionally interact with hematopoietic stem progenitor cells regulating hematopoiesis. However, MSCs have also emerged in recent years as key regulators of the tumor microenvironment. Indeed, they are now considered active players in the pathophysiology of hematologic malignancies rather than passive bystanders in the hematopoietic microenvironment. Once a malignant event occurs, the BMME acquires cellular, molecular, and epigenetic abnormalities affecting tumor growth and progression. In this context, MSC behavior is affected by signals coming from cancer cells. Furthermore, it has been shown that stromal cells themselves play a major role in several hematological malignancies' pathogenesis. This bidirectional crosstalk creates a functional tumor niche unit wherein tumor cells acquire a selective advantage over their normal counterparts and are protected from drug treatment. It is therefore of critical importance to unveil the underlying mechanisms which activate a protumor phenotype of MSCs for defining the unmasked vulnerabilities of hematological cancer cells which could be pharmacologically exploited to disrupt tumor/MSC coupling. The present review focuses on the current knowledge about MSC dysfunction mechanisms in the BMME of hematological cancers, sustaining tumor growth, immune escape, and cancer progression.

The immunological role of mesenchymal stromal cells in patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a common hematological malignant disease, characterized by malignant hematopoietic stem cell proliferation in the bone marrow (BM); clinically, it mainly manifests clinically mainly by as pathological hematopoiesis, hemocytopenia, and high-risk transformation to acute leukemia. Several studies have shown that the BM microenvironment plays a critical role in the progression of MDS. In this study, we specifically evaluated mesenchymal stromal cells (MSCs) that exert immunomodulatory effects in the BM microenvironment. This immunomodulatory effect occurs through direct cell-cell contact and the secretion of soluble cytokines or micro vesicles. Several researchers have compared MSCs derived from healthy donors to low-risk MDS-associated bone mesenchymal stem cells (BM-MSCs) and have found no significant abnormalities in the MDS-MSC phenotype; however, these cells have been observed to exhibit altered function, including a decline in osteoblastic function. This altered function may promote MDS progression. In patients with MDS, especially high-risk patients, MSCs in the BM microenvironment regulate immune cell function, such as that of T cells, B cells, natural killer cells, dendritic cells, neutrophils, myeloid-derived suppressor cells (MDSCs), macrophages, and Treg cells, thereby enabling MDS-associated malignant cells to evade immune cell surveillance. Alterations in MDS-MSC function include genomic instability, microRNA production, histone modification, DNA methylation, and abnormal signal transduction and cytokine secretion.

Relationship of HIF‑1α expression with apoptosis and cell cycle in bone marrow mesenchymal stem cells from patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a group of abnormal clonal disorders with ineffective hematopoiesis, which are incurable with conventional therapy. Of note, MDS features an abnormal bone marrow microenvironment, which is related to its incidence. The hypoxia-inducible factor-1α (HIF-1α) transcriptional signature is generally activated in bone marrow stem/progenitor cells of patients with MDS. To analyze the expression of HIF-1α in bone marrow mesenchymal stem cells (BM-MSCs) and the apoptosis and cell cycle features associated with the disease, BM-MSCs were obtained from 40 patients with a definitive diagnosis of MDS and 20 subjects with hemocytopenia but a negative diagnosis of MDS as a control group. Reverse transcription-quantitative PCR and western blot analyses were used to measure HIF-1α expression in cells from the two groups and apoptosis and cell cycle were also analyzed and compared between the groups using flow cytometry assays. BM-MSCs from both the control group and the MDS group exhibited a fibroblast-like morphology, had similar growth cycles and were difficult to passage stably. It was observed that BM-MSCs from the MDS group had significantly higher HIF-1α expression levels than the control group (P<0.05). Furthermore, the BM-MSCs from the MDS group had a higher proportion of cells in early apoptosis (5.22±1.34 vs. 2.04±0.08%; P<0.0001) and late apoptosis (3.38±0.43 vs. 1.23±0.11%; P<0.01) and exhibited cell cycle arrest. This may be a noteworthy aspect of the pathogenesis of MDS and may be related to high HIF-1α expression under a hypoxic state in the bone marrow microenvironment. Furthermore, the expression of HIF-1α in bone marrow tissue sections from patients with MDS in the International Prognostic Scoring System (IPSS) lower-risk group was higher than that from patients with MDS in the IPSS high-risk group. These results revealed the role of HIF-1α as a central pathobiology mediator of MDS and an effective therapeutic target for a broad spectrum of patients with MDS, particularly for patients in the lower-risk group.

Epigenetic Silencing of PTEN and Epi-Transcriptional Silencing of MDM2 Underlied Progression to Secondary Acute Myeloid Leukemia in Myelodysplastic Syndrome Treated with Hypomethylating Agents

In myelodysplastic syndrome (MDS), resistance to hypomethylating agents (HMA) portends a poor prognosis, underscoring the importance of understanding the molecular mechanisms leading to HMA-resistance. In this study, P39 and Kasumi-1 cells and their azacitidine-resistant and decitabine-resistant sublines were evaluated comparatively with transcriptomic and methylomic analyses. Expression profiling and genome-wide methylation microarray showed downregulation of PTEN associated with DNA hypermethylation in P39 cell lines resistant to azacitidine and decitabine. This pattern of PTEN dysregulation was also confirmed in a cohort of patients failing treatment with HMA. DNA hypomethylation of MDM2 was detected with downregulation of MDM2 in HMA resistant cell lines. Long-read sequencing revealed significant RNA hypomethylation of MDM2 resulting in alternative splicing and production of a truncated MDM2 transcript in azacitidine-resistant P39 cells. The expression of this MDM2 truncated transcript was also significantly increased in HMA-resistant patients compared with HMA-responsive patients. In conclusion, epigenetic and epi-transcriptomic dysregulation of PTEN and MDM2 were associated with resistance to hypomethylating agents.

Differential activation of Ca2+ influx channels modulate stem cell potency, their proliferation/viability and tissue regeneration

Stem cells have indefinite self-renewable capability; however, factors that modulate their pluripotency/function are not fully identified. Here we show that store-dependent Ca²⁺ entry is essential for modulating the function of bone marrow-derived mesenchymal stem cells (MSCs). Increasing external Ca²⁺ modulated cell cycle progression that was critical for MSCs survival. Additionally, Ca²⁺ was critical for stem proliferation, its differentiation, and maintaining stem cell potential. Ca²⁺ channel characterization, including gene silencing, showed two distinct Ca²⁺ entry channels (through Orai1/TRPC1 or via Orai3) that differentially regulate the proliferation and viability of MSCs. Importantly, NFκB translocation, but not JNK/ERK into the nucleus, was observed upon store depletion, which was blocked by the addition of Ca²⁺ channel inhibitors. Radiation lead to a decrease in saliva secretion, decrease in acinar cell number, and enlarged ducts were observed, which were restored by the transplantation of stem cells that were propagated in higher Ca²⁺. Finally radiation showed a decrese in TRPC1 expression along with a decrese in AQP5, which was again restored upon MSC tranplantation. Together these results suggest that Ca²⁺ entry is essential for stem cell function that could be critical for regenerative medicine.

Increasing cytosolic Ca2+ levels restore cell proliferation and stem cell potency in aged MSCs

Aging is an inescapable complex physiological but extendable process, and all cells, including stem cells, are altered over time. Diverse mechanism(s) could modulate stem cell number, their proliferation rate, and promote tissue repair during aging that leads to longevity. However, the factors that could restore aging stem cell potency and would lead to healthy aging are not fully identified. Here we show that maintaining cytosolic Ca²⁺ levels was essential for modulating stem cells function in aged mesenchymal stem cells (MSCs). Increasing external Ca²⁺ induced spindle shape stem cell morphology and maintained stem cell surface marker expression in aged bone marrow-derived MSCs. Similarly, stem cell survival and proliferation of aged MSCs was dependent on cytosolic Ca²⁺ levels. Importantly, Ca²⁺ entry potentiated cell cycle progression, and stem cell potential was increased in cells incubated with higher external Ca²⁺. Moreover, blocking Ca²⁺ entry using SKF 96365, decreased stem cell survival and its proliferation but, treatment with 2-APB did not significantly affected cell proliferation, rather only modulated cell viability. Evaluation of Ca²⁺ entry channels, showed that TRPC1/Orai1/Orai3 and their regulator STIM1 was essential for MSCs proliferation/viability as gene silencing of Orai1/Orai3/TRPC1/STIM1 significantly inhibited stem cell viability. Finally, MSCs isolated from aged mice that were subjected to higher Ca²⁺ levels, were able to rescue age-induced loss of MSCs function. Together these results suggest that Ca²⁺ entry is essential for preventing the loss of aged stem cell function and supplementing Ca²⁺ not only restored their proliferative potential but, allowed them to develop into younger stem cell lineages that could be critical for regenerative medicine.

Cancer Stem Cells and their Management in Cancer Therapy

BACKGROUND

In the last decade, the proposed Cancer Stem Cell (CSC) hypothesis has steadily changed the way cancer treatment is approached. CSCs may be the source of the heterogeneous non-tumorigenic cell population included in a neoplasm. Intratumor and intertumoral heterogeneity is a well-known phenomenon that massively entangles the diagnosis and treatment of cancer. The literature seems to suggest that heterogeneity develops progressively within tumor-initiating stem cells. CSCs harbor genetic and/or epigenetic alterations that allow them to differentiate into multiple tumor cell types sequentially.

OBJECTIVE

The CSC hypothesis, cellular therapy, and the most recent patents on CSCs were reviewed.

METHODS

PubMed, Scopus, and Google Scholar were screened for this information. Also, an analysis of the most recent data targeting CSCs in pediatric cancer developed at two Canadian institutions is provided. The genes involved with the activation of CSCs and the drugs used to antagonize them are also highlighted.

RESULTS

It is underlined that (1) CSCs possess stem cell-like properties, including the ability for self-renewal; (2) CSCs can start carcinogenesis and are responsible for tumor recurrence after treatment; (3) Although some limitations have been raised, which may oppose the CSC hypothesis, cancer progression and metastasis have been recognized to be caused by CSCs.

CONCLUSION

The significant roles of cell therapy may include an auto-transplant with high-dose treatment, an improvement of the immune function, creation of chimeric antigen receptor T cells, and the recruitment of NK cell-based immunotherapy.

Predicting outcome in higher-risk myelodysplastic syndrome patients treated with azacitidine

5-Azacitidine (5-AZA) is widely used for the treatment of higher-risk myelodysplastic syndromes. However, response and survival rates vary considerably, while indicated treatment duration remains undefined. For these reasons, factors determining response and survival are of major importance. Clinical, morphological, flow cytometry, cytogenetic and molecular factors are discussed in this review. Biomarkers predictive of response and prognosis, as well as their link to the mode of action of 5-AZA are also addressed, shifting the focus from clinical practice to investigational research. Their use could further improve prognostic classification of 5-AZA treated higher-risk myelodysplastic syndromes in the near future.

Epigenetic therapy in combination with a multi-epitope cancer vaccine targeting shared tumor antigens for high-risk myelodysplastic syndrome - a phase I clinical trial

BACKGROUND

Standard care for patients with high-risk myelodysplastic syndrome (MDS) is hypomethylating agents such as azacitidine (AZA), which can induce expression of methylated tumor-associated antigens and therefore potentiate immunotherapeutic targeting.

METHOD

In this phase 1 trial, we combined AZA with a therapeutic peptide vaccine targeting antigens encoded from NY-ESO-1, MAGE-A3, PRAME, and WT-1, which have previously been demonstrated to be upregulated by AZA treatment.

RESULT

Five patients who had responded to AZA monotherapy were included in the study and treated with the vaccine. The combination therapy showed only few adverse events during the study period, whereof none classified as serious. However, no specific immune responses could be detected using intracellular cytokine staining or ELISpot assays. Minor changes in the phenotypic composition of immune cells and their expression of stimulatory and inhibitory markers were detected. All patients progressed to AML with a mean time to progression from inclusion (TTP) of 5.2 months (range 2.8 to 7.6). Mean survival was 18.1 months (range 10.9 to 30.6) from MDS diagnosis and 11.3 months (range 4.3 to 22.2) from inclusion. Sequencing of bone marrow showed clonal expansion of malignant cells, as well as appearance of novel mutations.

CONCLUSION

The patients progressed to AML with an average time of only five months after initiating the combination therapy. This may be unrelated to the experimental treatment, but the trial was terminated early as there was no sign of clinical benefit or immunological response. Why the manuscript is especially interesting This study is the first to exploit the potential synergistic effects of combining a multi-peptide cancer vaccine with epigenetic therapy in MDS. Although our results are negative, they emphasize challenges to induce immune reactivity in patients with high-risk MDS.

Calcium channels and their role in regenerative medicine

Stem cells hold indefinite self-renewable capability that can be differentiated into all desired cell types. Based on their plasticity potential, they are divided into totipotent (morula stage cells), pluripotent (embryonic stem cells), multipotent (hematopoietic stem cells, multipotent adult progenitor stem cells, and mesenchymal stem cells [MSCs]), and unipotent (progenitor cells that differentiate into a single lineage) cells. Though bone marrow is the primary source of multipotent stem cells in adults, other tissues such as adipose tissues, placenta, amniotic fluid, umbilical cord blood, periodontal ligament, and dental pulp also harbor stem cells that can be used for regenerative therapy. In addition, induced pluripotent stem cells also exhibit fundamental properties of self-renewal and differentiation into specialized cells, and thus could be another source for regenerative medicine. Several diseases including neurodegenerative diseases, cardiovascular diseases, autoimmune diseases, virus infection (also coronavirus disease 2019) have limited success with conventional medicine, and stem cell transplantation is assumed to be the best therapy to treat these disorders. Importantly, MSCs, are by far the best for regenerative medicine due to their limited immune modulation and adequate tissue repair. Moreover, MSCs have the potential to migrate towards the damaged area, which is regulated by various factors and signaling processes. Recent studies have shown that extracellular calcium (Ca²⁺) promotes the proliferation of MSCs, and thus can assist in transplantation therapy. Ca²⁺ signaling is a highly adaptable intracellular signal that contains several components such as cell-surface receptors, Ca²⁺ channels/pumps/exchangers, Ca²⁺ buffers, and Ca²⁺ sensors, which together are essential for the appropriate functioning of stem cells and thus modulate their proliferative and regenerative capacity, which will be discussed in this review.

Characterization of human bone marrow niches with metabolome and transcriptome profiling

Bone marrow (BM) niches are special microenvironments that work in harmony with each other for the regulation and maintenance of hematopoiesis. Niche investigations have thus far been limited to various model organisms and animal studies; therefore, little is known about different niches in healthy humans. In this study, a special harvesting method for the collection of BM from two different anatomical regions in the iliac crest of humans was used to investigate the presence of different niches in BM. Additionally, metabolomic and transcriptomic profiles were compiled using comparative 'omics' technologies, and the main cellular pathways and corresponding transcripts and metabolites were identified. As a result, we found that the energy metabolism between the regions was different. This study provides basic broad data for regenerative medicine in terms of the design of the appropriate microenvironment for in vitro hematopoietic niche modeling, and identifies the normal reference values that can be compared in hematological disease.

Senescent Mesenchymal Stem Cells in Myelodysplastic Syndrome: Functional Alterations, Molecular Mechanisms, and Therapeutic Strategies

Myelodysplastic syndrome (MDS) is a group of clonal hematopoietic disorders related to hematopoietic stem and progenitor cell dysfunction. However, therapies that are currently used to target hematopoietic stem cells are not effective. These therapies are able to slow the evolution toward acute myeloid leukemia but cannot eradicate the disease. Mesenchymal stem cells (MSCs) have been identified as one of the main cellular components of the bone marrow microenvironment, which plays an indispensable role in normal hematopoiesis. When functional and regenerative capacities of aging MSCs are diminished, some enter replicative senescence, which promotes inflammation and disease progression. Recent studies that investigated the contribution of bone marrow microenvironment and MSCs to the initiation and progression of the disease have offered new insights into the MDS. This review presents the latest updates on the role of MSCs in the MDS and discusses potential targets for the treatment of MDS.

Altered Spatial Composition of the Immune Cell Repertoire in Association to CD34+ Blasts in Myelodysplastic Syndromes and Secondary Acute Myeloid Leukemia

Simple Summary

Despite a relationship between immune dysregulation and the course of myelodysplastic syndromes (MDS) has been discussed, a detailed understanding of this phenomenon is still missing. Therefore, multiplex analyses of bone marrow biopsies (BMB) from patients with MDS and secondary acute myeloid leukemia (sAML) were performed in order to determine the repertoire of lymphocyte subpopulations and their distance to CD34⁺ blasts. In MDS and sAML samples, the composition, quantity, and spatial proximity of immune cell subsets to CD34⁺ blasts were heterogeneous and correlated to the blast counts, but not to the genetics of the diseases, while in non-neoplastic BMB no CD8⁺ and FOXP3⁺ T cells and only single MUM1p⁺ B/plasma cells were detected in a distance of ≤10 μm to CD34⁺ hematopoietic progenitor cells (HPSC). We conclude that CD8⁺ and FOXP3⁺ T cells are not part of the immediate surrounding of CD34⁺ HPSC.

Abstract

Background: Myelodysplastic syndromes (MDS) are caused by a stem cell failure and often include a dysfunction of the immune system. However, the relationship between spatial immune cell distribution within the bone marrow (BM), in relation to genetic features and the course of disease has not been analyzed in detail. Methods: Histotopography of immune cell subpopulations and their spatial distribution to CD34⁺ hematopoietic cells was determined by multispectral imaging (MSI) in 147 BM biopsies (BMB) from patients with MDS, secondary acute myeloid leukemia (sAML), and controls. Results: In MDS and sAML samples, a high inter-tumoral immune cell heterogeneity in spatial proximity to CD34⁺ blasts was found that was independent of genetic alterations, but correlated to blast counts. In controls, no CD8⁺ and FOXP3⁺ T cells and only single MUM1p⁺ B/plasma cells were detected in an area of ≤10 μm to CD34⁺ HSPC. Conclusions: CD8⁺ and FOXP3⁺ T cells are regularly seen in the 10 μm area around CD34⁺ blasts in MDS/sAML regardless of the course of the disease but lack in the surrounding of CD34⁺ HSPC in control samples. In addition, the frequencies of immune cell subsets in MDS and sAML BMB differ when compared to control BMB providing novel insights in immune deregulation.

Infiltrating Immune Cells in Gastric Cancer: A Novel Predicting Model for Prognosis

Objective: Immune cells infiltrating has been proved to be associated with prognosis in gastric cancer (GC) by studies. This study aims to explore the prognosis value of infiltrating immune cells in gastric cancer. Methods: In our study, the CIBERSORT algorithm was used to calculate the fraction of 22 tumor-infiltrating immune cells (TIIC) in 100 normal and 300 tumor samples from the GEO cohort and 30 normal and 344 tumor samples from the TCGA cohort. Univariate and multivariate Cox regression were used to construct an immune risk score model. Multivariate cox regression was also used to validate whether our risk score model could predict prognosis in GC independently. Furthermore, the model was validated in different patient subgroups to test its independence. P<0.05 was considered statistically significant. Results: The results showed that the fraction of 3 immune cells increased in tumor tissues compared with normal tissues in both the GEO and TCGA cohort. Univariate cox regression analysis showed four cells significantly correlated with survival rate in GC (P<0.05). The immune risk score model was constructed based on the four cells through multivariate cox regression and further validated. The KM survival curve suggested that patients with high risk had poor prognosis than patients with low risk (P<0.05). ROC curve indicated the model was reliable (AUC= 0.67 in the GEO cohort, AUC = 0.65 in the TCGA cohort). Furthermore, multivariate Cox regression showed the model was an independent factor for overall survival predicting in GC (hazard ratio (HR) = 2.35, 95% confidence interval (CI) = 1.63~3.40 in the GEO cohort, HR = 2.87, 95% CI = 1.94~4.25 in the TCGA cohort). Finally, we validated the model in patient subgroups by the KM survival curve. Conclusion: In summary, tumor-infiltrating immune cells play an essential role in GC progression and affect the outcome of GC patients. The immune risk score can predict overall survival for GC independently, and high immune risk score is associated with poor prognosis.

Therapy-related acute myeloid leukemia and its prevention

BACKGROUND

Secondary tumors, including therapy-related acute myeloid leukemia (t-AML), represent one of the most undesirable side effects of chemotherapy, which arise several years after primary cancer treatment. This review aims to analyze the current data on molecular pathogenesis of t-AML revealing potential criteria for predicting predisposition to the disease. Another objective is to analyze the information on promising approaches for t-AML prevention.

METHODS

We analyzed studies regarding t-AML and possible approaches for cancer prevention of drug-induced tumors. Publications in the databases, such as SciVerse Scopus (948), PubMed (1837) and Web of Science (935) were used. Among 92 the most important publications cited in the review, 79 were published during the last decade.

RESULTS

The review provides the information concerning t-AML pathogenesis, molecular markers of primary cancer patients with high risk of t-AML. The role of the bone marrow niche in clonal hematopoiesis and t-AML pathogenesis is discussed. Current approaches for t-AML prevention both at the stage of therapy and at the latent period are described. Inhibition effects of polyphenols on cell proliferation and on the appearance of hemopoetic clones of indeterminate potential are proposed for t-AML prevention.

CONCLUSION

The problem of the t-AML, a cancer induced by genotoxic chemotherapeutic drugs, is considered from the point of view of the fundamental mechanisms of chemical carcinogenesis, highlighting initiation and promotion stages. It enables to reveal the possible markers for the group of patients with high risk for t-AML and to demonstrate perspectives for the use of plant polyphenols for t-AML prevention.

Mesenchymal Stem Cells in Aplastic Anemia and Myelodysplastic Syndromes: The "Seed and Soil" Crosstalk

There is growing interest in the contribution of the marrow niche to the pathogenesis of bone marrow failure syndromes, i.e., aplastic anemia (AA) and myelodysplastic syndromes (MDSs). In particular, mesenchymal stem cells (MSCs) are multipotent cells that contribute to the organization and function of the hematopoietic niche through their repopulating and supporting abilities, as well as immunomodulatory properties. The latter are of great interest in MDSs and, particularly, AA, where an immune attack against hematopoietic stem cells is the key pathogenic player. We, therefore, conducted Medline research, including all available evidence from the last 10 years concerning the role of MSCs in these two diseases. The data presented show that MSCs display morphologic, functional, and genetic alterations in AA and MDSs and contribute to immune imbalance, ineffective hematopoiesis, and leukemic evolution. Importantly, adoptive MSC infusion from healthy donors can be exploited to heal the "sick" niche, with even better outcomes if cotransplanted with allogeneic hematopoietic stem cells. Finally, future studies on MSCs and the whole microenvironment will further elucidate AA and MDS pathogenesis and possibly improve treatment.

Bone marrow niches in myeloid neoplasms

Pathological phenotypes of myeloid neoplasms are closely related to genetic/chromosomal abnormalities of neoplastic cells whereas the bone marrow microenvironment, including stromal elements and hematopoietic stem cell niche cells, have a great influence on the differentiation/proliferation of both hematopoietic and neoplastic cells. The pathology of myeloid neoplasms might be generated through the interaction of hematopoietic (stem) cells and stromal cells. The present study aims to provide the morphological/functional aspects of the bone marrow environment in myeloid neoplasms. Among the myeloid neoplasms, myelodysplastic syndromes (MDS) exhibit significant and complex interactions between neoplastic cells and stromal cells. Hematopoietic cells in MDS are greatly influenced by macrophages/niche cells via several signaling pathways. As such, the pathological significance of cell proliferation, cell apoptosis, and anti‐apoptosis signals in the bone marrow of myeloid neoplasms, especially MDS bone marrow, will be discussed.

Phenotype of mesenchymal stem cells from patients with myelodyplastic syndrome maybe partly modulated by decitabine

Mesenchymal stem cells (MSCs) derived from myelodysplastic syndromes (MDSs) have been demonstrated to accelerate the progression of MDS. However, whether the phenotype of MSCs derived from MDS (MDS-MSCs) may be reversed and serve as a potential target for the treatment of MDS remains unclear. The present study investigated the functional alternations of MDS-MSCs following in vitro decitabine-treatment. Primary MSCs were cultured from the bone marrow aspirates of 28 patients with MDS. The impact on the growth of MDS-MSCs treated with decitabine was analyzed using the MTT assay. Changes in the gene expression levels of runt related transcription factor 2 (RUNX2), Sp7 transcription factor (SP7), cyclin dependent kinase inhibitor 1A (CDKN1A) and CD274 in MDS-MSCs following treatment with decitabine were analyzed by reverse transcription-quantitative polymerase chain reaction. The effects of decitabine on apoptosis and the cell cycle were examined using flow cytometry. The effect of decitabine on the immune regulation of MDS-MSCs was tested by the co-culture of MSCs with activated T cells in vitro. The results revealed that proliferation, apoptosis and the mRNA expression levels of RUNX2 and SP7 in MDS-MSCs did not significantly change following treatment with decitabine compared with control MDS-MSCs. However, treatment with decitabine resulted in a smaller population of cells in the G1 phase and an increase in the number of cells in the G2/M phase compared with control MDS-MSCs. This change was associated with decreased expression of CDKN1A in cells treated with decitabine compared with control cells. Notably, the ability of MDS-MSCs treated with decitabine to induce the differentiation of T cells into regulatory T cells was significantly reduced compared with control MDS-MSCs. This was associated with a decreased expression of CD274 in MDS-MSCs treated with decitabine compared with control MDS-MSCs. In conclusion, the phenotype of MSCs derived from patients with MDS was partially reversed by treatment with decitabine, presenting a potential therapeutic intervention.

Self-Assembly of Artificial Sweetener Aspartame Yields Amyloid-like Cytotoxic Nanostructures

Recent reports have revealed the intrinsic propensity of single aromatic metabolites to undergo self-assembly and form nanostructures of amyloid nature. Hence, identifying whether aspartame, a universally consumed artificial sweetener, is inherently aggregation prone becomes an important area of investigation. Although the reports on aspartame-linked side effects describe a multitude of metabolic disorders, the mechanistic understanding of such destructive effects is largely mysterious. Since aromaticity, an aggregation-promoting factor, is intrinsic to aspartame's chemistry, it is important to know whether aspartame can undergo self-association and if such a property can predispose any cytotoxicity to biological systems. Our study finds that aspartame molecules, under mimicked physiological conditions, undergo a spontaneous self-assembly process yielding regular β-sheet-like cytotoxic nanofibrils of amyloid nature. The resultant aspartame fibrils were found to trigger amyloid cross-seeding and become a toxic aggregation trap for globular proteins, Aβ peptides, and aromatic metabolites that convert native structures to β-sheet-like fibrils. Aspartame fibrils were also found to induce hemolysis, causing DNA damage resulting in both apoptosis and necrosis-mediated cell death. Specific spatial arrangement between aspartame molecules is predicted to form a regular amyloid-like architecture with a sticky exterior that is capable of promoting viable H-bonds, electrostatic interactions, and hydrophobic contacts with biomolecules, leading to the onset of protein aggregation and cell death. Results reveal that the aspartame molecule is inherently amyloidogenic, and the self-assembly of aspartame becomes a toxic trap for proteins and cells, exposing the bitter side of such a ubiquitously used artificial sweetener.

BM-MSCs-derived ECM modifies multiple myeloma phenotype and drug response in a source-dependent manner

Multiple myeloma (MM) malignant plasma cells accumulate in the bone marrow (BM) where their interaction with the microenvironment promotes disease progression and drug resistance. Previously, we have shown that MM cells cocultured with BM-mesenchymal stem cells (MSCs) comodulated cells' phenotype in a MAPKs/translation initiation (TI)-dependent manner. Dissection of the coculture model showed that BM-MSCs secretomes and microvesicles (MVs) participate in this crosstalk. Here, we addressed the role of the BM-MSCs extracellular matrix (ECM). MM cell lines cultured on decellularized ECM of normal donors' (ND) or MM patients' BM-MSCs were assayed for phenotype (viability, cell count, death, proliferation, migration, and invasion), microRNAs (MIR125a-3p, MIR199a-3p) and targets, MAPKs, TI epithelial-to-mesenchymal transition (EMT), CXCR4, and autophagy. Drug (doxorubicin, velcade) response of MM cells cultured on ND/MM-MSCs' ECM with/without adhered MVs was also evaluated. ECM evoked opposite responses according to its origin: MM cells cultured on ND-MSCs' ECM demonstrated a rapid and continued decrease in MAPK/TI activation (↓10%-25%, P < 0.05) (15-24 hours) followed by diminished viability, cell count, proliferation, migration, and invasion (16-72 hours) (↓10%-50%, P < 0.05). In contrast, MM cells cultured on MM-MSCs' ECM displayed activated MAPK/TI, proliferation, EMT, and CXCR4 (↑15%-250%, P < 0.05). Corresponding changes in microRNAs relevant to the MM cells' altered phenotype were also determined. The hierarchy and interdependence of MAPKs/TI/autophagy/phenotype cascade were demonstrated. Finally, we showed that the ECM cooperates with MVs to modulate MM cells drug response. These data demonstrate the contribution of BM-MSCs' ECM to MM niche design and underscore the clinical potential of identifying targetable signals.

Flaming and fanning: The Spectrum of inflammatory influences in myelodysplastic syndromes

The myelodysplastic syndromes (MDS) represent neoplasms derived from the expansion of mutated clonal hematopoietic cells which often demonstrate aberrant differentiation potential with resultant cytopenias and a propensity to evolve into acute myelogenous leukemia. While multiple mutations have been identified which may serve as drivers of the MDS clone, there is accumulating evidence that MDS clones and subclones are subject to modulation by the marrow microenvironment and its inflammatory milieu. There is also a strong link between autoimmune disorders and MDS. In this review, we examine the role of inflammatory cytokines, toll like receptors, pyroptosis, stromal cells, and cellular inflammatory mediators in MDS initiation, propagation, and progression. These contributions in a background of mutational, epigenetic, and aging changes in the marrow are also reviewed. Such inflammatory mediators may be subject to therapeutic agents which will enhance suppression of the MDS clone with potential to improve therapeutic outcomes in this disease which is usually incurable in aged patients not eligible for stem cell transplantation.

The Role of Tumor Microenvironment and Impact of Cancer Stem Cells on Breast Cancer Progression and Growth

Breast cancer is not only a mass of genetically abnormal tissue in the breast. This is a well-organized system of a complex heterogeneous tissue. Cancer cells produce regulatory signals that stimulate stromal cells to proliferate and migrate; then, stromal elements respond to these signals by releasing components necessary for tumor development that provide structural support, vasculature, and extracellular matrices. Developing tumors can mobilize a variety of cell types from both local and distant niches via secret chemical factors derived from cancer cells themselves or neighboring cells disrupted by growing neoplasm, such as fibroblasts, immune inflammatory cells, and endothelial cells. CSCs are a group of very few cells that are tumorigenic (able to form tumors) and are defined as those cells within a tumor that can self-renew and lead to tumorigenesis. BCSCs represent a small population of cells that have stem cell characteristics and are related to breast cancer. There are different theories about the origin of BCSCs. BCSCs are responsible for breast carcinoma metastasis. Usually, there is a metastatic spread to the bones, and rarely to the lungs and liver. A phenomenon that allows BCSCs to make the transition from epithelial to mesenchymal expression and thus avoid the effect of cytotoxic agents is the epithelial-mesenchymal transition (EMT). During this process, cells change their molecular characteristics in terms of loss of epithelial characteristics taking the mesenchymal phenotype. This process plays a key role in the progression, invasion, and metastasis of breast tumors.

Expression of interferon regulatory factors (IRF-1 and IRF-2) during radiation-induced damage and regeneration of bone marrow by transplantation in mouse

Interferon regulatory factors (IRF-1 and IRF-2) are transcription factors of IRF-family that regulate expression of genes for cytokines, chemokines and growth factors in mammalian cells. IRF-1 and IRF-2 play crucial roles in the differentiation of bone marrow cells for immune response. Bone marrow (BM) is the soft lymphoid organ that contains many types of stem cells and produces different types of cells of the blood and immune system. Genetic alterations and damage of the bone marrow cells can lead to different types of blood and immune system-related diseases including anemia and cancer. We have studied the expression of IRF-1 and IRF-2 during radiation-induced damage and regeneration of bone marrow cells after transplantation of freshly isolated bone marrow cells in the mouse. Cell cycle analysis, colony forming unit-fibroblast (CFU-F) assay and bone marrow histology showed that after radiation-induced damage, the bone marrow transplantation resulted in regeneration of the bone marrow up to 24-35% recovery. Real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) for the mRNA expression showed that IRF-1 and IRF-2 were expressed at higher levels in the bone marrow cells of the irradiated (4.34× fold for IRF-1, and 3.87× fold for IRF-2) compared to control and transplanted (1.13× fold for IRF-1, and 1.12× fold IRF-2) mice and immuno-fluorescence analysis for the protein expression showed that IRF-1 and IRF-2 were expressed at higher levels in the bone marrow cells of the irradiated (2.12× fold for IRF-1 and 1.71× fold for IRF-2) compared to control and transplanted (1.73× fold for IRF-1 and 1.21× fold for IRF-2) mice. Thus, IRF-1 and IRF-2 are sensitive and responsive to radiation-induced damage in the bone marrow cells and may also be involved in the bone marrow regeneration process.

Evaluation of bone marrow microenvironment could change how myelodysplastic syndromes are diagnosed and treated

Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic disorders. However, the therapies used against the hematopoietic stem cells clones have limited efficacy; they slow the evolution toward acute myeloid leukemia rather than stop clonal evolution and eradicate the disease. The progress made in recent years regarding the role of the bone marrow microenvironment in disease evolution may contribute to progress in this area. This review presents the recent updates on the role of the bone marrow microenvironment in myelodysplastic syndromes pathogenesis and tries to find answers regarding how this information could improve myelodysplastic syndromes diagnosis and therapy.

Aging- and Senescence-associated Changes of Mesenchymal Stromal Cells in Myelodysplastic Syndromes

Hematopoietic stem and progenitor cells reside within the bone marrow (BM) microenvironment. By a well-balanced interplay between self-renewal and differentiation, they ensure a lifelong supply of mature blood cells. Physiologically, multiple different cell types contribute to the regulation of stem and progenitor cells in the BM microenvironment by cell-extrinsic and cell-intrinsic mechanisms. During the last decades, mesenchymal stromal cells (MSCs) have been identified as one of the main cellular components of the BM microenvironment holding an indispensable role for normal hematopoiesis. During aging, MSCs diminish their functional and regenerative capacities and in some cases encounter replicative senescence, promoting inflammation and cancer progression. It is now evident that alterations in specific stromal cells that comprise the BM microenvironment can contribute to hematologic malignancies, and there is growing interest regarding the contribution of MSCs to the pathogenesis of myelodysplastic syndromes (MDSs), a clonal hematological disorder, occurring mostly in the elderly, characterized by ineffective hematopoiesis and increased tendency to acute myeloid leukemia evolution. The pathogenesis of MDS has been associated with specific genetic and epigenetic events occurring both in hematopoietic stem cells (HSCs) and in the whole BM microenvironment with an aberrant cross talk between hematopoietic elements and stromal compartment. This review highlights the role of MSCs in MDS showing functional and molecular alterations such as altered cell-cycle regulation with impaired proliferative potential, dysregulated cytokine secretion, and an abnormal gene expression profile. Here, the current knowledge of impaired functional properties of both aged MSCs and MSCs in MDS have been described with a special focus on inflammation and senescence induced changes in the BM microenvironment. Furthermore, a better understanding of aberrant BM microenvironment could improve future potential therapies.

Tumor Trp53 status and genotype affect the bone marrow microenvironment in acute myeloid leukemia

The genetic heterogeneity of acute myeloid leukemia (AML) and the variable responses of individual patients to therapy suggest that different AML genotypes may influence the bone marrow (BM) microenvironment in different ways. We performed gene expression profiling of bone marrow mesenchymal stromal cells (BM-MSC) isolated from normal C57BL/6 mice or mice inoculated with syngeneic murine leukemia cells carrying different human AML genotypes, developed in mice with Trp53 wild-type or nullgenetic backgrounds. We identified a set of genes whose expression in BM-MSC was modulated by all four AML genotypes tested. In addition, there were sets of differentially-expressed genes in AML-exposed BM-MSC that were unique to the particular AML genotype or Trp53 status. Our findings support the hypothesis that leukemia cells alter the transcriptome of surrounding BM stromal cells, in both common and genotype-specific ways. These changes are likely to be advantageous to AML cells, affecting disease progression and response to chemotherapy, and suggest opportunities for stroma-targeting therapy, including those based on AML genotype.

Mesenchymal Stem Cells in Myeloid Malignancies: A Focus on Immune Escaping and Therapeutic Implications

The importance of the bone marrow microenvironment forming the so-called niche in physiologic hemopoiesis is largely known, and recent evidences support the presence of stromal alterations from the molecular to the cytoarchitectural level in hematologic malignancies. Various alterations in cell adhesion, metabolism, cytokine signaling, autophagy, and methylation patterns of tumor-derived mesenchymal stem cells have been demonstrated, contributing to the genesis of a leukemic permissive niche. This niche allows both the ineffective haematopoiesis typical of myelodysplastic syndromes and the differentiation arrest, proliferation advantage, and clone selection which is the hallmark of acute myeloid leukemia. Furthermore, the immune system, both adaptive and innate, encompassing mesenchymal-derived cells, has been shown to take part to the leukemic niche. Here, we critically review the state of art about mesenchymal stem cell role in myelodysplastic syndromes and acute myeloid leukemia, focusing on immune escaping mechanisms as a target for available and future anticancer therapies.

The microenvironment in human myeloid malignancies: emerging concepts and therapeutic implications

Similar to their healthy counterpart, malignant hematopoietic stem cells in myeloid malignancies, such as myeloproliferative neoplasms, myelodysplastic syndromes, and acute myeloid leukemia, reside in a highly complex and dynamic cellular microenvironment in the bone marrow. This environment provides key regulatory signals for and tightly controls cardinal features of hematopoietic stem cells (HSCs), including self-renewal, quiescence, differentiation, and migration. These features are essential to maintaining cellular homeostasis and blood regeneration throughout life. A large number of studies have extensively addressed the composition of the bone marrow niche in mouse models, as well as the cellular and molecular communication modalities at play under both normal and pathogenic situations. Although instrumental to interrogating the complex composition of the HSC niche and dissecting the niche remodeling processes that appear to actively contribute to leukemogenesis, these models may not fully recapitulate the human system due to immunophenotypic, architectural, and functional inter-species variability. This review summarizes several aspects related to the human hematopoietic niche: (1) its anatomical structure, composition, and function in normal hematopoiesis; (2) its alteration and functional relevance in the context of chronic and acute myeloid malignancies; (3) age-related niche changes and their suspected impact on hematopoiesis; (4) ongoing efforts to develop new models to study niche-leukemic cell interaction in human myeloid malignancies; and finally, (5) how the knowledge gained into leukemic stem cell (LSC) niche dependencies might be exploited to devise novel therapeutic strategies that aim at disrupting essential niche-LSC interactions or improve the regenerative ability of the disease-associated hematopoietic niche.

Reactivation of dormant anti-tumor immunity - a clinical perspective of therapeutic immune checkpoint modulation

In favor of their outgrowth, cancer cells must resist immune surveillance and edit the immune response. Cancer immunoediting is characterized by fundamental changes in the cellular composition and the inflammatory cytokine profiles in the microenvironment of the primary tumor and metastatic niches, with an ever increasing complexity of interactions between tumor cells and the immune system. Recent data suggest that genetic instability and immunoediting are not necessarily disparate processes. Increasing mutational load may be associated with multiple neoepitopes expressed by the tumor cells and thus increased chances for the immune system to recognize and combat these cells. At the same time the immune system is more and more suppressed and exhausted by this process. Consequently, immune checkpoint modulation may have the potential to be most successful in genetically highly altered and usually extremely unfavorable types of cancer. Moreover, the fact that epitopes recognized by the immune system are preferentially encoded by passenger gene mutations opens windows of synergy in targeting cancer-specific signaling pathways by small molecules simultaneously with antibodies modifying T-cell activation or exhaustion.

This review covers some aspects of the current understanding of the immunological basis necessary to understand the rapidly developing therapeutic endeavours in cancer treatment, the clinical achievements made, and raises some burning questions for translational research in this field.