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Cancer Res. Author manuscript; available in PMC 2017 March 01.
Published in final edited form as:
Cancer Res. 2016 March 1; 76(5): 999–1008. doi:10.1158/0008-5472.CAN-15-1439.
STK11/LKB1 deficiency promotes neutrophil recruitment and
proinflammatory cytokine production to suppress T cell activity
in the lung tumor microenvironment
Author Manuscript
Shohei Koyama1,2,*, Esra A. Akbay2,3,*, Yvonne Y. Li2,3,*, Amir R. Aref2,3, Ferdinandos
Skoulidis4, Grit S. Herter-Sprie2,3, Kevin A. Buczkowski3, Yan Liu2,3, Mark M. Awad2,3,
Warren L. Denning4, Lixia Diao5, Jing Wang5, Edwin R. Parra-Cuentas6, Ignacio I.
Wistuba6, Margaret Soucheray7, Tran C. Thai3, Hajime Asahina2,3, Shunsuke Kitajima3,
Abigail Altabef3, Jillian D. Cavanaugh3, Kevin Rhee3, Peng Gao3, Haikuo Zhang2,3, Peter E.
Fecci8, Takeshi Shimamura9, Matthew D. Hellmann10, John V. Heymach4, F. Stephen
Hodi2,3, Gordon J. Freeman1,2, David A. Barbie2,3, Glenn Dranoff11,**, Peter S.
Hammerman2,3,**, and Kwok-Kin Wong2,3,12,**
1Department
of Medical Oncology and Cancer Vaccine Center, Dana Farber Cancer Institute,
Boston, MA
2Department
of Medicine, Brigham and Women’ s Hospital and Harvard Medical School, Boston
MA
3Department
of Medical Oncology, Dana Farber Cancer Institute, Boston MA
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4Department
of Thoracic/Head and Neck Medical Oncology, The University of Texas MD
Anderson Cancer Center, Houston, Texas
5Department
of Bioinformatics and Computational Biology, The University of Texas MD Anderson
Cancer Center, Houston, Texas
6Department
of Translational Molecular Pathology, The University of Texas MD Anderson Cancer
Center, Houston, Texas
7University
of California San Francisco
8Division
of Neurosurgery, Department of Surgery, Duke University Medical Center, Durham,
North Carolina
9Department
Author Manuscript
of Molecular Pharmacology and Therapeutics, Oncology Research Institute, Loyola
University Chicago, Illinois
10Department
of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY
**
Address correspondence to: Kwok-Kin Wong, kwong1@partners.org, phone: 617-582-7683, and fax: 617-582-7839, Peter
Hammerman, peter_hammerman@dfci.harvard.edu, phone: 617-632-3647, and fax: 617-632-5786, or Glenn Dranoff
glenn.dranoff@novartis.com, phone: 617 871 4700.
*These authors equally contributed to this work
Disclosure of Potential Conflicts of Interest:
G.D. received sponsored research support from Bristol-Myers Squibb and Novartis, and is currently an employee of Novartis. He is
currently an employee of Novartis. G.J.F. receives patent royalties on the PD-1 pathway from Bristol-Myers-Squibb, Roche, Merck,
EMD-Serrono, Boehringer-Ingelheim, Amplimmune/AstraZeneca, and Novartis. F.S.H. is a Bristol-Myers Squibb nonpaid consultant,
Novartis, Merck and Genentech consultant and receives clinical trial support to the institution from these companies.
Koyama et al.
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11Novartis
Author Manuscript
12Belfer
Institutes for BioMedical Research, Cambridge, MA
Institute for Applied Cancer Science, Dana Farber Cancer Institute, Boston, MA
Abstract
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STK11/LKB1 is among the most commonly inactivated tumor suppressors in non-small cell lung
cancer (NSCLC), especially in tumors harboring KRAS mutations. Many oncogenes promote
immune escape, undermining the effectiveness of immunotherapies, but it is unclear whether
inactivation of tumor suppressor genes such as STK11/LKB1 exert similar effects. In this study, we
investigated the consequences of STK11/LKB1 loss on the immune microenvironment in a mouse
model of KRAS-driven NSCLC. Genetic ablation of STK11/LKB1 resulted in accumulation of
neutrophils with T cell suppressive effects, along with a corresponding increase in the expression
of T cell exhaustion markers and tumor-promoting cytokines. The number of tumor-infiltrating
lymphocytes was also reduced in LKB1-deficient mouse and human tumors. Furthermore, STK11/
LKB1 inactivating mutations were associated with reduced expression of PD-1 ligand PD-L1 in
mouse and patient tumors as well as in tumor-derived cell lines. Consistent with these results,
PD-1 targeting antibodies were ineffective against Lkb1-deficient tumors. In contrast, treating
Lkb1-deficient mice with an IL-6 neutralizing antibody or a neutrophil-depleting antibody yielded
therapeutic benefits associated with reduced neutrophil accumulation and proinflammatory
cytokine expression. Our findings illustrate how tumor suppressor mutations can modulate the
immune milieu of the tumor microenvironment, and they offer specific implications for addressing
STK11/LKB1 mutated tumors with PD-1 targeting antibody therapies.
Introduction
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The discovery of a series of oncogene driver mutations and the concept of oncogene
addiction has changed the therapeutic approach for subsets of patients with non-small cell
lung cancers (NSCLCs) (1). While this targeted approach for tumors with specific kinase
alterations has been successful, KRAS mutation is the most common genetic alteration
driving NSCLCs and remains refractory to targeted treatment strategies. KRAS mutated
NSCLCs are genomically more complex than those harboring mutated EGFR or EML4-ALK
and the concurrent loss of key tumor suppressors such as TP53 or STK11 is common in
KRAS mutated lung adenocarcinomas.
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STK11/LKB1 is inactivated in approximately one-third of KRAS mutated lung
adenocarcinomas, a frequency comparable to TP53 loss in this background, though STK11
and TP53 mutations rarely overlap in KRAS mutant lung tumors (2). Lkb1-deficient Krasmutated (Kras/Lkb1) tumors show a more invasive and metastatic phenotype with
significantly reduced survival (3) and differential drug sensitivities as compared to Kras
mutant Lkb1-wild type tumors and Kras mutated compound Tp53 deficient animals (4). A
more metastatic phenotype in Kras/Lkb1 tumors has also been described in clinical studies
(5,6).
Recent clinical trials in NSCLC have demonstrated response to immune checkpoint
blockade and nominated predictive markers for the efficacy of specific immunotherapies (7–
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9). Our previous work suggests that oncogenes impact immune evading mechanisms by
directly activating immune checkpoints (10). Immune evasion can also be achieved by the
release of proinflammatory cytokines into the tumor microenvironment that play an
important role in promoting tumor growth, metastasis and immune suppression (11,12).
Previous work has shown that Kras-mutated tumors display activation of the non-canonical
IkappaB kinase TBK1 (13,14) that activation of this signaling pathway induces several
proinflammatory cytokines, such as IL-6 and CXC-chemokine ligands. Myeloid cells,
especially tumor-associated macrophages (TAM) and neutrophils (TAN), support tumor cell
proliferation and impede host immune surveillance through cytokine production and cellcell interactions (15).
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To elucidate how Stk11/Lkb1 (hereafter referred to as Lkb1 in the mouse model) -loss affects
the inflammatory phenotype in Kras-driven lung cancer, we compared immune cell
populations and cytokine/chemokine profiles among Kras and Kras/Lkb1 mouse lung cancer
models. We found that neutrophil attracting soluble factors and neutrophil numbers were
significantly increased and both T cell numbers and function were significantly decreased in
Lkb1-deficient tumors. Moreover, Lkb1-loss of function negatively impacted PD-L1
expression in lung tumor cells in mouse and human tumors and cell lines. By depleting the
neutrophils in Kras/Lkb1 mutant mice, T cell numbers and function were significantly
improved affirming the immune suppressive properties of this cell type. Finally, we
functionally validated the therapeutic utility of blocking the cytokine feedback loop with a
neutralizing anti-IL-6 antibody, which resulted in an increase of T cell numbers and
function. Together, the results suggest that in the Lkb1-deficient tumors, immune evasion is
achieved through suppressive myeloid cells and aberrant cytokine production and not the
PD-1:PD-L1 interaction.
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Methods
Murine cell line and in vivo studies
Mouse strains were described previously (3). Mice were dosed with 200 micrograms of IL-6
neutralizing antibody (MP5-20F3, BioXcell), anti Ly-6G/Gr-1 antibody (RB6-8C5,
BioXcell), PD-1 blocking antibody (clone 29F.1A12) and isotype controls (BioXcell) three
times a week via intraperitoneal injections. MRI quantification was performed as described
previously (10). Murine cell lines bearing mutated Kras and p53-loss (Kras/p53:KP) and
mutated Kras and both p53 and Lkb1-loss (Kras/p53/Lkb1:KPL) were established and
characterized previously (16). Recombinant mouse IL-1α was from PeproTech.
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Immune cell isolation, analysis and sorting
Lung cell isolation, mononuclear cell enrichment and characterization of immune cell
populations in murine tissue samples were described previously (10). Total cell count was
divided by tumor-bearing lung weight utilized for each assay. Antibodies are listed in
Supplementary Methods. Intracellular staining for Ki-67, IFNγ, CTLA-4, FOXP3 and
LGALS9 was performed according to the manufacturer’ s protocol (eBioscience and BD
biosciences). Sorting of tumor cells (CD45−EpCAM+) and neutrophils
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(CD45+CD11b+Ly-6G+) was performed on a BD FACS Aria II. Gating methods for
immune analysis and sorting are in Supplementary Methods.
Sample preparation for RNA sequencing
RNA isolation from sorted cells was performed using the PicoPure RNA Isolation kit (Life
technologies) according to the manufacturer’ s protocol. 10–100 ng of total RNA was used as
input for the generation libraries using the Nugen Ovation Kit. Libraries were quality
controlled on an Agilent high sensitivity DNA chip and sequencing of pooled libraries
performed on the Illumina HiSeq platform to a minimum depth of 30 million reads.
Mouse RNA sequencing and patient tumor gene expression and proteomic data analysis
(CCLE, TCGA, and PROSPECT)
Methods for these are described in supplementary methods.
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Preparation of isogenic human cell lines and IL1-α stimulation
Human lung cancer cell lines were obtained from ATCC and used prior to six months of
passage in culture and not further authenticated. Short hairpin RNA constructs and stable
isogenic cell lines were established as described previously (17). Recombinant human IL-1α
was from PeproTech (18).
Immunohistochemistry
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Immunohistochemistry for TUNEL and Ki-67 was performed as previously described (19).
For the PROSPECT samples 4μm- thick tissue sections were stained using an automated
staining system (Leica Bond Max, Leica Microsystems, Vista, CA, USA), according to
standard protocols. The38 Aperio Image Analysis Toolbox (Aperio, Leica Microsystems)
was used for digital analysis of images obtained from scanned slides. PDL1 clone E1L3N
from Cell Signaling Technologies, CD3 A0452 from Dako and CD8 C8/144B from Thermo
Scientific were used.
Western blotting
Tumor nodules resected from Kras and Kras/Lkb1 mice were homogenized in RIPA buffer
and proteinase inhibitor (Cell Signaling Technology). Western blotting was performed as
described previously (18) with anti pSTAT3, STAT3, LKB1 and actin antibodies (Cell
Signaling Technology).
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Measurement of soluble factor concentrations in BALFs from mice and culture
supernatants from murine and human cell lines
Methods for these are described in supplementary methods.
Statistical analysis
All numerical data are presented as mean ± SD. Data were analyzed using two-tailed
unpaired Student’ st test for comparisons of two groups and one-way ANOVA with Tukey
post-test for three groups. P values for the survival curves have been calculated using a logrank test. Mann-Whitney U tests were used to assess correlation of PD-L1 and T cell
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markers in human tumor samples with LKB1 status. Multivariate testing of TCGA data with
respect to genotype and clinical factors (sex, primary tumor stage, nodal stage, metastasis
stage, overall stage, age, and smoking) was performed using one-way ANOVA.
Results
Lkb1-deficient tumor cells stimulate neutrophil recruitment through the production of
cytokines and chemokines
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We previously showed that oncogene activation contributes to escape from immune
surveillance by modulating the tumor microenvironment (10). However, the loss of tumor
suppressors has not been previously investigated in this context. To elucidate how Lkb1deficiency impacts the immune microenvironment in lung tumors, we compared the immune
cell populations and cytokine profiles of Kras (K) and Kras/Lkb1 (KL) mouse models with
similar degrees of tumor burden (Supplementary Fig. S1A). We found that Lkb1-deficient
tumors showed a greater variation in the number of total hematopoietic (CD45+) cells
(Supplementary Fig. S1B) and an increase in the total CD11b+ myeloid cell population
among three major clusters (CD11c−CD11b−, CD11c+CD11b−, CD11b+) in the lung (Fig.
1A). Detailed analysis of these myeloid cell populations showed that total numbers of
tumor-associated neutrophils (TAN: CD11b+Ly-6G+) are significantly elevated and tumorassociated alveolar macrophages (TAM: CD11c+CD11b−CD103−) are significantly
decreased in KL tumors compared to K tumors (Fig. 1A). Minor myeloid cell populations
including eosinophils, Ly-6Chi inflammatory monocytes and CD103+ dendritic cells did not
show significant differences (Supplementary Fig. S1C). Interestingly, the increase of
neutrophils was also observed in the spleen and peripheral blood of KL mice (Fig. 1B).
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To identify the cytokines and chemokines driving the immune phenotype of Lkb1-deficient
tumors, we sorted CD45−EpCAM+ cells from Kras and Kras/Lkb1 lung tumors using
fluorescence-activated cell sorting (FACS) and performed mRNA sequencing. We
discovered higher expression of a number of chemokines in the KL tumor cells: Ppbp (proplatelet basic protein: chemokine (C-X-C motif) ligand 7 (Cxcl7)), Cxcl3 and Cxcl5, all of
which act through chemokine receptor CXCR2 on neutrophils (Supplementary Methods),
and cytokines: Csf3 (Colony stimulating factor 3: granulocyte colony stimulating factor (GCsf)) and two of the IL-1 family of proinflammatory cytokines; Il33, Il1α (Fig. 1C). On the
contrary, we identified a decrease in the expression of chemokine (C-C motif) ligand 5
(Ccl5) and Cxcl12 in KL tumor cells as compared to Kras. Both of these chemokines play an
important role in recruiting lymphocytes and dendritic cells (20,21) and these cell types are
underrepresented in KL tumors (Supplementary Fig. S1C and D).
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In addition to tumor cells, we sorted TAN from KL tumors and compared gene expression
profiles with TAN from the uninduced normal lung from mice with the same genetic
background. Analysis of mRNA sequencing revealed that TAN from the KL tumors
produced elevated T cell suppressive factors (22) including Il10, Lgals9, Arginase 1 (Arg1)
and Milk fat globulin EGF factor 8 protein (Mfge8) and the tumor promoting cytokine Il6,
as compared to neutrophils from normal lung (Supplementary Fig. 2A).
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To confirm these findings at the protein level, we analyzed CXCL7, G-CSF, and IL-1α in
culture supernatants from cell lines derived from mouse tumors (16). There was a significant
increase in CXCL7 and G-CSF in Kras-mutated Tp53-deficient Lkb1-deficient cell lines
(KPL) compared to Kras-mutated Tp53-deficient Lkb1-wild type cell lines (KP) (Fig. 1D)
but IL-1α was under the detection limit in all cell lines (data not shown). In addition to the
cytokines identified as differentially expressed in mRNA sequencing, we analyzed IL-6 and
IL-17, two well characterized cytokines that contribute to neutrophil accumulation and
production (23,24), and found that IL-6 was significantly increased in KPL compared to KP
(Fig. 1D) but IL-17 was not detected (data not shown). We further evaluated the cytokines in
BALFs which showed a significant increase of CXCL7 in KL versus control and G-CSF,
MFG-E8, and IL-10 in KL versus control and K (Fig. 1E and Supplementary Fig. 2B).
While Il-6 upregulation was not apparent at the mRNA level in EpCAM+ KL tumors cells
(data not shown), we detected the cytokine in BALFs from KL lungs and in cultured sorted
CD45−EpCAM+ cells and TAN from KL tumors (Supplementary Fig. 2C). Considering the
higher number of neutrophils in KL tumors as compared to K tumors, TAN likely play an
important role in aberrant production of this cytokine in addition to tumor cells. Given that
IL-6 mediates its downstream affects through STAT3 (25) we measured levels of
phosphorylated STAT3. We found that Kras/Lkb1 tumor tissue had higher levels of
phospho-STAT3 (pSTAT3) than the Kras tumors (Fig. 1F). These findings suggest that
Lkb1-inactivation is associated with neutrophil accumulation to the immune
microenvironment and overproduction of tumor-promoting cytokines.
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In concordance with RNA sequencing data, IL-1α showed a significant increase in BALFs
in Kras/Lkb1 versus that from control (Fig. 1G). Mouse BALFs, similar to the supernatants
from cultured cells, did not have detectable IL-17 (data not shown). To assess whether
IL-1α might promote feed forward cytokine signaling in Lkb1-deficient tumors, we
stimulated a Kras-mutated, p53-loss, Lkb1-loss mouse lung cancer cell line (KPL cell line)
with IL-1α and analyzed cytokine secretion. Among the cytokines, we detected an increase
in IL-6, CXCL7 and G-CSF production in a dose-dependent manner (Fig. 1H and
Supplementary Fig. S3A). These results are consistent with Lkb1-loss increasing IL-1α
production, which then promotes the activation of IL-6-STAT3 signaling.
Lkb1-loss negatively impacts the number and function of tumor infiltrating T cells and PDL1 expression on tumor cells
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Clinical studies have demonstrated that the density of tumor-infiltrating lymphocytes is
associated with a favorable prognosis and response immunotherapy in cancer (7–9). We
found that total counts of both CD4 and CD8 T cells were significantly decreased in Kras/
Lkb1 mouse tumors (Fig. 2A) as compared to Kras tumors. Infiltrating T cells showed a
significantly higher expression of T cell inhibitory markers: Programmed cell death protein
1 (PD-1), T cell immunoglobulin mucin-3 (TIM-3), Lymphocyte-activation gene 3 (LAG-3)
and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) (Fig. 2B). We also confirmed
expression of the ligand for TIM-3, LGALS9, in both tumor cells and TAN from Kras/Lkb1
tumors by flow cytometry (Supplementary Fig. S2D). The ratio of regulatory T cells
(FOXP3+) to total CD4 T cells was also significantly increased in Kras/Lkb1 tumor as
compared to Kras tumors (Fig. 2B). We evaluated T cell function in Kras/Lkb1 and Kras
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tumors with similar levels of disease (Supplementary Fig. S3B) and found significantly less
IFNγ and Ki-67 expression in total CD4 and CD8 T cells from the Kras/Lkb1 tumors than
those from Kras tumors (Fig. 2C). Thus, Lkb1 inactivation is associated with reduced T cell
number and increased markers of T cell exhaustion.
To understand the role of neutrophils in this model, we used a neutrophil depleting (anti
Ly-6G/Gr-1:RB6-8C5) antibody in mice with established tumors (Supplementary Fig. S4A
and B). Kras/Lkb1 mice treated with anti Ly-6G/Gr-1 antibody for 1 or 2 weeks showed a
significant reduction of TAN and of IL-6 and G-CSF in BALFs (Supplementary Fig. S4C
and D), resulting in a significant increase in total CD8 T cell numbers, proliferation (Ki-67+)
and T cell function represented by IFNγ production (Supplementary Fig. S4E).
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PD-L1 expression on tumor cells is a biomarker associated with a response to PD-1
blockade treatment (7,10). Lkb1-deficient tumor cells expressed significantly lower levels of
PD-L1 in CD45−EpCAM+ cells as compared to Kras tumor cells (Fig. 2D). PD-L1
expression is influenced by a variety of factors that include non-cell autonomous factors
such as release of IFNγ from T cells (26) in the tumor microenvironment in vivo. To dissect
the intrinsic role of Lkb1 inactivation on PD-L1 expression specifically in tumor cells, we
analyzed PD-L1 expression in cultured cell lines derived from mouse tumors of the KP and
KPL genotypes. PD-L1 levels were significantly lower in KPL as compared to KP (Fig. 2E).
To confirm that our findings in mouse models and cell lines were applicable to humans, we
studied human lung cancer cell lines with endogenous KRAS mutation and wild type or
inactivated LKB1. We either performed knockdown of LKB1 using shRNA or reconstituted
LKB1 with wild type (WT) or kinase dead (KD) LKB1 to develop isogenic cell lines (wild
type cells: H441, H1792 and LKB1 mutant cell: A549) (Supplementary Fig. S5A). PD-L1
expression was lower in both of the LKB1 WT lines when expressing sh-LKB1 (Fig. 2F).
Expression of LKB1 (WT and KD) in the LKB1-deficient A549 cell line resulted in a modest
increase in PD-L1 levels (Supplementary Fig. S5B). These data suggest LKB1 inactivation
decreased PD-L1 levels independent of IFNγ.
Functional loss of LKB1 in human cell lines is phenotypically similar to mouse Kras/Lkb1
tumors
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We next assessed the cytokine and chemokine profiles in human isogenic cell lines to
determine whether similar patterns would be observed. We analyzed culture supernatants
from these cell lines and found that IL-6 and G-CSF were significantly increased in LKB1inactivated cells as compared to LKB1-intact cells (Fig. 3A and Supplementary Fig. S5C).
There was also a significant increase of CXCL7 that was only detected in A549 cells
(Supplementary Fig. S5C). IL-1α stimulation of these cell lines led to an increase in IL-6,
G-CSF and CXCL7 in a dose-dependent manner (Fig. 3B and Supplementary Fig. S5D),
which was consistent with the Lkb1-deficient mouse cell line data (Fig. 1D). We also found
that IL-6 induction by IL-1α stimulation was more pronounced in LKB1-deficient cell lines
as compared to LKB1-intact cell lines (Supplementary Fig. S5E) except for H1792 which
showed modest stimulation. This line has high baseline IL-1α production (Fig. 3A) and the
shRNA only partially knocked down LKB1 (Supplementary Fig. S5A) which makes this
result difficult to interpret.
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Analysis of lung cancer cell lines from The Cancer Cell Line Encyclopedia (CCLE) (27)
confirmed that PD-L1 expression is significantly lower in cell lines with LKB1 mutation (32
LKB1 WT and 4 LKB1 mutant cell lines) (Fig. 3C), though the small number of LKB1
mutant lines precluded any significant associations among the immune related genes
displayed in Figures 1C and S2A and LKB1 status when corrected for multiple hypotheses.
In addition, analysis of KRAS-mutated lung adenocarcinomas from The Cancer Genome
Atlas (TCGA-52 LKB1 WT, 15 LKB1 mutant) (2) showed that PD-L1 expression was
significantly reduced in LKB1-mutated NSCLCs (Fig. 3C). In a multivariate analysis of the
TCGA dataset with respect to LKB1 status and clinical factors, PD-L1 and LKB1 status were
also significantly associated (p=0.005). To validate these findings in an independent dataset,
PD-L1 mRNA was assessed in the MD Anderson PROSPECT (Profiling of Resistance
Patterns and Oncogenic Signaling Pathways in Evaluation of Cancers of the Thorax and
Therapeutic Target Identification) cohort (MDACC-108 LKB1 WT, 44 LKB1 MUTANT
cases). We again observed an association among PD-L1 expression and LKB1 status. We
also validated and quantitated the expression of PD-L1 at the protein level by reverse phase
protein arrays (RPPA) in 106 cases from the MDACC cohort and detected significantly
lower levels of PD-L1 in LKB1 mutant tumors (Fig. 3D). As the current clinical standard
detection method for the PD-L1 expression is immunohistochemistry, we confirmed the
difference in PD-L1 expression by immunohistochemistry (Fig. 3E).
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Next, to evaluate the functional effect of LKB1-loss in the tumor microenvironment in
patient tumors, we analyzed the T cell infiltrate in the tumors by immunohistochemistry. In
19 LKB1 WT and 11 LKB1 mutant tumors, total T cell (CD3+) and CD8 T cell counts and
densities were significantly lower in LKB1-inactivated tumors as compared to LKB1-intact
tumors (Fig. 3F), In sum, observations in patient cell lines and tumor samples are consistent
with our findings in Kras/Lkb1 mice, suggesting that LKB1 mutation negatively regulates
PD-L1 expression and reduces CD8 T cell infiltration.
Neutralizing IL-6 leads to a therapeutic benefit in Kras/Lkb1 mice
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Supporting the notion that PD-L1 expression in tumor cells is critical in the response to
PD-1 blockade, treatment of the Kras/Lkb1 mouse model with a PD-1 blocking antibody did
not show a significant treatment response (Fig. 4A). Given our observation of elevated
IL-1α and IL-6 in BALFs (Fig. 1E and G) and aberrant activation of pSTAT3 in tumor
nodules (Fig. 1F) from Kras/Lkb1 mice as compared to Kras mice, we hypothesized that
targeting aberrant cytokine production could be a rational therapeutic strategy in Kras/Lkb1
mutant tumors. To evaluate in vivo efficacy of IL-6 blockade, we treated Kras/Lkb1 mice
with a neutralizing IL-6 antibody (MP5-20F3). The therapeutic anti IL-6 antibody
significantly inhibited tumor progression as compared to anti PD-1 antibody (Fig. 4A). In
addition, IL-6 antibody treated mice showed significantly improved survival as compared to
control mice (Fig. 4B). However, treatment of Kras/Lkb1 tumors with other checkpoint
blocking antibodies against CTLA-4 or a combination of PD-1 and TIM-3 also did not
demonstrate any efficacy (data not shown). Taken together, these findings suggest that
Lkb1-loss results in a T cell suppressed environment as a consequence of autocrine and
neutrophil induced cytokine production and not engagement of the PD-L1:PD-1 immune
checkpoint.
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To further investigate the effect of IL-6 neutralizing antibody on the immune profile of
Kras/Lkb1 tumors, we treated the mice for 2 weeks and then performed immune and
histological analyses (Supplementary Fig. S6A). There was a significant reduction in
detectable IL-6 as expected as well as G-CSF in BALFs from the treated mice (Fig. 4C). In
keeping with the neutrophil attracting cytokines and chemokines observed in BALFs, there
was a significant reduction in the counts of total TAN with IL-6 neutralization (Fig. 4D),
resulting in functional recovery of T cells (Fig. 4E). Treated tumors also exhibited elevation
of CD4 T cells, CD8 T cells, and TAM to levels that are comparable to Lkb1 wild type
tumors (Supplementary Fig. S6B). In addition to the immune related effects, IL-6 antibody
treated tumor cells exhibited significantly less proliferation and increased apoptosis (Fig.
4F). Although therapeutic IL-6 blockade improved T cell function, concurrent therapy
combining anti IL-6 and PD-1 treatment did not demonstrate additional benefit as compared
to IL-6 blockade alone in terms of survival (Supplementary Fig. S6C). This suggests a need
to further define contexts in which cytokine suppression and immune checkpoint blockade
might be utilized together to enhance therapeutic benefit as compared to either treatment
alone.
Discussion
Author Manuscript
Oncogenes and tumor suppressors promote self-sufficient signaling for autonomous
proliferation of tumor cells. Recent work has shown that oncogenic mutations alter the
tumor microenvironment, cause immune suppression and can impact the response to
immune modulating treatment strategies (10). Somatic mutations also produce neo-antigens
which are recognized by the immune system and mediate sensitivity of the tumors to
immunotherapies (28–30). Here, we have shown that inactivation of the tumor-suppressor
gene STK11/LKB1 causes dramatic changes in the tumor microenvironment in addition to
the previously reported effects on cell cycle, metabolism, differentiation, polarity and other
cellular pathways (16,31).
We have shown that LKB1 inactivation promoted the production of proinflammatory
cytokines CXCL7, G-CSF and IL-6 in both mouse tumors and cell lines, which contributes
to neutrophil accumulation. Elevation of the proinflammatory cytokine IL-1α was confirmed
in vivo but not robustly in cell culture supernatants from Lkb1-deficient cells. Previous
studies have shown that IL-1α is released only under specific conditions including necrotic
cell death and inflammasome activation (32,33), suggesting that the release of IL-1α could
be caused by necrotic cell death in Kras/Lkb1 tumor microenvironment and that this
facilitates the activation of IL-6-STAT3 signaling pathway in Kras/Lkb1 tumors together
with IL-6, producing neutrophil accumulation.
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The tumor microenvironment in Kras/Lkb1 tumors displayed characteristics of T cell
suppression with fewer lymphocytes, higher levels of checkpoint receptor expression in
those, and an increase in TANs with suppressive properties compared to Kras tumors. TANs
expressing high levels of Il10, Arginase1 and Mfge8 that have been implicated in T cell
suppression and Treg induction (15,22,34). Depleting TAN using an anti Ly-6G/Gr-1
antibody improved T cell function. Although the role of TAN in suppressing T cell function
is controversial (35), TAN appear to act in an immunosuppressive fashion in this context,
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suggesting that therapies suppressing TAN should be further explored as
immunomodulatory therapies.
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Moreover, we found that Lkb1 inactivation caused a decrease in PD-L1 levels on tumor cells
from Kras/Lkb1 tumors and in cultured cells from mice and patients. Conforming to the
previous observations proposing an association of tumor cell PD-L1 expression, the
magnitude of T cell accumulation in the tumors and response to PD-1 blockade (7,8,36),
treatment with a PD-1 blocking antibody did not show efficacy in the treatment of the Kras/
Lkb1 mouse model. A recent study (30) as well as our own institutional experience suggest
that while KRAS mutated patients respond favorably to PD-1 blockade (PFS of 15 months
on pembrolizumab) this is not seen in patients with LKB1 mutations though large cohorts
will be needed to define genotype-response associations in detail. Additionally contributing
to low PD-1:PD-L1 levels in Kras/Lkb1 tumors is the greater proportion of TAN which
express low levels of PD-L1 as compared to TAM. The coordinated role of PD-L1
expression in the tumor cells and the cells constituting the immune microenvironment in this
model requires further study to define improved immunotherapeutic strategies.
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Treatment of Kras/Lkb1 tumors with an IL-6 blocking antibody decreased tumor cell
proliferation and increased T cell function, resulting in a therapeutic effect in Kras/Lkb1
mouse model while immune checkpoint blockade was not efficacious. These data suggest
that mouse models can be used to model the tumor microenvironment and predict response
to novel immune modulating treatment strategies based on rational predictions from studies
of the tumor microenvironment. Future studies will examine whether cytokines other than
IL-6 also contribute to STAT3 activation (37), and whether combined cytokine blockade
(e.g, with IL-1 neutralization) will lead to more durable therapeutic effects. Although we
found that neutralizing IL-6 antibodies improved T cell number and function in Lkb1deficient tumors, the combination of anti PD-1 plus anti IL-6 antibodies did not improve
outcome when given concurrently. There may be technical limitations to this considering
both of the antibodies are Rat IgG isotype and combination treatment can lead to antibody
neutralization. Further, dosing schedules of cytokine suppression and combinations with
other therapeutic agents such as immune checkpoint blockade will need to be studied.
Author Manuscript
In summary, we have presented a novel set of findings which suggest that not only oncogene
driver mutations but also tumor-suppressor gene mutations can modify the immune
microenvironment in lung cancer. In this example focusing on Lkb1 loss we observed a
marked increase in inflammatory cytokines that recruited neutrophils and inhibited the
function of T cells. We also showed that PD-1 checkpoint blockade was ineffective in Lkb1
mutant cancers, whereas targeting IL-6 displayed a significant albeit short-lived treatment
response in the Kras/Lkb1 model. These findings suggest that IL-6 dependent signaling
activation can be a therapeutic target in Lkb1 deficient Kras-driven lung tumors and
potentially other tumors with high levels of IL-6, and also suggest targeting aberrant
inflammation by inhibiting cytokine signaling may represent a promising
immunotherapeutic strategy in selected patients.
Cancer Res. Author manuscript; available in PMC 2017 March 01.
Koyama et al.
Page 11
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Supplementary Material
Refer to Web version on PubMed Central for supplementary material.
Acknowledgments
The authors thank Suzan Lazo-Kallanian, John Daley, Kristen Cowens and Steven Paul for help with flow
cytometry anlaysis, Christine Lam for tissue processing, Mei Zhang for immunohistochemistry, Xiaoen Wang for
helping with mouse studies, and the Dana Farber Center for Cancer Genome Discovery for RNA sequencing.
Financial support
Author Manuscript
P.S.H. is supported by a Clinical Investigator Award from the Damon Runyon Cancer Research Foundation and the
Starr Consortium for Cancer Research. P.S.H., K.K.W., J.V.H. and M.D.H. are supported by a Stand Up To Cancer
- American Cancer Society Lung Cancer Dream Team Translational Research Grant (Grant Number: SU2CAACR-DT17-15). Stand Up To Cancer is a program of the Entertainment Industry Foundation. Research grants are
administered by the American Association for Cancer Research, the scientific partner of SU2C. K.K.W. is
supported by NCI R01 CA195740. S.K. is supported by Margaret A. Cunningham Immune Mechanisms in Cancer
Research Fellowship Award and The Kanae Foundation for the Promotion of Medical Science Fellowship Award.
G.S.H.-S. was supported by the Deutsche Forschungsgemeinschaft (HE 6897/1-1) and the Claudia Adams Barr
Program for Innovative Cancer Research. T.S. is supported by Uniting Against Lung Cancer Legacy Program and
American Cancer Society Research Scholar Award.
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Figure 1. Tumor-suppressor Lkb1 inactivation promotes neutrophil accumulation via
proinflammatory cytokines and chemokines
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A. Immune cell populations in the lung tumors from Kras (K) and Kras/Lkb1 (KL) mouse
models. Representative flow cytometry data (live/single/total CD45+ cells) from each mouse
model (left). Total counts of tumor associated neutrophils (TAN): CD11b+Ly-6G+ cells and
tumor associated macrophages (TAM): CD11c+CD11b−CD103− from K (n=8) and KL
(n=8) mice. **p<0.01, ***p<0.001. B. Neutrophil counts in the spleen and peripheral blood
from K (n=8) or KL (n=8) mice (right). **p<0.01. C. Expression of immune modulating
factors from RNA sequencing of the sorted tumor cells (CD45−EpCAM+) in Kras (K Ep) or
Kras/Lkb1 (KL Ep) mice and uninduced normal lung CD45−EpCAM+ cells (Control). Each
column consists of a combination of samples derived from 3–4 mice. Log-transformed
FPKM values are shown, colored blue/red for low/high expression, respectively. Epcam and
Cd45 expression are shown as positive and negative controls. Differential expression is
shown as fold-change values, colored blue/red for under/over-expression compared to
controls. D, E. Chemokine and cytokine levels in the culture supernatants after 48hr
incubation from Kras/p53 (KP) (n=3) versus Kras/p53/Lkb1 (KPL) (n=3) cell lines
generated from mouse lung tumors, ***p<0.001. Data indicate three replicate wells and are
representative of three independent experiments (D) and bronchoalveolar lavage fluid
(BALF)s from littermate controls (n=5), K mice (n=8) or KL mice (n=8). *p<0.05,
**p<0.01 (E). F. Western blot analysis for pSTAT3, STAT3 levels in K versus KL tumors.
Each column represents tumor from a different mouse and actin represents loading control.
G. IL-1α level in the BALF from C (n=5), K (n=8) or KL (n=8) mice. *p<0.05. H. IL-6
levels in culture supernatants measured 24hr after IL-1α stimulation (0, 5 and 20ng/ml) of
KP (n=3) versus KPL (n=3) cell lines. Data indicate three replicate wells and are
representative of three independent experiments.
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Figure 2. Lkb1 inactivation leads to a T cell suppressive tumor microenvironment with low PDL1 expression in tumor cells
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A. Total counts of CD4 T cells (top) and CD8 T cells (bottom). **p<0.01. B. Expression of
checkpoint receptors in CD4 T cells (top) and CD8 T cells (bottom) in K or KL tumors.
*p<0.05, **p<0.01, ***p<0.001. C. IFNγ expression and proliferation marker (Ki-67)
positivity for CD4 or CD8 T cells in K or KL tumors. Representative flow cytometry data
(total CD3+ T cells) from each mouse model (left). Percentage of Ki-67+ and IFNγ+ in CD4
or CD8 T cells from K (n=6) or KL (n=6) mice. *p<0.05, **p<0.01. D. PD-L1 expression in
gated CD45−EpCAM+ cells in K (n=5) or KL (n=5) tumors evaluated by flow cytometry.
*p=0.0384. E. PD-L1 expression in KP (n=3) versus KPL (n=3) cell lines evaluated by flow
cytometry. *p=0.0495. Data is representative of three independent experiments. F. PD-L1
expression in H441 or H1792 cells stably transfected with sh-non-target (NT) or sh-LKB1.
Data are representative of three independent experiments.
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Figure 3. LKB1 inactivation in human KRAS mutated cell lines showed similar phenotype with
mouse Kras/Lkb1 tumor
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A. Analysis of IL-6 in the culture supernatants after 48hr incubation of KRAS mutated LKB1
wild type H441 or H1792 cells stably transfected with sh-NT or sh-LKB1 and KRAS, LKB1
mutant A549 cells reconstituted with empty vector (Vector), wild type LKB1 or Kinase dead
LKB1 (LKB1KD). *p<0.05, ***p<0.001. Data indicate three replicate wells and are
representative of three independent experiments. B. IL-6 levels in culture supernatants
measured 24hr after IL-1α stimulation (0, 5 and 20ng/ml) of three LKB1-deficient cell lines.
Data indicate three replicate wells and are representative of three independent experiments.
C. PDL1 expression in KRAS (K) or KRAS and LKB1 mutated (KL) cell lines from CCLE
database (*p=0.04) and PDL1 expression in K or KL lung adenocarcinoma samples from
TCGA database (***p=0.00004). D. PD-L1 mRNA levels determined by microarray (p=0.1)
and protein levels (**p=0.009) determined by RPPA from the MDACC dataset. E.
Representative immunohistochemistry for PD-L1 on the KRAS mutated LKB1 wt or mutant
patient tumors from the MDACC cohort. F. CD3 (**p=0.002) and CD8 (***p=0.0003)
positive cell densities by immunohistochemistry on the MDACC patient cohorts.
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Figure 4. IL-6 neutralizing treatment showed clinical efficacy in Kras/Lkb1 mouse model
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A. Representative images of Magnetic resonance imaging (MRI) and quantification of MRI
from KL mice treated with PD-1 or IL-6 blocking antibodies or controls. B. Survival of
untreated mice vs mice treated with IL-6 blocking antibody (***p=0.0002, n=6 vs 12
respectively). C, D. IL-6 and G-CSF levels in BALFs (C) and TAN counts (D) for untreated
KL mice (n=7) or KL mice treated with IL-6 neutralizing antibody (n=8) with comparable
tumor burden. *p<0.05, **p<0.01. E. Ki-67 and IFNγ positive CD8 T cell counts in
untreated KL mice (n=7) or KL mice treated with IL-6 neutralizing antibody (n=8) with
comparable tumor burden. F. Representative Ki-67 and TUNEL immunohistochemistry and
quantification per the microscopic field on the KL mice untreated or treated with IL-6
neutralizing antibody. Each data point represents a different microscopic field. For Ki-67
n=9 and 5 and for TUNEL n=8 and 5 for untreated and IL-6 ab treated mice respectively.
**p=0.0049 for Ki-67 and **p=0.0024 for TUNEL.
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