Download CR75th Anniversary Commentary

CR 75th Anniversary Commentary
Special Lecture
We Are Standing on the Shoulders of Giants
Anton Berns
See related article by Olson, Cancer Res 1941;1:384-92.
Being asked to write a commentary on an article published in
the first volume of Cancer Research (1), celebrating its 75th
anniversary, I said somewhat reluctantly "yes" after going over
my other commitments. But after taking the effort to read the
article by Carl Olson published in 1941 and trying to put it in the
context of the time, it was the most rewarding span of time I have
devoted to a commentary in quite some time. If I was the "God of
Scientists," I would impose a new commandment next to the
others that I had already implemented, such as complete honesty,
making sure that the data in the article are rock solid, giving
appropriate credit to both colleagues and competitors in the field,
not claiming discoveries that are insufficiently substantiated or
were already made by others, and imposing a maximum of 5
articles per year as a senior author. I would, in addition,
demand that after every 10 articles published, one should write
a commentary on an article published 40þ years ago and point
out its relevance for the field. It would help to not only
recognize the importance of the work done in the past, but
also enhance our appreciation for the ingenuity and robustness
of the work of our predecessors and therefore an incentive to
maintain similar high standards in our research practices.
Let us look at the article published by Carl Olson in the first
volume of Cancer Research in 1941. No cloning, no PCR, no
Eppendorf tubes, no restriction enzymes, but yes, a microscope,
a shelf with chemicals, glassware, benches, a Bunsen burner, and
cages with chickens, rats, and mice were probably the most critical
armature. From the description of how they monitored their
animals it is also evident that they handled their animals with
great care without being under the scrutiny of animal right
activists.
The experiments conducted by Olson that focused on the
propagation of lymphoid tumors by consecutive graft experiments were inspired by the problems encountered in chicken
farms. With the increase in their scale, infectious diseases became
a serious problem. Understanding the exact nature of the infectious agents, being either Rous Sarcoma virus, Leukosis virus, one
of the other oncogenic retroviruses, or Marek disease virus was still
far away, but the foundation that made it possible to characterize
these "agents" was laid down in the first half of the 20th century.
Some important milestone work preceded the work published by
Carl Olson in 1941. Peyton Rous showed three decades earlier
that a cell-free filtrate from chicken tumors could transmit sarcomas to chickens (2), the first demonstration that not only chemicals, such as tar, can cause cancer but also cell-free extracts from
The Netherlands Cancer Institute, Amsterdam, the Netherlands.
Note: Anton Berns is senior group leader and director emeritus of the Netherlands Cancer Institute in Amsterdam.
Corresponding Author: Anton Berns, Netherlands Cancer Institute, Plesmanlaan 121, Amsterdam, 1066 CX, Netherlands. Phone: 312-0512-1991; Fax: 312-05122011; E-mail: [email protected]
doi: 10.1158/0008-5472.CAN-16-1870
Ó2016 American Association for Cancer Research.
some tumors can do this. Interestingly, at that time, neither
Peyton Rous nor Carl Olson seemed particularly excited by the
observation that cell-free extracts rather than a cell suspension
could transfer the disease, even though it yielded Rous the Nobel
Prize 45 years later, but then I realized what could, overthinking
what was known at the time, have been the "next experiment" to
further identify such agent? Not so obvious. Furthermore, there
was much disbelief among his peers that a cell-free extract could
cause cancer. The transmission of disease itself was considered
more relevant than whether this was achieved through a cellcontaining suspension or a cell-free extract. Cell culture was not
yet established, except the temporary outgrowth of cells from the
amphibian embryo in a culture as described by Ross Granville
Harrison in the first decade of the last century. Biological activity
could only be demonstrated in animals.
So what about Olson? Carl Olson, born in 1910 in Sac City, IA,
worked at the Department of Veterinary Science at Massachusetts
State College. Later, he would join the Department of Veterinary
Science at the University of Wisconsin where he continued work
on papilloma viruses and sarcomatoid tumors. In the thirties, he
became intrigued by leukosis that was ravaging chicken farms.
This led to the research that he published in 1941 in Cancer
Research. At that time, it was unclear how the disease was transmitted. Although several investigators had been able to propagate
tumors in chickens, mostly by cell-containing or cell-free filtrates
(the "agent"), this resulted in a range of pathologies, from tumors
such as lymphocytoma, leukosis, erythroblastosis, and sarcoma to
paralysis, the latter caused by Marek Herpes virus as was found out
later. The tumor descriptions given by the different investigators
were not unequivocal and created quite some confusion. In part,
this was certainly due to the range of different viruses involved,
each giving rise to distinct tumors. In the article published in
Cancer Research, Olson describes in meticulous detail how he
propagated a lymphoid tumor carried by a chicken brought to the
laboratory. It did regard a crossbreed between a Rhode Island Red
female and a Barred Plymouth Rock male purchased from a
commercial hatchery. The "patient" was carefully followed by
regularly measuring the blood count, temperature, and weight.
Actually, the blood count numbers remained rather normal over
time, with short episodes of deviating values. However, at the
205th day, the chicken was sacrificed after it became seriously ill
and was unable to stand. A number of small gray nodules were
found in the liver and spleen next to a large 4.5-cm tumor mass
dorsal to the cloaca. Olson provided a detailed necropsy report.
This tumor was the starting material for subsequent grafting
experiments. Much care was given to assure aseptic handling of
the tissue to prevent contamination. Cell suspensions were inoculated in the breast muscle of the recipient chicken of different
ages. Thirty (!) consecutive passages were performed over several
years. This finally resulted in 443 inoculated chickens, of which
300 showed tumor growth, 133 tumor regression, 116 only local
growth, and 51 both local growth and metastasis. These were
laborious experiments but did show trends that over time became
significant thanks to the sheer numbers. Olson noted that the
interval between passages decreased in subsequent passages,
going from an average of approximately 25 days during the first
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4307
CR 75th Anniversary Commentary
10 passages to 16 days during passage 20–30. Inoculation in older
chickens showed a higher propensity of regression, probably
relating to a more effective immune response. The local growth
of the tumor and subsequent experiments conducted by Olson
and published in 1944 (3) in a follow-up article in Cancer Research
suggest that the transplanted tumor cells were expanding in the
recipient chickens rather than the cells producing the "agent" that
subsequently infected the host thereby giving rise to tumors of
host origin. In the discussion, he pointed out: "the transmissible
neoplasm is unlike any other transmissible tumor described in the
chicken."
When reading the article, it became evident how our way of
writing articles has changed over time. Olson does give a very
detailed account of his experiment, much more so than we are
accustomed to today. He mentions the problem chicken farms
have with disease outbreaks but does not use this as a reason
why he did this experiment. He also does not elaborate on the
significance of the rather endless propagation of the same cell
line, and how to interpret the observation that a fraction of the
chicken showed tumor regression after initial growth. But the
experimental description warrants that anyone could repeat the
experiment if provided with the same cell suspensions and
recipient strains. The great care with which he conducted his
experiments and the modesty in drawing conclusions are
exemplary.
The other aspect that is apparent is the patience to perform the
graft experiments over such extended period. One realizes this
even more acutely when reading the article he published in 1944
with the description of an additional 3 years of tumor propagation
with gradually increasing aggressiveness of the tumor and higher
take rate when transferred every 10 days rather than a longer time.
What is the meaning of this work for us? Why is this important?
Well, Olson's work is part of the broader effort to propagate
tumors and cells in vivo and in vitro, thereby laying the groundwork
for the identification of the "agents" that causes leukosis and
sarcomas in chickens.
Retroviruses and in particular the oncogenic retroviruses of
chicken have been instrumental for the major advances that were
made in the seventies and eighties in our understanding of the
nature of cancer-causing genes. The efforts of investigators from
these early days, Ellermann, Rous, Furth, Harrison, Claude, Murphy, Olson, and many others, made it possible that retroviruses
were isolated and characterized. They did set the stage for the
breakthroughs that followed: the overturn of the dogma that
genetic instructions flow from DNA to RNA to protein with the
discovery of reverse transcriptase by Temin and Baltimore, and the
subsequent identification of viral oncogenes and the recognition
that they originated from a cellular counterpart that can drive
tumorigenesis when mutated or aberrantly expressed, another
major revolution in our thinking thanks to the groundbreaking
work of Varmus and Bishop. Both Temin and Baltimore as well as
Varmus and Bishop received Nobel prizes for their discoveries, as
did Rous. Without the work that provided the basis for virus
propagation, isolation, and tissue culture techniques, the farreaching breakthrough discoveries in the 1970s and 1980s could
not have been made. Applications that make a difference for
human health often follow much later. Already in the fifties, the
capacity to propagate cells in vitro made it possible to produce the
polio vaccine and the research on retroviruses, receiving much
support because of their suspected involvement in human cancer,
allowed investigators to rather quickly identify HIV as the agent
causing AIDS. It illustrates that "translational research" is not a
recent invention. It also shows that worthwhile applications
follow unexpected discoveries that are the result of curiositydriven research often performed in unrelated areas and mostly
focused on learning how nature works rather than trying to make
science immediately applicable—an important lesson we should
keep in mind.
With the knowledge of today, one might think that the experiments Olson did were simple in concept, being fully focused on
tumor propagation without drawing major conclusions. However, if we try to imagine how little was known at that time, and how
it did set the stage for what was going to come, our predecessors
did pretty well and were as excited about their experiments as we
are about ours. As Olson wrote in 1975 in a review (4) citing
Claude Bernard: "Those who do not know the torment of the
unknown cannot have the joy of discovery."
What happened to Carl Olson? From Boston, he relocated to
the veterinary institute at Wisconsin continuing work on avian
leukosis and papillomaviruses. There, his laboratory discovered
the bovine leukosis virus that subsequently served as a model for
HIV. After his retirement in 1981, he remained active in research
for many years. He received many awards for his work. He died on
February 28, 2002 at the age of 91 years, leaving behind a career as
an internationally respected veterinary pathologist and a pioneer
in cancer research, one of the many giants on whose shoulders we
stand.
In writing this commentary, I was struck by the poor accessibility of the old scientific literature. In some cases, it takes a small
fortune as some publishers exploit the fact that libraries did not
retain their old journal volumes. This is a shame.
Received July 8, 2016; accepted July 8, 2016; published OnlineFirst August 1,
2016.
References
1. Olson C Jr. A transmissible lymphoid tumor of chicken. Cancer Res 1941;
1:384–92.
2. Rous P. A sarcoma of the fowl transmissible by an agent separable from the
tumor cells. J Exp Med 1911;13:397–411.
4308 Cancer Res; 76(15) August 1, 2016
3. Olson C Jr. The serial passage of an avian lymphoid tumor of the chicken.
Cancer Res 1944;4:707–12.
4. Olson C. Avian leukosis - historical perspectives. Avian Diseases 1975;
19:277–80.
Cancer Research
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We Are Standing on the Shoulders of Giants
Anton Berns
Cancer Res 2016;76:4307-4308.
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