STAP Cells: The Plot Thickens Even More

You might remember that Charles Vacanti and researchers at the RIKEN Institute in Japan reported a protocol for reprogramming mature mouse cells into pluripotent stem cells that could not only integrate into mouse embryos, but could also contribute to the formation of the placenta. To convert mature cells into pluripotent cells, Vacanti and others exposed the cells to slightly acidic conditions or other types of stressful conditions and the cells reverted to a pluripotent state.

Even though Vacanti and others published these results in the prestigious journal Nature, as other scientists tried to replicate the results in these papers, they found themselves growing more and more frustrated. Also, some gaffes with a few of the figures contributed to a kind of pall that has hung over this research in general.

The original makers of these cells, stress-acquired acquisition of pluripotency or STAP cells, have now made a detailed protocol of how they made their STAP cells publicly available at the Nature Protocol Exchange. Already. it is clear that a few things about the original paper are generating many questions.

First of all, Charles Vacanti’s name does not appear on the protocol. He was the corresponding author of the original paper. Therefore the absence of his name raises some eyebrows. Secondly, the authors seem to have backed off a few of their original claims.

For example one of the statements toward the beginning of the protocol says, “Despite its seeming simplicity, this procedure requires special care in cell handling and culture conditions, as well as in the choice of the starting cell population.” Whereas the original paper, on the first reading at least, seemed to convey that making STAP cells was fairly straightforward, this seems to no longer be the case, if the words of this protocol are taken at face value.

Also, the protocol notes that cultured cells do not work with their protocol. The authors write, “Primary cells should be used. We have found that it is difficult to reprogram mouse embryonic fibroblasts (MEF) that have been expanded in vitro, while fresh MEF are competent.”  This would probably explain inability of several well-regarded stem cell laboratories to recapitulate this work, since the majority of them probably used cultured cells. This, however, seems to contradict claims made in the original paper that multiple, distinct cell types could be converted into STAP cells.

Another clarification that the protocol provides that was not made clear in the original paper is that STAP cells and STAP stem cells are not the same thing. According to the authors, the protocol provided at Nature Protocol Exchange produces STAP cells, which have the capacity to contribute to the embryo and the placenta. On the other hand, STAP stem cells, are made from STAP cells by growing them in ACTH-containing medium on feeder cells, after which the cells are switched to ESC media with 20% Fetal Bovine Serum. STAP stem cells have lost the ability to contribute to extra-embryonic tissues.

Of even greater concern is a point raised by Paul Knoepfler at UC Davis. Knoepfler noticed that the original paper argued that some of their STAP cells were made from mature T cells. T cells rearrange the genes that encode the T cell receptor. If these mature T cells were used to make STAP cells, then they should have rearranged T cell receptor genes. The paper by Vacanti and others shows precisely that in a figure labeled 1i. However, in the protocol, the authors state that their STAP cells were NOT made from T-cells. In Knoepfler’s words: “On a simple level to me this new statement seems like a red flag.”

Other comments from Knoepfler’s blog noted that the protocol does not work on mice older than one week old. Indeed, the protocol itself clearly states that “Cells from mice older than one week showed very poor reprogramming efficiency under the current protocol. Cells from male animals showed higher efficiency than those from female.”  Thus the universe of cells that can be converted into STAP cells seems to have contracted by quite a bit.

From all this it seems very likely that the STAP paper will need to go through several corrections. Some think that the paper should be retracted altogether. I think I agree with Knoepfler and we should take a “wait and see” approach. If some scientists can get this protocol to work, then great. But even then, multiple corrections to the original paper will need to be submitted. Also, the usefulness of these procedure for regenerative medicine seems suspect, at least at the moment. The cells types that can be reprogrammed with this protocol are simply too few for practical use. Also, to date, we only have Vacanti’s word that this protocol works on human cells. Forgive me, but given the gaffes associated with this present paper, that’s not terribly reassuring.

Results of STAP Cell Paper Questioned

Reports of Stimulus-Triggered Acquisition of Pluripotency or STAP cells has rocked the stem cell world. If adult cells can be converted into pluripotent stem cells so easily, then perhaps personalized, custom stem cells for each patient are just around the corner.

However, the RIKEN institute, which was heavily involved in the research that brought STAP cells to the world has now opened an investigation into this research, since leading scientists have voiced discrepancies about some of the figures in the paper and others have failed to reproduce the results in the paper.

Last week, Friday (February 14, 2014, spokespersons for the RIKEN centre, which is in Kobe, Japan, announced that the institute is looking into alleged irregularities in the work of biologist Haruko Obokata, who works at the institution. Obokata was the lead author listed on two papers that were published in the international journal Nature. These papers (Obokata, H. et al. Nature 505, 641–647 (2014), and Obokata, H. et al. Nature 505, 676–680 (2014) described a rather simple protocol for deriving pluripotent stem cells from adult mouse cells by exposing them to acidic conditions, other types of stresses such as physical pressure on cell membranes. The cells, according to these two publications, had virtually all the characteristics of mouse embryonic stem cells, but had the added ability to form placental structures, which is an ability that embryonic stem cells do not have. The investigation initiated by the RIKEN centre comes at the behest of scientists who have noticed that some of the images used in these papers might have been duplicated from other papers. Also, several scientists have notes that they have been unable, to date, to replicate her results.

These concerns came to a head last week when the science blog PubPeer, and others, noted some problems in these two Nature papers and in an earlier paper from 2011. Obokata is also the first author of this 2011 paper (Obokata, H. et al. Tissue Eng. Part A 17, 607–15 (2011), and this paper contains a figure that seems to have been used for one of the figures in the 2014 paper. Also, there is another figure duplication.

Harvard Medical School anesthesiologist Charles Vacanti who was the corresponding author of one of the Nature papers has said that has learned last week about a data mix up in the paper and has contacted the journal to request a correction. “It certainly appears to have been an honest mistake [that] did not affect any of the data, the conclusions or any other component of the paper,” says Vacanti. Note that Vacanti is a co-author on both papers and a corresponding author on one of them.

In the other paper, Obokata serves as the corresponding author and this paper contains an image of two placentas that appear to be very similar. Teruhiko Wakayama works at Yamanashi University in Yamanashi prefecture, and he is a co-author on both of these papers. According to Wakayama, he sent more than a hundred images to Obokata and suggests that there was confusion over which to use. He says he is now looking into the problem.

Additionally, ten prominent stem-cell scientists have been unable to repeat Obokata’s results. One particular blog listed eight failures from scientists in the field. However, most of those attempts did not use the same types of cells that Obokata used.

Some scientists think that this could simply be a case of experienced scientists working with a system that they know very well and can manipulate easily, unlike outsiders to this same laboratory. For example, Qi Zhou, a cloning expert at the Institute of Zoology in Beijing, who says most of his mouse cells died after treatment with acid, says that “setting up the system is tricky; as an easy experiment in an experienced lab can be extremely difficult to others, I won’t comment on the authenticity of the work only based on the reproducibility of the technique in my lab,” says Zhou.

However, others are more deeply concerned. For example, Jacob Hanna, a stem-cell biologist at the Weizmann Institute of Science in Rehovot, Israel, however, says “we should all be cautious not to persecute novel findings” but that he is “extremely concerned and sceptical”. He plans to try for about two months before giving up.

It could be that the protocol is far more complicated that thought. For example, even Wakayama has been having trouble reproducing the results. To be sure, Wakayama and a student of his were able to replicate the experiment independently before publication, but only after being coached by Obokata. But since he moved to Yamanashi, he has had no luck. “It looks like an easy technique — just add acid — but it’s not that easy,” he says.

Wakayama says that his own success in replicating Obokata’s results has convinced him that her technique works. “I did it and found it myself,” he says. “I know the results are absolutely true.”

Clearly one way to clear this up is for the authors of this groundbreaking paper to publish a detailed protocol on how to make STAP cells. This should clear up any problems with the papers. Vacanti says he has had no problem repeating the experiment and says he will let Obokata supply the protocol “to avoid any potential for variation that could lead to confusion”.

The journal Nature has said that there are aware of the problems with the papers and looking into the matter.

For now, that’s where the issue sits. Frustrating I know, but until we know more we will have to just “wait and see.”

Histones Might Hold the Key to the Generation of Totipotent Stem Cells

Reprogramming adult cells into pluripotent stem cells remains a major challenge to stem cell research. The process remains relatively inefficient and slow and a great deal of effort has been expended to improve the speed, efficiency and safety of the reprogramming procedure.

Researchers from RIKEN in Japan have reported one piece of the reprogramming puzzle that can increase the efficiency of reprogramming. Shunsuke Ishii and his colleagues from RIKEN Tsukuba Institute in Ibaraki, Japan have identified two variant histone proteins that dramatically enhance the efficiency of induced pluripotent stem cell (iPS cell) derivation. These proteins might be the key to generating iPS cells.

Terminally-differentiated adult cells can be reprogrammed into a stem-like pluripotent state either by artificially inducing the expression of four factors called the Yamanaka factors, or as recently shown by shocking them with sublethal stress, such as low pH or pressure. However, attempts to create totipotent stem cells capable of giving rise to a fully formed organism, from differentiated cells, have failed.  However, a paper recently published in the journal Nature has shown that STAP or stimulus-triggered acquisition of pluripotency cells from mouse cells have the capacity to form placenta in culture and therefore, are totipotent.

The study by Shunsuke Ishii and his RIKEN colleagues, which was published in the journal Cell Stem Cell, attempted to identify molecules in mammalian oocytes (eggs) that induce the complete reprograming of the genome and lead to the generation of totipotent embryonic stem cells. This is exactly what happens during normal fertilization, and during cloning by means of the technique known as Somatic-Cell Nuclear Transfer (SCNT). SCNT has been used successfully to clone various species of mammals, but the technique has serious limitations and its use on human cells has been controversial for ethical reasons.

Ishii’s research group focused on two histone variants named TH2A and TH2B, which are known to be specific to the testes where they bind tightly to DNA and influence gene expression.

Histones are proteins that bind to DNA non-specifically and act as little spool around which the DNA winds.  These little wound spools of DNA then assemble into spirals that form thread-like structures.  These threads are then looped around a protein scaffold to form the basic structure of a chromosome.  This compacted form of DNA is called “chromatin,” and the DNA is compacted some 10,000 to 100,000 times.  Histones are the main arbiters of chromatin formation.  In the figure below, you can see that the “beads on a string” consist of histones with DNA wrapped around them.


There are five “standard” histone proteins: H1, H2A, H2B, H3, and H4.  H2A, H2B, H3 and H4 form the beads and the H1 histone brings the beads together to for the 30nm solenoid.  Variant histones are different histones that assemble into beads that do not wrap the DNA quite as tightly or wrap it differently than the standard histones.  Two variant histones in particular, TH2A and TH2B, tend to allow DNA wrapped into chromatin to form and more loosely packed structure that allows the expression of particular genes.

When members of Ishii’s laboratory added these two variant histone proteins, TH2A/TH2B, to the Yamanaka cocktail (Oct4, c-Myc, Sox2, and Klf4) to reprogram mouse fibroblasts, they increased the efficiency of iPSC cell generation about twenty-fold and the speed of the process two- to threefold. In fact, TH2A and TH2B function as substitutes for two of the Yamanaka factors (Sox2 and c-Myc).

Ishii and other made knockout mice that lacked the genes that encoded TH2A and TH2B. This work demonstrated that TH2A and TH2B function as a pair, and are highly expressed in oocytes and fertilized eggs. Furthermore, these two proteins are needed for the development of the embryo after fertilization, although their levels decrease as the embryo grows.

Graphical Abstract1 [更新済み]

In early embryos, TH2A and TH2B bind to DNA and induce an open chromatin structure in the paternal genome (the genome of sperm cells), which contributes to its activation after fertilization.

These results indicate that TH2A/TH2B might induce reprogramming by regulating a different set of genes than the Yamanaka factors, and that these genes are involved in the generation of totipotent cells in oocyte-based reprogramming as seen in SCNT.

“We believe that TH2A and TH2B in combination enhance reprogramming because they introduce a process that normally operates in the zygote during fertilization and SCNT, and lead to a form of reprogramming that bears more similarity to oocyte-based reprogramming and SCNT” explains Dr. Ishii.

Human STAP cells – Troubling Possibilities

Soon after the publication of this paper that adult mouse cells could be reprogrammed into embryonic-like stem cells simply by exposing them to acidic environments or other stresses , Charles Vacanti at Harvard Medical School has reported that he and his colleagues have demonstrated that this procedure works with human cells.

STAP cells or stimulus-triggered acquisition of pluripotency cells were derived by Vacanti and his Japanese collaborators last year. These new findings show that adult cells can be reprogrammed into embryonic-like stem cells without genetic engineering. However, this technique worked well in mouse cells, but it was not clear that it would work with human adult cells.

Vacanti and others shocked the world when they published their paper in the journal Nature earlier this year when they announced that adult cells in mice could be reprogrammed through exposure to stresses and proper culture conditions.

Now Vacanti has made good on his promise to test his protocol on human adult cells. In the photo below, provided by Vacanti, human adult cells were reprogrammed to a pluripotent state by exposing them to stresses, followed by growth in culture under specific conditions.

Human STAP cells
Human STAP cells

“If they can do this in human cells, it changes everything, said Robert Lanza of Advanced Cell Technologies in Marlborough, Massachusetts. Such a procedure promises cheaper, faster, and potentially more flexible cells for regenerative medicine, cancer therapy and cell and tissue cloning.

Vacanti and his colleagues say they have taken human fibroblast cells and tested several environmental stressors on them to recreate human STAP cells. He will not presently disclose which particular stressors were applied, he says the resulting cells appear similar in form to the mouse STAP cells. His team is in the process of testing to see just how stem-cell-like these cells are.

According to Vacanti, the human cells took about a week to resemble STAP cells, and formed spherical clusters just like their mouse counterparts. Vacanti and his Harvard colleague Koji Kojima emphasized that these results are only preliminary and further analysis and validation is required.

Bioethical problems potentially emerge with STAP cells despite their obvious potential. The mouse cells that were derived and characterized by Vacanti’s group and his collaborators were capable of making placenta as well as adult cell types. This is different from embryonic stem cells, which can potentially form all adult cell types, but typically do not form placenta. Embryonic stem cells, therefore, are pluripotent, which means that they can form all adult cell types. However, the mouse STAP cells can form all embryonic and adult cell types and are, therefore, totipotent. Mouse STAP cells could form an entirely new mouse. While it is now clear if human STAP cells, if they in fact exist, have this capability, but if they do, they could potentially lead to human cloning.

Sally Cowley, who heads the James Martin Stem Cell Facility at the University of Oxford, said of Vacanti’s present experiments: “Even if these are STAP cells they may not necessarily have the same potential as mouse ones – they may not have the totipotency – which is one of the most interesting features of the mouse cells.”

However the only cells known to be naturally totipotent are in embryos that have only undergone the first couple of cell divisions immediately after fertilization. According to Cowley, any research that utilizes totipotent cells would have to be under very strict regulatory surveillance. “It would actually be ideal if the human cells could be pluripotent and not totipotent – it would make everyone’s life a lot easier,” she opined.

Cowley continued: “However, the whole idea that adult cells are so plastic is incredibly fascinating,” she says. “Using stem cells has been technically incredibly challenging up to now and if this is feasible in human cells it would make working with them cheaper, faster and technically a lot more feasible.”

This is all true, but Robert Lanza from Advanced Cell Technology in Marlborough, Massachusetts, a scientist with whom I have often deeply disagreed, noted: “The word totipotent brings up all kinds of issues,” says Robert Lanza of Advanced Cell Technology in Marlborough, Massachusetts. “If these cells are truly totipotent, and they are reproducible in humans then they can implant in a uterus and have the potential to be turned into a human being. At that point you’re entering into a right-to-life quagmire”

A quagmire indeed, for Vacanti has already talked about using these STAP cells to clone human embryos. Think of it: the creation of very young human beings just for the purpose of ripping them apart and using their cells for research or medicine. Would we allow this if the embryo were older; say the age of a toddler? No we would rightly condemn it as murder, but because the embryo is very young, that somehow counts against it. This is little more than morally grading the embryo according to astrology.

Therefore, whole Vacanti’s experiments are exciting and novel, they hold chilling possibilities. Lanza is right, and it is doubtful that scientists would show the same deference or sensitivities to the moral exigencies he has shown.

Stimulus-Triggered Acquisition of Pluripotency Cells: Embryonic-Like Stem Cells Without Killing Embryos or Genetic Engineering

Embryonic stem cells have been the gold standard for pluripotent stem cells. Pluripotent means capable of differentiating into one of many cell types in the adult body. Ever since James Thomson isolated the first human embryonic stem cell lines in 1998, scientists have dreamed of using embryonic stem cells to treat diseases in human patients.

However, deriving human embryonic stem cell lines requires the destruction or molestation of a human embryo, the smallest, youngest, and most vulnerable member of our community. In 2006, Shinya Yamanaka and his colleges used genetic engineering techniques to make induced pluripotent stem (iPS) cells, which are very similar to embryonic stem cells in many ways. Unfortunately, the derivation of iPSCs introduces mutations into the cells.

Now, researchers from Brigham and Women’s Hospital (BWH), in Boston, in collaboration with the RIKEN Center for Developmental Biology in Japan, have demonstrated that any mature adult cell has the potential to be converted into the equivalent of an embryonic stem cell. Published in the January 30, 2014 issue of the journal Nature, this research team demonstrated in a preclinical model, a novel and unique way to reprogram cells. They called this phenomenon stimulus-triggered acquisition of pluripotency (STAP). Importantly, this process does not require the introduction of new outside DNA, which is required for the reprogramming process that produces iPSCs.

“It may not be necessary to create an embryo to acquire embryonic stem cells. Our research findings demonstrate that creation of an autologous pluripotent stem cell – a stem cell from an individual that has the potential to be used for a therapeutic purpose – without an embryo, is possible. The fate of adult cells can be drastically converted by exposing mature cells to an external stress or injury. This finding has the potential to reduce the need to utilize both embryonic stem cells and DNA-manipulated iPS cells,” said senior author Charles Vacanti, MD, chairman of the Department of Anesthesiology, Perioperative and Pain Medicine and Director of the Laboratory for Tissue Engineering and Regenerative Medicine at BWH and senior author of the study. “This study would not have been possible without the significant international collaboration between BWH and the RIKEN Center,” he added.

The inspiration for this research was an observation in plant cells – the ability of a plant callus, which is made by an injured plant, to grow into a new plant. These relatively dated observations led Vacanti and his collaborators to suggest that any mature adult cell, once differentiated into a specific cell type, could be reprogrammed and de-differentiated through a natural process that does not require inserting genetic material into the cells.

“Could simple injury cause mature, adult cells to turn into stem cells that could in turn develop into any cell type?” hypothesized the Vacanti brothers.

Vacanti and others used cultured, mature adult cells. After stressing the cells almost to the point of death by exposing them to various stressful environments including trauma, a low oxygen and acidic environments, researchers discovered that within a period of only a few days, the cells survived and recovered from the stressful stimulus by naturally reverting into a state that is equivalent to an embryonic stem cell. With the proper culture conditions, those embryonic-like stem cells were propagated and when exposed to external stimuli, they were then able to redifferentiate and mature into any type of cell and grow into any type of tissue.

To examine the growth potential of these STAP cells, Vacanti and his team used mature blood cells from mice that had been genetically engineered to glow green under a specific wavelength of light. They stressed these cells from the blood by exposing them to acid, and found that in the days following the stress, these cells reverted back to an embryonic stem cell-like state. These stem cells then began growing in spherical clusters (like plant callus tissue). The cell clusters were introduced into developing mouse embryos that came from mice that did not glow green. These embryos now contained a mixture of cells (a “chimera”). The implanted clusters were able to differentiate into green-glowing tissues that were distributed in all organs tested, confirming that the implanted cells are pluripotent.

Thus, external stress might activate unknown cellular functions that set mature adult cells free from their current commitment to a particular cell fate and permit them to revert to their naïve cell state.

“Our findings suggest that somehow, through part of a natural repair process, mature cells turn off some of the epigenetic controls that inhibit expression of certain nuclear genes that result in differentiation,” said Vacanti.

Of course, the next step is to explore this process in more sophisticated mammals, and, ultimately in humans.

“If we can work out the mechanisms by which differentiation states are maintained and lost, it could open up a wide range of possibilities for new research and applications using living cells. But for me the most interesting questions will be the ones that let us gain a deeper understanding of the basic principles at work in these phenomena,” said first author Haruko Obokata, PhD.

If human cells can be made into embryonic stem cells by a similar process, then someday, a simple skin biopsy or blood sample might provide the material to generate embryonic stem cells that are specific to each individual, without the need for genetic engineering or killing the smallest among us. This truly creates endless possibilities for therapeutic options.