In 2007, Françoise Baylis and Jason Scott Robert published “Part-Human Chimeras: Worrying the Facts, Probing the Ethics” in The American Journal of Bioethics. Within their article, hereafter “Part-Human Chimeras,” the authors offer corrections on “Thinking About the Human Neuron Mouse,” a report published in The American Journal of Bioethics in 2007 by Henry Greely, Mildred K. Cho, Linda F. Hogle, and Debra M. Satz, which discussed the debate on the ethics of creating part-human chimeras. Chimeras are organisms that contain two or more genetically distinct cell lines. Both publications discuss chimeras with DNA from different species, specifically in response to studies in which scientists injected human brain cells into mice. “Part-Human Chimeras,” contributes to a chain of ethical and scientific discussion that occurred in the mid-2000s on whether people should be able to conduct research on chimeras, especially in embryos.

In 2006, bioethicist Jason Scott Robert published “The Science and Ethics of Making Part-Human Animals in Stem Cell Biology” in The FASEB Journal. There, he reviews the scientific and ethical justifications and restrictions on creating part-human animals. Robert describes part-human animals, otherwise known as chimeras, as those resulting from the intentional combination of human and nonhuman cells, tissues, or organs at any stage of development. He specifically criticizes restrictions against creating part-human animals made by the National Academy of Sciences, or NAS, in 2005, arguing that while they ensure that such research is morally justifiable, they might limit scientists from conducting useful science using part-human animals or entities. Robert challenges the moral rationales behind prohibiting chimera research, arguing that they may impede scientists from conducting research that could have important benefits to biology and medicine, and suggests how to balance the conflicting moral and scientific needs of such science.

In 2015, biologist Helena D. Zomer and colleagues published the review article “Mesenchymal and Induced Pluripotent Stem Cells: General Insights and Clinical Perspectives” or “Mesenchymal and Induced Pluripotent Stem Cells” in Stem Cells and Cloning: Advances and Applications. The authors reviewed the biology of three types of pluripotent stem cells, embryonic stem cells, or ESCs, mesenchymal stem cells, or MSCs, and induced pluripotent stem cells, or iPS cells. Pluripotent stem cells are a special cell type that can give rise to other types of cells and are essential for development. The authors describe the strengths and weaknesses of each type of stem cell for regenerative medicine applications. They state that both MSC and iPS types of stem cells have the potential to regenerate tissues among many other therapeutic possibilities. In their article, Zomer and colleagues review the potential for MSCs and iPS cells to reshape the field of regenerative and personal medicine.

The California Stem Cell Research and Cures Act, also called Proposition 71, was a ballot initiative proposed by California voters in 2004 to allocate three billion dollars of state funds for stem cell research over ten years. Endorsed by California scientists and patient-advocates, Prop 71 passed on 2 November 2004, amending the state constitution to make stem cell research a constitutional right. In addition, Prop 71 led to the creation of the California Institute for Regenerative Medicine (CIRM), in San Francisco, California to allocate funds and oversee stem cell research in the state.

Alan Osborne Trounson is a scientist from Australia who studies embryology and stem cells. His research has improved the success rates of in vitro fertilization, or IVF. IVF is a medical procedure in which scientists fertilize an egg cell with sperm outside of the body, often in a laboratory petri dish, then transfer the fertilized egg to a woman’s uterus to start pregnancy. Trounson also researched embryonic stem cells, or stem cells collected from embryos, and their potential for treating injuries and diseases. Additionally, Trounson led the Californian Institute for Regenerative Medicine, or CIRM, one of the largest agencies to fund stem cell research in California, from 2007 to 2014. Over the course of his career, Trounson developed several techniques that improved the effectiveness of IVF, including fertility treatments and cryopreservation, and supported stem cell research as a scientist and administrator.

Irving Lerner Weissman is a researcher and professor in developmental biology at the Stanford University School of Medicine in Stanford, California. Weissman is also a professor of pathology and Virginia & D. K. Ludwig professor of clinical investigation in cancer at the Stanford University School of Medicine. Weissman studies the biology of stem cells and immune cells and has conducted research in those fields during the late twentieth and early twenty-first centuries. In the late 1980s, Weissman’s team developed methods to identify hematopoietic stem cells, or HSCs, which give rise to the body’s blood and immune cells. Also, in the early 2000s, Weissman also co-authored California’s Proposition 71, which secured three billion dollars in state funding for stem cell research after the federal government restricted human embryonic stem cell work. Weissman’s efforts have demonstrated the therapeutic potential of stem cell transplantation in the treatment of diseases, including blood cancer.

Sir Martin John Evans researched developmental biology in the United Kingdom during the twentieth and early twenty-first centuries. He was among the first to isolate and grow embryonic stem cells in the lab. Embryonic stem cells have the ability to develop into many different cell types. Using those cells, Evans and his colleagues developed methods for introducing changes to the DNA of early mouse embryos. He found that when he introduced those modified embryos into foster mothers, the genetic alterations also appeared in subsequent generations. That finding helped him produce some of the first living mice with desired genetic changes, later dubbed knockout mice. In 2007, Evans received the Nobel Prize in Physiology or Medicine along with Mario Capecchi and Oliver Smithies for their work on introducing specific gene modifications in mice using embryonic stem cells. Evans’s scientific contributions have permitted scientists to better understand the roles of different genes in both embryological development and disease.

In the 1990s, John E. Dick and Dominique Bonnet, researchers at the University of Toronto, in Toronto, Ontario, investigated how a blood cancer called acute myeloid leukemia, or AML, arises from blood-forming cells. Researchers in the field at the time did not know which cells initiate and maintain AML in the body, and there were conflicting hypotheses about which cells were responsible. Scientists hypothesized that AML might be mainly composed of more specialized and differentiated blood cells. Dick and Bonnet conducted experiments in which they grew human AML cells in mice and investigated which cells initiated and maintained the cancer to explore that hypothesis. Their study was one of the first to use sensitive mouse models to characterize and uncover which cells initiated and comprised AML, which contributed to the understanding of its cellular origin and aided in the development of targeted therapies for leukemia treatment.

In 2006, Shideng Bao and colleagues published “Glioma Stem Cells Promote Radioresistance by Preferential Activation of the DNA Damage Response,” hereafter “Glioma Stem Cells,” in Nature. The study describes how cells within a glioblastoma, a type of fast-growing brain tumor, have a high expression of a protein called CD133, which is associated with neural stem cells. Among those cells with high expression of CD133, there exist many stem cells called glioma stem cells. In the paper, Bao and colleagues demonstrate that glioma stem cells are more resistant to radiation compared to other cells within a glioblastoma tumor, and that their resistance has to do with their ability to repair DNA. “Glioma Stem Cells” was one of the first studies to identify the role of glioma stem cells in resistance to radiation and laid the framework for future studies that investigated their role in tumor progression and recurrence as well as novel treatments targeting those cells.

In 2003, Sheila Singh and colleagues published “Identification of a Cancer Stem Cell in Human Brain Tumors” in the journal Cancer Research. The study examines a small population of cells within brain cancers that have abilities similar to those of neural stem cells and can maintain the growth of a brain tumor. The researchers identified the brain cancer stem cells by looking at the expression of proteins CD133 and nestin, which are usually present in neural stem cells. In addition, they characterized brain cancer stem cells as having the ability to quickly proliferate and self-renew, form tumor spheres, as well as differentiate in a manner that resembles characteristics of the original brain tumor from which those cells originated. “Identification of a Cancer Stem Cell in Human Brain Tumors” was one of the first studies to identify cancer stem cells in brain cancer and laid the framework for future research investigating the role of brain cancer stem cells in response to treatment, as well as the recurrence of a tumor after treatment.