The genesis of human hematopoietic stem cells

Rebuilding and rebooting immunity with stem cells

Advances in modern medicine have enabled a rapid increase in lifespan and, consequently, have highlighted the immune system as a key driver of age-related disease. Immune regeneration therapies present exciting strategies to address age-related diseases by rebooting the host's primary lymphoid tissues or rebuilding the immune system directly via biomaterials or artificial tissue. Here, we identify important, unanswered questions regarding the safety and feasibility of these therapies. Further, we identify key design parameters that should be primary considerations guiding technology design, including timing of application, interaction with the host immune system, and functional characterization of the target patient population.

Influence of donor-recipient sex on engraftment of normal and leukemia stem cells in xenotransplantation

Immunodeficient mouse models are widely used for the assessment of human normal and leukemic stem cells. Despite the advancements over the years, reproducibility, as well as the differences in the engraftment of human cells in recipient mice remains to be fully resolved. Here, we used various immunodeficient mouse models to characterize the effect of donor-recipient sex on the engraftment of the human leukemic and healthy cells. Donor human cells and recipient immunodeficient mice demonstrate sex-specific engraftment levels with significant differences observed in the lineage output of normal CD34+ hematopoietic stem and progenitor cells upon xenotransplantation. Intriguingly, human female donor cells display heightened sensitivity to the recipient mice's gender, influencing their proliferation and resulting in significantly increased engraftment in female recipient mice. Our study underscores the intricate interplay taking place between donor and recipient characteristics, shedding light on important considerations for future studies, particularly in the context of pre-clinical research.

Modelling post-implantation human development to yolk sac blood emergence

Implantation of the human embryo begins a critical developmental stage that comprises profound events including axis formation, gastrulation and the emergence of haematopoietic system1,2. Our mechanistic knowledge of this window of human life remains limited due to restricted access to in vivo samples for both technical and ethical reasons3-5. Stem cell models of human embryo have emerged to help unlock the mysteries of this stage6-16. Here we present a genetically inducible stem cell-derived embryoid model of early post-implantation human embryogenesis that captures the reciprocal codevelopment of embryonic tissue and the extra-embryonic endoderm and mesoderm niche with early haematopoiesis. This model is produced from induced pluripotent stem cells and shows unanticipated self-organizing cellular programmes similar to those that occur in embryogenesis, including the formation of amniotic cavity and bilaminar disc morphologies as well as the generation of an anterior hypoblast pole and posterior domain. The extra-embryonic layer in these embryoids lacks trophoblast and shows advanced multilineage yolk sac tissue-like morphogenesis that harbours a process similar to distinct waves of haematopoiesis, including the emergence of erythroid-, megakaryocyte-, myeloid- and lymphoid-like cells. This model presents an easy-to-use, high-throughput, reproducible and scalable platform to probe multifaceted aspects of human development and blood formation at the early post-implantation stage. It will provide a tractable human-based model for drug testing and disease modelling.

Ex vivo hematopoietic stem cell expansion technologies: recent progress, applications, and open questions

Hematopoietic stem cells (HSCs) are a rare but potent cell type that support life-long hematopoiesis and stably regenerate the entire blood and immune system following transplantation. HSC transplantation represents a mainstay treatment for various diseases of the blood and immune systems. The ex vivo expansion and manipulation of HSCs therefore represents an important approach to ask biological questions in experimental hematology and to help improve clinical HSC transplantation therapies. However, it has remained challenging to expand transplantable HSCs ex vivo. This review summarizes recent progress in ex vivo HSC expansion technologies and their applications to biological and clinical problems and discusses current questions in the field.

Linking GATA2 to myeloid dysplasia and complex cytogenetics in adult myelodysplastic neoplasm and acute myeloid leukemia

ABSTRACT

GATA binding protein 2 (GATA2) is a conserved zinc finger transcription factor that regulates the emergence and maintenance of complex genetic programs driving development and function of hematopoietic stem and progenitor cells (HSPCs). Patients born with monoallelic GATA2 mutations develop myelodysplastic neoplasm (MDS) and acute myeloid leukemia (AML), whereas acquired GATA2 mutations are reported in 3% to 5% of sporadic AML cases. The mechanisms by which aberrant GATA2 activity promotes MDS and AML are incompletely understood. Efforts to understand GATA2 in basic biology and disease will be facilitated by the development of broadly efficacious antibodies recognizing physiologic levels of GATA2 in diverse tissue types and assays. Here, we purified a polyclonal anti-GATA2 antibody and generated multiple highly specific anti-GATA2 monoclonal antibodies, optimized them for immunohistochemistry on patient bone marrow bioosy samples, and analyzed GATA2 expression in adults with healthy bone marrow, MDS, and acute leukemia. In healthy bone marrow, GATA2 was detected in mast cells, subsets of CD34+ HSPCs, E-cadherin-positive erythroid progenitors, and megakaryocytes. In MDS, GATA2 expression correlates with bone marrow blast percentage, positively correlates with myeloid dysplasia and complex cytogenetics, and is a nonindependent negative predictor of overall survival. In acute leukemia, the percent of GATA2+ blasts closely associates with myeloid lineage, whereas a subset of lymphoblastic and undifferentiated leukemias with myeloid features also express GATA2. However, the percent of GATA2+ blasts in AML is highly variable. Elevated GATA2 expression in AML blasts correlates with peripheral neutropenia and complex AML cytogenetics but, unlike in MDS, does not predict survival.

Advancements in medical research using fetal sheep: Implications for human health and treatment methods

Sheep are typically considered as industrial animals that provide wool and meals. However, they play a significant role in medical research in addition to their conventional use. Notably, sheep fetuses are resistant to surgical invasions and can endure numerous manipulations, such as needle puncture and cell transplantation, and surgical operations requiring exposure beyond the uterus. Based on these distinguishing characteristics, we established a chimeric sheep model capable of producing human/monkey pluripotent cell-derived blood cells via the fetal liver. Furthermore, sheep have become crucial as human fetal models, acting as platforms for developing and improving techniques for intrauterine surgery to address congenital disorders and clarifying the complex pharmacokinetic interactions between mothers and their fetuses. This study emphasizes the significant contributions of fetal sheep to advancing human disease understanding and treatment strategies, highlighting their unique characteristics that are not present in other animals.