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.
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.
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.
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.
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.
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.
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.
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.
Ovarian aging may contribute to systemic aging via the ovarian-systemic axis. This review outlines intrinsic ovarian cellular defects such as genomic instability, epigenetic shifts, and mitochondrial and proteostasis damage, which may trigger senescence-associated secretory phenotype (SASP)-related inflammaging, fibrosis, and distal pro-aging signals. Ovarian-derived endocrine disruption, especially estrogen decline, broadly affects bodily physiology. We summarize emerging multimodal interventions, including senolytics, metabolic reprogramming, regenerative medicine, and systemic approaches, and we discuss their dual potential to preserve fertility and intercept ovarian contributions to systemic aging. Ovarian aging is possibly associated with female age-related multimorbidity. Ovary-targeted prevention may extend healthspan, as assessed by combined reproductive and systemic clinical evaluations.
Therapeutic management of heart valve disease is currently hampered by a lack of mechanistic understanding of human valve development and pathobiology. Here, we develop a protocol to generate three-dimensional human heart valve-like tissues from pluripotent stem cells with enhanced maturational properties that partially recapitulate key molecular features of native valves. This includes an abundance of valve interstitial cells, resident macrophage cells, and the transcriptional profile of native heart valves. Importantly, we define a heart valve maturation signature from proteomic analysis and show that maturation of stem cell-derived valve cells is enhanced under 3D culture. We demonstrate that bioengineered valve-like microtissues can be used for modeling valve disease. Namely, treatment with inflammatory cytokines augmented tissue passive tension and induced molecular hallmarks of valve calcification, consistent with the pathological signature of clinical samples from diseased valves. Thus, bioengineered human heart valve-like tissues provide a platform to understand human heart valve development, maturation, and disease pathogenesis.
Heart valves maintain unidirectional blood flow, yet most understanding of their development and disease comes from animal models that do not fully capture human valve behavior. We present a human induced pluripotent stem cell (iPSC)-derived valve-like assembloid platform that models key aspects of in vivo valve features at the cellular and molecular levels. We found that mechanical forces, endothelial culture conditions, and fluidic shear stress respectively promote valve induction, maintenance, and extracellular matrix stratification. We further used this system to model human valve defects, including genetic mutations, injury, and hyperglycemia-related abnormalities. This assembloid platform enables the in vitro study of human valve development and disease mechanisms.
Programmable gene activation has broad therapeutic potential but remains constrained by the large effector size, limited multiplexing capacity, and challenges in in vivo delivery. Here, we develop the TIGR-TasR-mediated activator (TIGRa), a compact transcriptional activator derived from the tandem interspaced guide RNA (TIGR)-TIGR-associated protein (TasR) system that is mechanistically distinct from CRISPR-based activators. TIGRa is less than half the size of dSpCas9-based activators while achieving comparable or greater activation efficiency. Its native TIGR array architecture enables efficient multiplexed regulation, supporting simultaneous activation of up to 12 endogenous genes from a single compact construct. TIGRa-mediated multi-gene activation efficiently reprogrammed human fibroblasts into induced pluripotent stem cells. In addition, an all-in-one adeno-associated virus (AAV)-TIGRa vector activated endogenous CaMKII in vivo, promoting retinal ganglion cell survival and preserving visual function in a mouse model of N-methyl-D-aspartic (NMDA)-induced retinal injury. These results establish TIGRa as a compact and multiplexable platform for therapeutic gene regulation and in vivo genetic medicine.
Cellular development unfolds across both space and time, with lineage history influencing cellular identity and tissue organization. In this issue of Cell Stem Cell, Jia et al.1 combine CRISPR lineage recording with spatial transcriptomics to reconstruct the clonal relationships and spatial organization of cells during mouse development and cancer progression.
Living therapeutic depots enable localized, adaptive therapy, but their success depends on persistence, activation, and therapeutic output. Harimoto et al.1 define mechanical requirements for durable bacterial containment, whereas Luo et al.2 integrate transient photosynthetic hydrogen production with cardiac therapy. Together, the studies demonstrate that therapeutic needs shape living therapeutic design.
Modeling of cardiac pathologies in tissue-engineered models is coming of age. Two independent studies by Reid et al.1 and Tani et al.2 present in-depth multi-phenomics data from a human cardiac organoid (hCO) model and explore hCOs and engineered heart tissues (EHTs) for modeling of diastolic dysfunction.
The generation of highly plastic cell states in colorectal cancer that are prone to metastatic dissemination involves complex epigenetic reprogramming, rather than new genetic traits. Goto et al.1 implement a serial orthotopic organoid transplantation framework to uncover the idea that losing Gata6, a guardian of the colonic lineage, promotes metastatic competence.
Large-scale perturbation atlases have transformed systems biology, yet no equivalent resource exists for the human heart, where contractile function and transcriptomic state must be measured together. Here, we establish Cardiopedia-Ligand, a comprehensive perturbation-function-transcriptome atlas generated by stimulating human cardiac organoids (hCOs) with 87 ligands targeting 98 cell-membrane receptors expressed in the human heart. We developed an automated high-throughput pipeline enabling individualized contractility measurements and single-organoid mRNA sequencing. We use this pipeline to define both recognized and previously unrecognized functional and transcriptional clusters, including inotropes, endothelin peptides, extracellular matrix regulators, and multiple inflammatory clusters. Clustering analysis, machine learning, and the “fingerprinting” of human heart failure biopsies revealed previously underappreciated similarities between ligands and an interferon-γ signaling signature driving heart failure with preserved ejection fraction (HFpEF). Together, this comprehensive Cardiopedia-Ligand dataset provides a valuable and accessible resource for interrogating cardiac biology and human disease.
Using a xenogeneic reconstituted testis transplanted beneath the kidney capsule, Whelan et al. advance human and rhesus macaque pluripotent stem cell-derived germ cells beyond fetal prospermatogonia.1 Their study highlights developmental time, niche organization, and lineage history as central challenges for reconstructing faithful primate gametogenesis.
