Hematopoietic stem cell (HSC) therapy remains essential in treating blood disorders, autoimmune diseases, neurodegenerative conditions, and cancers. Despite its potential, challenges arise from the inherent heterogeneity of HSCs and the complexity of their regulatory niche. Recent advancements in single-cell RNA sequencing and chromatin accessibility sequencing have provided deeper insights into HSC markers and chromatin dynamics, highlighting the intricate balance between intrinsic and extrinsic regulatory mechanisms. Zebrafish models have emerged as valuable tools in HSC research, particularly through live imaging and cellular barcoding techniques. These models have allowed us to describe critical interactions between HSCs and embryonic macrophages, involving reactive oxygen species and calreticulin signaling. These are essential for ensuring HSC quality and proper differentiation, with implications for improving HSC transplant outcomes. Furthermore, the review examines clonal hematopoiesis, with a focus on mutations in epigenetic regulators such as DNMT3A, TET2, and ASXL1, which elevate the risk of myelodysplastic syndromes and acute myeloid leukemia. Emerging technologies, including in vivo cellular barcoding and CRISPR-Cas9 gene editing, are being investigated to enhance clonal diversity and target specific mutations, offering potential strategies to mitigate these risks. Additionally, macrophages play a pivotal role in maintaining HSC clonality and ensuring niche localization. Interactions mediated by factors such as VCAM-1 and CXCL12/CXCR4 signaling are crucial for HSC homing and the stress response, opening new therapeutic avenues for enhancing HSC transplantation success and addressing clonal hematopoiesis. This review synthesizes findings from zebrafish models, cutting-edge sequencing technologies, and novel therapeutic strategies, offering a comprehensive framework for advancing HSC biology and improving clinical outcomes in stem cell therapy and the treatment of hematologic diseases.

Sickle Cell Disease (SCD) is a pervasive monogenic disorder characterized by chronic hemolytic anemia, unpredictable vaso-occlusive crises, and progressive multi-organ damage, representing a significant global health burden. Driven by a point mutation in the β-globin gene, the resulting abnormal Hemoglobin S (HbS) polymerizes under deoxygenated conditions, leading to erythrocyte sickling and systemic endothelial dysfunction. While supportive therapies such as hydroxyurea and transfusions manage symptoms, the mandate for definitive curative therapies is urgent. Historically, allogeneic hematopoietic stem cell transplantation (HSCT) utilizing matched sibling donors (MSD) has been the sole curative option, offering high survival rates but constrained by limited donor availability and the risk of graft-versus-host disease (GVHD). Consequently, alternative donor sources, including matched unrelated donors, umbilical cord blood, and haploidentical donors, have expanded patient access, particularly with the integration of post-transplant cyclophosphamide (PTCy) to mitigate alloreactivity. Concurrently, the advent of autologous gene therapy, encompassing lentiviral gene addition (Lyfgenia) and CRISPR-Cas9 gene editing (Casgevy) offers a revolutionary donor-independent approach that eliminates GVHD risk. Lyfgenia employs a lentiviral vector to introduce an anti-sickling βT87Q hemoglobin variant into autologous hematopoietic stem cells, while Casgevy employs CRISPR-Cas9 to disrupt the erythroid-specific enhancer of the BCL11A transcription factor, derepressing γ-globin expression and elevating fetal hemoglobin. This review synthesizes the pathophysiological mechanisms of SCD, evaluates the clinical outcomes and limitations of both allogeneic HSCT and autologous gene therapies, and outlines the clinical decision-making paradigms and future innovations required to achieve equitable global access to these transformative treatments.