Interview with Prof Dr. Med Thomas Skutella on Stem Cells

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Deniz Kaya: Prof. Skutella, our topic today stems cells; their value in medicine today, and maybe even the medicine of tomorrow? 

Again and again, we read about fantastic breakthroughs in medicine thanks to novel therapeutic options involving stem cells, but also of the difficulties and limitations associated with this therapy.

Prof. Skutella, could you briefly tell us what you are currently researching in your department and what potential you see in stem cells, now and in the future? What can these “Supercells” actually do? 

Prof. Skutella: Together with my team and our cooperating partners, I am working on various important issues of regenerative medicine and stem cell research.

Our focus points are the development and regeneration of nerve cells in the brain and spinal cord, injured tendon tissue with clinical research in the ‘Large Animal Model’, the artificial formation of red blood cells, and working with germ cells. We work with the latest methods of cell programming and directed differentiation, along with studying extracellular vesicles (very small biological spheres which transport important messengers to regenerating cells and tissues).

Deniz Kaya: So, you and your team cover a wide range of topics in the field of stem cell research. May I ask something more specific…you had a scientific breakthrough in your much-discussed work on stem cell generation from testicular tissue. Can you tell us more about this? How did you come to reach this breakthrough? 

Prof. Skutella: As the director of the Center for Regenerative Medicine in Tübingen, I worked with so-called ‘adult’ stem cells (stem cells of non-embryonic origin), until 2010, due to the ethical and legal constraints on working with embryonic stem cells in Germany. Together with clinicians and other working groups, both national and international, I tried to develop new methods of targeting adult stem cells for the treatment of diseases.

Deniz Kaya: In this context, in 2012, there were plenty of discussions and doubts about the authenticity of one of your discoveries…could you give us an update? 

Prof. Skutella: Yes, I have to go further into detail:

In cooperation with the Department of Urology, research on the regenerative potential of stem cells from the testes was conducted. We were able to relatively quickly recognize that these germline stem cells from the human testes — under certain cultivation conditions — no longer produced only sperm, but transformed into bone, cartilage, muscle, insulin-producing cells and nerve tissue when in the cell culture. We believed that these cells might be an alternative to the ethically controversial embryonic stem cells – that was a small sensation. We characterized the cells in detail and submitted them for publication in 2008 at “Nature”.

The cells referenced in our Nature publication are very specific and come from a human germline, and as with almost all of these cell types, there was no approval to release the cells to third parties.

Due to the competitive atmosphere of top-level research and the inability to pass over the cell line we ́ve published in nature, unfortunately, the press began talking of “misconduct” and “possible fraud”, even before a scientific discourse amongst colleagues could take place.

Deniz Kaya: It was certainly not easy for you to be so publicly attacked and accused of data falsification or even data fabrication 

Prof. Skutella: Yes, you’re right! I had never experienced anything like that before. That’s why I would like to clarify this point by point and go further into detail:

First, you must not forget that we were not the only research department to be working with human germ cells. Parallel to our work, the findings of several other international working groups studying this topic were published.

This makes it all the more strange why exactly it was just our work where the fundamental potency of re-differentiation of germ cells into pluripotent (similar to embryonic) stem cells was doubted.

So then, at my insistence, with the desire to dispel the doubts of my colleagues, an independent commission was called in Tübingen to verify the authenticity of the data and accusations of data falsifications. Result of the commission for scientific misconduct, Tübingen; The Tübingen Commission came to the explicit conclusion that no “evident misconduct in science”

could be detected (21.11.2011) in the sense of §14VerfO. 

Ultimately, the only thing we missed was to include/insert the original illustrations in the supplementary section. The alligations of data falsification or even data fabrication, as reported by the press, were able to be completely disproved!

Deniz Kaya: But that didn’t clear up everything… 

Prof Skutella: Right, I was informed by the former Heidelberg Dean following the Tübingen decision and certainly also because of all the media attention, to temporarily reset my department to using minimal equipment.

The reason was, that the transfer of ongoing cell culture experiments, especially on human germ stem cells, was not to be guaranteed. Amongst other things, the — by now considerably limited research funds — and the circumstances

surrounding my move from University of Tübingen to Heidelberg, which took place at the same time, and the fact that not all members of my research team moved with me, made the continuation of the experiments from Nature 2008 became considerably more difficult. Important cell lines were lost during the move.

The cell line which I used in my Nature publication was not allowed to be released due to ethical grounds, as mentioned, concerning the wish of the donor that the cells be destroyed after three years and not be given to third parties without explicit consent (which was not given). As it should be, the personal rights of individuals have priority over science – so I was in a stalemate.

Due to these problems, but also because I wanted to put an end to the very ‘unscientific’ discussions surrounding the issue and wanted to avert any possible harm stem cell science may endure, I – in agreement with Nature – decided to withdraw my work.

The authors have provided new data to correct errors presented in this Article. Nature has peer-reviewed all evidence provided by the authors to the editors. The images presented in the original version of the Article made the data appear more robust than newly conducted experiments show. The new data have brought to light that the original conclusions are not as robust as presented in the original paper. Nature does not dispute the main claim that the cells are pluripotent to some level, but the level of proof of pluripotency shown is not in line with regular criteria for such papers in Nature. Consequently, the authors have agreed to retract their manuscript.

After I had appealed against the University of Heidelberg regarding our appeal agreements and was proven right by the regional court, an out of court settlement was reached (Prozessnummer) As a result, we continued to do scientific research with the support of the university.

Deniz Kaya: Prof. Skutella, please tell us how the situation, now almost 5 years later, looks. You were not idle in the meantime: 

Prof. Skutella: In recent experiments on human spermatogonia, we were able to show how long-term cultures of spermatogonia can be derived from a testicular biopsy from healthy tissue. Such cells were first described in our Nature, 2008, publication and have since been reproduced by other groups directly referencing our work. For example, other international research groups have attempted to improve our in vitro spermatogenesis procedures and, like us, have been able to breed human spermatogonia over a longer period of time.

Characterizations carried out by us have shown that spermatogonia can be isolated and cultured from testicular tissue and that they differ in their molecular fingerprint from somatic cells as e.g.fibroblasts.

So let me point out: we have proven that the cells we derived from germ cells were NOT fibroblasts as claimed by certain jealous press articles or colleagues. 

These cells represent an indispensable prerequisite for the spontaneous conversion to human adult germ cell cultures which is carried out in a further step. Differential gene expression profiling of enriched human spermatogonia after short- and longterm culture. Conrad S, Azizi H, Hatami M, Kubista M, Bonin M, Hennenlotter J, Renninger M, Skutella T.

Biomed Res Int. 2014;2014:138350. DOI: 10.1155/2014/138350. Epub 2014 Mar 12. PMID: 24738045 

In a further study, we were able to use modern molecular investigation methods to show that adult human germ cell cultures share similarities with human embryonic stem cells and clearly prove that these cells have an epithelial phenotype and are not fibroblasts.

Expression of Genes Related to Germ Cell Lineage and Pluripotency in Single Cells and Colonies of Human Adult Germ Stem Cells. Conrad S, Azizi H, Hatami M, Kubista M, Bonin M, Hennenlotter J, Sievert KD, Skutella T. Stem Cells Int. 2016;2016:8582526. DOI: 10.1155/2016/8582526. Epub 2015

Nov 8. PMID: 26649052 

The aim of this study was to elucidate the molecular status of individual adult human stem cells and colonies which developed spontaneously from the selected fraction of enriched spermatogonia.

Molecular characterizations of a long-term cultured human adult germline cell cluster compared to human embryonic stem cells (hESCs) and human fibroblasts (hFibs) revealed that some haGSCs had a characteristic germ and pluripotency-associated gene expression profile with similarities to hESCs and a significant difference to somatic hFibs. Genome-wide comparisons confirmed that several human adult germline cell colonies had more or less pluripotent gene expression heterogeneity.

The results of this study confirm that human adult germline stem cells are adult stem cells with a specific in vitro molecular expression profile that is related, but not identical, to true pluripotent stem cells. Under ES cell conditions, human adult germinal cell colonies may be selected that are in a partial pluripotent state at the molecular level, which may be related to their cell plasticity and the potential for differentiation in cells of all germ layers. Finally, Id likes to express my pleasure of reaching an agreement with the medical facility of the University of Heidelberg and receiving their support in the subsequent years.

Deniz Kaya: What is to be done, now? 

Prof. Skutella: It’s not so easy to produce pluripotent cells, even from adult mice.

In another study, we found that pluripotent stem cells cannot be produced by adult mice, but only by postnatal and juvenile mice. The transfer of research results from postnatal and juvenile mice is not transferable to the germ cells of our adult patients. In human testes, however, we observed that if no hormonal or cytostatic treatment was performed on human donors for medical reasons, the cells of younger patients were significantly easier to culture.

The age of the donor has an influence on the -pluripotent conversion of mouse spermatogonial stem cells. After six-year experiments to generate ESC-like cells from adult mouse spermatogonial stem cells, it has been concluded that the derivation of pluripotent cells from mouse SSCs appears to be age-dependent. Derivation of Pluripotent Cells from Mouse SSCs Seems to Be Age-Dependent. Azizi H, Conrad S, Hinz U, Asgari B, Nanus D, Peterziel H, Hajizadeh Moghaddam A, Baharvand H, Skutella T. Stem Cells Int.

2016;2016:8216312. DOI: 10.1155/2016/8216312. Epub 2015 Nov 9. PMID: 26664410 

In order to further clarify these pitfalls, human testicular stem cells from childhood, adolescence, and adulthood should be investigated in a comparative fashion. The cultivation of human spermatogonia, especially if a greater proliferation of cells is to be achieved, must be improved.

The researcher should begin to analyze, in more detail, the cellular niche in which the cells live throughout their lives. Testicular tissues should be analyzed using modern techniques, that are more specific to gene expression, in order to identify factors such as single-cell sequencing.

Here arises the question: does a modern culture medium exist, which allows for a better proliferation of germ stem cells and which supports increased numbers during long-term reproduction?

In summary, the foundation for a new chapter in stem cell research is laid: the isolation of human testicular stem cells. Equipped with the knowledge of the specific problems related to these cells and with the new technologies developed in the last decade, we continue to work with the highest intensity on this topic.

Compared to authentic pluripotent stem cells — real, adult, mouse germ stem cells and human adult germ cell cultures are not completely reprogrammed. For this reason, an investigation into the molecular pluripotency of adult germ cells is required. It would be very interesting to improve the culture conditions and apply small molecules in order to remove the molecular blockade — which hinders the complete pluripotent transformation of adult-mouse germ stem cells or human adult germline cell cultures into complete pluripotent stem cells.

Deniz Kaya: Thank you for these explanations! So that means that we can expect, at some point soon, to be able to use our own bodies reserve cells to cure certain diseases we may have? 

Prof. Skutella: Yes, that might be possible.

Deniz Kaya: What would diseases or areas of application for these “supercells” be? 

Prof. Skutella: Since these supercells can be differentiated into a true pluripotent state — in principle — in all cells of the body and can produce small organs (so-called organoids) by themselves in culture, it is possible that they can be used in many areas of regenerative medicine.

As cell reprogramming can rejuvenate cells, it is conceivable that reprogrammed and subsequently re-differentiated cells or their secretomes could be used in geriatric medicine as an autologous ‘fountain of youth’. 

Deniz Kaya: Thank you for the interview Prof. Skutella