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April 13, 2011

A plan for conducting research on the induction of differentiation of human ES / iPS cells into germ cells

CiRA gained approval on April 8 from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), on a research plan with the objective of "establishing a method for inducing human induced pluripotent stem (iPS)1 cells to differentiate into germ cells2."Dr. Kazutoshi Takahashi, a principal investigator at the Department of Reprogramming Science, will lead the research.

In addition, an application for an amendment to the ongoing research program to use human embryonic stem (ES)3 cells, "Research on the differentiation capacity of pluripotent stem cells derived from human ES cells and their safety after transplantation, with a view to establishing a new treatment method" was also approved on March 9th. Dr. Shinya Yamanaka is responsible for the use of human ES cells for the plan.

As a result, CiRA is now ready to conduct germ cell research using ES/iPS cells. The research is aimed at developing a method for the induction of differentiation of human ES / iPS cells into germ cells and will be carried out in cooperation with the group led by Professor Renee Reijo Pera at Stanford University.

Purpose of the research
1) Optimization of the method for the in vitro induction of differentiation of human ES / iPS cells into germ cells
In no studies on the induction of differentiation of human ES / iPS cells into germ cells, which have been reported in the past, were mature normal germ cells obtained. So this research plan is aimed at establishing an appropriate as well as efficient method for the induction of differentiation.

2) Establishing a method of generating iPS cells that are most optimal for inducing germ cells
Various methods for generating iPS cells, using different somatic cells, different combinations of pluripotency-inducing factors, and different methods to introduce the factors, have been reported. However, at the same time, it has been suggested that the types of cells that can differentiate as well as their capacity to differentiate into specific tissues may vary depending on the differences of these methods. We will therefore establish a method of selecting iPS cell lines that are most optimal for this research plan, before the full-fledged launch of research on the induction of differentiation of human iPS cells into germ cells.

We believe that continuing research on the differentiation induction of pluripotent stem cells, e.g. ES cells and iPS cells, into germ cells will contribute to the establishment of a research base for clarification of the etiologies of infertility, the establishment of new methods for diagnosing, preventing and treating infertility, as well as the development of new drugs in the future.

Background of the research
It has been reported that, although the sperm cells generated through induction of differentiation of mouse ES cells would, after fertilization, die immediately after birth, it was possible to generate a fetus grown to full term. On the other hand, induction of differentiation was attempted using various kinds of growth factors in the study, which was conducted using cynomolgus monkey ES cells. As a result, gene expression as an indicator of germ cells had been observed to a very limited degree, according to the report.

Although research on deriving human ES cells into germ cells is being carried out in other countries, the reality remains that its efficacy is low, and a so-called "normal and mature gamete" has not been generated. As such, a method to induce and differentiate mature germ cells in an efficient manner needs to be established. In addition, it is believed that further research is necessary to identify whether iPS cells differentiate into germ cells as ES cells do.

Conducting research on the induction of differentiation of ES/iPS cells into germ cells may provide us with knowledge of the mechanisms by which germ cells are generated - a topic that has been difficult to investigate until now. Some causes of infertility are hereditary. It is believed that generating iPS cells from various patients and investigating the process of their differentiation into the sperm and egg will enable us to clarify the causes of infertility attributable to germ cell damage, thereby substantially contributing to the development of drugs and treatment strategies.

Bioethics-related issues
In vitro generation of germ cells may lead to new ethical issues. The MEXT enforced on May 20, 2010 the "Guidelines for conducting research to generate germ cells from human iPS cells or from human tissue stem cells (germ cell guidelines)." The MEXT also amended on May 20, 2010 the "Guidelines for the Use of Human ES Cells." Our research will be conducted in strict compliance with these guidelines. We will continue to discuss how to proceed the research.

1) Induced pluripotent stem (iPS) cells
iPS cells are a type of pluripotent stem cells established by introducing specific factors into somatic cells and are similar to ES cells. The world's first successful establishment of iPS cells through the work of Prof. Shinya Yamanaka using mouse somatic cells was reported in 2006.

2) Germ cells
Cells that work to transfer hereditary information from one generation to the next. They are derived from primordial germ cells, and those in the human body differentiate into mature germ cells through very complex processes, including meiosis, over more than a decade. They are called different names at different stages in the process but are all referred to as "germ cells," including cells within the same lines.

3) Embryonic stem (ES) cells
ES cells are a type of pluripotent stem cells derived from the inner cell mass of the blastocyst six to seven days after fertilization and culturing them. They can differentiate into cells of any tissue in the body. However, it has been noted that immune rejection will be a problem in cell transplantation therapy as the cells cannot be created from those of the patient's own body.

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