Caltech Mourns the Passing of President Emeritus and Nobel Laureate David Baltimore
David Baltimore, President Emeritus and the Judge Shirley Hufstedler Professor of Biology, Emeritus, at Caltech and a co-recipient of the 1975 Nobel Prize in Physiology or Medicine, passed away on September 6, 2025. He was 87 years old.
Baltimore led a multifaceted career and life as an internationally influential researcher, leader in higher education and public policy, and devoted mentor, colleague, friend, father, and husband.
"David Baltimore's contributions as a virologist, discerning fundamental mechanisms and applying those insights to immunology, to cancer, to AIDS, have transformed biology and medicine," says Caltech President Thomas F. Rosenbaum, the Sonja and William Davidow Presidential Chair and professor of physics. "David's profound influence as a mentor to generations of students and postdocs, his generosity as a colleague, his leadership of great scientific institutions, and his deep involvement in international efforts to define ethical boundaries for biological advances fill out an extraordinary intellectual life."
Baltimore was awarded the Nobel Prize for his discovery that the genetic material of tumor viruses could make DNA from their RNA genome, changing the widely held perception that genetic information could only be transferred in one direction, from DNA to RNA. Baltimore's research contributed to the understanding of the molecular basis of the immune response and shaped advances in biotechnology and the development of national science policy regarding recombinant DNA research and the AIDS epidemic.
More recently, his research was focused on investigating the development and function of the mammalian immune system and on developing viral vectors that can carry genes into cells to increase the range of diseases (from cancer to HIV to influenza) the body can effectively fight.
Beyond his contributions to science, Baltimore was a prominent higher-education leader and science-policy advocate. Baltimore served as Caltech's seventh president from 1997 to 2006, a tenure marked by the completion of a fundraising initiative for the biological sciences, the construction and dedication of the Broad Center for the Biological Sciences, and the launch of a $1.4 billion capital campaign. His presidency also featured many successful space and planetary missions at the Jet Propulsion Laboratory, which is managed by Caltech for NASA, notably the Mars Exploration Rovers.
"David brought to Caltech scientific eminence and an ambitious vision for the future that he was uniquely qualified to realize," says David W. Thompson (MS '78), chair of the Caltech Board of Trustees." He elevated the Institute's stature globally with his ability to engage audiences spanning a wide range of interests and successfully oversaw two high-impact fundraising campaigns that advanced research across disciplines, enhanced education, and defined the campus's landscape. His legacy will echo through our halls for generations to come."
As president, Baltimore worked toward increasing diversity at Caltech, particularly by bringing more women into administrative roles and, with an interest in enhancing quality of undergraduate life, appointed the first full-time vice president for student affairs and started a $3 million fund for supporting student-life activities and services.
"During my time in the president's office, I have worked to keep Caltech the unique and highly effective university that was imagined into existence by George Ellery Hale almost 100 years ago," Baltimore wrote in a note to campus when announcing his retirement in 2005. "Its dedication to excellence has been undiminished, requiring that it continually be in flux, reaching for the altering frontiers of knowledge."
Baltimore's personal sentiments are echoed in the memories and reflections of colleagues who recounted his insatiable curiosity and pursuit of new knowledge, instinct to identify and foster brilliance, and a deep and personal commitment to the people he surrounded himself with and the institutions where he dedicated his time.
"Looking at the many chapters of David's scientific life beginning as an undergraduate at Swarthmore, through times at MIT, the Salk, Rockefeller, and ultimately at Caltech, the through-line aspiration was the rigorous pursuit of what is new, true, and fundamental—in his own work and in the work of others. Mostly he succeeded, and when he did not, he always learned," says Barbara Wold (PhD '78), Caltech's Bren Professor of Molecular Biology and Merkin Institute Professor. "At Caltech, as our president and as a professor of the biology and biological engineering division, he often saw in people possibilities they did not see in themselves."
Paul Sternberg, Bren Professor of Biology and the William K. Bowes Jr. Leadership Chair of the Division of Biology and Biological Engineering, adds, "From a personal perspective, I knew David from my graduate student years at MIT and then for several decades at Caltech. What I remember most was his continual willingness to share his wisdom and exquisite intellectual taste. There are hundreds of scientists who benefited from his attention."
Baltimore began his PhD in 1960 at MIT, with a focus on studying bacteriophages, viruses that infect and replicate within bacteria. But after a summer course on animal virology at Cold Spring Harbor Laboratory, Baltimore transferred to The Rockefeller University to work with Richard Franklin, a pioneer in the molecular biology of animal viruses.
By 1970, after working on the replication of RNA viruses such as polio- and mengovirus for several years, viruses that make RNA copies of their RNA genomes to replicate, Baltimore began to investigate whether another class of RNA viruses, retroviruses, contains an enzyme that produces a DNA copy of the viral RNA. To confirm this, he performed an experiment to demonstrate the existence of this viral enzyme, reverse transcriptase, so named because it reversed the then-assumed direction of genetic information (DNA to RNA to protein). This experiment would become the basis of the Nobel Prize in Physiology or Medicine he was awarded in 1975 along with former Caltech faculty member Renato Dulbecco and Howard Temin (PhD '60), who completed his doctoral studies in Dulbecco's lab.
"The experiment is an exemplar of elegance and simplicity," says Baltimore's Caltech colleague Carlos Lois, research professor of biology. "In a single stroke, David demonstrated that genetic information can flow from RNA to DNA, something that had been considered to be impossible for more than 20 years. It is a testament to David's acumen that he had never worked with retroviruses before! For this experiment, he requested purified retroviral particles from a core facility at the National Institutes of Health. The viruses were sent to him by mail, and he did the experiment. So, the first time that he had ever worked with retroviruses, he did an experiment that got him a Nobel Prize."
The discovery of reverse transcriptase enabled laboratories throughout the world to study the molecular biology of retroviruses. When the AIDS pandemic started in the early 1980s, the scientific community was able to rapidly identify HIV—a retrovirus—as its cause. Additionally, the biotechnology revolution of the early 1980s was a direct consequence of the application of reverse transcriptase to clone and manipulate genes.
After the discovery of reverse transcriptase, Baltimore continued to work with retroviruses for several years before turning his focus to immunology. His laboratory first discovered one of the major regulators for inflammatory processes: a protein called NFkappaB, the dysregulation of which is implicated in many forms of autoimmune diseases and cancer. Additionally, his students discovered the genes responsible for the production of antibody diversity, allowing researchers to understand at the molecular level how the genome of an animal can generate billions of different antibodies.
"Throughout his career, David demonstrated a rare trait among scientists: intellectual agility," Lois says. "Whenever he thought that there were important questions that were ready to be attacked, he jumped into the field even if he had never worked in that area before."
Lois was a postdoctoral fellow in Baltimore's laboratory at Caltech from 1996 to 2002. "Joining his lab was a very formative experience," Lois recalls. "In the lab meetings, you could, on the same afternoon, hear about the effects of an oncogene, memory cells for the immune system, rearrangements of the genome, the structure of a protein domain, the control of repair of DNA damage, or the signal cascades implicated in cell death. Every lab meeting was an opportunity to learn something new from the people who were doing the leading research on the topic. I have never seen, before or after that, a group of people more motivated and driven to do science. The atmosphere in the lab was electrifying, and it was tremendously inspiring to be surrounded by such intellectually ambitious people."
After his retirement from the Caltech presidency in 2006, Baltimore remained at the Institute to continue his teaching and his scientific research. Among other work, Baltimore established a new methodology to help fight cancer, developed a new highly effective gene therapy to prevent HIV from infecting individual cells in the immune system, and created a new methodology for producing transgenic mice. He also joined with others in pursuing a global effort to create an HIV vaccine. In 2005, he was awarded a $13.9 million grant by the Grand Challenges in Global Health initiative at the Bill & Melinda Gates Foundation for his proposal to "engineer immunity" against HIV and other chronic disease pathogens.
"David Baltimore will go down in history as not only a great scientist but also as one of the great presidents of Caltech," said entrepreneur, philanthropist, and late Caltech trustee Eli Broad, when Baltimore's retirement was announced. "It is rare to find someone of his intelligence, integrity, and leadership who can relate so well to people both within and outside the world of science."
Baltimore was active in public policy throughout his career. In the 1970s, he played an instrumental role in shaping national science policy regarding recombinant DNA research, serving as co-organizer of the Asilomar Conference on Recombinant DNA held in 1975, and he was an early advocate of federal AIDS research. In 1986, he co-chaired the National Academy of Sciences committee on a National Strategy for AIDS and, in 1996, was appointed to head the National Institutes of Health (NIH) AIDS Vaccine Research Committee, which became known as "the Baltimore Committee" and is now an NIH subcommittee. He worked with the NIH while director of the Whitehead Institute at MIT, helping the government establish guidelines for the Human Genome Project.
After the 2000 presidential election, Baltimore established the Caltech/MIT Voting Technology Project along with MIT President Charles Vest. The group was formed of political scientists, economists, and engineers to address challenges in how elections are conducted. The team testified to Congress, resulting in the passing of the Help America Vote Act in 2002.
In 2015, he was among an acclaimed group of scientists who called for a worldwide moratorium on the use of genome-editing techniques to alter inheritable human DNA; in 2018, he chaired the organizing committee for the second such summit.
"It's part of my general belief that modern medicine will have the ability to ameliorate much of the burden of the diseases that we still suffer with as human beings, like cancer, inherited disease, heart disease," Baltimore said in an interview after the 2018 summit. "I'm hopeful that we will ameliorate those and that the world will become, in that sense, a better place because of modern biology."
Baltimore was born on March 7, 1938, in New York City. He received his BA in chemistry with high honors from Swarthmore College in 1960 and his PhD in biology from The Rockefeller University in 1964. He joined MIT as an associate professor in 1968, became a professor in 1972, and was named American Cancer Society Research Professor in 1973. In 1974, he joined the staff of the MIT Center for Cancer Research and was a founding director of the Whitehead Institute in 1982, where he served as director until 1990. He was president of Rockefeller from 1990 to 1991 and a member of the Rockefeller faculty until 1994, when he rejoined the MIT faculty until he assumed the presidency of Caltech in October of 1997.
Among other honors and awards, Baltimore was the recipient of the National Medal of Science (1999), the National Academy of Sciences Award in Molecular Biology (1974), the Warren Alpert Foundation Prize (2000), the Eli Lilly and Co. Award in Microbiology and Immunology (1971), the Gustav Stern Award in Virology (1970), and the Lasker~Koshland Special Achievement Award in Medical Science (2021).
He was a member of the National Academy of Sciences and the National Academy of Medicine, and was a fellow of the American Academy of Arts and Sciences and the American Institute of Immunologists, becoming a Distinguished Fellow in 2019; in addition, he was a foreign member of the Royal Society of London and the French Academy of Sciences. From 2007 to 2008, he served as the president and chair of the American Association for the Advancement of Science. He received honorary doctorates in science from Mount Sinai Medical Center, the University of Helsinki, Cold Spring Harbor Laboratory, Columbia University, Yale University, The Rockefeller University, Harvard University, the University of Alabama, California Polytechnic State University, the Weizmann Institute of Science, Swarthmore College, Bard College, and Mount Holyoke College.
In 2006, in honor of his mother, Baltimore established the Gertrude Baltimore Chair in Experimental Psychology. In 2017, the Eli and Edythe Broad Foundation established the David Baltimore Professorship in Biology and Biological Engineering at Caltech, a title which is currently held by Pamela Bjorkman.
"David was generous," says Elliot Meyerowitz, the George W. Beadle Professor of Biology and Howard Hughes Medical Institute Investigator. "His knowledge of biology was profound and he shared it freely, along with his experience, his advice, and his time. His experience was massive, not only in science, but as a leader and builder of universities, companies, and laboratories, including his extremely successful time as president of Caltech. He was always happy to give advice when asked. David was extremely generous with his time, always stopping to discuss, to advise, and to share his knowledge—not only scientific, but also of the latest restaurants, of books and concerts he enjoyed—despite being more busy than most of us could imagine. David and Alice were generous and stimulating hosts, both at Caltech and at their home in Pasadena. He will be sorely missed by all of us."
Thomas Palfrey, the Flintridge Foundation Professor of Economics and Political Science, Emeritus, who first met Baltimore during the presidential search process and later again worked closely with him as the Caltech lead of the Caltech/MIT Voting Technology Project, maintained a close friendship with Baltimore over decades. "One thing, obviously, he was a brilliant scientist—one of the greatest scientists of his generation, a university leader, and important in public service. Everyone knows about that," Palfrey says. "But what they probably don't know is how diverse and broad his interests were: music, classical, jazz, art, wine, exceptional food. He led a very multifaceted life, one of these people who put his foot on the accelerator and never let up his whole life. The amount of things that he did—traveling for pleasure and work—were mind-boggling. I think that it's important to know that he did all sorts of things as a person as well as scientist. He cared about his friends, and he cared about the world. A lot of his work was trying to improve the human condition. He should be remembered for that."
Baltimore is survived by Alice Huang, a senior faculty associate in biology at Caltech and his wife of 56 years, and by their daughter, TK Baltimore.