The goal of our work is to derive new human embryonic stem cell lines for distribution to stem cell researchers. During the past year, we produced 11 new lines that we think will be valuable tools for all phases of work toward regenerative medicine therapies including discovery, translational, and eventually, early clinical applications. Along the way, this work is teaching us a great deal about early embryonic development and the specialized processes that distinguish critical steps in humans as compared to animal models.
What is the source of the embryos for our derivations? We use embryos that are left over after the conclusion of fertility treatments such as in vitro fertilization. In all cases, we obtain written informed consent from both individuals whose reproductive material was used to make the embryos. Additionally, researchers in our group have no direct contact with the couple making the donation. This process is handled by the University of California San Francisco Gamete and Embryo Bank. It is important to note that the embryos that we use would otherwise be destroyed, a point that is sometimes overlooked.
What are the methods that we used to derive these new human embryonic stem cell lines? The work that was carried out in the last 12 months employed two techniques. One line was derived using standard methods that have been employed for many years to produce stem cell lines in many species including humans. In general, early-stage human embryos are thawed and grown for a few days in the laboratory until a cluster of tightly packed cells, termed human embryonic stem cell colonies, emerges. Stem cell researchers can spot these special cells based on their appearance under a microscope. The advantage of this technique is that it is a straightforward method for reliably producing human embryonic stem cell lines. The disadvantage is that the progenitors we seek are exposed for extended periods of time to other cell types in the culture, which could impact their genetic makeup and, subsequently, their developmental potential.
Accordingly, we used a different method to derive the other ten embryonic stem cell lines that we produced during this grant period. The overall approach was to grow human embryos donated from a single couple until they contained 8-12 cells. Then we used specialized equipment to remove single cells from five sibling embryos. Each cell was allowed to develop in isolation. Four cells from one embryo gave rise to cell lines as did three cells from another embryo. The remaining three embryos each produced one cell line. This unique set of lines will enable stem cell researchers to understand the role that genetics plays in specifying the basic characteristics of human embryonic stem cells as compared to environmental signals that are inevitably transmitted as the lines are propagated in the laboratory. We are also interested in the concept that single cells that are extracted from very early stage embryos, which have not received signals from other cell types that are found at later stages of development, are more likely to be truly pluripotent as evidenced by their genetic and molecular signatures.
Why do we need additional human embryonic stem cell lines? Many of the most commonly used stem cells have been in culture for many years. This creates several problems. First, the extended length of time that the most commonly studied human embryonic stem cells have been in culture means that they are likely to have accumulated errors that are the result of mistakes made during the self-renewal process. This is all the more likely to occur because we do not yet understand the optimal conditions for growing the cells in the laboratory. Accordingly, ongoing studies in many groups, including our own, are designed to improve the environment for maintaining human embryonic stem cells, which we think will improve the fidelity with which they make carbon copies of themselves. Second, nearly all of the existing lines have been exposed to animal products, which raises the possibility that they could contain disease vectors. For this reason, the Food and Drug Administration makes it difficult (but not impossible) for cell-based therapies that are used in clinical applications to be approved once they have experienced these types of exposures. Therefore, all of our derivation work has employed solely human reagents, which we think will streamline their approval for use in clinical applications.