In the early 2000s, Richard S. Legro, Mark V. Sauer, Gilbert L. Mottla, Kevin S. Richter, William C. Dodson, and Duanping Liao studied the relationship between air pollution and reproductive complications. In the United States, Legro’s team tracked thousands of women undergoing in vitro fertilization, or IVF, along with the air quality of both the IVF clinics and patients’ home locations. IVF is a reproductive technology during which a physician obtains mature eggs from a patient’s ovaries and fertilizes them with sperm in a lab setting outside of the body, after which the physician transfers the fertilized eggs into the patient’s uterus. As stated in Legro’s publication, Legro suspected that poor air quality would adversely affect live birth rates during IVF, so he compiled and analyzed the various types of pollutants that IVF patients were naturally exposed to in their homes and clinics. Legro’s experiment led to an increased awareness among patients about the dangers of conceiving via IVF in highly polluted areas.

This thesis shows us the history of how some of the first attempts at IVF in humans using various options such as donated egg cells and cryopreserved embryos, often ended in early miscarriages. At that time, most members of the scientific community and general public responded to those trials by regarding them as insignificant. In 1998, the success rate of women under the age of 38 having children with the use of IVF was 22.1%. Over time, scientists began to acknowledge those published findings that detailed various “failed” human IVF experiments. Scientists learned to use them as a guide for what to do differently in future IVF experiments. Because of that, scientists have since developed more effective IVF methods which have ultimately improved the procedure’s success rate.

In 1972, David Whittingham, Stanley Leibo, and Peter Mazur published the paper, “Survival of Mouse Embryos Frozen to -196 ° and -269 °C,” hereafter, “Survival of Mouse Embryos,” in the journal Science. The study marked one of the first times that researchers had successfully cryopreserved, or preserved and stored by freezing, a mammalian embryo and later transferred that embryo to a live mouse who gave birth to viable offspring. Previously, scientists had only been successful cryopreserving single cells, like red blood cells. Mammalian embryos, on the other hand, were more difficult to cryopreserve because they are more complex and therefore more easily weakened or destroyed by the formation of ice within its cells. Whittingham, Leibo, and Mazur’s work provided a successful model for mammalian embryo cryopreservation, a technology that later expanded to cryopreserve more complex embryos, such as human embryos.

In 2018, He Jiankui uploaded a series of videos to a YouTube channel titled “The He Lab” that detailed one of the first instances of a successful human birth after genome editing had been performed on an embryo using CRISPR-cas9. CRISPR-cas9 is a genome editing tool derived from bacteria that can be used to cut out and replace specific sequences of DNA. He genetically modified embryos at his lab in Shenzhen, China, to make them immune to contracting HIV through indirect perinatal transmission from their father, who was infected with the virus. HIV is a virus that attacks the immune cells of its host and weakens their ability to fight off diseases. At the time of He’s experiment, various treatments already existed at that could prevent the fetuses from contracting HIV without the need for gene surgery. Nonetheless, He’s experiment led to one of the first successful births of fetuses resulting from genetically modified embryos. He kept his experiment secret until he uploaded the videos announcing the birth of the fetuses, born as two twin girls. The experiment discussed in the videos was successful, but many scientists criticized the experiment due to ethical concerns with the way He conducted it.

In 1964, authors James Till, Ernest McCulloch, and Louis Siminovitch, published A Stochastic Model of Stem Cell Proliferation, Based on The Growth of Spleen Colony-Forming Cells, which discussed possible mechanisms that control stem cell division. The authors wrote the article following their experiments with spleens of irradiated mice to demonstrate the existence of stem cells, had unknown properties. In their previous experiments, Till and McCulloch noticed that many similar-looking colonies of cells formed on the spleens of irradiated mice, but those colonies had a highly variable number of stem cells. They could not explain why some stem cells gave rise to many stem cells while others only gave rise to a few. In the article, the authors propose an explanation for how stem cells divide and renew, and provide both a greater understanding as to how cancerous tissues may arise due to unchecked stem cell division as well how stem cells can aid in cancer therapy.

James Edgar Till is a biophysicist known for establishing the existence of stem cells along with Ernest McCulloch in 1963. Stem cells are undifferentiated cells that can shift, or differentiate, into specialized types of cells and serve as a repair system in the body by dividing indefinitely to replenish other cells. Till’s work with stem cells in bone marrow, which produces the body’s blood cells, helped form the field of modern hematology, a medical discipline that focuses on diseases related to the blood. He also worked on issues in the medical field including patient inclusion in clinical trials, matters of effective and ineffective clinical communication, and limitations of public access to medical and scientific research. Till’s work with stem cells furthered scientists’ understanding of abnormal blood cell development, which helped set the foundation for regenerative medicine.