Pooja Chaudhari

Efficient and Allele-Specific Genome Editing of Disease Loci in Human iPSCs

Efficient and precise genome editing is crucial for realizing the full research and therapeutic potential of human induced pluripotent stem cells (iPSCs). Engineered nucleases including CRISPR/Cas9 and transcription activator like effector nucleases (TALENs) provide powerful tools for enhancing gene-targeting efficiency. In this study, we investigated the relative efficiencies of CRISPR/Cas9 and TALENs in human iPSC lines for inducing both homologous donor-based precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption. Significantly higher frequencies of NHEJ-mediated insertions/deletions were detected at several endogenous loci using CRISPR/Cas9 than using TALENs, especially at nonexpressed targets in iPSCs. In contrast, comparable efficiencies of inducing homologous donor-based genome editing were observed at disease-associated loci in iPSCs. In addition, we investigated the specificity of guide RNAs used in the CRISPR/Cas9 system in targeting disease-associated point mutations in patient-specific iPSCs. Using myeloproliferative neoplasm patient-derived iPSCs that carry an acquired JAK2-V617F point mutation and α1-antitrypsin (AAT) deficiency patient-derived iPSCs that carry an inherited Z-AAT point mutation, we demonstrate that Cas9 can specifically target either the mutant or the wild-type allele with little disruption at the other allele differing by a single nucleotide. Overall, our results demonstrate the advantages of the CRISPR/Cas9 system in allele-specific genome targeting and in NHEJ-mediated gene disruption.

Reprogramming of EBV-immortalized B-lymphocyte cell lines into induced pluripotent stem cells

EBV-immortalized B lymphocyte cell lines have been widely banked for studying a variety of diseases, including rare genetic disorders. These cell lines represent an important resource for disease modeling with the induced pluripotent stem cell (iPSC) technology. Here we report the generation of iPSCs from EBV-immortalized B-cell lines derived from multiple inherited disease patients via a nonviral method. The reprogramming method for the EBV cell lines involves a distinct protocol compared with that of patient fibroblasts. The B-cell line-derived iPSCs expressed pluripotency markers, retained the inherited mutation and the parental V(D)J rearrangement profile, and differentiated into all 3 germ layer cell types. There was no integration of the reprogramming-related transgenes or the EBV-associated genes in these iPSCs. The ability to reprogram the widely banked patient B-cell lines will offer an unprecedented opportunity to generate human disease models and provide novel drug therapies.

Liver engraftment potential of hepatic cells derived from patient-specific induced pluripotent stem cells

Human induced pluripotent stem cells (iPSCs) are potential renewable sources of hepatocytes for drug development and cell therapy. Differentiation of human iPSCs into different developmental stages of hepatic cells has been achieved and improved during the last several years. We have recently demonstrated the liver engraftment and regenerative capabilities of human iPSC-derived multistage hepatic cells in vivo. Here we describe the in vitro and in vivo activities of hepatic cells derived from patient specific iPSCs, including multiple lines established from either inherited or acquired liver diseases, and discuss basic and clinical applications of these cells for disease modeling, drug screening and discovery, gene therapy and cell replacement therapy.

Expression kinetics of hepatic progenitor markers in cellular models of human liver development recapitulating hepatocyte and biliary cell fate commitment

Due to the limitations of research using human embryos and the lack of a biological model of human liver development, the roles of the various markers associated with liver stem or progenitor cell potential in humans are largely speculative, and based on studies utilizing animal models and certain patient tissues. Human pluripotent stem cell-based in vitro multistage hepatic differentiation systems may serve as good surrogate models for mimicking normal human liver development, pathogenesis and injury/regeneration studies. Here, we describe the implications of various liver stem or progenitor cell markers and their bipotency (i.e. hepatocytic- and biliary-epithelial cell differentiation), based on the pluripotent stem cell-derived model of human liver development. Future studies using the human cellular model(s) of liver and biliary development will provide more human relevant biological and/or pathological roles of distinct markers expressed in heterogeneous liver stem/progenitor cell populations.

IFNL3 genotype is associated with differential induction of IFNL3 in primary human hepatocytes

BACKGROUND Lambda interferons (IFNLs) have potent antiviral activity against HCV, and polymorphisms within the IFNL gene cluster near the IFNL3 gene strongly predict spontaneous- and treatment-related HCV infection outcomes. The mechanism(s) linking IFNL polymorphisms and HCV control is currently elusive. METHODS IFNL induction was studied in primary human hepatocytes (PHH) from 18 human donors, peripheral blood mononuclear cells (PBMCs) from 18 human donors, multiple cell lines and induced pluripotent stem cell-derived hepatocyte-like cells (iPSC-hepatocytes) from 7 human donors. After stimulation with intracellular RNA and infectious HCV, quantitative PCR (qPCR) primers and probes were designed to distinguish and quantify closely related IFNL messenger (m)RNAs from IFNL1, IFNL2 and IFNL3. RESULTS PHH demonstrated the most potent induction of IFNLs, although had lower pre-stimulation levels compared to PBMCs, monocytes and cell lines. PHH stimulation with cytoplasmic poly I:C induced >1,000-fold expression of IFNL1, IFNL2 and IFNL3. PHH from donors who were homozygous for the favourable IFNL3 allele (IFNL3-CC) had higher IFNL3 induction compared to PHH from IFNL3-TT donors (P=0.03). Baseline IFNL mRNA expression and induction was also tested in iPSC-hepatocytes: iPSC-hepatocytes had significantly higher baseline expression of IFNLs compared to PHH (P<0.0001), and IFNL3 induction was marginally different in iPSC-hepatocytes by IFNL genotype (P=0.07). CONCLUSIONS Hepatocytes express IFNLs when stimulated by a synthetic viral RNA that signals the cell through the cytoplasm. IFNL induction may be greater in persons with the favourable IFNL3 allele. These data provide insight into the strong linkage between IFNL3 genetics and control of HCV infection.

Determination of Functional Activity of Human iPSC-Derived Hepatocytes by Measurement of CYP Metabolism.

The advent of induced pluripotent stem cell (iPSC) technology has enabled the modeling of an array of specific human disease phenotypes, aiding in the increasingly important and indispensable understanding of disease progression and pathogenesis. Pluripotent stem cell-derived hepatocytes present a new avenue for drug screening and personalized drug testing toward precision medicine. CYP450 microsomal enzymes play a critical role in drug metabolism. Hence, CYP activity measurement of iPSC-derived hepatocytes is a vital prerequisite, to ensure metabolic functionality before proceeding to drug testing. Herein, we describe the protocol for measurement of different CYP450 enzyme activities in human iPSC-derived hepatocytes.

Applications of Human Induced Pluripotent Stem Cell Derived Hepatocytes

Human induced pluripotent stem cells (iPSCs) are potential sources of hepatocytes for drug development and cell therapy. In vitro differentiation of iPSCs into hepatic cells has been achieved and improved during the last several years. More recently the in vivo functionality of human iPSC-derived hepatic cells at various differentiation stages has also been demonstrated. In this chapter, we describe the recent advance in human iPSC generation and hepatic differentiation technologies, the in vitro and in vivo activities of human iPSC derived hepatocytes, and discuss both basic and clinical applications of these cells including disease modeling, drug toxicity screening, drug discovery, gene therapy and cell replacement therapy.

Derivation of a disease-specific human induced pluripotent stem cell line from a biliary atresia patient

Biliary atresia (BA) is a common cause of pediatric end-stage liver disease. While its etiology is not yet clear, evidence has suggested that BA results from interactions between genetic susceptibility and environmental factors. Disease relevant human cellular models of BA will facilitate identification of both genetic and environmental factors that are important for disease prevention and treatment. Here we report the generation of a human induced pluripotent stem cell line from a BA patient using episomal vectors. Patient-specific BA iPSC lines provide valuable tools for disease mechanism study and drug development.