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Portrait of David Baltimore
Photo: Bob Paz · CC BY-SA 3.0 via Wikimedia Commons

Nobel Prize in Physiology or Medicine · 1975

David Baltimore

He found the enzyme that lets viruses write RNA back into DNA, a key to understanding and treating HIV.

The Nobel citation: “for their discoveries concerning the interaction between tumour viruses and the genetic material of the cell”
Born
March 7, 1938, New York, NY, USA
Died
September 6, 2025, Woods Hole, MA, USA
Shared with
Renato Dulbecco, Howard M. Temin
Affiliation at the time
Massachusetts Institute of Technology (MIT), USA

Medicine prize

1975

Shared with 2 other laureates.

Age that year

37years

Born in 1938.

Headline credited impact

538,000–568,000lives saved

AIDS deaths averted worldwide by antiretroviral therapy, whose main drug classes block reverse transcriptase. How it was built

Sources cited

37

Fact-checked September 24, 2026.

  • He was 37 when he shared the 1975 Nobel Prize for finding reverse transcriptase, the enzyme that copies RNA into DNA.
  • As a high-school student at a summer science camp in Maine, he met Howard Temin, a camp counselor who would later share his Nobel Prize.
  • When the US invaded Cambodia in 1970, in the middle of his reverse transcriptase experiments, he put his samples in the freezer and went to protest the war.
  • In 1986, when the US had no national AIDS plan, he co-chaired a national committee that urged the government to spend $1 billion on AIDS research.
  • His 1971 scheme for sorting viruses by how they make messenger RNA grew into the Baltimore classification, which today sorts viruses into seven groups.

The breakthrough

Reverse transcriptase: genetic information can flow from RNA back into DNA

In the 1960s biology had a firm rule, the central dogma: genetic information flows one way, from DNA to RNA to protein. DNA is the master copy and RNA the working copy. Yet some viruses that cause tumors in animals carry only RNA and still change the cells they infect for good. Howard Temin argued that they must copy their RNA into DNA and splice it into the cell's own genes. Most scientists doubted him. Baltimore had spent years studying the enzymes viruses use to copy their genes, and had just found one packed inside the particles of another virus, so he decided to look inside these tumor viruses too. In 1970, working first with a mouse leukemia virus and then with Rous sarcoma virus, he found an enzyme packed in the virus that builds DNA using RNA as its template. Temin and Satoshi Mizutani found the same thing at the same time, and the two papers appeared back to back in Nature. A Nature writer nicknamed the enzyme reverse transcriptase. Picture a library where books (DNA) are only ever photocopied into handouts (RNA). These viruses carry a machine that turns a handout back into a book and slips it onto the shelf, where it stays. The discovery showed that the one-way rule had exceptions and explained how this virus family, now called retroviruses, survives. The same enzyme later explained HIV and became a basic laboratory tool.[1],[3],[4],[6],[7],[8]

“Luckily, I had no experience in the field and so no axe to grind”
David Baltimore, Nobel Lecture, 12 December 1975, explaining why in 1970 he was willing to test Howard Temin's idea, then doubted by most scientists, that RNA tumor viruses copy their genes into DNA.[4]

What it meant for humanity

Reverse transcriptase mattered far beyond the chicken and mouse viruses where it was found. When AIDS appeared, researchers in Paris identified its cause in 1983 partly by detecting reverse transcriptase activity, the telltale sign of a retrovirus. The enzyme then became the first target for HIV drugs. AZT, which blocks it, became the first US-approved HIV medicine in 1987, and two of today's main drug classes still work by jamming this enzyme. Combination treatment turned HIV from a death sentence into a chronic condition. UNAIDS estimates that treatment has averted 26.9 million AIDS deaths, and 32.1 million people were taking it in 2025. Baltimore also pushed the public response: in 1986, when the US had no national plan, he co-chaired a National Academy of Sciences committee that urged a $1 billion AIDS research effort. The enzyme became a basic tool of biotechnology too. Copying messenger RNA into DNA let scientists isolate the working parts of genes, and the same step underlies RT-PCR tests used to track HIV, hepatitis C and COVID-19. In cancer, his lab showed that the protein made by the Abelson mouse leukemia virus is a tyrosine kinase, and later that the human BCR-ABL gene causes a disease closely resembling chronic myeloid leukemia in mice. That line of work helped lead to imatinib (Gleevec); in its main trial, 89 percent of patients were alive five years after diagnosis, compared with about 60 percent in earlier studies of interferon, the older treatment. His lab also built an early packaging cell line for making crippled, gene-carrying retroviruses, a type of tool later used in gene therapy.

  • UNAIDS estimates that HIV treatment has averted 26.9 million deaths since the epidemic began. In 2025, 32.1 million people were on antiretroviral therapy.[14],[15]
  • AZT, which blocks HIV's reverse transcriptase, became the first FDA-approved HIV medicine in March 1987. Two major drug classes, NRTIs and NNRTIs, work by blocking this enzyme.[12],[13]
  • HIV's discoverers spotted the virus in 1983 partly by detecting reverse transcriptase activity, a direct sign that a retrovirus was multiplying.[8],[11]
  • In 1986 he co-chaired the National Academy of Sciences and Institute of Medicine committee on a national AIDS strategy, which urged a $1 billion AIDS research effort.[6],[29]
  • Reverse transcriptase copies RNA into DNA, the first step of RT-PCR tests used to measure HIV and hepatitis C and to detect SARS-CoV-2, including in CDC's COVID-19 test.[8],[16]
  • His lab showed the Abelson leukemia virus protein is a tyrosine kinase and that human BCR-ABL causes a CML-like disease in mice, groundwork for the drug imatinib.[6],[17],[18],[19],[21]

Impact in numbers

Baltimore's main gift was knowledge: proof that genetic information can flow from RNA back into DNA, and the enzyme that does it. Its value spread in three directions. In medicine, it made HIV understandable and treatable; the first claim below gives him a small share of AIDS deaths averted by treatment, equal to Howard Temin's, and leaves most credit to those who found HIV, developed the drugs and delivered them. In biotechnology, reverse transcriptase became a standard tool for copying messenger RNA into DNA to clone genes and run RT-PCR tests; the second claim credits a very small share of sales of genetically engineered medicines, and diagnostics are not counted. In cancer, his lab's work on the ABL kinase fed into imatinib, counted with a small share. Not counted at all: his virus classification, his immunology discoveries such as NF-kB and the RAG genes, the institutions he built, and his leadership on the safety of recombinant DNA and human gene editing.

HealthFundamental scienceEconomy

Each number is the laureate’s credited share of a real-world outcome, cumulative to 2025. The whole outcome, the share of credit, and the reasoning are shown so you can check the arithmetic. Outcomes shared with other laureates are counted once on the impact page.

  • Medium confidenceRippleSourced totalHealth

    AIDS deaths averted worldwide by antiretroviral therapy, whose main drug classes block reverse transcriptase

    538,000–568,000

    lives saved, credited share

    That is 2% of 26.9–28.4 million lives saved since 1987.

    How this number was built

    Same outcome, range and share as the Howard Temin profile. Low: UNAIDS (2025 Global AIDS Update) says 26.9 million deaths have been averted through treatment since the epidemic began (data to 2024). High adds 2025: 2.1 million AIDS deaths at the 2004 peak minus 570,000 in 2025 = about 1.5 million, so 28.4 million (likely low, with 32.1 million on treatment). From 1987, when AZT was approved. Why reverse transcriptase: HIV was first recognized by reverse transcriptase activity (1983), and AZT and the NRTI and NNRTI classes block the enzyme. Share 0.02 (about 540,000-570,000): Baltimore and Temin found the enzyme independently and simultaneously (0.04 together), while HIV's discoverers, AZT's developers, later drug classes such as protease and integrase inhibitors, and treatment programs were essential.[7],[8],[11],[12],[13],[14],[15]

    Sources: UNAIDS; UNAIDS; The Nobel Assembly at Karolinska Institutet; US National Institutes of Health; Proceedings of the National Academy of Sciences; Molecular Biology of the Cell (American Society for Cell Biology); Nature

  • Low confidenceRippleModeledEconomy

    Cumulative global sales of genetically engineered non-antibody protein medicines (a proxy for economic activity)

    $7.5–10

    billion in economic value, credited share

    That is 0.5% of $1.5–2 trillion in economic value since 1982.

    How this number was built

    Same outcome, range and share as the Temin profile (range from the Berg, Kornberg and Luria profiles). Inputs: 2013 antibody sales (~$75B) were about half of biopharma sales, so non-antibody ~$75B (Ecker 2015); 2021 non-antibody originator proteins $53.6B and biosimilars $11.1B (Walsh 2022). Low: quadratic ramp 1982-2013 ($0.81T) + linear fall to $53.6B over 2014-21 ($0.50T) + flat 2022-25 ($0.21T) = ~$1.5T. High: linear ramp ($1.2T) + same later years + half of biosimilar sales (~$0.07T) = ~$2.0T. Nominal dollars; sales measure spending, not benefit. Share 0.005 (~$7.5-10B): reverse transcriptase makes cDNA, DNA copies of messenger RNA, a standard way to isolate and clone the protein-coding parts of genes. Baltimore shares it equally with Temin; restriction enzymes, ligase, vectors, expression systems and manufacturing were others' work.[6],[8],[33],[34]

    Sources: Nature Biotechnology; mAbs; Lasker Foundation; Molecular Biology of the Cell (American Society for Cell Biology)

  • Low confidenceRippleModeledHealth

    Chronic myeloid leukemia deaths averted by imatinib and later BCR-ABL kinase inhibitors, 2001-2025

    1,050–3,900

    lives saved, credited share

    That is 3% of 35,000–130,000 lives saved since 2001.

    How this number was built

    Range reused from the Harold Varmus profile so totals line up: CML deaths averted by BCR-ABL inhibitors (imatinib approved 2001), modeled from SEER US CML death rates against the last pre-imatinib level (0.65 per 100,000 in 1999-2000, held flat or falling 2% a year) versus about 0.30 since 2007, scaled to other high-income countries, plus a small allowance for poorer countries. Other targeted drugs are excluded, so this is a floor for the outcome. Imatinib's main trial: five-year survival 89% vs about 60% in earlier interferon studies. Share 0.03: Baltimore's lab showed in 1980 that the Abelson virus cancer protein is a tyrosine kinase and in 1990 that human BCR-ABL alone causes a CML-like disease in mice, pinpointing the drug target (credited by the Lasker Foundation). Nowell, Rowley, Hunter, Witte, Druker, Lydon, Sawyers and Novartis chemists were also essential.[2],[6],[17],[18],[19],[20],[21]

    Sources: National Cancer Institute, SEER Program; Lasker Foundation; National Cancer Institute; Nature; Science (PubMed record); Lasker Foundation; NobelPrize.org (Nobel Foundation, from Les Prix Nobel 1975)

  • Medium confidenceRippleSourced totalHealth

    Children spared HIV by antiretroviral drugs given to their mothers, 2000-2024

    62,000–128,000

    people benefited, credited share

    That is 2% of 3.1–6.4 million people benefited since 2000.

    How this number was built

    UNAIDS (Global AIDS Update 2025): programmes to prevent vertical transmission averted nearly 4.4 million [3.1-6.4 million] HIV infections in children in 2000-2024; low and high are that range (UNICEF gives the same 4.4M). Rich-country use from 1994 and 2025 excluded. Counterfactual: no drug prophylaxis. Chain: the first proof, PACTG 076 (1994), showed zidovudine, a reverse-transcriptase blocker, cut transmission from 25.5% to 8.3%; single-dose nevirapine and today's triple therapy, built on two such drugs, followed. Counts children never infected, so it is disjoint from the treatment claim, which counts deaths among people living with HIV. Share 0.02, same as Temin: Baltimore and Temin found the enzyme independently and at the same time (0.04 together); HIV's discoverers, drug makers, trialists and programmes did the rest.[8],[12],[14],[35],[36],[37]

    Sources: UNAIDS; UNICEF; New England Journal of Medicine, via PubMed; UNAIDS; US National Institutes of Health; Molecular Biology of the Cell (American Society for Cell Biology)

The double edge

Reverse transcriptase itself harmed no one, but Baltimore's career included serious controversies. The largest, often called the Baltimore affair, began in 1986, when a junior scientist, Margot O'Toole, questioned data in an immunology paper he had co-written with Thereza Imanishi-Kari. Baltimore stood by the paper for years. In 1991 a draft NIH report accused Imanishi-Kari of fabricating data and criticized his handling of the challenge. He joined most co-authors in retracting the paper, acknowledged he had accepted her explanations too readily, and resigned as president of Rockefeller University that December. In 1996 a federal appeals panel found the charges against her unproven. Retroviral tools also carry risks: in a French gene-therapy trial, gene-carrying retroviruses of the kind his lab helped pioneer later triggered leukemia in 4 of 9 successfully treated children, one of whom died. In 2005 MIT fired a former postdoc from his lab for fabricating data. And in 2021 he said he regretted a remark, widely cited by lab-leak proponents, that seemed to treat a feature of the COVID-19 virus as proof of a lab origin.

  • Moderate

    The Imanishi-Kari affair

    In 1986 Margot O'Toole, a postdoc in Imanishi-Kari's lab, questioned data in a Cell paper Baltimore co-wrote. He defended it until a 1991 draft NIH report accused Imanishi-Kari of fabrication and faulted his response. He joined in retracting the paper, said he had not checked her data enough, and resigned as Rockefeller's president. A 1996 federal panel found the charges unproven.[24],[25],[26]

  • Moderate

    Gene-therapy vectors that caused leukemia

    In 1983 his lab built a packaging cell line to make crippled retroviruses that carry genes but cannot multiply on their own, a basic gene-therapy tool. In a French trial, similar vectors successfully treated 9 of 10 children with an inherited immune disease, but 4 of the 9 later developed leukemia, and one of them died.[22],[23]

  • Minor

    Fabricated data by a former postdoc

    MIT fired Luk Van Parijs in 2005 after he admitted fabricating and falsifying data. He had trained in Baltimore's lab at MIT and Caltech, and Caltech was examining two 1999 papers from that period. Baltimore said follow-up work in his lab had confirmed much of Van Parijs's research.[27]

  • Minor

    A regretted remark on COVID-19's origin

    In 2021 a much-cited magazine article quoted Baltimore saying a feature of the COVID-19 virus's genome strongly challenged a natural origin. He later said he should have softened his wording, that the feature did not prove a lab origin, and that he could not rule out either explanation.[28]

Against the odds

Baltimore grew up in comfort, and no source we found describes antisemitism aimed at him personally. His family's story began in hardship. His father, Richard, grew up very poor in New York. He was orphaned at about 14 after having only one parent for most of his childhood, mostly because of tuberculosis, and his sisters left school to work so that he could finish high school, where his education ended. He and Baltimore's mother then made a living in the city's garment trade, even through the Depression. The wider climate for American Jews in Baltimore's youth was less welcoming. From the 1920s most US medical schools capped Jewish admissions, and the quotas were still entrenched in 1945. Columbia and Yale universities had explicit quotas from 1918 and 1920, and a New York State inquiry found that Jewish applicants were being selectively turned away from Columbia's and Cornell's medical schools. The quotas faded after the war and were gone by 1970. Pressure showed in smaller ways too: Baltimore recalled that the mother of Jack Whitehead, who later funded the Whitehead Institute, had changed the family name from Weisskopf so it would seem less Jewish. Baltimore himself moved through Swarthmore, MIT and Rockefeller with no recorded barrier, as those old exclusions were falling away.

  • —

    Poverty

    His father grew up very poor in New York, orphaned at about 14 and with only one parent for most of his childhood, mostly because of tuberculosis. His sisters left school to work so he could finish high school, which was the end of his formal education.[5]

  • —

    Quota

    Baltimore grew up while most US medical schools still capped Jewish admissions; Columbia and Yale had explicit quotas from 1918 and 1920. The quotas faded after World War II and were gone by 1970. No source says they affected his own path.[31],[32]

Jewish background

Jewish fatherCulturally Jewish

Baltimore was born in New York to Richard and Gertrude Baltimore. His father was raised as an Orthodox Jew and chose Orthodox synagogues as an adult; his mother was a committed atheist who respected her husband's faith. The family kept the major Jewish holidays and fasted on Yom Kippur, and David walked with his father to synagogue and had a bar mitzvah. He said he left religion behind the day after his bar mitzvah, and when his interviewer suggested that his tie to Judaism was cultural, he agreed; afterward he rarely went to synagogue except for events such as weddings. The sources we found describe his mother's beliefs but not her religious background.[5]

Key dates

  1. March 7, 1938

    Born in New York City to Richard Baltimore, who worked in the garment trade, and Gertrude Baltimore, later a psychology professor.[1],[5]

  2. 1955

    Spends a summer at the Jackson Laboratory in Bar Harbor, Maine, where Howard Temin is a counselor; the experience turns him toward biology.[2],[5],[8]

  3. 1964

    Earns his PhD at Rockefeller in New York, studying how viruses make RNA.[2],[4]

  4. 1968

    Joins MIT as associate professor of microbiology after two and a half years at the Salk Institute.[2]

  5. June 27, 1970

    Reports in Nature an enzyme in RNA tumor viruses that copies RNA into DNA, back to back with a matching paper by Temin and Satoshi Mizutani.[7],[8]

  6. 1971

    Proposes sorting animal viruses by how they make messenger RNA, the scheme now called the Baltimore classification.[9],[10]

  7. October 1975

    Awarded the Nobel Prize in Physiology or Medicine at 37, shared with Temin and Renato Dulbecco.[1],[3],[6]

  8. 1980

    With Owen Witte, shows the Abelson leukemia virus protein adds phosphate to the amino acid tyrosine, a kind of enzyme activity imatinib would later block.[6],[17],[19]

  9. 1982

    Becomes founding director of the Whitehead Institute for Biomedical Research at MIT.[6],[29]

  10. 1986

    Co-chairs the National Academy of Sciences and Institute of Medicine committee on a national strategy for AIDS.[6],[29]

  11. December 1991

    Resigns as president of Rockefeller University, a post he took in 1990, amid controversy over a retracted 1986 paper.[25],[29]

  12. October 15, 1997

    Becomes president of Caltech, serving until 2006.[29],[30]

  13. 2015

    Chairs the first International Summit on Human Gene Editing, and the second in 2018.[6]

  14. September 6, 2025

    Dies in Woods Hole, Massachusetts, aged 87.[1],[2]

Sources

  1. 1.David Baltimore - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.David Baltimore - Biographical (with 2005 addendum) · NobelPrize.org (Nobel Foundation, from Les Prix Nobel 1975), 1975
  3. 3.The Nobel Prize in Physiology or Medicine 1975 - Press release · Karolinska Institutet / NobelPrize.org, 1975
  4. 4.Viruses, Polymerases and Cancer (Nobel Lecture, 12 December 1975) · NobelPrize.org (Nobel Foundation), 1975
  5. 5.David Baltimore Oral History Interview (interviewed by Sara Lippincott, October-November 2009) · Caltech Archives Oral History Project, 2009
  6. 6.Fundamental discoveries, academic leadership, and public advocacy (2021 Lasker~Koshland Special Achievement Award: David Baltimore) · Lasker Foundation, 2021
  7. 7.Viral RNA-dependent DNA polymerase: RNA-dependent DNA polymerase in virions of RNA tumour viruses (Baltimore D), Nature 226:1209-1211 · Nature, 1970
  8. 8.50th anniversary of the discovery of reverse transcriptase (Coffin JM), Molecular Biology of the Cell 32(2):91-97 · Molecular Biology of the Cell (American Society for Cell Biology), 2021
  9. 9.Expression of animal virus genomes (Baltimore D), Bacteriological Reviews 35(3):235-241 · Bacteriological Reviews (American Society for Microbiology), 1971
  10. 10.Baltimore classification (ViralZone) · SIB Swiss Institute of Bioinformatics
  11. 11.The Nobel Prize in Physiology or Medicine 2008 - Press release · The Nobel Assembly at Karolinska Institutet, 2008
  12. 12.FDA-Approved HIV Medicines (HIVinfo fact sheet) · US National Institutes of Health
  13. 13.3'-Azido-3'-deoxythymidine (BW A509U): an antiviral agent that inhibits the infectivity and cytopathic effect of HTLV-III/LAV in vitro (Mitsuya H, ... Broder S), PNAS 82:7096-7100 · Proceedings of the National Academy of Sciences, 1985
  14. 14.Countries must urgently step up to transform their HIV responses amid an international funding crisis that risks millions of lives (2025 Global AIDS Update press release) · UNAIDS, 2025
  15. 15.Global HIV & AIDS statistics - Fact sheet (2025 data) · UNAIDS, 2026
  16. 16.CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel: Instructions for Use · US Centers for Disease Control and Prevention (via US Food and Drug Administration), 2023
  17. 17.Abelson murine leukaemia virus protein is phosphorylated in vitro to form phosphotyrosine (Witte ON, Dasgupta A, Baltimore D), Nature 283:826-831 · Nature, 1980
  18. 18.Induction of chronic myelogenous leukemia in mice by the P210bcr/abl gene of the Philadelphia chromosome (Daley GQ, Van Etten RA, Baltimore D), Science 247:824-830 · Science (PubMed record), 1990
  19. 19.Molecularly targeted treatments for chronic myeloid leukemia (2009 Lasker~DeBakey Clinical Medical Research Award: Druker, Lydon, Sawyers) · Lasker Foundation, 2009
  20. 20.Cancer Stat Facts: Leukemia - Chronic Myeloid Leukemia (CML) · National Cancer Institute, SEER Program
  21. 21.How Imatinib Transformed Leukemia Treatment and Cancer Research · National Cancer Institute
  22. 22.Construction of a retrovirus packaging mutant and its use to produce helper-free defective retrovirus (Mann R, Mulligan RC, Baltimore D), Cell 33:153-159 · Cell (PubMed record), 1983
  23. 23.Insertional oncogenesis in 4 patients after retrovirus-mediated gene therapy of SCID-X1 (Hacein-Bey-Abina S et al.), Journal of Clinical Investigation 118:3132-3142 · Journal of Clinical Investigation, 2008
  24. 24.Thereza Imanishi-Kari, Ph.D., DAB No. 1582 (Research Integrity Adjudications Panel decision, 21 June 1996) · US Department of Health and Human Services, Departmental Appeals Board (Internet Archive copy), 1996
  25. 25.David Baltimore's Final Days, Science 254:1576-1579 (13 December 1991) · Science (AAAS), archived copy, 1991
  26. 26.Fraud charge leaves a career in shambles (Judy Foreman, 6 May 1991) · The Boston Globe, archived copy, 1991
  27. 27.More doubts raised on fired MIT professor (29 October 2005) · The Boston Globe, 2005
  28. 28.A Nobel laureate backs off from claiming a 'smoking gun' for the COVID-19 lab-leak theory (Michael Hiltzik, 8 June 2021) · Los Angeles Times, 2021
  29. 29.Nobel Prize-winning Biologist David Baltimore Named President of the California Institute of Technology · California Institute of Technology, 1997
  30. 30.Baltimore to Retire as Caltech President; Will Remain at Institute as Biology Professor · California Institute of Technology, 2005
  31. 31.Why Did the United States Medical School Admissions Quota for Jews End? (Halperin EC), American Journal of the Medical Sciences 358:317-325 · American Journal of the Medical Sciences (PubMed record), 2019
  32. 32.Jewish American Heritage Month: The Forgotten History of Quotas in American Medical School Admissions · Himmelfarb Health Sciences Library, George Washington University, 2023
  33. 33.Biopharmaceutical benchmarks 2022 (Walsh G, Walsh E), Nature Biotechnology 40:1722-1760 · Nature Biotechnology, 2022
  34. 34.The therapeutic monoclonal antibody market (Ecker DM, Jones SD, Levine HL), mAbs 7(1):9-14 · mAbs, 2015
  35. 35.AIDS, crisis and the power to transform: UNAIDS Global AIDS Update 2025 · UNAIDS, 2025
  36. 36.Reduction of maternal-infant transmission of human immunodeficiency virus type 1 with zidovudine treatment (Connor EM et al., PACTG 076, N Engl J Med 331:1173-1180) · New England Journal of Medicine, via PubMed, 1994
  37. 37.Fast Facts: World risks reversing HIV progress as children continue to face treatment gap (27 November 2025) · UNICEF, 2025

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 6 corrections made. How we check

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