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Thomas O’Brien Retires from the NCI

, by Jennifer K. Loukissas, M.P.P.

Headshot of Thomas O'Brien

Thomas R. O'Brien, M.D., M.P.H., senior investigator in the Infections and Immunoepidemiology Branch, retired from the NCI in September 2025 after 33 years of federal service. Dr. O’Brien is an internationally recognized expert in the transmission and natural history of oncogenic viruses, including human immunodeficiency virus type 1 and hepatitis C virus (HCV).

Dr. O’Brien’s research program targeted viruses that cause cancer through interdisciplinary studies that emphasized human genetics. He focused on studies with the potential to improve clinical practice or yield public health benefits. He organized a trans-disciplinary group of investigators to refine our understanding of the genetic basis for spontaneous HCV clearance and response to treatment for chronic hepatitis C. This collaboration led to the discovery of interferon lambda 4 (IFNL4), a novel gene that appears to underlie observed differences in HCV clearance (Prokunina-Olsson et al, Nature Genetics, 2013).  

In other work, he focused on hepatitis viruses, surveillance for hepatocellular carcinoma in the United States, and phenotypic expressions of the IFNL4 genotype.

Dr. O’Brien received undergraduate and medical degrees from the University of Michigan, Ann Arbor, and an M.P.H. from the Harvard School of Public Health, Boston, MA. He was an Epidemic Intelligence Service Officer and Medical Epidemiologist with the Centers for Disease Control and Prevention before joining the NIH Intramural Research Program in 1992.  

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