PhD Candidate Hannover Medical School Hannover, Niedersachsen, Germany
Abstract: Deriving hematopoietic stem and progenitor cells (HSCs/HPCs) in vitro remains challenging for both developmental studies and therapeutic applications. This difficulty arises from the limited understanding of the niche-like induction and stabilization of these cells within their proper developmental context, compounded by the ethical and technical constraints of studying human embryogenesis in vivo. Consequently, human in vitro models that recapitulate the complex cellular and molecular mechanisms and dynamics of hematopoietic development in a native-like environment are of significant interest. By modulating our human pluripotent stem cell (hPSC)-based heart-forming organoid (HFO) model via stage-specific supplementation of hemato-endothelial factors, we have recently established the novel, so-called blood-generating HFO (BG-HFO). BG-HFOs comprise functional cardiac tissue with a ventricular-like phenotype, while featuring distinct endothelial subtypes, including a mesenchyme-embedded endothelial layer that generates hematopoietic cells through endothelial-to-hematopoietic transition. Functional assays demonstrated that BG-HFO-derived hemato-endothelial cells possess erythroid, myeloid and lymphoid potential. The morphological structure of BG-HFOs reflects aspects of both embryonic/primitive and definitive hematopoiesis in vivo. Recent single-cell RNA sequencing data from BG-HFOs, collected at different developmental stages, revealed time-dependent transcriptional patterning consistent with hemogenic endothelial and HSCs/HPCs development and, at later stages, the emergence of hematopoietic derivatives including erythroid, megakaryocytic and myeloid cells. This corroborates our findings that BG-HFOs indeed recapitulate hemogenic endothelial development and both primitive and definitive hematopoiesis known from the native embryo. Taken together, our work introduces the first human in vitro model of self-organized, morphologically structured co-development of cardiac, endothelial, and multipotent hematopoietic tissues. It provides a robust platform for pharmacological testing advancing mechanistic research of hematopoiesis, and overcoming the limitations of studying these processes in human embryos.
