Rosana Pelayo

Lineage Switching in Acute Leukemias: A Consequence of Stem Cell Plasticity?

Acute leukemias are the most common cancer in childhood and characterized by the uncontrolled production of hematopoietic precursor cells of the lymphoid or myeloid series within the bone marrow. Even when a relatively high efficiency of therapeutic agents has increased the overall survival rates in the last years, factors such as cell lineage switching and the rise of mixed lineages at relapses often change the prognosis of the illness. During lineage switching, conversions from lymphoblastic leukemia to myeloid leukemia, or vice versa, are recorded. The central mechanisms involved in these phenomena remain undefined, but recent studies suggest that lineage commitment of plastic hematopoietic progenitors may be multidirectional and reversible upon specific signals provided by both intrinsic and environmental cues. In this paper, we focus on the current knowledge about cell heterogeneity and the lineage switch resulting from leukemic cells plasticity. A number of hypothetical mechanisms that may inspire changes in cell fate decisions are highlighted. Understanding the plasticity of leukemia initiating cells might be fundamental to unravel the pathogenesis of lineage switch in acute leukemias and will illuminate the importance of a flexible hematopoietic development.

Active protection of mice against Salmonella typhi by immunization with strain-specific porins

NIH mice were immunized with between 2.5 and 30 micrograms of two highly purified porins, 34 kDa and 36 kDa, isolated from the virulent strain Salmonella typhi 9,12, Vi:d. Of mice immunized with 10 micrograms of porins, 90% were protected against a challenge with up to 500 LD50 (50% lethal doses) of S. typhi 9,12,Vi:d and only 30% protection was observed in mice immunized with the same dose of porins but challenged with the heterologous strain Salmonella typhimurium. These results demonstrate the utility of porins for the induction of a protective status against S. typhi in mice.

Early Lymphoid Development and Microenvironmental Cues in B-cell Acute Lymphoblastic Leukemia

B-cell acute lymphoblastic leukemia (B-ALL) is a hematological disorder characterized by malignant and uncontrolled proliferation of B-lymphoid precursor cells in bone marrow. Over the last few years remarkable advances have been made in identifying genetic aberrations, patterns of abnormal transcriptional activity controlling early fate decisions and environmental cues that may influence leukemic development. In this review we focus on the structure of the early lymphoid system and the current knowledge about cell composition and function of the hematopoietic microenvironment that might control progenitor cell activity and lead to differentiation, proliferation and survival of developing B leukemic precursors. Learning the biology of special leukemic niches is central to understanding the pathogenesis of B-ALL and for the development of novel therapies.

B cell precursors are targets for Salmonella infection

We previously reported that, in mice, B cells are a reservoir for bacteria during Salmonella infection. Here, we show that, within the bone marrow, B cells and their precursors are targeted for infection by Salmonella enterica serovar typhimurium. Our data suggest that B cells within the bone marrow may be a bacterial niche during chronic Salmonella infection.

In vitro effects of stromal cells expressing different levels of Jagged-1 and Delta-1 on the growth of primitive and intermediate CD34+ cell subsets from human cord blood

In trying to contribute to our knowledge on the role of Notch and its ligands within the human hematopoietic system, we have assessed the effects of the OP9 stroma cell line - naturally expressing Jagged-1 - transduced with either the Delta-1 gene (OP9-DL1 cells) or with vector alone (OP9-V), on the in vitro growth of two different hematopoietic cell populations. Primitive (CD34(+) CD38(-) Lin(-)) and intermediate (CD34(+) CD38(+) Lin(-)) CD34(+) cell subsets from human cord blood were cultured in the presence of 7 stimulatory cytokines under four different conditions: cytokines alone (control); cytokines and mesenchymal stromal cells; cytokines and OP9-V cells; cytokines and OP9-DL1 cells. Proliferation and expansion were determined after 7days of culture. Culture of CD34(+) CD38(-) Lin(-) cells in the presence of OP9-V or OP9-DL1 cells resulted in a significant increase in the production of new CD34(+) CD38(-) Lin(-) cells (expansion), which expressed increased levels of Notch-1; in contrast, production of total nucleated cells (proliferation) was reduced, as compared to control conditions. In cultures of CD34(+) CD38(+) Lin(-) cells established in the presence of OP9-V or OP9-DL1 cells, expansion was similar to that observed in control conditions, whereas proliferation was also reduced. Interestingly, in these latter cultures we observed production of CD34(+) CD38(-) Lin(-) cells. Our results indicate that, as compared to MSC, OP9 cells were more efficient at inducing self-renewal and/or de novo generation of primitive (CD34(+) CD38(-) Lin(-)) cells, and suggest that such effects were due, at least in part, to the presence of Jagged-1 and DL1.

Acute myelogenous leukemia switch lineage upon relapse to acute lymphoblastic leukemia: a case report

Acute leukemia, the most common form of cancer in children, accounts for approximately 30% of all childhood malignancies, with acute lymphoblastic leukemia being five times more frequent than acute myeloid leukemia. Lineage switch is the term that has been used to describe the phenomenon of acute leukemias that meet the standard French-American-British system criteria for a particular lineage (either lymphoid or myeloid) upon initial diagnosis, but meet the criteria for the opposite lineage at relapse. Many reports have documented conversions of acute lymphoblastic leukemia to acute myeloid leukemia.Here, we report the case of a 4-year-old child with acute myeloid leukemia, which upon relapse switched to acute lymphoblastic leukemia. The morphologic, phenotypic, and molecular features suggest the origin of a new leukemic clone.

Modeling the Pro-inflammatory Tumor Microenvironment in Acute Lymphoblastic Leukemia Predicts a Breakdown of Hematopoietic-Mesenchymal Communication Networks

Lineage fate decisions of hematopoietic cells depend on intrinsic factors and extrinsic signals provided by the bone marrow microenvironment, where they reside. Abnormalities in composition and function of hematopoietic niches have been proposed as key contributors of acute lymphoblastic leukemia (ALL) progression. Our previous experimental findings strongly suggest that pro-inflammatory cues contribute to mesenchymal niche abnormalities that result in maintenance of ALL precursor cells at the expense of normal hematopoiesis. Here, we propose a molecular regulatory network interconnecting the major communication pathways between hematopoietic stem and progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs) within the BM. Dynamical analysis of the network as a Boolean model reveals two stationary states that can be interpreted as the intercellular contact status. Furthermore, simulations describe the molecular patterns observed during experimental proliferation and activation. Importantly, our model predicts instability in the CXCR4/CXCL12 and VLA4/VCAM1 interactions following microenvironmental perturbation due by temporal signaling from Toll like receptors (TLRs) ligation. Therefore, aberrant expression of NF-κB induced by intrinsic or extrinsic factors may contribute to create a tumor microenvironment where a negative feedback loop inhibiting CXCR4/CXCL12 and VLA4/VCAM1 cellular communication axes allows for the maintenance of malignant cells.

Normal vs. Malignant hematopoiesis: the complexity of acute leukemia through systems biology

Development of normal hematopoietic cells is an ordered multi-step process, tightly regulated by a complex network of intrinsic factors and microenvironmental cues that control cell fate decisions within the bone marrow (BM) (Pelayo et al., 2012; Purizaca et al., 2012; Boulais and Frenette, 2015). During malignant hematological disorders, including acute leukemias (AL), the uncontrolled differentiation of precursors of the lymphoid or myeloid series sustains tumor growth at the expense of normal blood cell production. Moreover, selection and dominance among leukemic clones occur while competing for niche resources and creating abnormal BM microenvironments that co-participate in the pathobiology of the disease (Colmone et al., 2008; Ayala et al., 2009; Purizaca et al., 2012; Kim et al., 2015; Vilchis-Ordonez et al., 2015). Thus, due to the complexity and health impact of AL (Gupta et al., 2014), new strategies to better predict cell population dynamics according to genetics, microenvironmental and clinical heterogeneous contexts may contribute to understand its pathobiology and to guide strategies for decreasing overall mortality. Mathematical modeling has emerged as a powerful tool in biomedical and health research because it enables the simulation of complex biological systems and the efficient generation of testable hypotheses. In recent years, leukemic cell dynamics has been addressed from the novel view of systems biology, resulting in helpful stochastic and deterministic models and providing clearer understanding of the disease by simplification ofmalignant clonal evolution processes (Vesely et al., 2011; Amir et al., 2013; Paguirigan et al., 2015). However, models fitted to experimental data must strike a balance between simplicity and reality, so that they can bring insights into clinical scenarios. Here we discuss the importance and challenges of incorporating the BM microenvironment into AL modeling, as a key element that will control the interplay between cell populations and the selective pressure leading to leukemic or normal hematopoiesis progression. By developing integrative tools that better mimic and predict the behavior of heterogeneous and polyclonal cells in the context of abnormal microenvironments within leukemic bone marrow, we may learn about crucial mechanisms co-participating in the etiology and progression of the disease.

CD38 expression in early B-cell precursors contributes to extracellular signal-regulated kinase-mediated apoptosis

CD38 is a 45 000 molecular weight transmembrane protein that is expressed in immature and mature lymphocytes. However, the expression and function of CD38 during B‐cell differentiation in mice is poorly understood. Here, we report that CD38 is expressed from the earliest stages of B‐cell development. Pre‐pro‐B, pro‐B, pre‐B and immature B cells from murine bone marrow all stained positive for CD38. Interestingly, CD38 expression increases with B‐cell maturation. To assess the role of CD38 during B‐cell maturation, CD38‐deficient mice were analysed. CD38−/− mice showed a significant increase in both the frequency of B‐lineage cells and the absolute numbers of pre‐pro‐B cells in bone marrow; however, no other differences were observed at later stages. CD38 cross‐linking in Ba/F3 cells promoted apoptosis and marked extracellular signal‐regulated kinase (ERK) phosphorylation, and these effects were reduced by treatment with the mitogen‐activated protein kinase/ERK kinase inhibitor PD98059, and similar effects were observed in B‐cell precursors from bone marrow. These data demonstrate that B‐cell precursors in mouse bone marrow express functional CD38 and implicate the early ligation of CD38 in the ERK‐associated regulation of the B‐lineage differentiation pathway.

Analysis of Normal Hematopoietic Stem and Progenitor Cell Contents in Childhood Acute Leukemia Bone Marrow

BACKGROUND AND AIMS Childhood acute leukemias (AL) are characterized by the excessive production of malignant precursor cells at the expense of effective blood cell development. The dominance of leukemic cells over normal progenitors may result in either direct suppression of functional hematopoiesis or remodeling of microenvironmental niches, contributing to BM failure and AL-associated mortality. We undertook this study to investigate the contents and functional activity of hematopoietic stem/progenitor cells (HSPC) and their relationship to immune cell production and risk status in AL pediatric patients. METHODS Multiparametric flow cytometry of BM aspirates was performed to classify AL on the basis of lineage and differentiation stages and to analyze HSPC and immune cell frequencies. Controlled co-culture systems were conducted to evaluate functional lineage potentials of primitive cells. Statistical correlations and inter-group significant differences were established. RESULTS Among 113 AL BM aspirates, 26.5% corresponded to ProB, 19.5% to PreB and 32% contain ProB and PreB differentiation stages, whereas nearly 9% of the cases were T- and 13% myeloid-lineage leukemias. We identified ProB-ALL as the subtype endowed with the highest relative contents of HSPC, whereas T-ALL and PreB-ALL showed a critically reduced size of both HSC and MLP compartments. Notably, lower cell frequencies of HSPC in ProB-ALL correlated to high-risk prognosis at disease debut. CONCLUSIONS HSPC abundance at initial diagnosis may aid to predict the clinical course of ALL and to identify high-risk patients. A clearer understanding of their population dynamics and functional properties in the leukemia setting will potentially pave the way for targeted therapies.