Baltimore, David (1938-), an American microbiologist, is one of the most influential and controversial biologists of his time and a pioneer in DNA recombinant techniques. He shared the 1975 Nobel Prize in physiology or medicine and received the 1999 National Medal of Science for his work in virology, molecular biology, and immunology. He also helped to establish federal guidelines on the Human Genome Project and has been an advocate for AIDS research.

Baltimore was born to Richard Baltimore and Gertrude Lipschitz. Baltimore traces his decision to become a molecular biologist back to high school, when he attended a summer program for scientifically gifted students at Jackson Memorial Laboratory in Bar Harbor, Maine. While there,

Baltimore was given the opportunity to interact with biologists and to conduct a few experiments of his own. He also met a future colleague, Howard Martin Temin, who at the time had just graduated from college and served as the “guru” of the group, according to Baltimore.

In 1956, Baltimore enrolled at Swarthmore College in Pennsylvania, and received a B.A. degree with high honors in for years time. He began graduate work at Massachusetts Institute of Technology (MIT) but transferred to the Rockefeller Institute, now called Rockefeller University, in New York City to work with Richard Franklin, a molecular biophysicist who specialized in animal viruses. By this time, Baltimore had focused his research on how an RNA virus, specifically poliovirus, multiplied in the cell.

After receiving his Ph.D. degree in 1964, Baltimore continued his research as a postdoctoral fellow at MIT and then studied at the Albert Einstein College of Medicine in New York City. In 1965, he accepted a position as research assistant at the Salk Institute for Biological Studies in La Jolla, California. While there, he worked with Renato Dulbecco, a virologist who had developed innovative laboratory techniques to research animal viruses. In 1968, Baltimore returned to MIT, where he was named associate professor of microbiology.

Baltimore had initially chosen to study the poliovirus, believing that all RNA viruses had the same replication system. In the late 1960's, however, scientists had demonstrated that poliovirus was not representative of all viruses and there were other replication systems. As Baltimore began classifying viruses according to their method of replication, he made the discoveries that led to his Nobel Prize in physiology or medicine. At almost the same time, Temin, working independently, made the same finding as Baltimore. The two scientists reported their discovery within days of each other and published papers in the June 1970 issue of the British journal Nature .

In 1964, Temin, then an associate professor at the University of Wisconsin in Madison, suggested that an RNA virus could replicate itself in the DNA of the host cell. Scientists criticized Temin's hypothesis because it went against conventional thought, which stated that genetic information passed in one direction, starting with DNA, then going to RNA, and finally to protein. Temin and Baltimore investigated how an RNA virus, which has no DNA, managed to pass its genetic information into the host cell. Both scientists found an enzyme that enabled the single-stranded RNA virus to replicate itself and thus become compatible with double-stranded DNA of the host cell.

Because this enzyme allowed genetic information to flow from RNA to DNA, it was called reverse transcriptase. For this discovery, Baltimore and Temin won the 1975 Nobel Prize in physiology or medicine, which they also shared with Dulbecco.

In 1972, Baltimore was appointed professor of biology at MIT. In the course of his research at MIT, Baltimore and his colleagues partially synthesized a mammalian gene, thus advancing the field of genetic engineering. A year later, Baltimore was named American Cancer Society Professor of Microbiology, an appointment that includes financial support for research throughout his life. From 1982 to 1990, he served as director of the Whitehead Institute for Biomedical Research at MIT. In 1990, he accepted the position as president of Rockefeller University, but, a year later, he was forced to step down from the post because of the controversy related to the investigation of scientist Thereza Imanishi-Kari.

In 1986, while Baltimore was still at MIT, Imanishi-Kari published a research paper outlining a theory about the immune system based on experiments she had conducted on mice. In addition to Imanishi-Kari, the paper listed five coauthors, including David Baltimore. Although the report suggested a nontraditional view of how the immune system works, it was the report's data, and not the theory, that sparked controversy. For the next 10 years, the integrity of Imanishi-Kari's work was questioned. Baltimore was never accused of any wrongdoing, but even so, his name would become inextricably associated with the longest-running U.S. investigation into scientific fraud.

When a postdoctoral student, Margot O'Toole, was unable to replicate Imanishi-Kari's results, O'Toole began to suspect that Imanishi-Kari had falsified data. O'Toole first notified the authorities at MIT. Two university review panels and the National Institutes of Health looked into the matter but found no evidence of unethical behavior on Imanishi-Kari's part. Representative John Dingell from Michigan persuaded the National Institutes of Health to reopen its investigation and initiated a congressional hearing. Dingell criticized Baltimore's handling of the situation, believing the scientist had not taken the allegations seriously enough. Dingell asked the Office of Scientific Integrity (which later was disbanded and replaced with the Office of Research Integrity, ORI) to examine the case. In 1994, the ORI found Imanishi-Kari guilty of 19 counts of scientific misconduct and recommended that she be barred from receiving any federal funding for 10 years.

After the 1994 ruling, Imanishi-Kari appealed her case to the research integrity adjudications panel of the Department of Health and Human Services. In 1995, the panel spent six weeks reading over 6,000 pages of testimony and reviewing 70 notebooks. In addition, for the first time, Imanishi-Kari was allowed to cross-examine her accusers. After reviewing all the evidence, the panel found that Imanishi-Kari had made errors but was not guilty of misconduct. The ruling vindicated Imanishi-Kari and Baltimore.

Within a year of the verdict, Baltimore's fortunes improved. He accepted the position as president of the California Institute of Technology in Pasadena and as chair of an Aids vaccine advisory committee at the National Institutes of Health.

Throughout his career, he has published more than 530 peer-reviewed papers. Much of his research in the 1980's was in the area of immunology and synthetic vaccines. In 1974, he became a member of the National Academy of Sciences and the American Academy of Arts and Sciences. He received the 1999 National Medal of Science for his work in virology, molecular biology, and immunology.

Baltimore has taken on a number of scientific causes. In the 1970's, when scientists and the public expressed concerns about potential hazards involved with gene-splicing procedures, he helped develop guidelines to ensure safety in the lab. A few years later, he lobbied equally as hard to have those regulations lessened as scientists grew more at ease with genetic research techniques. He also helped to establish federal guidelines on the Human Genome Project. He also has been an advocate for AIDS research and the race to find an AIDS vaccine.

While working at the Salk Institute, Baltimore met his future wife, Alice Shih-hou Huang, a microbiologist. The Baltimores married in 1968 and have one daughter.