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A controversial life

As he turns 90, Leonard Hayflick talks to George F Winter about his life.

Professor Leonard “Len” Hayflick was the first person to isolate Mycoplasma pneumoniae; the first person to develop cell strains of normal human fibroblasts; and in 2014 was co-recipient of the City of Philadelphia John Scott Award for his discoveries in aging, an award “given to the ‘most deserving’ men and women whose inventions have contributed in some outstanding way to the ‘comfort, welfare and happiness’ of mankind.”(1)

Yet Hayflick was described as “evil” by the Vatican.(2)

Currently professor of anatomy at the University of California, San Francisco, Hayflick celebrated his 90th birthday on 20th May this year. Here, he reflects on his life and times; from his early scientific development, to working as he says in the “golden age of virology”, to overthrowing dogma and courting controversy.

Early days

“My sister and I were raised in a terraced house in Philadelphia, Pennsylvania, during the Great Depression, so times weren’t easy. Aged nine, my scientific interest was aroused when an uncle bought me a chemistry set.” With Leonard and a friend exploring the chemistry of explosives, they acquired sodium. “There was a concreted area,” he recalls, “behind our house with holes for clothes-drying racks. One rainy day we threw small cubes of sodium into the holes. A minute later there was an explosion, and an orange flame shot out!”

After high school, in January 1946 Hayflick was accepted to study at the University of Pennsylvania, and after 18 months army service he majored in microbiology.

University and the Wistar Institute

Hayflick’s career was shaped when his adviser at university, Warren Stinebring took a course in cell culture at a hospital in New York State. “Under Stinebring I grew chick embryo tissue into which I introduced what at that time were called pleuropneumonia-like organisms (PPLOs). Today they're called mycoplasmas. As a master’s degree student, I did my research at the Wistar Institute ‒ on the University of Pennsylvania campus ‒ the oldest biological research institute in the United States. 

Gaining his doctorate in 1956, Hayflick accepted a post at the University of Texas: “We travelled to Galveston, my wife pregnant with the first of our five children. I worked in the microbiology department with the renowned cell culturist Charles M. Pomerat, who pioneered phase contrast time-lapse cine-microphotography, and I also met a cytogeneticist called Paul Moorhead, who played an important role in my career”. 

Golden age of virology

IIn 1958 Hayflick returned to the Wistar Institute, running its cell culture laboratory: “The director was Hilary Koprowski ‒ who I’d describe as a benevolent dictator ‒ and it’s a little-known fact that Koprowski was the first to produce and test a live poliovirus vaccine, contrary to the popular belief that it was Albert Sabin. I entered the field when cell culture was enjoying a renaissance, with the subsequent decade that I have called the golden age of virology.”

Hayflick’s daughter played an important role too: “Because my laboratory was close to the University of Pennsylvania Hospital, where my wife gave birth to our third child, Susan, I arranged with the obstetrician to obtain the placenta and amnion, which I cultured. After several weeks I noticed that these normal amnion cells had converted to an immortal cell population. I named the cell line WISH (Wistar Institute Susan Hayflick), which became popular.” 

Human diploid cell lines

Now investigating the role of viruses in human cancers, Hayflick sought normal human cells that could be cultured, and began working with aborted foetal tissue from the University of Pennsylvania Hospital, establishing a series of foetal diploid cell strains WI-1 to WI-25. The scientific dogma was that cultured cells, if properly treated, would replicate forever. But Hayflick found that after about fifty population doublings, the cells replicated more slowly before stopping, having reached what is now known as the Hayflick Limit: “I discovered that, upon freezing, and after reconstitution, the normal human foetal cells retained their ‘memory’ of what population doubling level they had attained upon freezing and, when thawed months or years later, replication continued until the maximum total of about fifty population doublings was reached. This suggested that normal human cells have a mechanism for counting DNA replications, an idea later confirmed by the 2009 Nobel laureates who discovered the molecular basis (telomere attrition) for my findings.” 

By determining that only normal cells are mortal, Hayflick established that only cultured cancer cells are immortal. Cell immortality was also celebrated in the 2009 Nobel awards for the awardees’ discovery of telomerase.  Hayflick interpreted his discovery as aging, or senescence, at the cellular level.

Overturning dogma

Would Hayflick and Moorhead confront established dogma? “Paul and I were young men, starting our careers,” says Hayflick. “George Gey, the man who established the HeLa cell line, warned, ‘Lenny, you're going to get yourself in a lot of trouble if you publish this.’ Further, the publicity-seeking fascist surgeon Alexis Carrel, working at the Rockefeller Institute in New York, claimed he had cultured cells from a chick heart for almost forty years, contradicting my observations. But we thought that Carrel had erred.”

Hayflick played a masterstroke: “I contacted three top cell culture experts ‒ including Harry Eagle, whose name is given to a widely used media formulation ‒ and they agreed to grow my cells. After six months they phoned: ‘Len, the cultures you sent us have stopped dividing.’ Well, I figured that if I'm wrong and go down in flames, I'll have important company.”

Hayflick and Moorhead submitted their paper to the Journal of Experimental Medicine … who rejected it, with (later to be) Nobel laureate Peyton Rous insisting that cells cultured properly in vitro would replicate indefinitely. “That was precisely the dogma,” recalls Hayflick, “we thought we’d torpedoed.” 

However, their paper was published, without alteration, in Experimental Cell Research (3), prompting a surge of interest in the biology of cellular aging and becoming one of the most cited papers in biomedical science.

Then disaster: “My recollection,” says Hayflick, “is that while the paper was in press our electrical freezer failed, and we lost everything. So I started another cell population called WI-26, since the first lost 25 were named WI one through 25. The WI-26 cell strain came from a male foetus and it was widely circulated, nationally and internationally.” In 1962, Hayflick, in collaboration with the UK’s Common Cold Research Unit, described a new rhinovirus isolated in WI-26 cells. (4)


“The suggestion I made,” recalls Hayflick, “that the finite lifetime of cultured normal cells relates to aging was dismissed by many as foolish, but it’s been confirmed thousands of times since, worldwide. The relationship that this work had to aging was then picked up by many people worldwide. However, those working in the field of the biology of aging in the 1960s were outside the scientific mainstream.” 

In 2007, Hayflick referred to a prevailing belief that resolving age-associated diseases will advance our understanding of the fundamental aging process: “It will not. The distinction between disease and aging is also critical for establishing science policy because although policy makers understand that the funding of research on age-associated diseases is an unquestioned good, they also must understand that the resolution of age-associated diseases will not provide insights into understanding the fundamental biology of age changes.”(5)

Interestingly, with Hayflick now aged 90, he revealed that his mother lived to the age of 106 years.

Leonard Hayflick in quotes

Because my laboratory was close to the hospital, where my wife gave birth to our third child, Susan, I arranged with the obstetrician to obtain the placenta and amnion, which I cultured.

George Gey, the man who established the HeLa cell line, warned, ‘Lenny, you're going to get yourself in a lot of trouble if you publish this.’

Well, I figured that if I'm wrong and go down in flames, I'll have important company.

My recollection is that while the paper was on press our electrical freezer failed, and we lost everything.

The suggestion I made that the finite lifetime of cultured normal cells relates to ageing was dismissed by many as foolish.

I put all my several hundred ampoules into a liquid nitrogen container and strapped it to the back seat of my Pontiac sedan. Two of my children sat next to it, and off we went to California.

"Had I patented the cells, I might own the world's supply of WI-38, which would make me sufficiently wealthy to buy London, I think"

Mycoplasma pneumoniae

With news of the sensitivity of Hayflick’s WI diploid cell strains to human viruses spreading, a researcher named Robert Chanock, at the National Institutes of Health (NIH), Bethesda, Maryland, visited the Wistar Institute and told Hayflick that Monroe Eaton was working at Harvard with his eponymous “Eaton Agent”, believing that it was an unknown virus and caused primary atypical pneumonia. “I said to Bob,” Hayflick remembers, “‘have you and Eaton considered PPLOs?’ And Bob said, ‘What are they?’ Well, he educated me about Eaton agent, I educated him about PPLOs and we decided that Bob would send me embryonated egg yolk in which this organism grew, and I would test it for mycoplasmas.”

While Hayflick was undertaking this work, his boss Hilary Koprowski appeared in the laboratory one day: “He was worried that I would spread mycoplasmas, and said ‘Len, I didn't hire you to work on mycoplasmas. I hired you to work on cell cultures, and I’d appreciate it much if you stopped your mycoplasma work.’ I disobeyed him. My isolation and identification of the new mycoplasma ‒ Mycoplasma pneumoniae ‒ was published in Proceedings of the National Academy of Sciences (6) and because it was an important discovery, it made the front page of the New York Times. Koprowski returned to my laboratory and reluctantly congratulated me.”

WI-38 cell line

IIn 1962, following a legal abortion at a Swedish hospital, the lungs from a female foetus were flown from Stockholm to Hayflick’s laboratory, where he established the WI-38 cell strain of the first “normal” human cells to provide licensed human virus vaccines against poliomyelitis, measles, mumps, rubella, varicella, shingles, adenovirus, rabies and hepatitis A.

Hayflick’s discovery happened to be made at the same time that primary monkey kidney cells used to manufacture poliomyelitis vaccines were found to be contaminated with simian viruses.

Last year a report estimated that the number of cases treated or averted with WI-38-related vaccines was 4.5 billion globally (7). But in a letter from the Vatican dated 9 June 2005, (now) Cardinal Elio Sgreccia questioned the ethics of parents using such vaccines on their children: “Would it not be a matter of true (and illicit) cooperation in evil, even though this evil was carried out forty years ago?” (2)

In this context it is perhaps noteworthy that the “evil” rubella vaccine has prevented many abortions worldwide.

Stakeholder controversy

But that was not the only controversial aspect of Hayflick’s WI-38s. “The cells,” says Hayflick, “couldn’t be patented because in the early 1960’s the patent laws in the United States and most other countries prevented patenting of living materials. So I delivered ampoules of WI-38 worldwide freely to most virus vaccine manufacturers. For instance, I set up with Dr Frank Perkins in London a repository for WI-38s that I brought in a liquid nitrogen container on board an aircraft, which is impossible today. The aluminium vessel looked like a 500-pound bomb.” 

Meanwhile, Hayflick was unaware that Koprowski had arranged with Wellcome Laboratories that in return for providing WI-38 cells, royalty payments would be made to support full members of the Wistar Institute. “Technically I wasn’t,” notes Hayflick, “a full member of the Institute, so to learn that my efforts would yield returns only to full members of the Wistar and not to me, was bothersome. I decided to leave, accepting a professorship at Stanford University, California.”

But what about Hayflick’s WI-38 ampoules? “I decided to take all the ampoules to Stanford until this matter was resolved, so that all stakeholders could have a say. The stakeholders were Paul Moorhead; the Wistar; the WI-38 embryo’s estate; myself; and although the government may have had a stake, that remained undetermined. It couldn’t be a decision made to favour a single stakeholder, so I put all my several hundred ampoules into a liquid nitrogen container and strapped it to the back seat of my Pontiac sedan. Two of my children sat next to it, and the third in the front seat, and off we went to California.”

Hayflick could not personally pay to distribute WI-38 cultures to hundreds of colleagues worldwide who requested them. He decided to charge the same amount as the American Type Culture Collection did to ship WI-38s. Hayflick’s untouched “Cell Culture Fund” totalled $66,000 by the mid-1970s, when he asked the NIH to determine ownership of these funds before accepting an offer to direct the newly established National Institute on Aging.  The NIH sent an accountant, with no biomedical background, examined Hayflick’s freely given documentation and accused him of having stolen the WI-38s which the accountant believed belonged to the federal government.  Eighty-three scientists disagreed (8).  

Hayflick sued the NIH/Food and Drug Administration and the Department of Health Education & Welfare, who confiscated the WI-38s in Hayflick’s absence. Following seven years of litigation, and with Hayflick’s career stalled, an out-of-court settlement was reached: “The ‘Cell Culture Fund’, now worth $90,000, was awarded to me and it all went deservedly to my lawyers, and I became the sole scientist in the United States legally entitled to ownership of the cells. Had I patented the cells I might own the world's supply of WI-38, which would make me sufficiently wealthy to buy London, I think.”


What advice, I asked Professor Hayflick, would he offer to biomedical scientists embarking on their careers? “The purpose of research,” he observes, “is to ask questions. Don’t be afraid to challenge accepted wisdom, and have the courage to defend your findings and, where necessary, to challenge accepted dogma.”

Advice we can all benefit from.




1. Rattan S. (2014) International recognition for ageing research: John Scott Award ‒ 2014 to Leonard Hayflick and Paul Moorhead. Biogerontology 15: 415. DOI 10.1007/s10522-014-9524-1  

2. Hayflick L. (2018) Personal Communication.

3. Hayflick L, Moorhead PS. (1961) The serial cultivation of human diploid cell strains. Exp Cell Res 25: 585‒621.

4. Tyrell DAJ, Bynoe ML, Buckland FE, Hayflick L. (1962) The cultivation in human-embryo cells of a virus (DC) causing colds in man. Lancet 2 (7251): 320‒322.

5. Hayflick L. (2007) Biological aging is no longer an unsolved problem. Ann N Y Acad Sci 1100: 1‒13.

6. Chanock RM, Hayflick L, Barile MF. (1961) Growth on artificial medium of an agent associated with atypical pneumonia and its identification as a PPLO. Proc Natl Acad Sci 48: 41‒49.

7. Olshansky SJ, Hayflick L. (2017) The role of the WI-38 cell strain in saving lives and reducing morbidity. AIMS Public Health 4(2): 127‒138.

8. Strehler BL, Abraham S, Bayreuther K et al. (1982) Hayflick‒NIH Settlement. Science 215 (4530): 240‒242.

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