PERSPECTIVES
OPINION
Experimental mouse tumour models:
what can be learnt about human
cancer immunology?
Glenn Dranoff
Abstract | The recent demonstration that cancer immunotherapy extends patient
survival has reinvigorated interest in elucidating the role of immunity in tumour
pathogenesis. Experimental mouse tumour models have provided key mechanistic
insights into host antitumour immune responses, and these have guided the
development of novel treatment strategies. To accelerate the translation of these
findings into clinical benefits, investigators need to gain a better understanding of
the strengths and limitations of mouse model systems as tools for deciphering
human antitumour immune responses.
Immunotherapy has recently emerged as
a viable, and potentially transformative,
approach to cancer treatment. Within the
past 15 months, the US Food and Drug
Administration has approved two ‘firstinto-class’ immunotherapies, based on
their abilities to prolong patient survival.
These therapies are sipuleucel‑T (Provenge;
Dendreon), a cellular vaccine for prostate
cancer, and ipilimumab (Yervoy; BristolMyers Squibb), a blocking antibody specific
for cytotoxic T lymphocyte antigen 4
(CTLA4) that is used for treating advanced
melanoma (BOX 1).
The clinical success of these immuno­
therapies has motivated increasing numbers
of academic investigators and biotechnology
and pharmaceutical companies to reconsider
the role of immunotherapy in cancer treatment. Several new agents are already undergoing clinical examination, with promising
early signs of activity. The most compelling
candidates may be blocking antibodies
specific for the T cell co-inhibitory receptor
programmed cell death protein 1 (PD1) or
its ligand, PDL1, which can be expressed at
high levels on tumour cells as a consequence
of oncogenic signalling or local interferon‑γ
(IFNγ) production1. Furthermore, ‘offthe-shelf ’ cancer vaccines that combine
molecularly defined tumour antigens with
novel delivery systems and adjuvants are
being tested in large, randomized Phase III
clinical trials for efficacy against common
tumour types, including lung, prostate and
breast carcinomas, for which there are large
unmet treatment needs2,3. Beyond these
relatively advanced programmes, a range of
antibodies that target other immune regulatory molecules, bispecific antibodies that
induce adaptive immune responses and
engineered adoptive T cell strategies are in,
or about to enter, testing in patients4.
The new cancer immunotherapies arise, in
large part, from mechanistic insights obtained
from experimental studies in mice, which
have also served as the most common system
for obtaining ‘proof of principle’ for therapeutic antitumour activity. Given the expense of
the clinical development of immunotherapies
and the risk for inflammatory toxicity, model
systems are widely considered to be a required
prelude to investigation in humans. However,
many model systems are available, including
transplantable tumour models, models in
which tumours arise owing to transgenes
or gene knockouts, and models in which
humanized mice (which are immunodeficient
mice that have been reconstituted with various components of a human immune system)
NATURE REVIEWS | IMMUNOLOGY
are inoculated with human tumour xenografts. This diversity of mouse model systems
raises challenges for both newcomers to the
field and experienced workers. How does one
choose which system or systems to study?
Can the lessons derived from one model
system be generalized to others? Does any
system faithfully recapitulate tumour development in patients? How informative are comparative studies of different therapies in the
same model? Can the experimental systems
be used to prioritize particular combinations
of immunotherapies?
These difficult questions acquire some
urgency given the growing number of
potential targets and strategies for immuno­
therapy. Moreover, although the recent
clinical trials validate the overall approach of
immunotherapy and hint at a greater potential, most patients still need more effective
treatments, underscoring the heterogeneity
of human antitumour immune responses.
Unfortunately, our understanding of human
cancer immunology is currently too limited
to allow definitive answers to the questions
posed above. Ironically, an intensification
of the breadth and depth of clinical research
may be required to generate a sufficiently
rich framework to more effectively evaluate,
develop and apply experimental systems.
However, mouse tumour models remain
an almost obligatory stepping stone to
undertaking studies in patients with cancer.
In this Opinion article, I discuss some of
the strengths and limitations of three of the
most commonly used experimental mouse
model systems, juxtaposing relevant clinical
data in an effort to evaluate the predictability
of current models. Because of space constraints, this short commentary is not meant
to be exhaustive, but rather to highlight a
few central principles. Particular attention
is directed to studies of immune-checkpoint
blockade in light of the recent exciting
clinical data.
Transplantable tumours
Transplantable tumours have been the workhorse of cancer immunology for several
decades5 (FIG. 1). Studies using these systems
have uncovered many important mechanistic
features, including the existence of shared
and tumour-specific antigens, the intrinsic
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Box 1 | Clinical advances in immunotherapy
Sipuleucel‑T is an autologous cellular vaccine consisting of peripheral blood mononuclear cells
that have been exposed ex vivo to a recombinant fusion protein composed of prostatic acid
phosphatase (PAP; a prostate cancer differentiation antigen) linked to granulocyte–macrophage
colony-stimulating factor (GM-CSF; a cytokine that enhances antigen-presenting cell function)58.
Repetitive intravenous infusions of sipuleucel‑T to patients with metastatic, castrate-resistant
prostate carcinoma increased median overall survival by approximately 4 months, although
no tumour regressions or impact on time to disease progression were observed59. This clinical
improvement, albeit modest, was achieved with minimal toxicity and in a disease setting with
few therapeutic options — factors that collectively translate into meaningful benefits.
Ipilimumab is a fully human monoclonal antibody that blocks the T cell co-inhibitory molecule
cytotoxic T lymphocyte antigen 4 (CTLA4)22. In two large randomized clinical trials in patients
with advanced melanoma, ipilimumab augmented median overall survival to a greater extent than
dacarbazine (a cytotoxic chemotherapy considered as a standard of care) or vaccination with a
short peptide derived from GP100 (also known as PMEL; a melanocyte differentiation antigen),
which showed minimal, if any, efficacy60,61. Ipilimumab is the first agent that enhances survival in
patients with advanced melanoma and, most notably, treatment yielded long-term disease control
in approximately 20% of the subjects, with a follow-up of more than 4 years. Although treatment
is associated with a substantial (~15%) incidence of inflammatory toxicities (such as colitis and
hypophysitis), these conditions are usually straightforward to manage and considered acceptable
risks, given the clear likelihood for sustained antitumour activity.
immunogenicity of dying tumour cells
and the generation of antitumour immune
responses by the host. Moreover, they have
enabled the therapeutic manipulation of
tumour cells and/or the host to enhance or
diminish tumour resistance6–10. The commonly used cell lines in this model either
originated spontaneously or were induced
by carcinogens in inbred mouse strains, and
they have been selected for efficient propagation in vitro and in vivo. Among the most
thoroughly characterized are the B16 melan­
oma, CT26 colon carcinoma, 4T1 breast
carcinoma, EL4 T lymphoma, Lewis lung
carcinoma and methylcholanthrene-induced
fibrosarcoma cell lines.
When syngeneic mice are injected with
these cell lines, they must be sacrificed within
a few weeks owing to the rapid formation of
large tumours. Subcutaneous implantations
are frequently used because of the ease of
monitoring tumour growth, but bioluminescent imaging is a powerful tool for observing
visceral disease11. This technique allows
tumour cells that have been engineered to
emit visible light (owing to expression of a
luminescent protein) to be detected within
live animals using a specialized imaging
system. Surgical resection of subcutaneous
lesions may allow for spontaneous metastases
in some cases, whereas intravenous inoculation is an alternative approach to evaluate
disease dissemination to the lung, liver or
spleen. Another option is orthotopic injection
of the tumour cells, for example the intra­
cranial implantation of glioma cell lines. This
approach is advantageous over subcutaneous
injection, as it mimics the growth of tumours
within a relevant microenvironment.
Strengths and limitations. The speed and
reproducibility of tumour growth render
transplantable cell lines attractive for treatment studies. However, a single bolus of
large numbers of tumour cells and the tissue
damage associated with injection induce a
local inflammatory response that may affect
therapeutic responses.
Indeed, the intrinsic immunogenicity
of transplantable tumour cell lines varies
widely, and is perhaps related to differences
in the uptake of dying tumour cells by
phagocytes and/or in the release of
endogenous moieties that activate innate
immune receptors12,13. Poorly immunogenic tumours (such as B16 melanomas)
thus constitute a more stringent test for
intervention than moderately immunogenic lines (such as EL4 T lymphomas)14,
although the precise basis for these differences remains to be clarified. Furthermore,
immunosuppressive mechanisms may also
vary between transplantable tumour cell
lines, and again this could potentially affect
the outcome of a given intervention.
The enforced expression of model
antigens (such as ovalbumin) or viral gene
products in tumour cell lines provides
some advantages over the standard transplantable tumour models. These advantages
include the induction of enhanced immuno­
monitoring by T cells and the availability of
mice expressing transgenic T cell receptors
(TCRs) specific for the model antigen15.
However, the increased immunogenicity of
foreign antigens owing to decreasing T cell
tolerance tempers some of these gains. By
contrast, the characterization of endogenous
tumour antigens that are recognized by
62 | JANUARY 2012 | VOLUME 12
CD4+ and CD8+ T cells, and the development
of experimental tools for investigating these
responses against transplantable tumours
are important advances for immunotherapy
research16–18.
Transplantable tumours may be used
to evaluate both prophylactic and curative
therapies, and ideally the effects of the
therapy should be evaluated in multiple
models. When testing strategies aimed at
cancer prevention, transplantable tumour
models provide flexibility in the time at
which antitumour immunity is initiated
and allow the immune response to be optimized in the absence of tumour-induced
immunosuppression19. These advantages
facilitate the careful dissection of the cell­
ular and molecular interactions necessary
for protective immunity, and allow for
the comparison of different therapies that
might be applied in settings of minimal
residual disease.
The therapeutic eradication of
well-established transplantable tumours
presents complementary challenges20,21.
Among these is the requirement for the
extremely rapid induction of antitumour
effector immune cells that can navigate the
tumour vasculature and stroma, infiltrate
the growing lesion and overcome a myriad
of tumour-derived tolerizing and suppressive factors. Few therapeutic strategies
accomplish all of these requirements, and
effectuating the regression of advanced
lesions typically requires combinatorial
approaches that have a substantial risk
of toxicity.
Clinical correlates. The clinical success of
immune-checkpoint blockade (as exemplified by CTLA4 blockade) allows the predictive value of transplantable tumour models
for immunotherapy to be examined. First,
the ability of ipilimumab, as a monotherapy,
to prolong the survival of patients with
advanced melanoma affirms the finding
that transient, antibody-mediated blockade of CTLA4 potentiates antitumour
immunity 22. This result was initially
obtained using moderately immunogenic
transplantable cell lines, such as TRAMPC1
(also known as pTC1) prostate carcinoma,
ovalbumin-expressing EL4 T lymphoma
and Sa1N fibrosarcoma cells. This concord­
ance of preclinical and patient data is
profound in its implication, as earlier
failures of immunotherapy were frequently
attributed, at least in part, to a purported
inability of transplantable tumour systems
to accurately model human antitumour
immune responses5. The recent clinical
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© 2012 Macmillan Publishers Limited. All rights reserved
PERSPECTIVES
Tumour cell
Intracranial
injection
Culture dish
Subcutaneous
tumour
Tail vein
injection
Metastatic tumour
growth in lungs
Figure 1 | Transplantable tumour models. A variety of cell lines that represent a range of tumour
types are available for study. These lines are easy to grow in culture and rapidly form tumours after
Nature Reviews
| Immunology
inoculation into syngeneic mice. The cells may be inoculated subcutaneously,
intravenously
or orthotopically to induce tumours in different microenvironments. Therapeutic strategies may be evaluated
for protection against subsequent tumour challenge or for eradication of established tumours.
results suggest that the earlier failures may
have instead primarily reflected a lack of
sufficient immunogenicity. In addition,
some mechanistic aspects of CTLA4
blockade appear to be conserved between
transplantable tumour models and humans.
These aspects include the importance of
the intratumoural balance of effector and
regulatory T cells, and the upregulation of
T cell co-stimulatory molecules, such as
inducible T cell co-stimulator (ICOS)23–26.
This suggests that these parameters could
have potential as biomarkers.
Notwithstanding the clinical data,
CTLA4‑specific monoclonal antibodies
administered as a monotherapy displayed
minimal efficacy against B16 cells, which
are a widely used transplantable model of
melanoma22. These findings are in contrast with those obtained using the more
immunogenic cell lines mentioned above,
and they raise the possibility that the B16
transplantable tumour model might correspond to a subset of more refractory human
melanomas. Indeed, most patients with
advanced melanoma do not benefit from
ipilimumab. Thus, the poorly immunogenic
B16 cell line might prove useful for identifying combinatorial strategies that improve
the activity of CTLA4 blockade. One such
strategy that could be advanced to testing
in patients is the combination of CTLA4
blockade with vaccines containing tumour
cells that secrete granulocyte–macrophage
colony-stimulating factor (GM-CSF),
as synergy has been observed between
these two therapies27.
Albeit less clinically mature than
ipilimumab, PD1‑specific blocking anti­
bodies have been shown to stimulate tumour
regression in diverse human malignancies,
including melanoma, lymphoma and carcin­
omas of the kidney, colon and lung 28,29.
Surprisingly, these patient benefits appear to
exceed the impact of PD1‑specific blocking
antibodies as a monotherapy in a variety of
transplantable models. However, coupling
PD1‑specific blocking antibodies with
tumour vaccines, with adoptive T cell therapy
or with other immunoregulatory antibodies
has been shown to enhance their activity in
several model systems, and this should help
to guide further development of these therapies in patients30,31. Overall, investigations
of checkpoint blockade in mouse models
and humans indicate that transplantable
tumours may provide valuable information
for clinical translation. A better understanding of the differential activities of therapies in
poorly versus moderately immunogenic cell
lines may help to identify new approaches to
increase patient survival. However, important
limitations of these models include the failure
to fully recapitulate the toxicities observed
in patients treated with checkpoint-blocking
therapies and the potential pharmacokinetic
and pharmacodynamic differences between
mice and humans.
NATURE REVIEWS | IMMUNOLOGY
Genetically engineered tumour models
Studies of tumour formation in immuno­
deficient mice have elucidated many aspects
of the endogenous response to tumour
growth (FIG. 2), resulting in the concept
of immunoediting 32. In this concept, the
dynamic interplay between the tumour and
the immune response influences disease
development, while shaping characteristics
of the evolving transformed cells. Diverse
outcomes may arise from this interplay,
including tumour inhibition, promotion,
equilibrium and escape, but the key factors
that dictate the overall impact on the disease
course remain to be defined.
A large number of mouse strains that
harbour mutations in immune response
genes have been used to investigate the
mechanisms associated with immunoediting.
In one approach, gene-knockout mice
are exposed to carcinogens, and then
the frequency of tumour formation and the
kinetics of tumour development in these
mice are measured. These experiments have
underscored a central role in tumour inhibition for T helper 1 (TH1)-type immune
responses and cytotoxic T cells, as evidenced
by the enhanced tumour susceptibility of
mice lacking IFNγ, interleukin‑12 (IL‑12),
components of the MHC class I antigen
processing and presentation pathways, CD8+
T cells, perforin or granzymes33. In a complementary approach, spontaneous tumour
development is assessed in mice as they age,
and experiments using this approach have
revealed an elevated frequency of haematological malignancies and solid tumours in
several knockout mouse strains.
Excessive immune responses, however,
may increase cancer incidence, in part
through the deleterious consequences
of unresolved inflammation34. However,
crucial, tumour-promoting contributions
have been delineated in these models
for persistent microbial agents, nuclear
factor-κB (NF-κB) and signal transducer
and activator of transcription 3 (STAT3)
signalling, pro-inflammatory cytokines
and chemokines (such as IL‑1, IL‑6,
IL‑23, tumour necrosis factor (TNF) and
CC‑chemokine ligand 2 (CCL2)), and
various immune cell types, including
macrophages, mast cells, B cells, forkhead
box P3 (FOXP3)+ regulatory T cells and
myeloid-derived suppressor cells35–41.
Advances in cancer genetics have also
given rise to a wealth of new mouse tumour
systems that recapitulate the genetic lesions
that are characteristic of human cancers.
These models capitalize on transgenic
technologies that allow for the enforced
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PERSPECTIVES
a Immunodeficient mouse models
MCA-induced
fibrosarcoma
Inflammationassociated colon
carcinoma
Spontaneous lung
carcinoma
b Oncogene-driven models
Lung cancer driven
by KRAS and a lack
of p53 function
SV40 large
T antigen-driven
prostate cancer
ERBB2-driven
breast cancer
Commonly used immunodeficient
mice include mice deficient in
RAG, IFNγ, NF-κB or STAT3
Figure 2 | Genetically engineered mouse tumour models. a | Immunodeficient mice can have
enhanced tumour susceptibility, which may reflect a loss of protective immune responses and/or the
development of tumour-promoting inflammation. The figure shows examples of methylcholanthrene
(MCA)-induced fibrosarcoma, inflammation-associated colon carcinomaNature
and spontaneous
lung carcin­
Reviews | Immunology
oma. b | The tissue-specific and/or temporally controlled expression of oncogenes or the loss of tumour
suppressors can give rise to tumours that recapitulate genetic lesions found in human cancers. The
figure shows examples of breast cancer driven by ERBB2, prostate cancer driven by simian virus 40 (SV40)
large T antigen (which antagonizes the function of the host p53 and RB proteins), and lung cancer
driven by mutations in Kras and Tp53. These systems can be used to evaluate both endogenous and
therapy-induced antitumour immune responses. IFNγ, interferon‑γ; NF-κB, nuclear factor-κB;
RAG, recombination-activating gene; STAT3, signal transducer and activator of transcription 3.
expression of oncogenes and/or the loss of
function of tumour suppressors, often in
a tissue-specific and/or temporally controlled manner. In this context, the ability
to characterize how immune responses to
tumours vary in relation to specific cancer
genotypes is a significant advance towards
deconvoluting the heterogeneity in the
crosstalk between the tumour and the host
immune system.
A recent study used adenoviral vectors
encoding Cre recombinase to selectively
introduce mutations in the oncogene Kras
and the tumour suppressor gene Tp53 in
the pulmonary epithelia42. An important
role for T cells in attenuating lung tumour
formation was established in this system,
consistent with other experiments using
immunodeficient mouse strains43. The
concordance of interactions between the
tumour and host immune system in models
that traditionally are the workhorses of
cancer biologists and cancer immunologists
should help to identify common ground for
study and to promote broader interactions
between these disciplines.
Strengths and limitations. Compared
with transplantable tumours, genetically
engineered mice more faithfully model the
multistage pathogenesis of cancer and the
intimate interplay between neoplastic cells
and tissue microenvironments. However,
tumour formation in the transgenic animals is somewhat more variable than the
formation of transplantable tumours and
requires a longer period of time. Moreover,
the continuous expression of transforming
genes may restrict the ability of the host to
eradicate all malignant cells and could perpetuate inflammatory responses. Despite
these limitations, genetically engineered
systems have been used to help guide
immunotherapy development. For example, antibody-mediated blockade of CTLA4
prolongs survival in a transgenic model
of prostate cancer (induced by simian
virus 40 (SV40) large T antigen)44, and cancer vaccines and the inhibition of regulatory T cells mediate tumour destruction in
breast cancers driven by the kinase ERBB2
(also known as HER2 and neu)45. Such
results are qualitatively similar to those
obtained using transplantable tumours,
but the therapeutic activities of treatment
strategies are generally diminished in the
genetically modified animals.
The basis for this decreased efficacy is
not fully understood, but it might include
an increased level of tumour tolerance
that arises from early and/or persistent
transgene expression. In addition, antitumour effector mechanisms may differ between the models; for example,
64 | JANUARY 2012 | VOLUME 12
antibodies have a substantial role in
inhibiting breast cancer progression in
ERBB2‑transgenic mice, whereas both cell­
ular and humoral immunity is required to
confer protection in wild-type, syngeneic
animals challenged with ERBB2‑expressing
transplantable cell lines46,47. Lastly, mice
that are transgenic or deficient for key
immunoregulatory molecules provide
important systems for deciphering the
impact of therapeutic manipulation of
these pathways.
Clinical correlates. A renewed interest in
characterizing the human tumour microenvironment has underscored the importance of intratumoural immune infiltrates.
Several clinical pathological studies have
delineated a tight association between a
high density of CD8+ cytotoxic T cells (and
an accompanying TH1‑type gene signature)
and favourable patient outcomes in diverse
solid and haematological malignancies48–50.
Conversely, the presence of mast cells, proinflammatory cytokines and pro-angiogenic
myeloid cell populations and the constitutive
activation of NF‑κB and STAT3 signalling
are linked with many progressive human
cancers, which supports the clinical exploration of novel therapeutic strategies targeting
these pathways51–53. The conservation of
protective and tumour-promoting immune
parameters between mouse model systems
and clinical samples highlights the predictive
value of genetically engineered models for
deciphering human antitumour immune
responses.
Humanized mouse models of cancer
Human tumour xenografts that are
implanted in immunodeficient mice are
widely used in studies of cancer biology and targeted or cytotoxic therapy.
However, a meaningful analysis of
immuno­therapy is precluded by the
impaired or absent adaptive immune
responses in the immunodeficient mouse
models, which include athymic nude mice,
recombination-activating gene-deficient
(Rag–/–) mice and NOD-scid Il2rg–/– (NSG)
mice. In this regard, substantial effort is
currently directed towards reconstituting
these mice with a human immune system,
and evidence for functional interactions
among dendritic cells, B cells and T cells
has been obtained54 (FIG. 3). Using such an
approach, a recent study demonstrated
that human breast carcinomas generate a
tumour-promoting microenvironment that
involves crosstalk between plasmacytoid
dendritic cells and CD4+ TH2 cells, with a
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© 2012 Macmillan Publishers Limited. All rights reserved
PERSPECTIVES
Human
tumour cells
Immunodeficient mouse
reconstituted with human
DCs, B cells and T cells
Human tumour xenograft
(for example, a human breast tumour)
Figure 3 | Humanized mouse tumour models. Human tumour xenografts can be implanted in
immuno­deficient mice that have been reconstituted with human immune cells, including dendritic cells
Nature immune
Reviewsresponse
| Immunology
(DCs), B cells and T cells. This system can be used to characterize the human
that is
directed against a human cancer. Potential applications include the optimization of immunotherapy
and the identification of crucial immune pathways that promote tumour growth.
pro-tumorigenic role for thymic stromal
lymphopoietin, OX40 and IL‑13 (REF. 55).
In a second example, human T cells
engineered to express a tumour-targeted
chimeric antigen receptor incorporating
CD137‑derived signalling domains were
shown to mediate the regression of bulky
human tumours propagated in NSG mice56.
The potential clinical relevance of these
findings was suggested by the striking antitumour effects observed in patients with
advanced chronic lymphocytic leukaemia
who were treated with autologous T cells
expressing a chimeric antigen receptor
incorporating CD137 co-stimulatory
function (although the antibody-derived
targeting moiety was different to that used
in the mouse studies)57.
Although these examples highlight the
potential for humanized mouse models to
inform clinical investigations, their role in
prioritizing new therapeutic strategies for
translation to patients will require additional study. The efficiency of dendritic
cell-mediated stimulation of protective
B and T cell responses and the extent to
which tumour-induced tolerance and/or
suppression are recapitulated in these systems are largely unknown. Moreover, the
impact of mouse cytokines and cell-surface
molecules on human immune cell populations may complicate the interpretation of
some experimental results. Nonetheless,
further improvements in humanized mice
are likely to expand the application of these
preclinical models.
Perspectives
In this brief commentary, I have illustrated
how three classes of cancer models each
provide crucial insights into the mechanisms
of human antitumour immunity and the
potential clinical efficacy of immunotherapy.
The systems vary considerably in their
recapitulation of selected aspects of human
carcinogenesis, in the kinetics of tumour
development and in the complexity and cost
of experimentation (TABLE 1). The relative
importance of these differences is likely to
depend on the particular issue under investigation and the state of current knowledge.
For example, a comparison of potential new
checkpoint-blockade strategies might reasonably be initiated using several transplantable
tumours of varying immunogenicity, given
their convenience and the preclinical results
that have been obtained to date using this
system. However, the speed of tumour growth
in these models might limit the evaluation
of combinatorial strategies, especially if the
sequence of administration were to prove
decisive. In this case, a transgenic system
might be preferred in a second stage of characterization, and this would also facilitate
a preliminary assessment of the impact of
tumour-induced tolerance and immuno­
suppression on treatment activity. Exploratory
studies in a humanized mouse model might
then follow to allow the confirmation of key
experimental findings using clinical samples,
as a prelude to subsequent patient testing.
This progression, however, is predicated
on the convincing evidence that CTLA4and PD1‑specific monoclonal antibodies
offer meaningful benefits to patients with
cancer. This information permits one to
overlook, at least to some extent, the artificial
Table 1 | Strengths and weaknesses of experimental tumour models used for cancer immunology research
Experimental model
Strengths
Weaknesses
Clinical validation
Transplantable tumours
• Simplicity of experimentation
• Rapid tumour formation and evaluation of
therapeutic responses
• Limited recapitulation of tumour
microenvironment
• Checkpoint blockade
(CTLA4- or PD1-specific
monoclonal antibodies)
Genetically engineered
tumour models
• Tumours harbour genetic lesions found in
human cancers
• Improved modelling of tumour progression
and tumour microenvironment
• Tumour-induced tolerance and
immunosuppression show similarities to
human cancers
• Long time period for tumour
development and evaluation of
therapeutic response
• Increased cost and complexity of
generating and maintaining transgenic
mice
• Prognostic importance of
intratumoural lymphocyte
infiltrates
• CTLA4-specific monoclonal
antibodies
Humanized mice
• Human immune populations studied
directly
• Might be able to capture the heterogeneity
of patient responses
• Logistically difficult to obtain matched
donor and tumour samples
• Incomplete reconstitution of human
immune response
• Impact of mouse-derived factors on
human immune cells not fully defined
• Expensive
• Chimeric antigen receptor
T cell technology
CTLA4, cytotoxic T lymphocyte antigen 4; PD1, programmed cell death protein 1.
NATURE REVIEWS | IMMUNOLOGY
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nature of each of these models, which
cannot fully recapitulate the complexity
of human disease, and to focus instead on
lessons gained from these highly tractable
platforms. Such a perspective implies that a
fuller understanding of human antitumour
immune responses will promote more effective application and interpretation of experimental systems. Indeed, the considerable
heterogeneity in the human immune system
suggests that many more models will need to
be developed, and these in turn will inspire
further clinical investigation.
Glenn Dranoff is at the Department of Medical
Oncology and the Cancer Vaccine Center, Dana-Farber
Cancer Institute, and the Department of Medicine,
Brigham and Women’s Hospital and Harvard Medical
School, Boston, Massachusetts 02215, USA.e-mail:
glenn_dranoff@dfci.harvard.edu
doi:10.1038/nri3129
Published online 2 December 2011
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Keir, M. E., Butte, M. J., Freeman, G. J. & Sharpe, A. H.
PD‑1 and its ligands in tolerance and immunity.
Annu. Rev. Immunol. 26, 677–704 (2008).
Kantoff, P. W. et al. Overall survival analysis of a
Phase II randomized controlled trial of a poxviralbased PSA-targeted immunotherapy in metastatic
castration-resistant prostate cancer. J. Clin. Oncol.
28, 1099–1105 (2010).
Brichard, V. G. & Lejeune, D. GSK’s antigen-specific
cancer immunotherapy programme: pilot results
leading to Phase III clinical development. Vaccine 25
(Suppl. 2), B61–B71 (2007).
Dougan, M. & Dranoff, G. Immune therapy for cancer.
Annu. Rev. Immunol. 27, 83–117 (2009).
Ostrand-Rosenberg, S. Animal models of tumor
immunity, immunotherapy and cancer vaccines.
Curr. Opin. Immunol. 16, 143–150 (2004).
Prehn, R. T. & Main, J. M. Immunity to
methylcholanthrene-induced sarcomas. J. Natl Cancer
Inst. 18, 769–778 (1957).
Klein, G., Sjogren, H. O., Klein, E. & Hellstrom, K. E.
Demonstration of resistance against
methylcholanthrene-induced sarcomas in the primary
autochtonous host. Cancer Res. 20, 1561–1572
(1960).
Old, L., Clarke, D. & Benacerraf, B. Effect of bacillus
Calmette-Guerin (BCG) infection on transplanted
tumors in the mouse. Nature 184, 291–292 (1959).
Van Pel, A. & Boon, T. Protection against a nonimmunogenic mouse leukemia by an immunogenic
variant obtained by mutagenesis. Proc. Natl Acad. Sci.
USA 79, 4718–4722 (1982).
Basombrio, M. A. Search for common antigenicity
among twenty-five sarcomas induced by
methylcholanthrene. Cancer Res. 30, 2458–2462
(1970).
Craft, N. et al. Bioluminescent imaging of melanoma in
live mice. J. Invest. Dermatol. 125, 159–165 (2005).
Obeid, M. et al. Calreticulin exposure dictates the
immunogenicity of cancer cell death. Nature Med.
13, 54–61 (2007).
Apetoh, L. et al. Toll-like receptor 4‑dependent
contribution of the immune system to anticancer
chemotherapy and radiotherapy. Nature Med. 13,
1050–1059 (2007).
Dranoff, G. et al. Vaccination with irradiated tumor
cells engineered to secrete murine granulocytemacrophage colony-stimulating factor stimulates
potent, specific, and long-lasting anti-tumor immunity.
Proc. Natl Acad. Sci. USA 90, 3539–3543 (1993).
Gilboa, E. The makings of a tumor rejection antigen.
Immunity 11, 263–270 (1999).
Hanson, H. L. et al. Eradication of established tumors
by CD8+ T cell adoptive immunotherapy. Immunity
13, 265–276 (2000).
Overwijk, W. W. et al. Tumor regression and
autoimmunity after reversal of a functionally tolerant
state of self-reactive CD8+ T cells. J. Exp. Med. 198,
569–580 (2003).
18. Xie, Y. et al. Naive tumor-specific CD4+ T cells
differentiated in vivo eradicate established melanoma.
J. Exp. Med. 207, 651–667 (2010).
19. Cavallo, F., Offringa, R., van der Burg, S. H., Forni, G.
& Melief, C. J. Vaccination for treatment and
prevention of cancer in animal models.
Adv. Immunol. 90, 175–213 (2006).
20. Zhang, B., Karrison, T., Rowley, D. A. & Schreiber, H.
IFN‑γ‑ and TNF-dependent bystander eradication of
antigen-loss variants in established mouse cancers.
J. Clin. Invest. 118, 1398–1404 (2008).
21. Klebanoff, C. A. et al. Determinants of successful
CD8+ T‑cell adoptive immunotherapy for large
established tumors in mice. Clin. Cancer Res. 17,
5343–5352 (2011).
22. Korman, A., Peggs, K. & Allison, J. P. Checkpoint
blockade in cancer immunotherapy. Adv. Immunol.
90, 293–335 (2006).
23. Quezada, S. A., Peggs, K. S., Curran, M. A. &
Allison, J. P. CTLA4 blockade and GM‑CSF
combination immunotherapy alters the intratumor
balance of effector and regulatory T cells. J. Clin.
Invest. 116, 1935–1945 (2006).
24. Hodi, F. S. et al. Immunologic and clinical effects of
antibody blockade of cytotoxic T lymphocyteassociated antigen 4 in previously vaccinated cancer
patients. Proc. Natl Acad. Sci. USA 105, 3005–3010
(2008).
25. Fu, T., He, Q. & Sharma, P. The ICOS/ICOSL pathway
is required for optimal antitumor responses mediated
by anti‑CTLA‑4 therapy. Cancer Res. 71, 5445–5454
(2011).
26. Liakou, C. I. et al. CTLA‑4 blockade increases
IFNγ-producing CD4+ICOShi cells to shift the ratio
of effector to regulatory T cells in cancer patients.
Proc. Natl Acad. Sci. USA 105, 14987–14992 (2008).
27. van Elsas, A., Hurwitz, A. & Allison, J. Combination
immunotherapy of B16 melanoma using anti-cytotoxic
T lymphocyte-associated antigen 4 (CTLA‑4) and
granulocyte/macrophage colony-stimulating factor
(GM-CSF)-producing vaccines induces rejection of
subcutaneous and metastatic tumors accompanied
by autoimmune depigmentation. J. Exp. Med. 190,
355–366 (1999).
28. Berger, R. et al. Phase I safety and pharmacokinetic
study of CT‑011, a humanized antibody interacting
with PD‑1, in patients with advanced hematologic
malignancies. Clin. Cancer Res. 14, 3044–3051 (2008).
29. Brahmer, J. R. et al. Phase I study of single-agent
anti-programmed death‑1 (MDX‑1106) in refractory
solid tumors: safety, clinical activity, pharmacodynamics,
and immunologic correlates. J. Clin. Oncol. 28,
3167–3175 (2010).
30. Li, B. et al. Anti-programmed death‑1 synergizes with
granulocyte macrophage colony-stimulating factorsecreting tumor cell immunotherapy providing
therapeutic benefit to mice with established tumors.
Clin. Cancer Res. 15, 1623–1634 (2009).
31. Melero, I. et al. Palettes of vaccines and
immunostimulatory monoclonal antibodies for
combination. Clin. Cancer Res. 15, 1507–1509 (2009).
32. Schreiber, R. D., Old, L. J. & Smyth, M. J.
Cancer immunoediting: integrating immunity’s roles
in cancer suppression and promotion. Science 331,
1565–1570 (2011).
33. Vesely, M. D., Kershaw, M. H., Schreiber, R. D. &
Smyth, M. J. Natural innate and adaptive immunity to
cancer. Annu. Rev. Immunol. 29, 235–271 (2011).
34. Mantovani, A., Allavena, P., Sica, A. & Balkwill, F.
Cancer-related inflammation. Nature 454, 436–444
(2008).
35. Grivennikov, S. I., Greten, F. R. & Karin, M. Immunity,
inflammation, and cancer. Cell 140, 883–899 (2010).
36. Qian, B. Z. et al. CCL2 recruits inflammatory
monocytes to facilitate breast-tumour metastasis.
Nature 475, 222–225 (2011).
37. Yu, H., Kortylewski, M. & Pardoll, D. Crosstalk between
cancer and immune cells: role of STAT3 in the tumour
microenvironment. Nature Rev. Immunol. 7, 41–51
(2007).
38. Marigo, I. et al. Tumor-induced tolerance and immune
suppression depend on the C/EBPβ transcription
factor. Immunity 32, 790–802 (2010).
39. Schioppa, T. et al. B regulatory cells and the tumorpromoting actions of TNF-α during squamous
carcinogenesis. Proc. Natl Acad. Sci. USA 108,
10662–10667 (2011).
40. Rabinovich, G. A., Gabrilovich, D. & Sotomayor, E. M.
Immunosuppressive strategies that are mediated by
tumor cells. Annu. Rev. Immunol. 25, 267–296
(2007).
66 | JANUARY 2012 | VOLUME 12
41. Zou, W. Regulatory T cells, tumour immunity and
immunotherapy. Nature Rev. Immunol. 6, 295–307
(2006).
42. DuPage, M. et al. Endogenous T cell responses to
antigens expressed in lung adenocarcinomas delay
malignant tumor progression. Cancer Cell 19,
72–85 (2011).
43. Dougan, M. et al. A dual role for the immune response
in a mouse model of inflammation-associated lung
cancer. J. Clin. Invest. 121, 2436–2446 (2011).
44. Hurwitz, A. A. et al. Combination immunotherapy of
primary prostate cancer in a transgenic mouse model
using CTLA‑4 blockade. Cancer Res. 60, 2444–2448
(2000).
45. Ercolini, A. M. et al. Recruitment of latent pools of
high-avidity CD8+ T cells to the antitumor immune
response. J. Exp. Med. 201, 1591–1602 (2005).
46. Rovero, S. et al. DNA vaccination against rat
Her‑2/Neu p185 more effectively inhibits carcinogenesis
than transplantable carcinomas in transgenic BALB/c
mice. J. Immunol. 165, 5133–5142 (2000).
47. Reilly, R. et al. The collaboration of both humoral and
cellular HER‑2/neu-targeted immune responses is
required for the complete eradication of HER‑2/neuexpressing tumors. Cancer Res. 61, 880–883 (2001).
48. Zhang, L. et al. Intratumoral T cells, recurrence, and
survival in epithelial ovarian cancer. N. Engl. J. Med.
348, 203–213 (2003).
49. Galon, J. et al. Type, density, and location of immune
cells within human colorectal tumors predict clinical
outcome. Science 313, 1960–1964 (2006).
50. Wahlin, B. E. et al. A unifying microenvironment model
in follicular lymphoma: outcome is predicted by
programmed death‑1‑positive, regulatory, cytotoxic,
and helper T cells and macrophages. Clin. Cancer Res.
16, 637–650 (2010).
51. Ruffell, B. et al. Leukocyte composition of human
breast cancer. Proc. Natl Acad. Sci. USA 8 Aug 2011
(doi:10.1073/pnas.1104303108).
52. Qian, B. Z. & Pollard, J. W. Macrophage diversity
enhances tumor progression and metastasis. Cell 141,
39–51 (2010).
53. Ferrone, C. & Dranoff, G. Dual roles for immunity
in gastrointestinal cancers. J. Clin. Oncol. 28,
4045–4051 (2010).
54. Legrand, N. et al. Humanized mice for modeling
human infectious disease: challenges, progress, and
outlook. Cell Host Microbe 6, 5–9 (2009).
55. Pedroza-Gonzalez, A. et al. Thymic stromal
lymphopoietin fosters human breast tumor growth by
promoting type 2 inflammation. J. Exp. Med. 208,
479–490 (2011).
56. Carpenito, C. et al. Control of large, established tumor
xenografts with genetically retargeted human T cells
containing CD28 and CD137 domains. Proc. Natl
Acad. Sci. USA 106, 3360–3365 (2009).
57. Kalos, M. et al. T cells with chimeric antigen receptors
have potent antitumor effects and can establish
memory in patients with advanced leukemia. Sci.
Transl. Med. 3, 95ra73 (2011).
58. Higano, C. S. et al. Integrated data from 2
randomized, double-blind, placebo-controlled, phase 3
trials of active cellular immunotherapy with
sipuleucel‑T in advanced prostate cancer. Cancer 115,
3670–3679 (2009).
59. Kantoff, P. W. et al. Sipuleucel‑T immunotherapy for
castration-resistant prostate cancer. N. Engl. J. Med.
363, 411–422 (2010).
60. Hodi, F. S. et al. Improved survival with ipilimumab in
patients with metastatic melanoma. N. Engl. J. Med.
363, 711–723 (2010).
61. Robert, C. et al. Ipilimumab plus dacarbazine for
previously untreated metastatic melanoma. N. Engl.
J. Med. 364, 2517–2526 (2011).
Acknowledgements
Glenn Dranoff is supported by grants from the US National
Cancer Institute, the Leukemia and Lymphoma Society, the
Melanoma Research Alliance, the Alliance for Cancer Gene
Therapy and the Research Foundation for the Treatment of
Ovarian Cancer.
Competing interests statement
The author declares no competing financial interests.
FURTHER INFORMATION
Glenn Dranoff’s homepage: http://www.hms.harvard.edu/
dms/immunology/fac/Dranoff.php
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