I was born in deep winter in 1956 in Detroit, Michigan, to immigrant parents from markedly different parts of the world.  My father emigrated after World War II from what was at the time Czechoslovakia, now the Slovak Republic, from the small village of Štefanovce in the far east of the country.  Decades before his initial arrival at Ellis Island in New York, my mother’s family left the small town of Tel Keppe, near Mosul in Nineveh province, in present-day Iraq.  After relocating to Canada, long enough for my mother to be born in Thunder Bay, Ontario, her family settled in Michigan.  My parents met in Detroit, a city teeming at the time with immigrant groups from both Eastern Europe and the Middle East.  After the untimely death of my mother, my father moved our small family—my older sister, with whom I am very close, and me—to south Florida, which flourished with job opportunities for him in a more appealing climate.  Although he lacked higher education himself, it was clear that my father placed a high priority on our education.  My sister and I grew up with a great deal of freedom to pursue interests in diverse academic subjects, as well as in tennis and, in my case, the piano.  We both earned undergraduate degrees at a nearby state university, Florida Atlantic University, where my sister now teaches in the English Department.

My exposure to science during my youth, outside of extracurricular reading, came primarily from the US space programme, particularly the Apollo programme with its ultimate goal of a moon landing.  The keen interest that the Apollo missions generated in me was certainly shared nationwide and was reinforced with broadcasts of the rocket launches from Cape Canaveral, Florida, as well as the space walks, moon landings, and splashdowns.  Even the Sears telescope my father gave us, its lens trained on the moon, brought us a tiny bit closer to developments in the Apollo programme.  The fiftieth anniversary this year of the first moonwalk has helped me realize anew the impact of the Apollo missions on my developing interest in science, the sheer excitement for astronomy, mathematics, physics, and engineering it sparked in me.  Later, though, as an undergraduate learning for the first time about the new and quantitative discipline of molecular biology, I was drawn to biology as my field of study and, ultimately, my life’s work.

The Massachusetts Institute of Technology provided a deeply stimulating environment for graduate studies, and I was extremely fortunate to have been admitted into its PhD programme. MIT also provided an opportunity to establish lifelong friendships and relationships with colleagues. For my thesis research in the laboratory of Paul Schimmel, I performed one of the first structure-function analyses of a protein using site-directed mutagenesis of the gene.  Importantly, this project required me to perform targeted mutagenesis of the bacterial chromosome to have a “clean” genetic background, which allowed me to determine the protein activity encoded by gene fragments I created. Following approaches used in yeast, I was able to create a conditional null mutation of the gene I was studying through homologous recombination of the genome with genetically engineered DNA. These studies underscored the critical importance of targeted mutagenesis of genomes for understanding gene function, and I aspired to develop similar powerful approaches for mammalian genomes.

My first studies in this area were in Walter Schaffner’s laboratory at the University of Zürich on the ETH Hönggerberg campus. Walter’s observation of homologous recombination between plasmid and chromosomally-integrated SV40 viral genomes made it evident to me that recombination could occur at detectable frequencies in mammalian cells. Following the yeast paradigm, I determined that a double-strand break in the plasmid was highly recombinogenic. I continued these studies at Stanford University in the laboratory of Paul Berg and made a related set of observations more pertinent to genome modification: a double-strand break in the plasmid could also enhance its integration into the genome, although these events were not frequent in the total cell population.

Given that the DNA entity with the break is the recipient of genetic information, I reasoned that for efficient homologous recombination, the break needed to be introduced into the genome rather than the plasmid. To that end, my own laboratory at Memorial Sloan Kettering Cancer Center performed the first gene editing experiment, which was published in 1994, by expressing a rare-cutting endonuclease. By providing a homologous DNA fragment, we established a crucial role for homologous recombination in double-strand break repair, atodds with the current paradigm at the time. Thus, for the first time, a specific change could be efficiently introduced into a mammalian genome. These experiments also uncovered frequent nonhomologous repair, which often introduces small deletions, leading to current methods to make gene mutations.

The approach of introducing a double-strand break into the genome to direct its modification, together with the development of programmable nucleases by a number of labs, has led to a revolution in biology and medicine. This revolution brings the clear promise of disease cure/amelioration and allows gene editing of organisms across the phylogenetic tree, which is transforming our understanding of biological processes on this earth.

25 September 2019 Hong Kong