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Insight & Intelligence™ : Aug 6, 2013

Do VSELs Hold Water?

Very small embryonic-like stem cell research is even supported by the Vatican, but is raising serious questions from some researchers.
  • Patricia Fitzpatrick Dimond, Ph.D.

“Cells we have discovered in adult tissues change several dogmas in stem cell biology and challenge some patents as well,” commented Mariusz Ratajczak, M.D., Ph.D., D.Sci., director of the Developmental Biology Research Program at the University of Louisville, and the discoverer of very small embryonic-like stem cells (VSELs). Dr. Ratajczak and his colleagues reported in the May 20, 2006, issue of the journal Leukemia that he and his colleagues had found these cells with some of the properties of adult stem cells in the bone marrow (BM) of mice.

The cells, they reported, about 2–4 microns in size, neither looked nor behaved like BM hematopoietic stem cells (HSC) that give rise to erythrocytes, platelets, and lymphocytes. In vitro, the investigators said the cells could differentiate into all three germ-layer lineages. Cell numbers were highest when isolated from the bone marrow of young mice (about one month old), and decreased in number as mice aged. They also significantly diminished, the investigators said, in relatively short-lived DBA/2J mice as compared to relatively long-lived B6 animals.

More recently, the scientists described the cells as a “population of developmentally early stem cells residing in adult tissues. These rare cells, which are slightly smaller than red blood cells, become mobilized during stress situations into peripheral blood, are enriched in the Sca1+Lin-CD45- cell fraction in mice and the CD133+ Lin-CD45- cell fraction in humans, express markers of pluripotent stem cells such as Oct4, Nanog, and SSEA, and display a distinct morphology characterized by a high nuclear/cytoplasmic ratio and undifferentiated chromatin.”

The authors hypothesized that the cell population they found consisting of Sca-1(+)lin(-)CD45- VSELs is deposited early during development in BM and could be a source of pluripotent stem cells for tissue/organ regeneration. The cells were subsequently identified in human blood and bone marrow as well.

Ratajczak, with the University of Louisville, patented his VSEL discovery and in 2007, NeoStem, a New York-based biopharma company that describes itself as a leader in the emerging cell therapy market, exclusively licensed the rights to the technology. It also created its Stem for Life Foundation, which promotes adult stem cells as an ethical alternative to embryonic stem cell therapy. “Our interest was to see if these cells were present in humans,” Denis Rodgerson, Ph.D., founder and director of the company said upon obtaining the license. “It was an intriguing opportunity.”

The Vatican has supported VSEL research to the tune of about $1 million, and has hosted two international conferences on adult stem cells, co-organized by Stem for Life and NeoStem.

Last year, NeoStem announced that it has been awarded a two-year grant totaling $1,221,854 for “Repair of Bone Defects with Human Autologous Pluripotent Very Small Embryonic-Like Stem Cells (VSEL)” from NIH’s National Institute of Dental and Craniofacial Research. Dr. Rodgerson, NeoStem’s director of grants and academic liaison for the company, will head the study in collaboration with Russell Taichman, D.M.D, D.M.Sc, and Laurie McCauley, D.D.S., Ph.D., of the University of Michigan. Enrollment for this study is expected to begin in 2013. A trial has already begun in Poland.

The product candidate, an autologous therapy derived from a patient’s own stem cells, is to be developed for use in the regeneration of bone tissue damaged by this disease. Key advantages associated with VSEL cells, the company says, are that they avoid the ethical or moral dilemmas associated with the use of fetal cells, the potential negative biological effects associated with ESCL such as their propensity for tumor formation, and the use of autologous stem cells to avoid immune rejection.

But a rush to clinical trials, all wrapped up in a commercial venture can be tricky. In particular, a recently announced move to the clinic with these cells has prompted consternation and considerable concern in the larger stem cell community.

Repeatability In Question

Most critically, the research has thus far failed to meet criteria of repeatability in a well-known stem cell laboratory. Stanford University School of Medicine’s Irving L. Weissman, M.D., director of the Stanford Institute of Stem Cell Biology and Regenerative Medicine, said, “We found that every step of the way, we could not confirm the results of the Ratajczak group.”

In a nutshell, the Stanford investigators noted that they could not “find VSELs in mouse BM with any of the reported stem cell potentials, specifically for hematopoiesis. We found that: (1) most events within the ‘VSEL’ flow-cytometry gate had little DNA, and the cells corresponding to these events (2) could not form spheres, (3) did not express Oct4, and (4) could not differentiate into blood cells. These results provide a failure to confirm the existence of pluripotent VSELs.”

“Weissman’s evidence is a clincher—it is the end of the road for VSELs,” said Rüdiger Alt, head of research at Vita 34, a private bank for umbilical cord blood in Leipzig, Germany, who published research results last year that described the first failure to replicate claims for the cells.

Robin Smith, M.D., chairman and CEO at NeoStem, disagreed and compared the attacks on VSELs to setbacks suffered by Charles Darwin and Nicolaus Copernicus when they proposed their world-changing scientific theories.

As for Dr. Weissman, who presented some of the results published in the July 24 paper at an unrelated meeting of the Pontifical Academy of Sciences in Vatican City in April 2012, he says he was annoyed that representatives of the Catholic Church “act as if they don’t know the scientific data” and have continued to back VSELs.

But, work in the laboratory of Diane Krause, M.D., Ph.D., professor of laboratory medicine, cell biology, and of pathology and associate director, Yale Stem Cell Center, lends a modicum of support for the shadow cells if validated. Dr. Krause sent a post-doc to learn the technique for isolating the VSELs, and commented, “It was very challenging. We had to keep checking with Mariuscz on how to do things.” The team did succeed in isolating the cells from mouse BM, “coaxing” them into becoming endothelial cells, a cell type not normally expected to be derived from a BM cell precursor.

Specifically, Dr. Krause compared the level of BM derived epithelial cells after transplantation of VSELs, hematopoietic stem/progenitor cells, or other nonhematopoietic cells. VSELs, they said, clearly had the highest rate of epithelial cell formation in the lung. By transplanting VSELs from donor mice expressing H2B-GFP under a type 2 pneumocyte specific promoter, they showed that engraftment occurred by differentiation and not fusion, the investigators said. They noted that their paper is the first report of VSELs differentiating into an endodermal lineage in vivo, thereby potentially crossing germ layer lineages, and the data suggest that Oct4+ VSELs in the adult BM exhibit broad differentiation potential.

“I can only say that we manage to see these cells,” she says. “One of our postdocs went to the Ratajczak lab and learnt the technique properly.”

And the controversy will no doubt continue, as more labs try to validate the existence of VSELs and get them to differentiate. It would be good for everyone if they exist and eventually, become clinically useful. Most scientists agree that a lot more work is required to validate their existence and analyze their properties.

Meanwhile, on July 23, NeoStem announced NeoStem announced on that it will move its listing from NYSE MKT to the NASDAQ Capital Market effective with the start of trading on August 5, 2013. NeoStem will continue to trade under its existing ticker symbol “NBS”.

And according to Nature, NeoStem has expressed some caution in its recent statements about VSELs. In an email, NeoStem CEO Smith told Nature that the company “has studies in progress to determine, with robust data, whether or not VSELs have characteristics of pluripotent cells.”

This story has been corrected from an earlier version, which mistakenly referred to VSELs as VESLs. GEN regrets the error.