Native Hematopoiesis Research Articles

Continuous cell supply from Krt7-expressing hematopoietic stem cells during native hematopoiesis revealed by targeted in vivo gene transfer method

The nature of hematopoietic stem cells under normal hematopoiesis remained largely unknown due to the limited assays available to monitor their behavior in situ. Here, we develop a new mouse model to transfer genes specifically into the primitive hematopoietic stem cell compartment through the utilization of a modified Rcas/TVA system. We succeeded in transferring a GFP reporter gene into adult hematopoietic stem cells in vivo, which are predominantly quiescent, by generating pseudotyped-lentivirus. Furthermore, we demonstrate the utility of this system to study neonatal hematopoiesis, a developmental stage that has been difficult to analyze to date. Using the system developed in this study, we observed continuous multi-lineage hematopoietic cell supply in peripheral blood from Krt7-positive hematopoietic stem cells during unperturbed homeostatic condition. This powerful experimental system could provide a new standard tool to analyze hematopoiesis under physiological condition without transplantation.

Clonal Hematopoiesis Associated with Adverse Outcomes Following Autologous Stem Cell Transplantation for Non-Hodgkin Lymphoma

▪BackgroundClonal hematopoiesis of indeterminate potential (CHIP) is an age-related phenomenon characterized by the presence of somatic mutations in peripheral blood (PMIDs: 25426837, 25426838). Although CHIP was originally defined in healthy older adults without cytopenias, it can be found in other contexts as well. For example, one recent report described four patients with therapy-related myeloid neoplasm (TMN) arising after treatment for other cancers, all of which were driven by TP53 mutations that could be found at very low levels in samples drawn years before the development of TMN (PMID: 25487151). However, there has not yet been a more systematic study of CHIP in this type of context.In this study, we sought to understand how CHIP behaves and influences outcomes in the context of autologous stem cell transplantation (ASCT), arguably the most extreme selective pressure that can be studied in the context of native hematopoiesis. We hypothesized that in patients with Non-Hodgkin Lymphoma (NHL) undergoing ASCT, the presence of CHIP at the time of transplantation would be associated with an increased risk of TMN and other adverse outcomes.MethodsWe analyzed exome sequencing data from 10 patients with TMN after ASCT (City of Hope Cancer Center, Duarte, CA), and performed targeted sequencing of 116 genes on banked, mobilized peripheral blood from an additional 401 patients with NHL who underwent ASCT (Dana Farber Cancer Institute, Boston, MA), to determine whether there is a clonal connection between CHIP at the time of ASCT and subsequent TMN, and to determine whether the presence of CHIP at the time of ASCT influences subsequent outcomes.ResultsIn 7 of 10 TMN patients for whom we analyzed exome sequencing data, mutations present at the time of TMN were also detectable in the pre-ASCT sample. PPM1D, a key mediator of the DNA damage pathway, was mutated in 2 patients, as was TP53 (2 patients), TET2 (2 patients) and PRPF8 (1 patient). In our larger cohort of 401 unselected ASCT patients, CHIP was common (121 patients, 30.2%) and was associated with older age but not with other demographic or treatment-related factors. PPM1D was the most commonly mutated gene (54 mutations in 48 patients).In the ASCT cohort of 401 patients, 18 patients developed TMN. The presence of CHIP at the time of ASCT significantly increased this risk: the 10-year cumulative incidence of TMN, with death and allogeneic transplant as competing risks, was 12.4% for patients with CHIP, compared to 3.5% for patients without CHIP (P=0.002, Figure 1A). Moreover, the presence of CHIP at the time of ASCT conferred significant risks beyond TMN alone, as patients with CHIP had significantly inferior overall survival compared to patients without CHIP (10-year OS 30.6% versus 60.9%, P=0.0003, Figure 1B). This difference was driven primarily by late mortality and not by an increased risk of relapse or by the difference in rate of TMN. Although other variables were associated with OS in univariate analysis, multivariate analysis in a Cox proportional hazards model showed that only older age (60 or above), aggressive lymphoma, and presence of CHIP were significantly associated with survival.ConclusionWe show that CHIP at the time of ASCT for NHL is common and is associated with an increased risk of TMN and decreased overall survival independent of the TMN risk. These results have substantial clinical and translational implications. They suggest the need to specifically study the connection between CHIP and lymphoma more deeply, which could be accomplished by assessing CHIP in patients with newly diagnosed lymphoma prior to the administration of any chemotherapy or mobilizing agents. They also suggest the need to consider alternative therapeutic approaches for patients with lymphoma and a high risk of TMN who are being considered for ASCT. Finally, they underscore the need to study clonal hematopoiesis in the context of treatment for other cancers to determine whether these results may be relevant to an even larger number of patients. [Display omitted] DisclosuresLindsley:MedImmune: Research Funding; Takeda Pharmaceuticals: Consultancy. Mar:H3 Biomedicine: Other: Spouse's employment. LaCasce:Forty Seven: Consultancy; Seattle Genetics: Consultancy; Seattle Genetics: Consultancy. Koreth:LLS: Research Funding; amgen inc: Consultancy; takeda pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; kadmon corp: Membership on an entity's Board of Directors or advisory committees; prometheus labs inc: Research Funding; millennium pharmaceuticals: Research Funding. Ritz:Kiadis: Membership on an entity's Board of Directors or advisory committees. Soiffer:Kiadis: Membership on an entity's Board of Directors or advisory committees; Juno: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees.

Mitotic History Reveals Distinct Stem Cell Populations and Their Contributions to Hematopoiesis

SummaryHomeostasis of short-lived blood cells is dependent on rapid proliferation of immature precursors. Using a conditional histone 2B-mCherry-labeling mouse model, we characterize hematopoietic stem cell (HSC) and progenitor proliferation dynamics in steady state and following several types of induced stress. HSC proliferation following HSC transplantation into lethally irradiated mice is fundamentally different not only from native hematopoiesis but also from other stress contexts. Whereas transplantation promoted sustained, long-term proliferation of HSCs, both cytokine-induced mobilization and acute depletion of selected blood cell lineages elicited very limited recruitment of HSCs to the proliferative pool. By coupling mCherry-based analysis of proliferation history with multiplex gene expression analyses on single cells, we have found that HSCs can be stratified into four distinct subtypes. These subtypes have distinct molecular signatures and differ significantly in their reconstitution potentials, showcasing the power of tracking proliferation history when resolving functional heterogeneity of HSCs.

P.3.034 Brooding subtype of rumination is modulated by the interplay between serotonin receptor 2A gene and childhood adversity

In recent years, sophisticated fate-mapping tools have been developed to study the behavior of stem cells in the intact organism. These experimental approaches are beginning to yield a quantitative picture of how cell numbers are regulated during steady state and in response to challenges. Focusing on hematopoiesis and immune responses, we discuss how novel mathematical approaches driven by these fate-mapping data have provided insights into the dynamics and topology of cellular differentiation pathways in vivo. The combination of experiment and theory has allowed to quantify the degree of self-renewal in stem and progenitor cells, shown how native hematopoiesis differs fundamentally from post-transplantation hematopoiesis, and uncovered that the diversification of T lymphocytes during immune responses resembles tissue renewal driven by stem cells.

Single-Cell Analysis of Lymphoid-Primed Multipotent Progenitors (LMPPs) Reveal Alterations in Lineage Commitment during Aging

During aging, the hematopoietic compartment undergoes lineage skewing, biased toward myeloid differentiation at the expense of lymphoid differentiation. This skewing clinically presents as impaired adaptive immunity and an increased risk of myeloproliferative disorders. However, little is known of the regulatory mechanisms underlying these changes in differentiation potential due in part to the inadequacy of current analytic techniques to evaluate lineage potency of individual progenitor cells. Recent demonstration that long-lived hematopoietic progenitor cells drive steady-state hematopoiesis has shifted focus onto the progenitor cell compartment to understand clonal dynamics of native hematopoiesis. Here, we critically assess the functional and molecular alterations in the multipotent progenitor cell pool with aging at the single-cell level. We developed novel in vitro and in vivo assays to define the heterogeneity of the LMPP population and test cell-fate potential from single cells. Our results demonstrate, for the first time, distinct, intrinsic lineage potential of single in vitro LMPPs at the cellular and molecular level. We find that clonal alterations in the lymphoid-primed multipotent progenitor (LMPP) compartment contributes to the functional alterations in hematopoiesis observed during aging. Unbiased single-cell transcriptome analysis reveals that true multipotential clones and lymphoid-restricted clones are reduced with aging, while bipotential and myeloid-restricted clones are modestly expanded. Furthermore, myeloid-restricted clones gain myc driver signatures, molecularly identifying clones emerging during aging that are susceptible to transformation. Our study reveals that aging alters the clonal composition of multipotential progenitor cells, directly contributing to the global loss of the lymphoid compartment and increased susceptibility to myeloid transformation. DisclosuresNo relevant conflicts of interest to declare.

Clonal Features of Hematopoietic Stem and Progenitor Cells in Aging

It is traditionally thought that Hematopoietic Stem Cells (HSCs) maintain blood homeostasis through long-term self-renewal and multilineage differentiation. This concept, however, is challenged by two recent studies in which the fundamental features of unperturbed hematopoiesis are evaluated by different approaches of lineage tracing. Both the kinetic analysis of HSC output by the Rodewald group and our clonal analysis with transposon barcoding suggest a dominant role of non-transplantable short-term HSCs and progenitors, but not the long-term HSCs, in driving native blood cell production. In addition, our longitudinal analysis of peripheral blood demonstrates extensive clonal succession in granulocyte production. These findings collectively suggest a distinct mechanism of native hematopoiesis that differs significantly from what has been learned in transplantation experiments. At the same time, they bring to light new questions regarding the ultimate fate of the progenitor population and the exact contribution of HSCs under normal physiological conditions. To address these questions, we examined clonal features of HSCs and progenitors in aged mice. Our results show a progressive reduction in clonal complexity and a concurrent increase in clonal stability when blood granulocytes are analyzed up to a hundred ten weeks after transposon barcoding. As time elapses, clonal overlapping between granulocytes and B cells become much more extensive, suggesting an increased tendency toward multilineage differentiation during aging. Analysis of stem and progenitor cells in bone marrow of aged mice reveals prevalent lineage output by multipotent progenitors (MPPs), whereas a lower fraction of HSC clones are found to produce mature progeny. While this overall pattern of differentiation is reminiscent of what has been observed in young and middle-aged animals, a two-fold increase in HSC clonal output was observed in these old mice, indicating their increased contribution to blood cell production. A comparison of clonal compositions in blood and marrow cell populations demonstrates an MPP origin of stable peripheral blood clones, and a smaller fraction of these clones can even be traced back to HSCs. These observations hence suggest extensive self-renewal and asymmetric cell division of these two cell populations in aging. Taken together, our results indicate that the aged hematopoietic system is characterized by reduced clonal complexity, increased clonal persistence, and HSC activation. The higher propensity to self-renewal during aging may also explain the elevated risk of malignant transformation in the elderly population. DisclosuresCamargo:Cell Signaling Technologies: Consultancy; Vital Therapies: Consultancy.

Clonal analysis of native hematopoiesis

Clonal analysis of native hematopoiesis

Clonal dynamics of native haematopoiesis.

It is currently thought that life-long blood cell production is driven by the action of a small number of multipotent haematopoietic stem cells. Evidence supporting this view has been largely acquired through the use of functional assays involving transplantation. However, whether these mechanisms also govern native non-transplant haematopoiesis is entirely unclear. Here we have established a novel experimental model in mice where cells can be uniquely and genetically labelled in situ to address this question. Using this approach, we have performed longitudinal analyses of clonal dynamics in adult mice that reveal unprecedented features of native haematopoiesis. In contrast to what occurs following transplantation, steady-state blood production is maintained by the successive recruitment of thousands of clones, each with a minimal contribution to mature progeny. Our results demonstrate that a large number of long-lived progenitors, rather than classically defined haematopoietic stem cells, are the main drivers of steady-state haematopoiesis during most of adulthood. Our results also have implications for understanding the cellular origin of haematopoietic disease.

Declined Presentation: Clonal dynamics of native hematopoiesis

Declined Presentation: Clonal dynamics of native hematopoiesis