Ex vivo hematopoietic stem cell (HSC) gene therapy is effective for non-malignant blood disorders including sickle cell disease (SCD), but requires hospitalization, ex vivo cell manipulation, and conditioning. Direct in vivo gene delivery could remove these barriers and widen access. Here, we explore phagocytosis-shielded lentiviral and alpha-retroviral vectors pseudotyped with the baboon endogenous retrovirus glycoprotein variant BaEVRLess for in vivo HSC gene transfer. Vector injection into mobilized humanized mice yielded up to 8.8% gene marking in hCD45+ cells, which chemoselection enriched to 70% of hCD45+ cells and 54% of HSCs. Barcode analysis showed polyclonal reconstitution in over 90% of mice, which remained stable in secondary recipients. For SCD, we targeted BCL11A and ZNF410 selectively in erythroid cells using miRNA-embedded shRNAs to derepress gamma-globin, reaching therapeutically relevant levels of 61.5% of beta-like globins. In summary, BaEVRLess-pseudotyped lentiviral vectors enable clinically relevant in vivo gene transfer and fetal globin induction for SCD.

Pluripotent stem cell-derived immunocompetent organoids and assembloids, termed here "immunoids," are becoming important human models for studying immune-tissue interactions. Advances across organ systems now include incorporation of mature and immature immune populations into multiple organoid types, multilineage differentiation, and endogenous immune co-development. Defining standards for immunoid fabrication will be essential for improving physiological modeling and clinical translation. In the coming years, as these platforms mature, immunoids are poised to transform research by advancing our understanding of human development, disease mechanisms, and therapeutic responses, becoming a cornerstone of precision medicine.

Toward development of an autologous, induced pluripotent stem cell (iPSC)-based cell therapy for Parkinson's disease (PD), we demonstrate successful, reproducible genomic and transcriptomic qualification of patient-derived dopaminergic neuron precursor cells (DANPCs) across multiple donors. Our analysis includes whole-genome sequencing data from fibroblasts, iPSCs, and DANPCs and the development of NeuriTest, an RNAseq-based bioinformatic analysis of DANPCs designed to predict cell quality based on empirical animal data. Autologous cell therapies are immune matched to the patient, potentially augmenting durability of benefit compared to allogeneic cells while negating the need for immunosuppression and accompanying side effects. Patient-specific iPSCs are an autologous cell source that can be differentiated to dopaminergic neurons, the cell type lost in PD. We report here our preclinical manufacturing strategy and results demonstrating efficacy in a PD rodent model and safety in a 9-month GLP toxicology study.

Brainstem gliomas, particularly H3K27M-mutant diffuse midline gliomas (DMGs), lack effective therapies owing to anatomic inaccessibility, intact blood-brain barrier, and treatment resistance. Conventional models have low establishment rates and fail to preserve the native tumor microenvironment, limiting translational study for this rare disease. Here, we established a patient-derived brainstem glioma organoid (BSGO) platform with high success, faithfully recapitulating parental tumor features. Multi-omics and functional assays revealed that DMGs maintain oligodendrocyte precursor cell (OPC) stemness by dysregulating ACTIVIN signaling. To overcome delivery barriers and target stemness, we conducted an intrathecal drug screening and identified triple intrathecal therapy (methotrexate + cytarabine + dexamethasone, TIT) as a potent regimen against DMGs. In DMG patients, organoid-avatar guided personalized therapy induced sustained responses, with TIT-associated reductions in OPC markers reliably tracked by cerebrospinal fluid (CSF) proteomic profiling. Together, our study provides an organoid-based platform for mechanistic investigation and personalized intrathecal therapy screening and proposes TIT as a promising translational strategy for DMG.

β-Hemoglobinopathies are monogenic disorders. We previously applied a transformer base editor (tBE) to reactivate fetal hemoglobin (HbF) expression, and five Chinese transfusion-dependent β-thalassemia (TDT) patients achieved transfusion independence. However, the applicability of tBE to sickle cell disease (SCD) and genetically different TDT populations remained unknown. Here, we show a four-patient descriptive report from three trials, including one African SCD patient and three TDT patients carrying mutations common in South and Southeast Asia. All patients achieve hematopoietic recovery, and red blood cell transfusions are discontinued in all cases. After more than 12 months of follow-up, all patients show durable editing, sustained high-level pan-cellular HbF expression, and transfusion independence. No vaso-occlusive episodes occur in the SCD patient. No off-target mutations, malignancies, or deaths are observed. These initial results support the feasibility of applying tBE to treat SCD and the reported TDT genotypes, warranting broader evaluation across diverse populations. ClinicalTrials.gov identifiers are as follows: NCT06328764, NCT06065189, and NCT06565026.

Precise regulation of organ size is essential for proper function, yet the underlying logic remains unclear. Here, we identify a Hippo-IGF2 signaling axis as a regulator of organ growth. During mouse liver development, Igf2 is highly expressed in fetal and neonatal hepatocytes to fuel rapid growth but is directly silenced by the Hippo signaling pathway at the postnatal stage, enforcing growth arrest and determining liver size. In contrast, chronic liver injury inactivates Hippo signaling and induces Igf2 expression, which is essential for regeneration. Notably, this regenerative response is defective in aged mice but can be restored by ectopic Igf2 expression. As a hormone, circulating IGF2 can compensate for local deficiencies in response to organ-restricted perturbations, whereas whole-body Hippo activation or Igf2 deletion results in small mice with miniature organs. Hence, the Hippo-IGF2 axis is a general regulator of growth and organ size during development and regeneration.

Large bone defects remain a major clinical challenge, as current treatments cannot effectively regenerate them and fail to restore functionality. To recapitulate the cellular complexity of the early fracture callus, we engineered human endothelialized callus organoids (hECOs) by co-culturing periosteum-derived skeletal progenitors with endothelial cells. This co-culture resulted in cellular self-assembly, leading to spatially organized, callus-like structures. Endothelial cells promoted skeletal progenitor cell expansion, extracellular matrix maturation, and progression toward hypertrophic cartilage, hallmarks of endochondral ossification. Multi-omics analyses identified endothelial cell-mediated activation of regenerative programs associated with skeletal maturation, matrix remodeling, and angiogenesis. Following brief in vitro differentiation, macroscale aggregates of hECOs supported rapid host vascularization and regeneration of critical-size tibial defects in immunocompromised mice. Donor-derived cells actively contributed to early regeneration but were progressively replaced during remodeling, consistent with hECOs functioning as transient biological templates that guide host-mediated bone regeneration.

Epigenetic regulation may underlie asymmetric allelic expression of many genes during development and disease pathogenesis. Allele-specific epigenetic modification could provide an efficient therapy for dominant genetic diseases due to heterozygous mutations. We developed an allele-specific epigenetic editing method ("Epi-Allele") for silencing pathogenic alleles and found surprisingly elevated expression of the non-targeted alleles, leaving total gene expression unchanged. Genome-wide screening revealed that such compensated allelic expression represents a common phenomenon, suggesting that the Epi-Allele approach could avoid the haploinsufficiency induced by current allele-specific silencing therapies. This notion was validated by allele-specific epigenetic remodeling of Myh6 and MYH7 genes in ameliorating cardiac phenotypes in a hypertrophic cardiomyopathy (HCM) mouse model and HCM patient iPSC-derived cardiomyocytes, respectively. Thus, Epi-Allele offers an allele-specific haploinsufficiency-free therapeutic approach for treating dominant genetic diseases.

Radiopharmaceutical theranostics remains constrained by tumors lacking a validated molecular target. Yang et al.[1] engineer mesenchymal stem cells that sense tumor stiffness and respond by manufacturing a synthetic target in situ, making PET imaging and radionuclide therapy possible with existing clinical radioligands in tumors that were previously untargetable.

Two studies in this issue of Cell Stem Cell show that splenic extramedullary hematopoiesis in myelofibrosis develops within a remodeled hematopoietic, immune, and stromal environment. Austin et al.[1] define its cellular states, whereas Dugué et al.[2] reveal the spatial and temporal remodeling of the stromal niche.

In this issue of Cell Stem Cell, Mesentier-Louro et al. use a multi-cellular integrated brain (miBrain) system to uncover mechanisms underlying the accumulation of neuronal α-synuclein (α-Syn) inclusions in APOE4 carriers.[1] Their results suggest that APOE4 increases cholesterol levels and impairs lysosomal function in astrocytes, which release pathogenic α-Syn.

Heart valve research has long lacked accessible human model systems. In this issue of Cell Stem Cell, He et al. and Voges et al. introduce complementary stem cell-derived valve models that recreate key aspects of valve development, tissue organization, and disease, opening new avenues to investigate disease mechanisms and therapies.

Autologous-derived dendritic cells (DCs) are a promising source for cell-based cancer vaccines. However, their therapeutic potential is challenged by the number and quality produced and the diversity of antigens presented. To address these limitations, we present an approach that involves differentiating universal MHC-deficient human-induced pluripotent stem cells (hiPSCs) into CCR7[+] migratory DCs. These DCs are subsequently "dressed" with the full repertoire of MHC-antigen complexes derived from tumor cell membranes, transforming an allogeneic substrate into a personalized cancer vaccine product. The resulting "TumorDressed" DCs effectively activate T cells against tumor antigens. Their function is diminished when CD80/86 is deleted but significantly enhanced by the loss of PD-L1/2. PD-L1/2-null TumorDressed DCs demonstrate robust priming of anti-tumor T cell-mediated cytotoxicity both in vitro and in vivo, including against primary hematologic and solid tumors with matching patient T cells. These findings provide proof of concept for a universal, scalable, adaptable, and off-the-shelf DC cancer vaccine platform.

Myelofibrosis (MF) is a chronic, progressive myeloproliferative neoplasm characterized by bone marrow fibrosis, ineffective blood cell production, and neoplastic extramedullary hematopoiesis (EMH) occurring primarily within the spleen. To explore the molecular mechanisms underlying splenic EMH, we performed single-cell transcriptional and chromatin profiling of cells from MF spleens that had been surgically removed. We demonstrate significant expansion of hematopoietic stem and progenitor cells, coupled with aberrant differentiation toward the erythroid and megakaryocytic lineages, associated with a significant enrichment of inflammatory pathways with enhanced NF-κB signaling and IFN responses, as well as dysregulation of the inferred function of differentiation-defining transcription factors. Finally, we report a significant remodeling of the immune microenvironment in MF spleens, characterized by emergence of dysfunctional T cell subsets and inflammatory memory B cells, suggesting the concomitant establishment of a pro-inflammatory and immune-tolerant tumor microenvironment within the spleen that influences hematopoietic cell differentiation and impairs tumor immune surveillance.