Dr. Flossie Wong-Staal was the first scientist to clone H.I.V. and determine the function of its genes. Her work is now being deployed in the fight against the Covid-19.Credit...Bill Branson
 
A molecular biologist, that helped establish the virus as the cause of AIDS, then cloned it and took it apart to understand how it evades the immune system.

 Flossie Wong-Staal, a molecular biologist who helped establish H.I.V. as the cause of AIDS, revealed the virus’s inner-workings by cloning it and then laid the foundation for treatments, died on July 8 in San Diego. She was 73.Her death, at Jacobs Medical Center in the La Jolla section of the city, was caused by complications of pneumonia not related to Covid-19, her husband, Jeffrey McKelvy, said.

 Her former colleague Robert C. Gallo said Dr. Wong-Staal was a “whiz kid” in molecular biology when she went to work for the National Institutes of Health in the 1970s, adept at manipulating the components of living things like DNA and proteins. Calm and collected, she produced dozens of groundbreaking papers amid personal and professional turmoil in the lab at a time when Dr. Gallo, its leader, was caught up in investigations over his disputed claim to have discovered H.I.V. Dr. Wong-Staal was a member of the National Academy of Medicine and was inducted into the National Women’s Hall of Fame last year. Her work was so prolific and influential that the magazine "The Scientist" named her the most cited female scientist of the 1980s.

 “Flossie was the best of the best,” Dr. Gallo said in an interview.
 Dr. Wong-Staal joined Dr. Gallo after he had started studying what was then considered an obscure class of viruses known as retroviruses. Unlike ordinary viruses, retroviruses invade the cellular nucleus and insert their genes into the DNA of their hosts. Retroviruses had been observed in birds and mice but not humans, and Dr. Gallo’s research was ridiculed at first.
 
He soon discovered the first human retrovirus, called HTLV-1, which caused a kind of leukemia in humans. Dr. Wong-Staal went to work studying its various parts and how the virus interfered with human DNA to activate certain cancer-causing genes called oncogenes. Her work contributed to the broader understanding of the role of oncogenes in cancers not associated with viruses.

 In a strange coincidence, a year after HTLV-1 was discovered, Dr. Gallo and Dr. Wong-Staal suspected that another human retrovirus might be the cause of a new disease that was spreading in the gay community and elsewhere. Eventually called AIDS, the mysterious disease had many traits in common with HTLV-1: Both were transmitted sexually, through blood or from mother to child, and both infected T-cells, a type of white blood cell.

 Dr. Gallo and Dr. Wong-Staal turned out to be right, but they were not alone. While Dr. Gallo and a French group led by Luc Montagnier were locked into a protracted fight over who got credit for discovering H.I.V., Dr. Wong-Staal moved the science forward by figuring out how the virus worked.



 She took the virus apart, probing its genes and proteins to see what each component did. One protein became the target of the drug AZT; another became the target of a class of drugs known as protease inhibitors.
 

In Dr. Gallo’s 1991 book, “Virus Hunting,” Dr. Wong-Staal was quoted as saying: “Working with this virus is like putting your hand in a treasure chest. Every time you put your hand in, you pull out a gem.”
 

Her virology work is now being deployed in the fight against the novel coronavirus.

 “H.I.V. research built a strong foundation for Covid-19 research,” said David Ho, a Columbia University virologist, who directs the  Aaron Diamond AIDS Research Center there. “It’s why things are moving so fast on the vaccine front and the antibody front, as well as the development of drugs.”