In December of 2009, the paper "TGF beta in the
context of an inflammatory cytokine milieu supports de novo
differentiation of IL-17-producing T cells," (Veldhoen
M, et al., Immunity 24(2): 179-89,
February 2006) was named aCurrent
Classicin the field of Immunology. At
present, the paper ranks among the top 100 Highly Cited
Papers in this field in
Essential Science IndicatorsSMfrom
Thomson
Reuters, with 766 citations up to
October 31, 2009. In theWeb of Science®,
this paper currently shows 837 citations.
Lead author Dr. Marc Veldhoen is Senior Investigator in the
Stockinger Group, Division of Molecular Immunology at the National
Institute for Medical Research, London. In March 2010, Dr. Veldhoen will be
a Principal Investigator in the Lymphocyte Development and Activation
Laboratory at the Babraham Institute, Cambridge. His record in our database
includes 12 papers cited a total of 1,272 times.
In this interview, ScienceWatch.com talks with Dr. Veldhoen
about this paper and the impact it had on the research community.
What factors prompted you and your
coauthors to undertake this study?
The start of what ultimately resulted in the highlighted paper was two
papers published in 2003, the year I obtained my Ph.D.
This was at a time when many so called co-culture experiments, an in
vitro culture system consisting of undifferentiated T cells,
regulatory T cells (Treg) and dendritic cells (DC), were used to establish
the suppressive activity of Treg. Pasare and Medzhitov showed in a 2003
Science paper that the suppressive activity of Treg cells was
blocked when pathogen recognition receptors were stimulated on DC. Having
performed several of these experiments myself, I certainly agreed with the
observations made in this paper, but not with its conclusions. The readout
for the suppressive activity of Treg is the failure of the undifferentiated
T cells to proliferate, which is overcome when pathogen recognition
receptors are stimulated. However, this was not the only readout I was
using myself.
"Our data that TGF-beta, a cytokine widely thought of
as immune suppressive and anti-inflammatory, was involved
in driving the differentiation of this T cell came as a
surprise."
Since the mid-1980s, the undifferentiated T cells were known, upon
activation followed by proliferation, to be able to differentiate into two
effector stages; type I T cells (Th1), principally involved in immunity
against intracellular micro-organisms, and identified by their production
of interferon (IFN)-?, and type II (Th2) are instrumental in the fight
against parasites and identified by their production of interleukin (IL)-4.
In the presence of Treg the undifferentiated cells fail to proliferate, and
hence do not differentiate to effector cells. Using the production of IFN-?
and IL-4 as an additional read-out in my co-culture experiments I was
surprised to observe that in the presence of microbial products and despite
rapid proliferation of the undifferentiated T cells, these cells failed to
produce either IFN-? or IL-4. This was counterintuitive since it would be a
metabolic waste to have cells proliferate that have no function to perform.
In a second paper in 2003 published in Nature, Cua and colleagues
demonstrated that in the mouse model for multiple sclerosis, experimental
autoimmune encephalomyelitis (EAE), which had previously been thought to be
due to aberrant Th1 responses, it was not a factor (IL-12) involved in Th1
differentiation that was important but another cytokine, IL-23.
Interestingly the absence of IL-23 seemed to correlate with the absence of
T cells producing yet another cytokine; IL-17.
Although there was no direct relation between cells proliferating in the
presence of Treg, microbial products and IL-17 or IL-23, it was tempting to
speculate that the proliferating T cells, not belonging to the two known
effector subsets, might be producing IL-17 and constitute a third lineage
of effector T cells.
How was it conducted, and what were your
findings?
The crucial test here was to show that the undifferentiated cells,
co-cultured in the presence of DC, Treg, and microbial products, do have an
effector function. Prompted by the Cua and colleagues paper, which
highlighted the previously underappreciated cytokine IL-17, these cells
were first tested for their ability to make this effector molecule. The
breakthrough was two-way: these T cells indeed made IL-17, and were
distinct from Th1 and Th2.
Other immunologists had been trying to find out how IL-17 production was
initiated in T cells, largely focusing on IL-23. IL-23 was unable to
generate IL-17-producing T cells from undifferentiated precursors. It would
be a very hard job to try and find out how these cells are generated, since
there are a multitude of factors. However, we now had a culture condition
that provided us with IL-17-producing cells from an undifferentiated
starting population, providing possible clues on how these cells are
generated.
The Pasare and Medzhitov paper had shown that in order to overcome the
suppression of Treg on undifferentiated T cells, IL-6 is required. Indeed,
neutralizing IL-6 in our co-cultures blocked the generation of
IL-17-producing T cells. However, IL-6 alone was not sufficient to generate
them. Since these cultures crucially depend on the presence of Treg, I
focused on factors these cells could contribute. At the time these would
primarily be two: IL-10 and transforming growth factor (TGF)-beta. The
neutralization of TGF-beta, but not IL-10, prevented the generation of
IL-17-producing T cells. Importantly, we could show that only the combined
presence of IL-6 and TGF-beta was required for the development of
IL-17-producing T cells.
Obtaining these cells from undifferentiated precursors also allowed us to
establish that these cells were generated independently from Th1 and Th2
cells, and did not depend on specific transcription factors from either
lineage.
How was the paper received by the
community?
IL-17-producing T cells, now known as Th17, were associated early on with
autoimmune disorders. Our data that TGF-beta, a cytokine widely thought of
as immune suppressive and anti-inflammatory, was involved in driving the
differentiation of this T cell came as a surprise. Indeed, during the
lengthy reviewing process, concern was expressed regarding our
interpretation of the role of TGF-beta. However, our data reconciled
previously unexplained findings of a paradoxical pro-inflammatory role of
TGF-beta in an experimental arthritis model that predated the discovery of
IL-17-producing T cells, yet shows typical hallmarks of this T cell subset.
The apparent absence of a role of IL-23, so crucial in Th17 biology, in the
development of this subset also came under initial criticism. However,
IL-23 never was suggested to be a differentiation factor for T cells in the
published papers, but it certainly had been ambiguously phrased in some
papers, giving the perception of IL-23 as a differentiation factor, which
became widespread.
"The crucial test here was to show that the
undifferentiated cells, co-cultured in the presence of DC,
Treg, and microbial products, do have an effector
function."
Upon publication the paper was highlighted in other immunology journals.
Together with two papers that came out during our reviewing process, it
stood at the basis of breaking a 20-year dichotomous paradigm in adaptive
immunology, and it was the first to provide the "recipe" for the generation
of this subset. Th17 were already associated with autoimmune disorders and
infectious diseases, the ability to culture these cells in vitro
and the improved understanding of their development greatly accelerated
this research. The latter has been evident with an exponential growth in
publications relating to Th17 and the high number of quotations our paper
received.
Where have you taken this research since this
paper's publication?
Soon afterwards we were able to show the important role this subset plays
in the initiation of EAE. Interestingly, using detailed gene-expression
analysis comparing the new Th17 subset with other T cell subsets allowed us
to identify a Th17-specific transcription factor that could offer a
possible link between autoimmune disorders and environmental pollutants:
the aryl hydrocarbon receptor.
The opening up of the two-effector type T cells response has furthermore
contributed to more detailed analysis of T helper cell biology. This has
put more focus on greater flexibility of these cells after their initial
initiation, and has allowed us to contribute an additional subset, termed
Th9.
Does this work have, or is it expected to have,
any clinical applications?
It certainly has offered new insights in both auto-immune disorders as well
as infectious diseases. Genetic mutations have been identified impairing
the development of human Th17 and have been associated with increased
susceptibility to certain infections. Furthermore, genome-wide association
studies have identified genes associated with Th17 biology, most notably
the IL-23 receptor, which in addition to IL-17, is also targeted in numeral
clinical trials.
Dr. Marc Veldhoen
Stockinger Group
Division of Molecular Immunology
National Institute for Medical Research
London, England
and
Principal Investigator
Lymphocyte Development and Activation Laboratory
Babraham Institute
Cambridge, England
Marc Veldhoen's current most-cited paper in Essential Science
Indicators, with 766 cites:
Veldhoen M, et al., "TGF beta in the context of an inflammatory
cytokine milieu supports de novo differentiation of IL-17-producing T
cells," Immunity 24(2): 179-89, February 2006. Source:
Essential Science Indicators from
Clarivate.
