Dermatologic complications in pediatric patients after hematopoietic stem cell transplantation for sickle cell disease

Dermatologic complications are common following allogeneic hematopoietic stem cell transplantation, but dermatologic complications among pediatric patients undergoing hematopoietic stem cell transplantation for the treatment of sickle cell disease have been poorly characterized. In this case series of 17 patients (<21 years old) with sickle cell disease who underwent hematopoietic stem cell transplantation, 16 (94.1%) experienced one or more dermatologic complications after transplant, with the most common complications including acute or chronic mucocutaneous graft-versus-host disease (GVHD) (34.1% of complications), skin eruptions of unknown origin (15.9% of complications), infections (15.9% of complications), and chemotherapy-related pigmentary changes (11.4% of complications). Patients who developed acute or chronic skin GVHD were significantly older at the time of hematopoietic stem cell transplantation. These findings highlight the need to closely monitor for dermatologic complications in pediatric patients who undergo hematopoietic stem cell transplantation for sickle cell disease and underscore the importance of involving dermatology early on when skin complications occur, although further research with a larger multicenter study could help clarify the risk for dermatologic complications and help identify potential ways to mitigate this risk.

Engineering a niche supporting hematopoietic stem cell development using integrated single-cell transcriptomics

Hematopoietic stem cells (HSCs) develop from hemogenic endothelium within embryonic arterial vessels such as the aorta of the aorta-gonad-mesonephros region (AGM). To identify the signals responsible for HSC formation, here we use single cell RNA-sequencing to simultaneously analyze the transcriptional profiles of AGM-derived cells transitioning from hemogenic endothelium to HSCs, and AGM-derived endothelial cells which provide signals sufficient to support HSC maturation and self-renewal. Pseudotemporal ordering reveals dynamics of gene expression during the hemogenic endothelium to HSC transition, identifying surface receptors specifically expressed on developing HSCs. Transcriptional profiling of niche endothelial cells identifies corresponding ligands, including those signaling to Notch receptors, VLA-4 integrin, and CXCR4, which, when integrated in an engineered platform, are sufficient to support the generation of engrafting HSCs. These studies provide a transcriptional map of the signaling interactions necessary for the development of HSCs and advance the goal of engineering HSCs for therapeutic applications.

Multipotent progenitors and hematopoietic stem cells arise independently from hemogenic endothelium in the mouse embryo

During embryogenesis, waves of hematopoietic progenitors develop from hemogenic endothelium (HE) prior to the emergence of self-renewing hematopoietic stem cells (HSCs). Although previous studies have shown that yolk-sac-derived erythromyeloid progenitors and HSCs emerge from distinct populations of HE, it remains unknown whether the earliest lymphoid-competent progenitors, multipotent progenitors, and HSCs originate from common HE. In this study, we demonstrate by clonal assays and single-cell transcriptomics that rare HE with functional HSC potential in the early murine embryo are distinct from more abundant HE with multilineage hematopoietic potential that fail to generate HSCs. Specifically, HSC-competent HE are characterized by expression of CXCR4 surface marker and by higher expression of genes tied to arterial programs regulating HSC dormancy and self-renewal. Taken together, these findings suggest a revised model of developmental hematopoiesis in which the initial populations of multipotent progenitors and HSCs arise independently from HE with distinct phenotypic and transcriptional properties.