LABORATORY RESEARCH Quiescent Hematopoietic Stem Cells Accumulate DNA Damage during Aging that Is Repaired upon Entry into Cell Cycle Investigators quantified DNA damage in hematopoietic stem cells (HSCs) and downstream progenitors from young and old mice, revealing that strand breaks significantly accrue in HSCs during aging. [Cell Stem Cell] Abstract | Graphical Abstract Clonal Variegation and Dynamic Competition of Leukemia-Initiating Cells in Infant Acute Lymphoblastic Leukemia with MLL Rearrangement Through Ig/TCR rearrangement analysis of mixed lineage leukemia (MLL)-AF4+ infant acute lymphoblastic leukemia (ALL) at diagnosis and xenograft leukemias from mice transplanted with the same diagnostic samples, scientists established that MLL-AF4+ infant ALL is composed of a branching subclonal architecture already at diagnosis, frequently driven by a Ig/TCR-rearranged founder clone. [Leukemia] Abstract Mapping Hematopoiesis in a Fully Regenerative Vertebrate: The Axolotl The authors used white and CMV:GFP+ transgenic white axolotl strains to map sites of hematopoiesis and develop hematopoietic cell transplant methodology. They also established a FACS enrichment technique for major blood lineages and colony-forming unit assays for hematopoietic progenitors. [Blood] Abstract Deficiency of the NR4A Orphan Nuclear Receptor NOR1 in Hematopoietic Stem Cells Accelerates Atherosclerosis Investigators employed bone marrow transplantation to determine the selective contribution of NOR1 expression in hematopoietic stem cells to the development of atherosclerosis. [Stem Cells] Abstract Engineering the Human Thymic Microenvironment to Support Thymopoiesis In Vivo Scientists developed an implantable thymic microenvironment composed of two human thymic stroma populations critical for thymopoiesis; thymic epithelial cells and thymic mesenchyme. [Stem Cells] Abstract The Histone Methyltransferase Activity of MLL1 Is Dispensable for Hematopoiesis and Leukemogenesis Scientists showed that the SET domain, and thus histone methyltransferase activity of MLL1, is dispensable for maintaining hematopoietic stem cells and supporting leukemogenesis driven by the MLL-AF9 fusion oncoprotein. [Cell Rep] Full Article | Graphical Abstract | Press Release CLINICAL RESEARCH Hematopoietic SCT: A Useful Treatment for Late Metachromatic Leukodystrophy Allogeneic hematopoietic SCT (HSCT) is currently the only treatment for adult and late-onset juvenile metachromatic leukodystrophy (MLD), although it is still in question because of insufficient follow-up. Investigators aimed to determine whether HSCT could halt the progression of adult and late-onset juvenile MLD. [Bone Marrow Transplant] Abstract Combined Umbilical Cord Blood and Bone Marrow from HLA-Identical Sibling Donors for Hematopoietic Stem Cell Transplantation in Children with Hemoglobinopathies Investigators analyzed the feasibility and outcome of hematopoietic stem cell transplantation in 13 children with hemoglobinopathies after the co- infusion of cord blood and bone marrow from the same human leucocyte antigen (HLA) identical sibling donor. [Pediatr Blood Cancer] Abstract |