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Neural crest stem cells (NCSCs) compose a highly migratory,multipotent,stem cell population arising from the neural plate border of the embryonic ectoderm. Investigating the development of NCSCs is critical in understanding both embryonic development and abnormal events that underlie neurocristopathies. Suggested seeding densities in in vitro human induced pluripotent stem cells (hiPSCs) differentiation protocols,varying between 10,000 cells/cm 2 and 200,000 cells/cm 2,demonstrate a lack of consensus on the optimal conditions to obtain NCSCs. Aiming to maximize the differentiation efficiency of hiPSCs towards the NCSCs lineage,we investigated the effect of the initial seeding density on NCSCs lineage commitment,both in fibroblast- and human peripheral blood mononuclear cell (PBMC)-derived hiPSCs. Cultures were characterized with gene and protein expression analysis assessing stemness ( OCT3/4 and NANOG ),neural crest identity ( SNAI2 and SOX10 ) and neuroectoderm identity ( PAX6 and SOX1 ). We demonstrate that reaching a confluent monolayer of cells by the end of the differentiating protocol is crucial to obtaining NCSCs from hiPSCs. To achieve this,our results indicated 17,000 cells/cm 2 is the optimal initial seeding density. Under this protocol,a confluent monolayer was reached after 8 days of differentiation and an average of 89% SOX10 positive cells were obtained. The fold change of SNAI2 and SOX10 expression was 11-fold and 17-fold higher,respectively,in cultures seeded with 17,000 cells/cm 2,compared to the highest tested density of 200,000 cells/cm 2 . In contrast,seeding 200,000 cells/cm 2 induced neuroectoderm-like cells,confirmed by an average of 45% of cells marking positive for PAX6. With this work,we demonstrate the importance of achieving cellular confluency during NCSCs differentiation. View Publication

Pathogenic variants in MYH7 and MYBPC3 account for the majority of hypertrophic cardiomyopathy (HCM). Targeted drugs like myosin ATPase inhibitors have not been evaluated in children. We generate patient and variant-corrected iPSC-cardiomyocytes (CMs) from pediatric HCM patients harboring single variants in MYH7 ( V606M ; R453C ),MYBPC3 ( G148R ) or digenic variants ( MYBPC3 P955fs,TNNI3 A157V ). We also generate CMs harboring MYBPC3 mono- and biallelic variants using CRISPR editing of a healthy control. Compared with isogenic and healthy controls,variant-positive CMs show sarcomere disorganization,higher contractility,calcium transients,and ATPase activity. However,only MYH7 and biallelic MYBPC3 variant-positive CMs show stronger myosin-actin binding. Targeted myosin ATPase inhibitors show complete rescue of the phenotype in variant-positive CMs and in cardiac Biowires to mirror isogenic controls. The response is superior to verapamil or metoprolol. Myosin inhibitors can be effective in genotypically diverse HCM highlighting the need for myosin inhibitor drug trials in pediatric HCM. View Publication

Immunodeficiency,Centromeric instability and Facial anomalies (ICF) syndrome is a rare genetic disorder characterized by variable immunodeficiency. More than half of the affected individuals show mild to severe intellectual disability at early onset. This disorder is genetically heterogeneous and ZBTB24 is the causative gene of the subtype 2,accounting for about 30% of the ICF cases. ZBTB24 is a multifaceted transcription factor belonging to the Zinc-finger and BTB domain-containing protein family,which are key regulators of developmental processes. Aberrant DNA methylation is the main molecular hallmark of ICF syndrome. The functional link between ZBTB24 deficiency and DNA methylation errors is still elusive. Here,we generated a novel ICF2 disease model by deriving induced pluripotent stem cells (iPSCs) from peripheral CD34 + -blood cells of a patient homozygous for the p.Cys408Gly mutation,the most frequent missense mutation in ICF2 patients and which is associated with a broad clinical spectrum. The mutation affects a conserved cysteine of the ZBTB24 zinc-finger domain,perturbing its function as transcriptional activator. ICF2-iPSCs recapitulate the methylation defects associated with ZBTB24 deficiency,including centromeric hypomethylation. We validated that the mutated ZBTB24 protein loses its ability to directly activate expression of CDCA7 and other target genes in the patient-derived iPSCs. Upon hematopoietic differentiation,ICF2-iPSCs showed decreased vitality and a lower percentage of CD34 + /CD43 + /CD45 + progenitors. Overall,the ICF2-iPSC model is highly relevant to explore the role of ZBTB24 in DNA methylation homeostasis and provides a tool to investigate the early molecular events linking ZBTB24 deficiency to the ICF2 clinical phenotype. View Publication

Riboflavin transporter deficiency type 2 (RTD2) is a rare neurodegenerative autosomal recessive disease caused by mutations in the SLC52A2 gene encoding the riboflavin transporters,RFVT2. Riboflavin (Rf) is the precursor of FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide),which are involved in different redox reactions,including the energetic metabolism processes occurring in mitochondria. To date,human induced pluripotent stem cells (iPSCs) have given the opportunity to characterize RTD2 motoneurons,which reflect the most affected cell type. Previous works have demonstrated mitochondrial and peroxisomal altered energy metabolism as well as cytoskeletal derangement in RTD2 iPSCs and iPSC-derived motoneurons. So far,no attention has been dedicated to astrocytes. Here,we demonstrate that in vitro differentiation of astrocytes,which guarantee trophic and metabolic support to neurons,from RTD2 iPSCs is not compromised. These cells do not exhibit evident morphological differences nor significant changes in the survival rate when compared to astrocytes derived from iPSCs of healthy individuals. These findings indicate that differently from what had previously been documented for neurons,RTD2 does not compromise the morpho-functional features of astrocytes. View Publication

The ability to generate natural killer (NK) cells from induced pluripotent stem cells (iPSCs) has given rise to new possibilities for the large-scale production of homogeneous immunotherapeutic cellular products and opened new avenues towards the creation of “off-the-shelf” cancer immunotherapies. However,the differentiation of NK cells from iPSCs remains poorly understood,particularly regarding the ontogenic landscape of iPSC-derived NK (iNK) cells produced in vitro and the influence that the differentiation strategy employed may have on the iNK profile. To investigate this question,we conducted a comparative analysis of two sets of iNK cells generated from the same iPSC line using two different protocols: (i) a short-term,clinically compatible feeder-free protocol corresponding to primitive hematopoiesis,and (ii) a lymphoid-based protocol representing the definitive hematopoietic step. Our work demonstrated that both protocols are capable of producing functional iNK cells. However,the two sets of resulting iNKs exhibited distinct phenotypes and transcriptomic profiles. The lymphoid-based differentiation approach generated iNKs with a more mature and activated profile,which demonstrated higher cytotoxicity against cancer cell lines compared to iNK cells produced under short-term feeder-free conditions suggesting that the differentiation strategy must be considered when designing iNK cell–based adoptive immunotherapies. View Publication

Understanding the interaction between genetic and epigenetic variation remains a challenge due to confounding environmental factors. We propose that human induced Pluripotent Stem Cells (iPSCs) are an excellent model to study the relationship between genetic and epigenetic variation while controlling for environmental factors. In this study,we have created a comprehensive resource of high-quality genomic,epigenomic,and transcriptomic data from iPSC lines and three iPSC-derived cell types (neural stem cell (NSC),motor neuron,monocyte) from three healthy donors. We find that epigenetic variation is most strongly associated with genetic variation at the iPSC stage,and that relationship weakens as epigenetic variation increases in differentiated cells. Additionally,cell type is a stronger source of epigenetic variation than genetic variation. Further,we elucidate a utility of studying epigenetic variation in iPSCs and their derivatives for identifying important loci for GWAS studies and the cell types in which they may be acting. Subject terms: Epigenomics,Genomics,Transcriptomics View Publication

Fatty-acid-hydroxylase-associated neurodegeneration (FAHN) is a rare neurodegenerative disorder caused by loss-of-function mutations in the FA2H gene,leading to impaired enzymatic activity and resulting in myelin sheath instability,demyelination,and axonal degeneration. In this study,we established a human in vitro model using neurons and oligodendrocytes derived from induced pluripotent stem cells (hiPSCs) of a FAHN patient. This coculture system enabled the investigation of myelination processes and myelin integrity in a disease-relevant context. Analyses using immunofluorescence and Western blot revealed impaired expression and localisation of key myelin proteins in oligodendrocytes and cocultures. FA2H-deficient cells showed reduced myelination,shortened internodes,and disrupted formation of the nodes of Ranvier. Additionally,we identified autophagy defects—a hallmark of many neurodegenerative diseases—including reduced p62 expression,elevated LC3B levels,and impaired fusion of autophagosomes with lysosomes. This study presents a robust hiPSC-based model to study FAHN,offering new insights into the molecular pathology of the disease. Our findings suggest that FA2H mutations compromise both the structural integrity of myelin and the efficiency of the autophagic machinery,highlighting potential targets for future therapeutic interventions. View Publication

RAG2 severe combined immune deficiency (RAG2-SCID) is a lethal disorder caused by the absence of functional T and B cells due to a differentiation block. Here,we generated induced pluripotent stem cells (iPSCs) from a RAG2-SCID patient to study the nature of the T cell developmental blockade. We observed a strongly reduced capacity to differentiate at every investigated stage of T cell development,from early CD7-CD5- to CD4+CD8+. The impaired differentiation was accompanied by an increase in CD7-CD56+CD33+ natural killer (NK) cell-like cells. T cell receptor D rearrangements were completely absent in RAG2SCID cells,whereas the rare T cell receptor B rearrangements were likely the result of illegitimate rearrangements. Repair of RAG2 restored the capacity to induce T cell receptor rearrangements,normalized T cell development,and corrected the NK cell-like phenotype. In conclusion,we succeeded in generating an iPSC-based RAG2-SCID model,which enabled the identification of previously unrecognized disorder-related T cell developmental roadblocks. View Publication

Induced pluripotent stem cells (iPSC) and their differentiated derivatives offer a unique source of human primary cells for toxicity screens. Here,we report on the comparative cytotoxicity of 80 compounds (neurotoxicants,developmental neurotoxicants,and environmental compounds) in iPSC as well as isogenic iPSC-derived neural stem cells (NSC),neurons,and astrocytes. All compounds were tested over a 24-h period at 10 and 100$\$,in duplicate,with cytotoxicity measured using the MTT assay. Of the 80 compounds tested,50 induced significant cytotoxicity in at least one cell type; per cell type,32,38,46,and 41 induced significant cytotoxicity in iPSC,NSC,neurons,and astrocytes,respectively. Four compounds (valinomycin,3,3',5,5'-tetrabromobisphenol,deltamethrin,and triphenyl phosphate) were cytotoxic in all four cell types. Retesting these compounds at 1,10,and 100$\$ using the same exposure protocol yielded consistent results as compared with the primary screen. Using rotenone,we extended the testing to seven additional iPSC lines of both genders; no substantial difference in the extent of cytotoxicity was detected among the cell lines. Finally,the cytotoxicity assay was simplified by measuring luciferase activity using lineage-specific luciferase reporter iPSC lines which were generated from the parental iPSC line. This article is part of a Special Issue entitled SI: PSC and the brain. View Publication