The overall goal of this protocol is to derive homogenous human induced pluripotent stem cells. This method can be used to derive human induced pluripotent stem cells for many purposes including disease modeling, drug screening, or to derive cells for preclinical cell therapy trials. The advantage of this protocol is that it's robust and generates homogenous cells that are maintained in a user-friendly, Xeno-free, and fully chemically defined culture system.
Since human iPS cells recapitulate the genetic background of the donor tissue and can potentially be differentiated into any disease-relevant cell type, they provide excellent tools for thesis modeling. The biopsy dissection and colony picking are intricate procedures. Seeing them performed with experienced hands assists in the understanding of the procedures and makes it easier to repeat.
Demonstrating the procedure today will be Harriet RonnHolm and Kelly Day, two highly experienced laboratory technicians from the iPS Core Facility at Karolinska Institutet. Skin biopsy samples can be stored in PBS plus 1%penicillin streptomycin for up to 48 hours at four degrees Celsius, but should be processed as fast as possible after being obtained. Transfer the biopsy to a 35 millimeter dish.
Submerge the skin biopsy in a 35 millimeter dish with two milliliters of 70%ethanol for 30 seconds. Add one milliliter of sterile Hank's Balanced Salt Solution supplemented with 1%penicillin streptomycin to a new 35 millimeter dish and transfer the biopsy to the new dish. Transfer the biopsy to a four 35 millimeter dish filled with one milliliter of freshly-prepared 0.1%dispase solution.
Using sterile surgical scalpels and forceps, cut the skin biopsy into one to two cubic millimeter pieces. Transfer the biopsy pieces with the dispase solution into a 15 milliliter tube and add an additional two milliliters of dispase. Rinse the 35 millimeter dish with one milliliter of dispase solution and transfer the rinsed solution to the 15 milliliter tube.
Incubate the biopsy at four degrees Celsius overnight. On the following morning, add four milliliters of 0.1%collagenase I to the tube with the biopsy pieces and incubate at 37 degrees Celsius for four hours. Thirty minutes prior to seeding the cells, coat one well in a six-well tissue culture plate with one milliliter of 0.1%gelatin in DPBS.
Incubate at room temperature for 30 minutes. After four hours of incubation with collagenase, centrifuge the digested cells at 300 times g for three minutes at room temperature. Aspirate the supernatant and resuspend the digest in two milliliters of fibroblast medium.
Remove the gelatin solution from the previously prepared six-well tissue culture plate. Transfer the cell suspension including any remaining tissue pieces to the six-well plate. Incubate the cells at 37 degrees Celsius and 5%carbon dioxide in high humidity.
Fibroblasts are ready to be passaged to a T25 tissue culture flask when 80%confluent. Fibroblasts at passage two to four are optimal for reprogramming since reprogramming efficiency is generally higher for lower passage fibroblasts. Aspirate the cell culture medium from the flask and wash the cells with one milliliter of DPBS.
Aspirate the DPBS and add one milliliter of 0.5%Trypsin EDTA. Incubate at 37 degrees Celsius for five minutes or until cells are detached. Add two milliliters of fibroblast medium, resuspend the cells, and transfer the cell suspension to a 15 milliliter tube.
Centrifuge at 300 times g for three minutes at room temperature. Aspirate the supernatant and resuspend the pellet in two milliliters of fibroblast medium. After counting the fibroblasts using a hemacytometer, seed fives times 10 to the fourth cells in one well of a 24-well tissue culture plate.
Incubate cells at 37 degrees Celsius overnight. On the following day, because Sendai virus will be handled, continue the procedure in a designated BSL-2 laboratory while using the appropriate personal protective equipment. Aspirate the cell culture medium and add 250 microliters of Sendai virus solution.
Incubate the plate at 37 degrees Celsius. One day before picking the colonies, prepare LN-521 coated 24-well tissue culture plates. Pipette 250 microliters of LN-521 solution into one well of a 24-well plate.
Seal the plate using parafilm and incubate at four degrees Celsius overnight. On the following day, aspirate the LN-521 solution from the one well of the 24-well plate and add 500 microliters of E8 into the well. The use of a hairnet and procedure mask is recommended while picking colonies under the stereo microscope.
Colonies are ready to be picked when they reach a size of greater than one millimeter in diameter, display sharp edges, and are growing in homogenous monolayers. Do not pick colonies with fuzzy borders and large uncompact heterogeneous cell masses. Cut each colony with a scalpel into smaller pieces in a grid-like pattern.
Use a 200 microliter pipette to mechanically scrape the cell sheets from the dish and then transfer the sheet to a well of a 24-well tissue culture plate previously coated with LN-521. Colony selection is critical for the success of this protocol. Picking a few additional colonies will ensure attachment in sufficient numbers.
Allow the cells to attach without changing the E8 medium for 48 hours. Enzymatically passage the cells when the colonies have reached a size of greater than five millimeters. Aspirate the cell culture medium from the cells and wash with 250 microliters of DPBS.
Aspirate the DPBS and add 250 microliters of dissociation reagent. Incubate at 37 degrees Celsius for three minutes. Observe that the cells have started to round up.
Detach cells from the plate by rinsing the cells with dissociation reagent. Add 500 microliters of E8 medium to a 15 milliliter tube and transfer the cells and the dissociation reagent to the tube. Centrifuge at 300 times g for three minutes.
Aspirate the supernatant from the 15 milliliter tube and resuspend the cell pellet in 500 microliters of E8 medium. Count the cells using a hemacytometer and seed 2.5 to five times 10 to the fourth cells in another previously prepared LN-521 precoated well containing 500 microliters of room temperature E8 medium. Add ROCK inhibitor to a final concentration of 10 micromolar.
Incubate the cells at 37 degrees Celsius. Using this protocol, human induced pluripotent stem cell colonies emerge from transduced fibroblasts at about day 12 post-transduction. Colonies were ready to be picked at about three to four weeks post-transduction.
Preferred features include flattened compact cell masses, growth as homogenous monolayers, and sharp edges. These bright field images show an early passage homogenous fully reprogrammed human iPS cell line compared to a highly heterogeneous cell line. The loss of the Sendai virus vector was confirmed by the absence of Sendai virus vector-specific markers in human iPS cells at passage 12 in contrast to human iPS cells at passage three.
Immunocytochemistry staining of derived cells for pluripotency markers OCT4, SSEA-4, and NANOG yielded a homogeneously positive result. mRNA expression of endogenous pluripotency genes was shown by reverse transcriptase PCR. Cell cultures containing partially reprogrammed cells that did not express pluripotency factors were discarded.
The differentiation potential of human iPS cells was assessed by formation of embryoid bodies. Real-time PCR after 21 days of embryoid body differentiation detected mRNA expression of endoderm, mesoderm, and ectoderm-specific markers which confirmed the derived human iPS cells were capable of differentiation to the three germ layers. Once mastered, this technique can be done with about 22 hours of hands-on time during a time period of approximately 16 weeks.
The derived human induced pluripotent stem cells can be differentiated into any cell type of the adult human body to answer any questions relevant to your research field. After watching this video, we hope that you will have a good understanding of how to perform the steps necessary to derive induced pluripotent stem cells from skin biopsies.
