Generation of Integration-free Induced Pluripotent Stem Cells from Human Peripheral Blood Mononuclear Cells Using Episomal Vectors

Summary

This protocol describes a detailed method for efficient generation of integration-free iPSCs from human adult peripheral blood cells. With the use of four oriP/EBNA-based episomal vectors to express the reprogramming factors, KLF4, MYC, BCL-XL, or OCT4 and SOX2, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood.

Abstract

Induced Pluripotent Stem Cells (iPSCs) hold great promise for disease modeling and regenerative therapies. We previously reported the use of Episomal Vectors (EV) to generate integration-free iPSCs from peripheral blood mononuclear cells (PB MNCs). The episomal vectors used are DNA plasmids incorporated with oriP and EBNA1 elements from the Epstein-Barr (EB) virus, which allow for replication and long-term retainment of plasmids in mammalian cells, respectively. With further optimization, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood. Two critical factors for achieving high reprogramming efficiencies are: 1) the use of a 2A "self-cleavage" peptide to link OCT4 and SOX2, thus achieving equimolar expression of the two factors; 2) the use of two vectors to express MYC and KLF4 individually. Here we describe a step-by-step protocol for generating integration-free iPSCs from adult peripheral blood samples. The generated iPSCs are integration-free as residual episomal plasmids are undetectable after five passages. Although the reprogramming efficiency is comparable to that of Sendai Virus (SV) vectors, EV plasmids are considerably more economical than the commercially available SV vectors. This affordable EV reprogramming system holds potential for clinical applications in regenerative medicine and provides an approach for the direct reprogramming of PB MNCs to integration-free mesenchymal stem cells, neural stem cells, etc.

Introduction

After forced expression of several transcription factors (i.e. OCT4, SOX2, MYC and KLF4), somatic cells can be reprogrammed to induced Pluripotent Stem Cells (iPSCs), which hold great promise for applications in regenerative medicine and cell replacement therapy^1-3. To date, diverse methods have been developed to increase the success rate of reprogramming^4-7. Viral vectors-induced reprogramming is widely used for efficient generation of iPSCs, because viral integration leads to a high-level, stable expression of the reprogramming factors. However, permanent integration of the vector DNA into the cell genome may induce insertiona....

Protocol

All of the human PB samples were obtained from anonymous adult donors with no identification information available from Tianjin Blood Center with approval of the local research ethics committee.

1. Endo-free Plasmid Preparation

1. Use a commercial Plasmid Purification Maxi Kit to extract episomal vectors from E. coli according to manufacturer's protocol. For the final step, substitute TE buffer with endotoxin-free sterile water to dissolve the DNA pellet.
2. Measure DNA concentration using a commercial UV/Vis spectrophotometer. The concentration is usually greater than 1 µg/µL, with A260/A280 and ....

Results

Using this protocol, we can obtain hundreds of colonies from 1 x 10⁵ nucleofected PB MNCs (Figures 1A and 1B). The reprogramming efficiency is approximately 0.2 - 0.5% and the colonies express pluripotency markers (Figures 1C and 1D). iPSCs generated using the described protocol are integration-free and have the ability to form teratoma composing the 3 germ layers (Figures 1E and 1F

Discussion

Acquiring blood samples from healthy donors or patients is convenient and noninvasive, making it an attractive cell source for basic research and clinical cell therapy. Here we have described a protocol for highly efficient generation of integration-free iPSCs from peripheral blood samples. This reproducible and affordable approach should benefit the iPSC field.

We have reported that there are two critical factors responsible for the highly efficient PB reprogramming³⁰. One is equim.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Hematopoietic Stem Cell Expansion Medium	Sigma	S0192	Store at 4 °C
Human Stem Cell Factor (SCF)	Peprotech	300-07	Store at -20 or -80 °C
Interleukin-3 (IL-3)	Peprotech	AF-200-03	Store at -20 or -80 °C
Erythropoietin (EPO)	Peprotech	100-64	Store at -20 or -80 °C
Insulin Growth Factor-1 (IGF-1)	Peprotech	100-11	Store at -20 or -80 °C
Dexamethasone	Sigma	D4902	Store at -20 or -80 °C
1-thioglycerol (MTG)	Sigma	M6145	Store at -20 or -80 °C
DMEM/F12 medium	Gibco	112660-012	Store at 4 °C
L-glutamine (100x)	Gibco	25030-081	Store at -20 °C
Penicillin/Streptomycin (100x)	Gibco	15140-122	Store at -20 °C
Non-essential Amino Acids solution (100x)	Gibco	11140-050	Store at 4 °C
Fibroblast Growth Factor 2 (FGF2)	Peprotech	100-18B	Store at -20 or -80 °C
Insulin-Transferrin-Selenium (ITS, 100x)	Gibco	41400-045	Store at 4 °C
Ascorbic acid	Sigma	49752	Store at -20 °C
DMEM (high glucose) medium	Thermo	SH30243.01B	Store at 4 °C
Fetal Bovine Serum (FBS)	Hyclone	SV30087.01	Store at -20 °C
Ficoll	GE Healthcare, SIGMA	17-5442-02	Store at RT
Trehalose	Sigma	T9531	Store at 4 °C
Dimethylsulfoxide (DMSO)	Sigma	D2650	Store at RT, protect from light
Endofree Plasmid Maxi Kit (10)	Qiagen	12362	Store at RT
IMDM	Gibco	21056-023	Store at 4 °C
Human CD34+ Cell Nucleofection Kit	Lonza	VPA-1003	Store at RT, nucleofection buffer and supplement should be stored at 4 °C
Sodium Butyrate	Sigma	B5887	Store at -20 or -80 °C
ROCK inhibitor - Y27632	STEMGENT	04-0012-10	Store at -20 °C
Essential 8 basal medium (E8)	Gibco	A15169-01	Store at 4 °C, the supplement should be stored at -20 or -80 °C
Matrigel	BD	354277	Store at -20 or -80 °C
2x EasyTaq PCR SuperMix (+dye)	TransGen Biotech	AS111	Store at -20 °C
Cell detachment solution	STEMGENT	01-0006	Store at -20 °C, Accutase as a cell detachment solution to obtain a single-cell suspension
DAPI	Sigma	D9542-1MG	Store at 4 or -20 °C
Anti-Nanog AF488	BD	560791	Store at 4 °C, primary antibody used for Immunofluorescence, dilute 1/100 when used
Anti-OCT4	abcam	ab19857	Store at 4 °C, primary antibody used for Immunofluorescence, dilute 1/100 when used
AF488 donkey anti-mouse IgG	Invitrogen	A21202	Store at 4 °C, secondary antibody used for Immunofluorescence,  dilute 1/500 when used
PE anti-human TRA-1-60-R antibody	Biolegend	330610	Store at 4 °C, antibody used for flow cytometry
eFluor 570-conjugated anti-SSEA4	eBioscience	41-8843	Store at 4 °C, antibody used for flow cytometry
Isotype antibody	eBioscience	11-4011	Store at 4 °C, antibody used for flow cytometry
Alkaline Phosphatase Detection Kit	SiDanSai	1102-100	Store at 4 °C
Genomic DNA Extraction Kit	TIANGEN	DP304-02	Store at RT
Trypan Blue solution	Sigma	T8154	Store at RT
Flow cytometry cell analyzer	BD	LSRII
Spinning Disk Confocal microscope (SDC)	PerkinElmer	UltraVIEW VOX	for confocal imaging
Nucleofection device	Lonza	Nucleofector 2b	for the nucleofection of PB MNC
ImageQuant LAS-4010	GE		to take photos of AP staining in bulk