Chiemi Takenaka

Effective generation of iPS cells from CD34+ cord blood cells by inhibition of p53

OBJECTIVE Cord blood banks provide fully human leukocyte antigen-typed cells, from which a set of standard induced pluripotent stem (iPS) cells for use in allogenic transplantation can be derived. Hence, the ability to generate iPS cells from cord blood cells has the potential to provide a suitable source for clinical transplantation. The aim of this work is to determine the reprogramming methods, culture conditions, and cell fractions that can be used to generate iPS cells from cord blood cells effectively. MATERIALS AND METHODS CD34(+), mononucleated, and derived adherent cells from cord blood were cultured in hematopoietic medium (X-vivo10 containing 50 ng/mL interleukin-6, 50 ng/mL soluble interleukin-6 receptor, 50 ng/mL stem cell factor, 10 ng/mL thrombopoietin, and 20 ng/mL Flit3/4 ligand) 3 days prior to viral infection. Cells were then infected with retroviral constructs driving the expression of OCT3/4, SOX2, Krüppel-like factor 4, c-MYC, and enhanced green fluorescent protein together with or without the p53 knockdown lentiviral construct Shp53 pLKO.1-puro. Infected cells were then cultured for an additional 4 days in hematopoietic culture medium before being transferred onto mouse embryonic fibroblast (MEF) or SNL76/7 feeder cells in human embryonic stem cell medium (Dulbeccos modified Eagle medium/F-12 containing 20% knockout serum replacement, 200 mM L-glutamine, 1% non-essential amino acids (NEAA), 0.1 mM 2-mercaptoethanol, and 4 ng/mL basic fibroblast growth factor). Subsequently, the number of embryonic stem cell-like colonies that emerged in the following 4 weeks was scored. Expression of a number of pluripotency makers were examined by immunochemistry and reverse transcriptase polymerase chain reaction. Finally, the differentiation potential of selected colonies was determined by teratoma formation in severe combined immunodeficient mice and in vitro culture. RESULTS Repression of p53 expression by the addition of a lentiviral p53 short-hairpin RNA expression vector increased the frequency of formation of iPS-like colonies from 1 (on average) to around 100 per 2 x 10(4) cells when infected cells were grown on SNL feeder cells. CONCLUSIONS iPS cells can be generated easily from CD34(+) cord blood cells through the addition of p53 inhibition to standard reprogramming conditions.

Structure-based targeting of bioactive proteins into cypovirus polyhedra and application to immobilized cytokines for mammalian cell culture.

Certain insect viruses produce stable infectious micro-crystals called polyhedra which function to protect the virus after the death of infected larvae. Polyhedra form within infected cells and contain numerous virus particles embedded in a crystalline lattice of the viral protein polyhedrin. We have previously demonstrated that the N-terminal 75 amino acids of the Bombx mori cypovirus (BmCPV) turret protein (VP3) can function as a polyhedrin recognition signal leading to the incorporation of foreign proteins into polyhedra. Foreign proteins tagged with the VP3 polyhedrin recognition signal were incorporated into polyhedra by co-expression with polyhedrin in insect cells. We have used this method to encapsulate a wide variety of foreign proteins into polyhedra. The atomic structure of BmCPV polyhedrin showed that the N-terminal H1 alpha-helix of polyhedrin plays a significant role in cross-linking and stabilizing polyhedra. Here we show that the polyhedrin H1-helix can also function as a polyhedrin recognition signal and can be used like the VP3 N-terminal sequence to target foreign proteins into polyhedra. In addition, the two targeting methods can be used together to produce polyhedra containing both EGFP and Discosoma sp. Red Fluorescent Protein (DsRed). The modified polyhedra were imaged using dual-wavelength confocal microscopy showing that the two foreign proteins are uniformly incorporated into polyhedra at similar levels. We have investigated the biological and physiological properties of fibroblast growth factor-2 (FGF-2), FGF-7 and epidermal growth factor (EGF) immobilized on polyhedra with either the H1 or the VP3 tag. Growth factors produced by both methods were functional, inducing the growth of fibroblast cells and keratinocytes. The results demonstrate the utility and flexibility of modified polyhedra for encapsulating and stabilizing bioactive proteins.

Generation of virus-free induced pluripotent stem cell clones on a synthetic matrix via a single cell subcloning in the naïve state.

CD34+ cord blood cells can be reprogrammed effectively on dishes coated with a synthetic RGD motif polymer (PronectinF®) using a temperature sensitive Sendai virus vector (SeV TS7) carrying reprogramming factors OCT3/4, SOX2, KLF4 and c-MYC. Dish-shaped human ES cell-like colonies emerged in serum-free primate ES cell medium (supplemented with bFGF) in 20% O2 culture conditions. The copy numbers of SeV TS7 vectors in the cytoplasm were drastically reduced by a temperature shift at 38°C for three days. Then, single cells from colonies were seeded on PronectinF®-coated 96-well plates and cultured under naïve culture conditions (N2B27-based medium supplemented with LIF, forskolin, a MAPK inhibitor, and a GSK inhibitor in 5% O2) for cloning purpose. Dome-shaped mouse ES cell-like colonies from single cells emerged on PronectinF®-coated dishes. These cells were collected and cultured again in primate ES cell medium supplemented with bFGF in 20% O2 and maintained on PronectinF®-coated dishes. Cells were assessed for reprogramming, including the absence of residual SeV and their potential for three germ layer differentiation. Generation of virus-free induced pluripotent stem cell (iPSC) clones from single cells under feeder-free conditions will solve some of the safety concerns related to use of xeno- or allogeneic-material in culture, and contribute to the characterization and the standardization of iPS cells intended for use in a clinical setting.

A Simple and Highly Effective Method for Slow-Freezing Human Pluripotent Stem Cells Using Dimethyl Sulfoxide, Hydroxyethyl Starch and Ethylene Glycol

Vitrification and slow-freezing methods have been used for the cryopreservation of human pluripotent stem cells (hPSCs). Vitrification requires considerable skill and post-thaw recovery is low. Furthermore, it is not suitable for cryopreservation of large numbers of hPSCs. While slow-freezing methods for hPSCs are easy to perform, they are usually preceded by a complicated cell dissociation process that yields poor post-thaw survival. To develop a robust and easy slow-freezing method for hPSCs, several different cryopreservation cocktails were prepared by modifying a commercially available freezing medium (CP-1™) containing hydroxyethyl starch (HES), and dimethyl sulfoxide (DMSO) in saline. The new freezing media were examined for their cryopreservation efficacy in combination with several different cell detachment methods. hPSCs in cryopreservation medium were slowly cooled in a conventional −80°C freezer and thawed rapidly. hPSC colonies were dissociated with several proteases. Ten percent of the colonies were passaged without cryopreservation and another 10% were cryopreserved, and then the recovery ratio was determined by comparing the number of Alkaline Phosphatase-positive colonies after thawing at day 5 with those passaged without cryopreservation at day 5. We found that cell detachment with Pronase/EDTA followed by cryopreservation using 6% HES, 5% DMSO, and 5% ethylene glycol (EG) in saline (termed CP-5E) achieved post-thaw recoveries over 80%. In summary, we have developed a new cryopreservation medium free of animal products for slow-freezing. This easy and robust cryopreservation method could be used widely for basic research and for clinical application.

The use of leukemia inhibitory factor immobilized on virus-derived polyhedra to support the proliferation of mouse embryonic and induced pluripotent stem cells

Human leukemia inhibitory factor (LIF) was immobilized into insect virus-derived microcrystals (polyhedra) to generate LIF polyhedra (LIF-PH) that can slowly release LIF into embryonic stem (ES) cell culture media and thus maintain ES cells in an undifferentiated state. Assays of the biological activities of LIF-PH indicated that a single addition of LIF-PH to the ES cell culture medium can support the proliferation of mouse ES and induced pluripotent stem (iPS) cells continuously for 14 days, and suggest that LIF-PH can be successfully used in the place of a periodic addition of recombinant LIF to the media every 2-3 days. The release of LIF protein from LIF-PH was determined by enzyme-linked immunosorbent assay (ELISA). Maintenance of undifferentiated state of mouse ES and iPS cells cultured with LIF-PH was determined by the detection of pluripotency-related biomarkers Oct3/4 and stage-specific embryonic antigen-1 (SSEA-1) through immunostaining and measurement of alkaline phosphatase activity. In this paper, we propose a closed culture system for mass production of ES and iPS cells that utilize a slow-releasing agent of LIF.

Controlled Growth and the Maintenance of Human Pluripotent Stem Cells by Cultivation with Defined Medium on Extracellular Matrix-Coated Micropatterned Dishes

Here, we introduce a new serum-free defined medium (SPM) that supports the cultivation of human pluripotent stem cells (hPSCs) on recombinant human vitronectin-N (rhVNT-N)-coated dishes after seeding with either cell clumps or single cells. With this system, there was no need for an intervening sequential adaptation process after moving hPSCs from feeder layer-dependent conditions. We also introduce a micropatterned dish that was coated with extracellular matrix by photolithographic technology. This procedure allowed the cultivation of hPSCs on 199 individual rhVNT-N-coated small round spots (1 mm in diameter) on each 35-mm polystyrene dish (termed “patterned culture”), permitting the simultaneous formation of 199 uniform high-density small-sized colonies. This culture system supported controlled cell growth and maintenance of undifferentiated hPSCs better than dishes in which the entire surface was coated with rhVNT-N (termed “non-patterned cultures”). Non-patterned cultures produced variable, unrestricted cell proliferation with non-uniform cell growth and uneven densities in which we observed downregulated expression of some self-renewal-related markers. Comparative flow cytometric studies of the expression of pluripotency-related molecules SSEA-3 and TRA-1-60 in hPSCs from non-patterned cultures and patterned cultures supported this concept. Patterned cultures of hPSCs allowed sequential visual inspection of every hPSC colony, giving an address and number in patterned culture dishes. Several spots could be sampled for quality control tests of production batches, thereby permitting the monitoring of hPSCs in a single culture dish. Our new patterned culture system utilizing photolithography provides a robust, reproducible and controllable cell culture system and demonstrates technological advantages for the mass production of hPSCs with process quality control.

Differentiation potential of Pluripotent Stem Cells correlates to the level of CHD7

Embryonic Stem Cells (ESC) possesses two distinct features; self-renewal and the potential to differentiate. Here we show the differentiation potential and growth rate of ESC correlates positively with the expression level of the gene encoding chromodomain helicase DNA binding protein 7 (CHD7). When ESCs are maintained in feeder-free conditions and single cell seeding, ESC KhES-1 having 4520 copies or more of CHD7 in 5 ng total RNA show differentiation potential, but this is lost when the CHD7 copy number is reduced in KhES-1 to less than 696 by alternative culture conditions. Introduction of siCHD7 reduced differentiation potential and growth rate of KhES-1. Interestingly, KhES-1 underwent spontaneous differentiation when mCHD7 was introduced and we could not obtain CHD7-overexpressing ESC in culture. These data suggest that CHD7 drives differentiation, and there is a lower limit for CHD7 to initiate differentiation and an upper limit for CHD7 if maintained in undifferentiated state, and such upper limit varies depending on culture condition. As CHD7 drives cell growth, ESC with the highest permissible CHD7 level in the given culture become dominant in a couple of passages. Thus, we can select differentiation resistance-free cell clones by optimizing the culture system using CHD7 as an index.