4746?The?Journal?of?Clinical?Investigation? ? ? http://www.jci.org? ? ? Volume 121? ? ? Number 12? ? ? December 2011
IL-12 triggers a programmatic change
in dysfunctional myeloid-derived
cells within mouse tumors
Sid P. Kerkar,1 Romina S. Goldszmid,2 Pawel Muranski,1 Dhanalakshmi Chinnasamy,1
Zhiya Yu,1 Robert N. Reger,1 Anthony J. Leonardi,1 Richard A. Morgan,1 Ena Wang,3
Francesco M. Marincola,3 Giorgio Trinchieri,2 Steven A. Rosenberg,1 and Nicholas P. Restifo1
1Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, USA. 2Cancer and Inflammation Program,
National Cancer Institute, NIH, Frederick, Maryland, USA. 3Infectious Disease and Immunogenetics Section,
Department of Transfusion Medicine, Clinical Center and trans-NIH Center for Human Immunology, NIH, Bethesda, Maryland, USA.
Cancer growth, progression, and migration are dependent on
inflammatory cells residing within the tumor microenvironment
(1). These cells form critical components of a stromal network fos-
tering neovascularization and provide the optimal cytokine and
inflammatory support to drive the proliferation of transformed cells
into solid masses (2, 3). Although these stromal cells are essential for
tumor growth, they also possess the inherent capacity to function as
APCs. Many studies have highlighted the impairment in activation
and maturation of myeloid cells in cancer along with the ability of
these cells to create an immunosuppressive environment (4–11).
One of the barriers to obtaining long-term durable responses
following the adoptive transfer of T cells may be immune escape
mechanisms present within tumors (12–17). Lymphodepleting che-
motherapy regimens are effective in removing regulatory T cells,
but alternatively activated macrophages, immature dendritic cells,
and myeloid-derived suppressor cells (MDSCs) also contribute to
inhibiting antitumor T cell immunity (7, 18–20). Devising meth-
ods to alter myeloid-derived cells in situ may represent an attractive
strategy when combined with depleting regulatory T cells.
IL-12 is a hallmark inflammatory cytokine capable of eliciting
potent immune responses (21–25). The heterodimeric cytokine is
mainly produced by innate immune cells such as dendritic cells,
macrophages, and neutrophils and provides a critical bridge
between innate and adaptive immunity (22, 26). The antitumor
effects of IL-12 are thought to involve antiangiogenesis and
increased production of IFN-γ as well as enhanced lytic abilities of
CD8+ T cells, NK cells, and NKT cells to kill tumor targets (27–31).
Nevertheless, the mechanisms underlying the antitumor proper-
ties of IL-12 remain substantially unelucidated.
We recently showed that engineering pmel-1 CD8+ T cells to secrete
a functional single-chain IL-12 (Supplemental Figure 1; supplemental
material available online with this article; doi:10.1172/JCI58814DS1)
obviated the need for exogenous IL-2 and a vaccine and decreased the
number of cells needed for the treatment of established B16 mela-
nomas (32, 33). This therapeutic model also enabled us to uniquely
examine the effects of IL-12 directly at the immunologic synapse, a
difficult phenomenon to study when administering IL-12 systemi-
cally. Studies by Hans Schreiber’s group have highlighted the neces-
sity for high-avidity TCRs in order to recognize cognate antigen
cross-presented by tumor stromal cells (12–14, 16). In this study, we
show that IL-12 triggers a programmatic change in MDSCs, macro-
phages, and dendritic cells within tumors that enables the licensed
recognition of cross-presented antigen without altering TCR avidity.
Furthermore, the cross-talk between T cells and professional APCs
in the presence of an acute inflammatory environment triggered by
IL-12 within the tumor microenvironment was critical in causing the
regression of large established tumors.
IL-12–induced polarization of adoptively transferred CD8+ T cells into type I
effectors is not necessary for antitumor responses. Based on known mech-
anisms, we hypothesized that IL-12 secreted in culture polarized
Conflict?of?interest: The authors have declared that no conflict of interest exists.
Citation?for?this?article: J Clin Invest. 2011;121(12):4746–4757. doi:10.1172/JCI58814.
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
pmel-1 CD8+ T cells into type I effectors and that these changes
were responsible for the improvements in antitumor immunity.
To test this hypothesis, we expressed similar levels of IL-12 in WT
pmel-1 CD8+ T cells and Il12rb2–/– pmel-1 CD8+ T cells (Figure 1A).
IL-12–engineered pmel-1 CD8+ T cells (IL-12 cells) possessing
functional IL-12 receptors expressed a distinct CD62Lhi, IL-7Rαhi,
IL-2Rαhi, and Sca1hi phenotype not present on Il12rb2–/– cells
(Figure 1B). Furthermore, WT IL-12 cells were more activated and
capable of secreting higher amounts of IFN-γ and TNF-α compared
with Il12rb2–/– IL-12 cells (Figure 1C). We next adoptively trans-
ferred either 1 × 105 Il12rb2–/– or WT IL-12 cells into sublethally
irradiated mice (5 Gy) bearing well-established subcutaneous B16
melanomas and, surprisingly, observed similar levels of antitumor
immunity among the cell types (Figure 1D). We then transferred
1 × 105 WT IL-12 cells into WT or Il12rb2–/– host
mice and observed significant impairment in
tumor treatment in mice lacking the ability to
respond to IL-12 (Figure 1E). Thus, polariza-
tion of T cells into type 1 effectors did not play
a major role in enhancing antitumor immunity,
but sensitization of endogenous components of
the host’s immune system by IL-12 was neces-
sary for successful treatment responses.
IL-12–dependent sensitization of bone marrow–
derived cells is required for antitumor immunity.
We next created bone marrow chimeras using
C57BL/6 WT and Il12rb2–/– mice in order to bet-
ter decipher the particular cell populations that
may be sensitized by IL-12. We lethally irradiated
WT mice and reconstituted them with Il12rb2–/–
(Il12rb2–/–→WT) or WT (WT→WT) bone marrow
and 6 weeks later implanted B16 subcutaneous
melanomas. We then transferred IL-12 cells into
sublethally irradiated mice and found that anti-
tumor responses were impaired in Il12rb2–/–→
WT mice but not in WT→WT mice (Figure 2A).
We also created chimeras using host Il12rb2–/–
mice reconstituted with bone marrow derived
from Il12rb2–/– (Il12rb2–/–→Il12rb2–/–) or WT
mice (WT→Il12rb2–/–) and implanted them with
B16 subcutaneous melanomas 6 weeks later. We
transferred IL-12 cells into sublethally irradiated
mice and found that antitumor responses were
rescued in Il12rb2–/– mice reconstituted with WT
bone marrow (WT→Il12rb2–/–; Figure 2B). These
experiments together demonstrated that IL-12
acted directly on bone marrow–derived cells in
order to improve the antitumor immunity of
transferred T cells.
IFN-γ secretion and sensitization by endogenous cells is
required for antitumor immunity. Given the require-
ment for sensitization of bone marrow–derived
cells, we next tried to decipher the role of IFN-γ
in tumor regression. We gene transduced open-
repertoire WT or Ifng–/– CD8+ T cells with the
pmel-1 TCR (P-TCR) and IL-12 (P-TCR/IL-12)
and adoptively transferred equal numbers of
double-positive cells (2.5 × 105) into sublethally
irradiated WT or Ifng–/– mice bearing B16 mela-
nomas (Figure 3A). Surprisingly, Ifng–/– P-TCR/
IL-12 cells induced tumor regression to the same degree as WT
P-TCR/IL-12 cells in WT hosts, indicating that IFN-γ secretion by
transferred CD8+ T cells was not required for antitumor responses
(Figure 3A). Within the same experiment, we also transferred WT
P-TCR/IL-12 cells into WT or Ifng–/– mice and found that antitu-
mor immunity was significantly impaired in mice unable to pro-
duce IFN-γ (Figure 3A). These results indicate that the production
of IFN-γ by endogenous cells was necessary for tumor regression.
We next assessed the importance of IFN-γ in imparting a direct
effect on endogenous cells by transferring IL-12 cells into suble-
thally irradiated tumor-bearing Ifngr–/– mice and witnessed only a
partial impairment in antitumor immunity when host cells were
unable to respond to IFN-γ (Figure 3B). Taken together, these data
illustrate the need for host cells to produce IFN-γ, but show that
Antitumor immunity of IL-12–engineered pmel-1 CD8+ T cells (IL-12 cells) is not dependent
on type I self polarization but does require an endogenous response to secreted IL-12.
(A) Representative intracellular flow cytometry plot for IL-12 expression in WT or Il12rb2–/–
CD8+ cells. (B) Representative histogram for CD62L, IL-2Rα, IL-7Rα, and Sca-1 expres-
sion in WT or Il12rb2–/– IL-12 cells. (C) Intracellular staining for IFN-γ and TNF-α in WT or
Il12rb2–/– IL-12 cells stimulated with PMA/ionomycin. All flow cytometry data in A–C are
representative of at least 3 independent experiments. Numbers represent percentage of
cells in each quadrant. (D) Tumor treatment with 105 WT or Il12rb2–/– IL-12 cells transferred
into sublethally irradiated (5-Gy TBI) C57BL/6 mice bearing 10-day established subcutane-
ous B16 tumors (n = 5). All data are expressed as mean ± SEM and are representative of
2 independent experiments. *P < 0.05, Wilcoxon’s rank-sum test compared with no treat-
ment (NT) control. (E) Antitumor immunity of 105 WT IL-12 cells transferred into sublethally
irradiated WT or Il12rb2–/– C57BL/6 mice bearing subcutaneous B16 tumors established for
10 days. All data are expressed as mean ± SEM and are representative of 2 independent
experiments. *P < 0.05, Wilcoxon’s rank-sum test compared with no treatment control;
ΨP < 0.05, compared with WT IL-12 cells in Il12rb2–/– host.
4748?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
the requirement for IFN-γ receptors on endogenous cells is only
partial. These findings suggest that the direct effects of IFN-γ
on tumor cells may be mechanistically important for antitumor
immunity in this model.
IL-12–mediated improvements in antitumor immunity are independent
of host T cells, B cells, and NK cells. Based on our previous experiments
and published mechanisms of IL-12, we hypothesized that endoge-
nous CD8+ and NK cells were likely responsible for tumor destruc-
tion (17, 19). We therefore transferred IL-12 cells into sublethally
irradiated tumor-bearing WT or Rag1–/– mice that are devoid of
endogenous T and B cells and found that antitumor responses
remained robust in Rag1–/– mice, indicating that endogenous T or
B cells were not necessary to induce tumor regression (Figure 4A).
We next transferred IL-12 cells into tumor-bearing sublethally
irradiated WT or Rag1–/– mice depleted of NK cells (90%–95% NK
cell elimination 3 weeks after adoptive transfer) and found that
tumor destruction remained robust despite the lack of host T and
B cells and a significant depletion in NK cells (Figure 4B). Based
on our previous work indicating that IL-12 enhanced the infiltra-
tion of the adoptively transferred T cells within tumors and the
clear benefits gained by IL-12 sensitization of bone marrow cells,
we hypothesized that perhaps IL-12 might be altering bone mar-
row–derived APCs, leading to indirect effects on transferred T cells.
We harvested tumor samples 3 and 7 days following the transfer of
1 × 105 mock-transduced cells (mock) or IL-12 cells into sublethal-
ly irradiated tumor-bearing Rag1–/– mice depleted of NK cells and
found higher numbers of IL-12
cells infiltrating tumors compared
with mock cells (Figure 4C).
To visualize infiltrating T cells
within tumors, we captured immu-
nofluorescent confocal images
(transferred T cells, thy1.1+ green;
blood vessels, CD31+ red) from
tumor sections 7 days following cell
transfer into sublethally irradiated
mice and observed thy1.1+ trans-
ferred T cells infiltrating the extra-
vascular space of tumors treated
with IL-12 cells, but not mock cells
(Figure 4D). We also subjectively
witnessed disruptions in the vas-
cular integrity of tumors in mice
treated with IL-12 compared with
mock cells, although this observa-
tion was more an association than
a mechanistic finding. Thus, IL-12
within the tumor microenviron-
ment indirectly led to the increased
local proliferation of adoptively
transferred tumor antigen–spe-
cific T cells. This was unexpected,
but completely consistent with our
data showing that IL-12 did not
act directly on transferred T cells
and instead sensitized bone mar-
row–derived cells independently of
host T, B, and NK cells to indirectly
enhance the ability of transferred T
cells to infiltrate tumors.
An inflammatory gene signature and increased antigen processing and
presentation within tumors treated with IL-12–engineered CD8+ T cells. To
understand how IL-12 triggered tumor regression, we performed
whole transcriptome analysis of tumor samples from mice 3 and
7 days following treatment with IL-12 cells or mock cells (24, 28).
We examined select genes encoding for cytokines, chemokines,
chemokine receptors, inflammatory mediators, and costimulatory
molecules and observed an over 10-fold increase in the expression
for IL-1β, S100a8, and S100a9 from tumors of mice 3 days fol-
lowing treatment with IL-12 compared with mock cells (Table 1).
Interestingly, we also observed an increase in gene expression for
Nlrp3 and Nlrc5 within IL-12–treated tumors, indicating a possible
role for inflammasome formation in antitumor immunity.
Overall, we found 407 transcripts differentially expressed on
days 3 and 7, with 360 genes upregulated and 47 genes downregu-
lated (Figure 5A; fold change [FC] > 2, P value with false discovery
rate [FDR] < 0.05, n = 4). We performed an unbiased gene-ontol-
ogy enrichment analysis, and the highest enrichment score was
assigned to immune system processes in tumors treated with IL-12
compared with mock cells (Supplemental Figure 2). Under the
immune system category, pathway analysis identified antigen pro-
cessing and presentation as the most differentially increased path-
way (Figure 5B), and mRNA levels for several genes such as tap1,
tap2, tpn, clip, lmp2, lmp7, H2-Ab1, H2-Q6, H2-Aa, H2-DMa, H2-K1,
H2-D1, and H2-Ab1 were at least 2-fold higher in IL-12 compared
with mock-treated tumors (Figure 5C). Additionally, the most
IL-12–dependent sensitization of bone marrow–derived cells is critical for tumor regression. (A) WT
C57BL/6 mice were lethally irradiated (6-Gy + 6-Gy TBI) and reconstituted with either WT (WT→WT) or
Il12rb2–/– (Il12rb2–/–→WT) bone marrow. Six weeks after the formation of chimeras, mice (n = 10/group)
were implanted with subcutaneous B16 melanomas, sublethally irradiated (5-Gy TBI), and given 105
IL-12 cells after tumors were established for 10 days. Data are expressed as mean ± SEM and are
representative of 2 independent experiments. *P < 0.05, Wilcoxon’s rank-sum test compared with no
treatment control; **P < 0.05, compared with IL-12 cells into Il12rb2–/–→WT mice. (B) Il12rb2–/– C57BL/6
mice were lethally irradiated (6-Gy + 6-Gy TBI) and reconstituted with either WT (WT→Il12rb2–/–) or
Il12rb2–/– (Il12rb2–/–→Il12rb2–/– ) bone marrow. Six weeks after the formation of chimeras, mice (n = 10/
group) were implanted with subcutaneous B16 melanomas, sublethally irradiated, and given 105 IL-12
cells after tumors were established for 10 days. Data are expressed as mean ± SEM and are represen-
tative of 2 independent experiments. *P < 0.05, Wilcoxon’s rank-sum test compared with no treatment
control; **P < 0.05, compared with IL-12 cells in Il12rb2–/–→Il12rb2–/– mice.
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
differentially expressed transcript was Ifng (>62-fold) along with
mRNA levels for genes commonly found in effector T cells (Gzmb,
Il2ra, Gzma; Figure 5D).
We confirmed the transcript level by real-time PCR assays for
2 known inflammatory mediators and found significantly higher
expression of IL-10 and iNOS from tumors of mice treated with
IL-12 compared with mock cells (Supplemental Figure 3). We also
noted temporal changes within tumors, as 2,776 genes were dif-
ferentially expressed between days 3 and 7 in tumors treated with
IL-12 cells (Supplemental Figure 4). Although these results high-
lighted the dynamic nature of the tumor microenvironment prior
to the regression of established lesions, analyzing gene transcripts
differentially expressed consistently on both day 3 and day 7 pro-
vided valuable mechanistic insights. Given that tumor rejection
involved IL-12–mediated sensitization of bone marrow–derived
cells and that host T cells, B cells, and NK cells did not appear to
be involved, data generated by the whole transcriptome analysis
pointed toward antigen processing and presentation as an impor-
tant mechanistic pathway differentially expressed in mice treated
with IL-12 compared with mock cells.
Antitumor immunity of IL-12 cells is dependent on the functional repro-
gramming of myeloid-derived cells in situ to cross-present natural tumor
antigens. Based on our previous experiments, we hypothesized that
IL-12 may have an impact on the antigen-presenting capabilities
of bone marrow–derived stromal cells residing within tumors. We
therefore looked for IL-12 receptor β2 (Il12rb2) expression in sin-
gle-cell suspensions of whole tumors and found that the majority
of cells capable of functionally responding to IL-12 were indeed
CD11b+ myeloid–derived stromal cells (Figure 6A).
We next analyzed single-cell tumor suspensions from mice
1 week following treatment with mock or IL-12 cells and ana-
lyzed PI–, CD3–, B220–, NK1.1–, and CD11b+ myeloid–derived
cells. Tumor-infiltrating myeloid cells from mice treated with
IL-12 cells compared with mock cells appeared markedly differ-
ent based on forward and side scatter on flow cytometric analy-
sis (Figure 6B). To assess whether we had truly reprogrammed
tumor-infiltrating myeloid-derived cells in situ, we performed
a flow cytometry–based cell sort of PI–, CD3–, B220–, NK1.1–,
and CD11b+ cells from established tumors of treated mice and
carried out PCR-based arrays for transcripts common to APCs.
We observed an over 8-fold increase in transcript levels for Ifng,
Il2, Il8ra, Ccl11, and Ccl20 in 2 independent experiments from
myeloid-derived cells isolated from multiple pooled tumors
treated with IL-12 over mock cells (Supplemental Figure 5).
Interestingly, we also measured over 4-fold increases in mRNA
for B2m (Supplemental Figure 5) and recorded higher expression
of H-2Db on CD11b+ myeloid–derived cells from tumors of mice
treated with IL-12 over mock cells (Figure 6C).
To understand the functional importance of increased levels of
MHC class I, we transferred IL-12 cells into sublethally irradiated
tumor-bearing WT, B2m–/– (MHC class I deficient), or IAb–/– (MHC
class II deficient) mice. We observed a significant impairment in
antitumor immunity in mice lacking MHC class I but not MHC
class II (Figure 6D). Importantly, untreated tumors grew at an
identical pace in mice of all strains. These results clearly implicated
the need for in vivo cross presentation for successful antitumor
responses, an interesting finding given that we transferred cells that
were highly activated in vitro and the tumors grown on mice were
unmanipulated and fully capable of being directly recognized.
To further assess the importance of in vivo cross presenta-
tion, we transferred IL-12–engineered pmel-1 Ly 5.1+ (IL-12P-Ly5.1)
gene–marked CD8+ T cells and open-repertoire IL-12 engineered
thy1.1+ (IL-12OR-Thy1.1) gene–marked CD8+ T cells into the same
WT or B2m–/– mouse (Figure 6E). We observed an increase in the
proliferation of activated antigen-specific IL-12P-Ly 5.1 in WT mice
compared with B2m–/– mice. Notably, we saw no IL-12P-Ly 5.1 within
tumors of B2m–/– mice, but observed a clear population of cells
within tumors of WT mice. Furthermore, we observed no defects
in the longevity of open-repertoire IL-12OR-Thy1.1 CD8+ T cells in
B2m–/– mice compared with WT mice (Figure 6E). To visualize infil-
trating T cells within tumors in WT compared with B2m–/– mice,
we captured immunofluorescent confocal images (transferred T
cells, thy1.1+ green; blood vessels, CD31+ red) from tumor sections
7 days following the transfer of 1 × 105 IL-12 cells into sublethally
IL-12–induced IFN-γ production and sensitization by host cells are
partially required for antitumor immunity. (A) Antitumor immunity of
2.5 × 105 WT or Ifng–/– CD8+ T cells expressing the P-TCR and IL-12
transferred into sublethally irradiated (5-Gy TBI) C57BL/6 mice (n = 5/
group) bearing subcutaneous B16 tumors established for 10 days.
In the same experiment, 2.5 × 105 WT CD8+ T cells expressing the
P-TCR and IL-12 were adoptively transferred into sublethally irradiated
WT or Ifng–/– C57BL/6 mice (Ifng–/–h; n = 5) bearing subcutaneous B16
tumors established for 10 days. All data are expressed as mean ± SEM
and are representative of 2 independent experiments. *P < 0.05, Wil-
coxon’s rank-sum test compared with no treatment control; **P < 0.05,
compared with P-TCR + IL-12 (WT > Ifng–/–h). (B) Antitumor immunity
of 105 IL-12 cells following transfer into sublethally irradiated WT or
Ifngr–/– C57BL/6 recipient mice (Ifngr–/–h) bearing subcutaneous B16
tumors established for 10 days. All data are expressed as mean ± SEM
and are representative of 2 independent experiments. *P < 0.05, Wil-
coxon’s rank-sum test compared with no treatment control; **P < 0.05,
compared with IL-12 cells in Ifngr–/–h mice.
4750?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
irradiated WT or B2m–/– mice and observed thy1.1+ transferred T
cells infiltrating the extravascular space of tumors in WT but not
B2m–/– mice (Figure 6F). Thus, IL-12 secreted by tumor-specific
CD8+ T cells triggered the functional reprogramming of in situ
myeloid-derived cells, promoting the cross presentation of natu-
ral tumor antigens that enabled transferred T cells to infiltrate
tumors and induce the regression of well-established lesions.
Characterization and antigen-presenting capabilities of myeloid-derived
subpopulations within tumors. To analyze myeloid-derived stromal
populations within tumors in a more detailed manner, we per-
formed multicolor flow cytometry on single-cell suspensions
from well-established subcutaneous B16 tumors shortly follow-
ing (8 hours) a 5-Gy total body
irradiation (TBI) preconditioning
regimen and found a panoply of
myeloid-derived cell populations
residing within tumors. Due to the
redundancy of cell-surface mark-
ers between many of the myeloid-
derived cell subpopulations, we
used highly multicolored flow
cytometry to analyze unique sub-
populations of cells within tumors.
We first created single-cell suspen-
sions of established B16 tumors
and created a live gate by excluding
cells staining positive for the vivid
fixable violet live/dead stain.
We analyzed all endogenous
cells within tumors by gating on
CD45+ cells and found that the
majority of endogenous cells were
of myeloid origin and stained
positive for CD11b (Figure 7A).
The CD45+CD11b– population
consisted mostly of lympho-
cytes, with a small fraction of
NK cells (data not shown). With-
in the CD45+CD11b+ gate, we
observed a distinct population
of dendritic cells that stained for
CD11c and I-Ab. We next ana-
lyzed the CD45+CD11b+CD11clo
population and observed a clear
population of macrophages
that stained positive for F4/80
We then evaluated the frac-
tion of myeloid cells that were
and detected distinct populations
of cells expressing Ly6C and Ly6G.
These cells, commonly character-
ized as MDSCs (ref. 34), represent a
heterogeneous population of cells
from monocytic (MDSC-M) and
granulocytic (MDSC-G) origins
(Figure 7A). Within B16 tumors,
we observed a distinct popula-
tion of CD45+CD11b+CD11cloF4/
80loLy6ChiLy6Glo cells of monocytic origin that we categorized as
MDSC-M. There also existed a clear population of CD45+CD11b+
CD11cloF4/80loLy6Cmid-hiLy6Ghi cells that we characterized as
granulocytic in origin (MDSC-G), although this categorization is
still a matter of debate (Figure 7A and ref. 35). Thus, bone mar-
row–derived myeloid cells composing the tumor stroma are a het-
erogeneous population of phenotypically distinct immune cells.
We next sought to assess the ability of tumor-residing myeloid
populations to stimulate the division and activation of CD8+ T cells.
Single-cell suspensions of well-established B16 melanomas from
mice treated with IL-12 or mock cells were sorted by flow cytom-
etry for macrophages, dendritic cells, and MDSCs (sorting strategy
IL-12–induced sensitization of endogenous immunity is independent of host T, B, and NK cells, but
increases tumor infiltration of adoptively transferred T cells. (A) Antitumor immunity following the transfer
of 105 IL-12 cells into sublethally irradiated WT or Rag1–/– C57BL/6 mice (n = 5) bearing subcutaneous
B16 tumors established for 10 days. (B) Tumor treatment of 105 IL-12 cells adoptively transferred into
sublethally irradiated tumor-bearing WT or Rag1–/– C57BL/6 mice depleted of NK cells. All data in A
and B are expressed as mean ± SEM and are representative of 2 independent experiments. *P < 0.05,
Wilcoxon’s rank-sum test compared with no treatment control. (C) Representative flow cytometry plots
(left panel) and enumeration (right panel) of adoptively transferred T cells (CD8+ thy1.1+) from single-
cell tumor suspensions 3 and 7 days following treatment with 105 IL-12 or mock cells in NK-depleted
Rag1–/– mice. Data are expressed as mean ± SEM, *P < 0.05, Student t test. All flow cytometry plots
gated on live PI− cells and numbers represent percentage of CD8+ Thy1.1+ cells. (D) Tumor sections
from sublethally irradiated WT mice 7 days following the treatment of 105 IL-12 or mock cells were
stained for thy1.1 on transferred T cells (green), CD31 expressed on endothelial cells (red), and DAPI
(blue) to stain the nucleus. Stained sections were analyzed using fluorescence confocal microscopy.
Original magnification, ×40.
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
depicted in Supplemental Figure 6). These different populations
were then cocultured with CFSE-labeled CD8+ T cells isolated from
untouched splenocytes of P-TCR Tg mice in a 10:1 ratio of T cells
to APCs. Myeloid-derived populations isolated from B16 tumors of
mice treated with mock cells failed to induce the division of naive
pmel-1 CD8+ T cells (Figure 7B). In striking contrast, macrophages,
dendritic cells, and MDSCs from B16 tumors in mice treated with
IL-12 cells stimulated the in vitro division and activation of CD8+
T cells (Figure 7B). These results indicate that IL-12 triggered a
programmatic change in the major professional APC populations
present within tumors, although IL-12 sensitization of MDSCs
appeared to be the most potent in stimulating CD8+ T cells.
Recognition of cross-presented tumor antigen by IL-12–expressing CD8+ T
cells is sufficient to induce tumor regression. We sought to further examine
the importance of IL-12 in triggering the recognition of cross-present-
ed antigen by antitumor T cells. We developed a model to examine the
effects of in vivo cross presentation by implanting Cloudman S91 mel-
anomas (H-2d) on C57BL/6 × DBA F1 (H-2b/d) mice followed by the
adoptive transfer of pmel-1 CD8+ T cells (H-2b). To confirm the MHC
restriction of our tumor lines, we added IFN-γ in vitro for 48 hours
and witnessed an expected increase in H-2b expression in B16 mela-
noma cultures and an increase in H-2d expression in Cloudman S91
melanoma culture lines (Figure 8A). These results confirmed the
identities of the tumors used in MHC mismatch experiments.
To test the capacity of IL-12 cells to trigger killing of MHC
mismatched tumors incapable of direct antigen presentation, we
implanted Cloudman melanomas (H-2d) in C57BL/6 × DBA F1
H-2b/d mice and transferred IL-12 or mock cells (H-2b) into suble-
thally irradiated mice. We observed the regression of large estab-
lished tumors following the transfer of IL-12 compared with mock
cells (Figure 8B). The presence of IL-12 had a significant impact
on improving the antitumor immunity of tumor-specific CD8+
T cells, indicating that IL-12 triggered changes within tumors to
enhance the cross presentation of antigens in vivo.
We sought to assess the differential impact of transferred IL-12–
expressing cells on subpopulations of myeloid-derived cells capable
of cross-presenting tumor-associated antigens for recognition by
CD8+ T cells. We identified populations of myeloid-derived cells
(macrophages, dendritic cells, MDSC-M, and MDSC-G) residing
within Cloudman S91 melanomas (Figure 8C). Unlike the tumor
cells in which they reside, the myelomonocytic cells from C57BL/6
× DBA F1 mice expressed both H-2b and H-2d and could therefore
be recognized by IL-12 cells specific for gp10025–33 in the context of
H-2b. We examined the presence of these cells within tumors 10 days
following the adoptive transfer of either IL-12 or mock cells. Just
prior to a major drop in tumor size, 10 days following the transfer
of IL-12 cells, we observed a sudden decrease in CD11b+F4/80hi mac-
rophages, CD11b+CD11chi dendritic cells, and CD11b+LyChiLy6Glo
MDSC-M in tumors from mice treated with IL-12 cells compared
with mock cells (Figure 8C). These changes were not observed at
earlier time points such as day 3 and day 7 (data not shown).
The majority of myeloid-derived cells remaining within tumors
of mice treated with IL-12 cells were a uniform population of
CD11b+, Ly6CMid-hi, and Ly6Ghi cells (Figure 8C). Although the
fractional percentage of these “double-positive” granulocytic cells
appeared to be higher (Figure 8C), upon quantification, the abso-
lute number of cells within tumors appeared to be unchanged
(Figure 8D). We observed significant decreases in the number of
CD11b+F4/80hi macrophages, CD11b+CD11chi dendritic cells, and
CD11b+LyChiLy6Glo MDSC-M cells in tumors from mice treated
with IL-12 cells compared with mock cells (Figure 8D). We addi-
tionally found that changes in the CD11b+ myeloid–derived popu-
lations occurred only in tumors and not in the spleens of C57BL/6
mice treated with IL-12 cells (Supplemental Figure 7). Unresolved
by these experiments were whether decreased numbers of cells pos-
sessing the flow cytometric parameters identifying them as myelo-
monocytic cell subsets represented death of these cross-presenting
cells or whether it indicated altered cell differentiation or migra-
tion. However, the changes that we observed in myeloid-derived
subpopulations were confined to areas where tumor antigen was
present and were not a part of a generalized phenomenon.
The role for CD11b+, Ly6Cmid-hi, and Ly6Ghi granulocytic cells
within IL-12–treated tumors remains to be thoroughly explored.
In light of recent studies highlighting the capability of polariz-
ing tumor-infiltrating neutrophils to an N1 phenotype (36), we
hypothesized that perhaps the functional profile of Ly6Ghi cells
within IL-12–treated tumors may be altered. Given our earlier find-
ings highlighting the need for endogenous cells to secrete IFN-γ
Select genes significantly differentially expressed within tumors
of mice treated with IL-12–engineered CD8+ T cells
Cxcr6 Chemokine (C-X-C motif) receptor 6
Cxcl9 Chemokine (C-X-C motif) ligand 9
Ccrl2 Chemokine (C-C motif) receptor 2
Cxcl10 Chemokine (C-X-C motif) ligand 10
Ccl4 Chemokine (C-C motif) ligand 4
Ccr1 Chemokine (C-C motif) receptor 1
Ccl5 Chemokine (C-C motif) ligand 5
Tnf Tumor necrosis factor
Cxcl3 Chemokine (C-X-C motif) ligand 3
Ccl8 Chemokine (C-C motif) ligand 8
Ccl25 Chemokine (C-C motif) ligand 25
Ccl17 Chemokine (C-C motif) ligand 17
S100a8 S100 calcium binding protein A8
S100a9 S100 calcium binding protein A9
Saa3 Serum amyloid A3
Nos2 Nitric oxide synthase 2, inducible
Nlrc5 NLR family, CARD domain containing 5
Nlrp3 NLR family, pyrin domain containing 3
Aim2 Absent in melanoma
Icos Inducible T cell costimulator
Tnfrsf9 Tumor necrosis factor receptor
(4-1BB)?superfamily, member 9
Tnfrsf4 Tumor necrosis factor receptor
(OX-40)?superfamily, member 4
Tnfrsf18 Tumor necrosis factor receptor
(GITR)?superfamily, member 18
Slamf7 Slam family member 7
Slamf8 Slam family member 8
Icam1 Intercellular adhesion
molecule 1 (CD54)
Day?3? Gene?name? Day?7
4752?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
(Figure 3), we performed an intracellular stain for IFN-γ in addition
to staining for the different myeloid surface markers. We found that
CD11b+Ly6Gmid-hi cells, but not CD11b+Ly6Glo cells, from tumors
of mice treated with IL-12 compared with mock cells, showed an
increase in the ability to secrete IFN-γ (Supplemental Figure 8).
All experiments described so far were preceded by a 5-Gy TBI
preconditioning regimen. To determine whether this pretreatment
preparation in some manner had an impact on the observed in
vivo effects of IL-12, we transferred IL-12 cells into nonirradiated
Cd4–/– mice bearing B16 tumors and compared antitumor efficacy
Tumors from mice receiving IL-12 compared with mock cells display an increase in the intrinsic capabilities for antigen processing and presen-
tation. (A) Dendrogram of whole transcriptome analysis displaying the 407 gene transcripts common to both day 3 and day 7 that were differ-
entially expressed in tumors following the adoptive transfer of 105 IL-12 cells compared with mock cells into sublethally irradiated mice bearing
subcutaneous B16 tumors. Data are representative of 4 independent experimental samples. (B) Unbiased gene-ontology enrichment analysis
for pathways under immune system processes from tumors of mice sublethally irradiated and treated with 105 IL-12 compared with mock cells.
Pathway analysis formulated using Ingenuity software. (C) Expression pattern (FC) from tumors of mice treated with IL-12 over mock cells for
different gene transcripts involved in the antigen-processing and -presentation pathway. Data were generated using Ingenuity software analysis.
(D) The top 8 upregulated and downregulated gene transcripts from tumors of mice treated with 105 IL-12 over mock cells from A. Data represent
mean ± SEM of the FC from 4 independent samples. For A–D, differentially expressed genes were identified by 1-way repeated measures ANOVA
(P < 0.01) corrected by Benjamini-Hochberg FDR method (P < 0.05), and this gene list was further filtered for between-group α levels of P < 0.01
and an FC criterion of more than 2.0 for genes differentially expressed from tumors treated with IL-12 over mock cells.
?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
to that of WT mice that received the 5-Gy TBI pretreatment. We
observed identical antitumor responses between irradiated WT
mice and nonirradiated Cd4–/– mice, indicating that the effects of
IL-12 on myeloid cells were independent of pretreatment regimens
that were necessary to remove CD4+ T cell populations acting as
immune suppressors or sinks (Supplemental Figure 9). We sought
to further measure whether irradiation contributed to the effects
of IL-12 on tumor-infiltrating myeloid-derived populations in
vivo. We transferred cells into nonirradiated Rag1–/– mice and once
again observed a decrease in the number of CD11b+F4/80hi macro-
phages, CD11b+CD11chi dendritic cells, and CD11b+Ly6ChiLy6Glo
MDSC-M in tumors from mice 14 days following treatment with
Enhanced antitumor immunity triggered by IL-12 is dependent on in vivo cross presentation of tumor antigens. (A) The percentage of PI–,
NK1.1–, CD3–, CD11b+, and IL-12Rβ2+ cells from single-cell suspensions of well-established B16 tumors. (B) Flow cytometric analysis with
backgating for PI–CD3–B220–NK1.1–CD11b+ cells from tumors 7 days following treatment with 105 IL-12 or mock cells. (C) CD11b+ cells from
B were examined for expression of H-2Db with quantification of mean fluorescence intensity for 4 independent mice (right panel). *P < 0.05,
t tests compared with no treatment. All plots are representative of at least 3 independent experiments. (D) Antitumor immunity in sublethally irradi-
ated WT, Iab–/–, or B2m–/– C57BL/6 mice bearing established B16 tumors and treated with 105 IL-12 cells. All data are expressed as mean ± SEM
and are representative of 2 independent experiments. *P < 0.05, Wilcoxon’s rank-sum test compared with no treatment control; ΨP < 0.05,
compared with IL-12 cells into B2m–/– host. (E) Representative flow cytometry plots for transferred T cells in tumors and spleens harvested from
sublethally irradiated WT or B2m–/– C57BL/6 mice 7 days following the transfer of 105 IL-12–expressing pmel-1 Ly5.1+CD8+ T cells (IL-12P-Ly5.1)
and 105 IL-12–expressing open-repertoire thy1.1+CD8+ T cells (IL-12OR-Thy1.1) into the same mouse. Data are representative of 3 independent
samples. Numbers represent percentage of Thy1.1+Ly5.1– or Thy1.1–Ly5.1+ cells. (F) Confocal microscopy for tumor sections from mice treated
in D (Thy1.1, green; CD31, red; DAPI, blue). Original magnification, ×40.
4754?The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
IL-12 cells compared with mock cells (Supplemental Figure 10).
Overall, these experiments show the importance of IL-12 for
enhancing the in vivo cross presentation of tumor antigens, a
mechanism independent of NKp46+ innate lymphoid cells (Sup-
plemental Figure 11), and suggest that the functional reprogram-
ming of stromal cells such as macrophages, dendritic cells, and
MDSCs plays an important role in the regression of established
melanomas (Figure 9).
Solid tumors form complex masses composed of diverse popula-
tions of cells. Intriguingly, they closely resemble lymphoid struc-
tures consisting of a full gamut of inflammatory immune cells,
such as macrophages, dendritic cells, granulocytic cells, and imma-
ture myeloid cells (3, 37). However, unlike immune cells found
within lymphoid organs that productively respond to acute infec-
tions, cells residing within tumors are alternatively activated and
bathe in an immunosuppressive environment (4, 6, 9).
Overcoming immune escape mechanisms induced by established
tumors remains a critical barrier for tumor immunologists devising
methods to combat cancer (6, 38–40). Lymphodepleting chemo-
therapy regimens are effective in removing regulatory T cells that
act like sinks for homeostatic mediators, such as IL-7 and IL-15,
and are a major source of suppressive cytokines, such as IL-10 and
TGF-β (19, 41, 42). Immune evasion in cancer, however, extends far
beyond regulatory T cells, and multiple studies have highlighted
the suppressive role of alternatively activated macrophages, func-
tionally impaired dendritic cells, and MDSCs (4, 6, 9, 17).
Therapies to stimulate the immune system against cancer date
back to over a century ago, when William B. Coley made the initial
observation that tumors could regress after the administration of
a mixture of bacteria consisting of killed cultures of Streptococci and
Bacillus prodigiosus known as Coley’s toxins. More recently, several
clinical trials have tried to recapitulate these effects by adminis-
tering proinflammatory cytokines against metastatic cancer with
limited success (21, 43, 44). One of the major barriers with the
systemic administration of immunostimulatory mediators such
as IL-12 is likely the inability to reach high enough local concen-
trations within tumors to impart a meaningful effect on resident
immune cells (45).
Studies by Steven A. Rosenberg’s group for the first time safely
infused gene-modified lymphocytes into patients with metastatic
cancer (46–48). In this study, we show that adoptively transferring
tumor antigen–specific CD8+ T cells engineered to secrete IL-12
can functionally remodel the tumor microenvironment into an
activated inflammatory state. These profound changes dramati-
cally improved the ability of CD8+ T cells to mediate tumor regres-
sion. In contrast with much of the literature ascribing the benefits
of IL-12 and IFN-γ to unmasking the immunogenicity of tumor
cells (49), we surprisingly show that IL-12 reversed immune escape
mechanisms orchestrated by MDSCs, dysfunctional dendritic cells,
and alternatively activated macrophages within the tumor microen-
vironment. Furthermore, these changes enabled improved function
of activated CD8+ T cells, implying that the recognition of cross-
presented cognate antigen in the presence of an acute inflamma-
tory environment had direct effects on tumor regression.
This study also suggests that direct recognition and targeting of
the tumor stroma may be critical for attaining regression of large
vascularized lesions (12–14). When we adoptively transferred in
vitro–activated tumor-specific IL-12–expressing CD8+ T cells into
mice deficient in MHC class I, we witnessed dramatic impairments
in antitumor responses, even though mice had unmanipulated
B16 tumors fully capable of presenting antigen to T cells. Further-
more, IL-12–expressing CD8+ T cells (H-2b restricted) were able to
cause the regression of Cloudman S91 melanomas (H-2d restrict-
ed) in C57BL/6 × DBA F1 (H-2b/d) mice, indicating that even in the
absence of direct recognition of tumor cells, significant regression
of established lesions could occur. The likely mechanism for CD8+
T cell destruction of established lesions may be multi-fold, but our
study, along with others, indicates that the collapse of the tumor
MDSCs, macrophages, and dendritic cells residing within B16 tumors of mice treated with IL-12 cells potently stimulate the proliferation of pmel
CD8+ T cells. (A) B16 tumors established on C57BL/6 mice for 10 days were excised 8 hours following 5-Gy TBI and examined by multicolor flow
cytometry for CD45, NK1.1, TCRb, B220, CD11b, CD11c, I-Ab, F4/80, Ly6C, and Ly6G cells. Flow cytometry plot is representative of at least
3 independent samples and gated on live, NK1.1–, TCRb–, and B220– cells. Numbers represent percentage of cells within each quadrant. (B)
Single-cell tumor suspensions were created 5 days following treatment of established B16 tumors with IL-12 or mock cells, and CD11b+GR1hi
MDSCs, CD11b+F4/80hi macrophages, and CD11b+CD11chi dendritic cells were sorted by flow cytometry and cocultured for 72 hours with CFSE-
labeled untouched pmel CD8+ T cells at a 10:1 T cells/APC ratio. Flow cytometry plots represent 3 independent samples.
? The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
stroma along with its intertwined vasculature may be a critical
determining factor preceding tumor regression (16).
Following successful treatment with IL-12 cells, we witnessed
a complete remodeling of the tumor microenvironment and the
disappearance of Ly6ChiLy6Glo MDSCs, macrophages, and den-
dritic cells within regressing lesions 10 days following cell trans-
fer. Although these studies suggest that adoptively transferred
IL-12–expressing CD8+ T cells recognize and target cross-present-
ing myeloid populations, we cannot rule out the possibility that
these findings may be due to altered differentiation, homing to, or
egress of myeloid cells from the tumor site.
Another concept that may help explain some of the findings in
this manuscript is bystander killing (16). Adoptively transferred
CD8+ T cells may initially recognize cross-presented cognate antigen
by myeloid-derived cells, and the collapse of the surrounding stroma
and tumor cells requires bystander effects. Interestingly, we observed
regression of established tumors 1 cm in size (approximately 109
cell), although the number of antigen-specific T cells infiltrating
the tumor never exceeded 105 cells. Immunofluorescence staining
further showed that the number of transferred T cells were far out-
numbered by cells composing the tumor mass. Further studies will
need to be completed in order to understand the complex interac-
tions happening within the tumor microenvironment leading to T
cell–mediated regression of established lesions.
In summary, we demonstrate what we believe is a novel mecha-
nism for IL-12 in antitumor immunity. IL-12 at the tumor site dra-
matically reversed local immune evasion mechanisms by altering the
intrinsic capabilities of professional APCs residing within the tumor
stroma. This programmatic change in myeloid-derived cells within
tumors enabled direct recognition of cross-presented cognate anti-
gen by CD8+ T cells. Designing T cells capable of penetrating and
altering the tightly coordinated tumor microenvironment may dra-
matically improve future adoptive immunotherapy clinical trials and
enable current gene therapies to reach their full therapeutic poten-
tial against cancer (50–55). The findings generated from this study
have formed the basis for a clinical trial accruing patients at the time
of this writing at the National Cancer Institute (NCI) at the NIH.
Patients with metastatic melanoma will receive IL-12–engineered
tumor-infiltrating lymphocytes (TILs) following a lymphodepleting
chemotherapy regimen (ClinicalTrials.gov ID NCT01236573).
Mice and tumor lines. Female thy1.1+ P-TCR Tg mice were generated in our
laboratory (50) and made available at The Jackson Laboratory. Female
IL-12 cells (H-2b) are capable of
causing complete regression of
established Cloudman S91 mela-
nomas (H-2d) on C57BL/6 × DBA
F1 mice (H-2b/d). (A) H-2Db and
H-2Dd expression of B16 and
Cloudman S91 melanoma cell
lines exposed to 675 ng/ml of IFN-γ
for 48 hours. (B) Antitumor immu-
nity of 5 × 105 IL-12 or mock cells
adoptively transferred into suble-
thally irradiated C57BL/6 × DBA
F1 H-2b/d mice bearing subcu-
taneous Cloudman S91 tumors
established for 21 days. All data
are expressed as mean ± SEM
and are representative of 2 inde-
pendent experiments. *P < 0.05,
Wilcoxon’s rank-sum test com-
pared with no treatment and
mock. (C) Flow cytometry plots for
macrophages (CD11b+ F4/80hi),
dendritic cells (CD11b+CD11chi),
and MDSC-G (CD11b+Ly6CMid-hi
Ly6Ghi) within established
Cloudman S91 melanomas on
C57BL/6 × DBA F1 H-2b/d mice
10 days following treatment with
IL-12 or mock cells. All plots gated
on PI– live cells; numbers repre-
sent percentage of cells in each
quadrant. (D) Data from C were
quantified through a flow cytome-
try count and normalized to 1 gram
of tumor. Data are expressed as
mean ± SEM. *P < 0.05, 1-way
ANOVA compared with NT and
4756? The?Journal?of?Clinical?Investigation http://www.jci.org Volume 121 Number 12 December 2011
C57BL/6 mice, C57BL/6 CD90.1 (thy1.1+), C57BL/6 Cd4–/–, C57BL/6 Rag1–/–,
C57BL/6 Il12rb2–/–, C57BL/6 Ifng–/–, C57BL/6 Ifngr–/–, C57BL/6 B2m–/–,
C57BL/6 IAb–/–, and C57BL/6 × DBA F1 H-2b/d mice were obtained from
The Jackson Laboratory. C57BL/6 female ly5.1+ mice were crossed with
female C57BL/6 P-TCR Tg mice to generate ly5.1+ P-TCR Tg mice. C57BL/6
female Il12rb2–/– mice were crossed with female C57BL/6 P-TCR Tg mice to
generate Il12rb2–/– P-TCR Tg mice. Tumor lines used for in vivo experiments
included B16, an H-2b+/gp100+ murine melanoma, and Cloudman S91, an
H-2d+/gp100+ murine melanoma (56). Both tumor lines were purchased
from ATCC and established and maintained as previously described (57).
Retroviral production and transduction. Detailed descriptions of gene thera-
py protocols for mice have been previously described (58).
Adoptive cell transfer. A detailed description of cell transfer methodology
is described in the Supplemental Methods.
Analysis of transferred and tumor-infiltrating cells: flow cytometry, cell enumera-
tion, flow cytometry sorts, CFSE proliferation, RT-PCR arrays, real-time PCR,
and IL-12p70 ELISA. Prior to transfer, CD8+ T cells were characterized by
flow cytometry for CD8α, CD62L, CD44, IL-7Rα, IL-2Rα, and Sca-1 (BD
Biosciences). IL-12, IFN-γ, and TNF-α were analyzed using intracellular
staining kits (BD Biosciences) with or without a 4-hour stimulation with
phorbol myristate acetate (PMA) (50 ng/ml) and ionomycin (1 μg/ml;
Sigma-Aldrich). Following adoptive transfer, tumor samples were har-
vested, digested with 200 U/ml collagenase IV (Invitrogen) and 100 μg/ml
DNAse I (Roche), and evaluated by flow cytometry for B220, NK1.1, CD3,
TCRb, CD45, CD45.1 (ly5.1), CD90.1 (thy1.1), CD11b, F4/80, Ly6C, Ly6G,
CD11c, I-Ab, H-2Db, and H-2Dd (BD Biosciences). Transferred pmel-thy1.1+
cells were analyzed by flow cytometry for
thy1.1 and CD8α expression.
Accurate enumeration was accom-
plished through flow cytometry counts.
Two-hundred microliters of the single-
cell tumor suspension, initially in an
enzymatic mixture volume of 10 ml, were
stained with the appropriate antibod-
ies, and the entire 200 μl sample was run
through a CANTO II Flow Cytometry
Machine (BD Biosciences) to obtain a
digital count that could be evaluated
using FlowJo software (Tree Star Inc.).
Real-time RT-PCR was performed as pre-
viously described (42).
Flow cytometry cell sorts for PI–, NK–,
B220–, CD3–, CD11b+, CD11b+Gr-1hi,
CD11b+CD11chi, and CD11b+F4/80hi
cells from single-cell tumor suspensions
were performed using a FACSAria II cell
sorter (BD Biosciences). Sorted cells were
lysed using RLT buffer (QIAGEN), and
RNA was isolated using the RNeasy Mini
Kit (QIAGEN). For in vitro proliferation
assays, untouched CD8+ T cells isolated
(Miltenyi Biotec) from spleens of pmel-1
mice were labeled with 1 μM of CFSE
and cocultured for 72 hours with differ-
ent myeloid populations isolated from
tumors in a 10:1 T cell/APC ratio.
RT-PCR arrays (SABiosciences) for
known genes in the antigen-presentation
and -processing pathway were used to ana-
lyze functional reprogramming of CD11b+
cells from tumors treated with IL-12 compared with mock cells. Single-gene
RT-PCR assays and ELISAs were performed as previously described (42).
Whole genome expression analysis and immunofluorescent confocal microscopy. Please
refer to Supplemental Methods for detailed description (GEO GSE29164).
Statistics. Tumor growth slopes were compared using Wilcoxon’s rank-
sum test. All data are represented as mean ± SEM. One-way ANOVA and
2-tailed Student t tests were used to test for significant differences in enu-
meration assays. P < 0.05 was considered significant.
Study approval. All experiments were conducted with the approval of the
NCI Animal Use and Care Committee.
This research was supported by the Intramural Research Pro-
gram of the NIH, NCI, Center for Cancer Research. The authors
would like to thank Dorina Frasheri, Arnold Mixon, and Shawn
Farid for excellent technical assistance and Megan Bachinski for
Received for publication May 2, 2011, and accepted in revised form
September 28, 2011.
Address correspondence to: Sid P. Kerkar or Nicholas P. Restifo,
National Cancer Institute, National Institutes of Health, Room
3-5762, 10 Center Drive, Bethesda, Maryland 20892-1502, USA.
Phone: 301.496.6507; Fax: 301.451.6949; E-mail: kerkars@mail.
nih.gov (S.P. Kerkar); firstname.lastname@example.org (N.P. Restifo).
Schematic diagram summarizing the proposed mechanism for tumor destruction induced by IL-12.
Myeloid-derived cells within the tumor microenvironment are sensitized by IL-12 to create an acute
inflammatory environment and improve the ability of antigen-specific CD8+ T cells to collapse large
research article Download full-text
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1. Coussens LM, Werb Z. Inflammation and cancer.
2. Ostrand-Rosenberg S, Sinha P. Myeloid-derived
suppressor cells: linking inflammation and cancer.
J Immunol. 2009;182(8):4499–4506.
3. Hanahan D, Weinberg RA. Hallmarks of cancer:
the next generation. Cell. 2011;144(5):646–674.
4. Mantovani A, Sica A. Macrophages, innate immu-
nity and cancer: balance, tolerance, and diversity.
Curr Opin Immunol. 2010;22(2):231–237.
5. Huang AY, Golumbek P, Ahmadzadeh M, Jaffee E,
Pardoll D, Levitsky H. Role of bone marrow-derived
cells in presenting MHC class I-restricted tumor
antigens. Science. 1994;264(5161):961–965.
6. Gabrilovich DI, Nagaraj S. Myeloid-derived sup-
pressor cells as regulators of the immune system.
Nat Rev Immunol. 2009;9(3):162–174.
7. Gabrilovich DI, et al. Production of vascular
endothelial growth factor by human tumors inhib-
its the functional maturation of dendritic cells. Nat
8. Bronte V, et al. Apoptotic death of CD8+ T lympho-
cytes after immunization: induction of a suppressive
population of Mac-1+/Gr-1+ cells. J Immunol. 1998;
9. Bronte V. Myeloid-derived suppressor cells in
inflammation: uncovering cell subsets with
enhanced immunosuppressive functions. Eur J
10. Mapara MY, Sykes M. Tolerance and cancer: mecha-
nisms of tumor evasion and strategies for breaking
tolerance. J Clin Oncol. 2004;22(6):1136–1151.
11. Lu T, et al. Tumor-infiltrating myeloid cells induce
tumor cell resistance to cytotoxic T cells in mice.
J Clin Invest. 2011;121(10):4015–4029.
12. Zhang B, et al. Equilibrium between host and can-
cer caused by effector T cells killing tumor stroma.
Cancer Res. 2008;68(5):1563–1571.
13. Zhang B, Karrison T, Rowley DA, Schreiber H. IFN-
gamma- and TNF-dependent bystander eradica-
tion of antigen-loss variants in established mouse
cancers. J Clin Invest. 2008;118(4):1398–1404.
14. Zhang B, et al. Induced sensitization of tumor
stroma leads to eradication of established cancer
by T cells. J Exp Med. 2007;204(1):49–55.
15. Wigginton JM, Wiltrout RH. IL-12/IL-2 combina-
tion cytokine therapy for solid tumours: transla-
tion from bench to bedside. Expert Opin Biol Ther.
16. Spiotto MT, Rowley DA, Schreiber H. Bystander
elimination of antigen loss variants in established
tumors. Nat Med. 2004;10(3):294–298.
17. Serafini P, et al. Phosphodiesterase-5 inhibition
augments endogenous antitumor immunity by
reducing myeloid-derived suppressor cell function.
J Exp Med. 2006;203(12):2691–2702.
18. Gajewski TF, et al. Immune resistance orchestrated
by the tumor microenvironment. Immunol Rev. 2006;
19. Antony PA, et al. CD8+ T cell immunity against a
tumor/self-antigen is augmented by CD4+ T helper
cells and hindered by naturally occurring T regula-
tory cells. J Immunol. 2005;174(5):2591–2601.
20. Finke J, Ko J, Rini B, Rayman P, Ireland J, Cohen
P. MDSC as a mechanism of tumor escape from
sunitinib mediated anti-angiogenic therapy. Int
21. Weiss JM, Subleski JJ, Wigginton JM, Wiltrout
RH. Immunotherapy of cancer by IL-12-based
cytokine combinations. Expert Opin Biol Ther. 2007;
22. Trinchieri G. Interleukin-12 and the regulation of
innate resistance and adaptive immunity. Nat Rev
23. Colombo MP, Trinchieri G. Interleukin-12 in anti-
tumor immunity and immunotherapy. Cytokine
Growth Factor Rev. 2002;13(2):155–168.
24. Brunda MJ, et al. Antitumor and antimetastatic
activity of interleukin 12 against murine tumors.
J Exp Med. 1993;178(4):1223–1230.
25. Eisenring M, vom Berg J, Kristiansen G, Saller E,
Becher B. IL-12 initiates tumor rejection via lym-
phoid tissue-inducer cells bearing the natural
cytotoxicity receptor NKp46. Nat Immunol. 2010;
26. Szabo SJ, Sullivan BM, Stemmann C, Satoskar AR,
Sleckman BP, Glimcher LH. Distinct effects of T-
bet in TH1 lineage commitment and IFN-gamma
production in CD4 and CD8 T cells. Science. 2002;
27. Takemoto N, Intlekofer AM, Northrup JT, Wherry
EJ, Reiner SL. Cutting Edge: IL-12 inversely regu-
lates T-bet and eomesodermin expression during
pathogen-induced CD8+ T cell differentiation.
J Immunol. 2006;177(11):7515–7519.
28. Smyth MJ, Taniguchi M, Street SE. The anti-tumor
activity of IL-12: mechanisms of innate immunity
that are model and dose dependent. J Immunol.
29. Nastala CL, et al. Recombinant IL-12 adminis-
tration induces tumor regression in association
with IFN-gamma production. J Immunol. 1994;
30. Bhardwaj N, Seder RA, Reddy A, Feldman MV.
IL-12 in conjunction with dendritic cells enhances
antiviral CD8+ CTL responses in vitro. J Clin Invest.
31. Mazzolini G, et al. Intratumoral injection of den-
dritic cells engineered to secrete interleukin-12 by
recombinant adenovirus in patients with meta-
static gastrointestinal carcinomas. J Clin Oncol.
32. Kerkar SP, et al. Tumor-specific CD8+ T cells
expressing interleukin-12 eradicate established
cancers in lymphodepleted hosts. Cancer Res.
33. Zhang L, et al. Improving adoptive T cell therapy
by targeting and controlling IL-12 expression to the
tumor environment. Mol Ther. 2011;19(4):751–759.
34. Gabrilovich DI, et al. The terminology issue for
myeloid-derived suppressor cells. Cancer Res. 2007;
35. Movahedi K, et al. Identification of discrete tumor-
induced myeloid-derived suppressor cell subpopu-
lations with distinct T cell-suppressive activity.
36. Fridlender ZG, et al. Polarization of tumor-associ-
ated neutrophil phenotype by TGF-beta: “N1” ver-
sus “N2” TAN. Cancer Cell. 2009;16(3):183–194.
37. Kowanetz M, et al. Granulocyte-colony stimulating
factor promotes lung metastasis through mobiliza-
tion of Ly6G+Ly6C+ granulocytes. Proc Natl Acad
Sci U S A. 2010;107(50):21248–21255.
38. Peranzoni E, et al. Myeloid-derived suppressor cell
heterogeneity and subset definition. Curr Opin
39. Mocellin S, Marincola FM, Young HA. Interleu-
kin-10 and the immune response against cancer: a
counterpoint. J Leukoc Biol. 2005;78(5):1043–1051.
40. Hurwitz AA, et al. Combination immunotherapy
of primary prostate cancer in a transgenic mouse
model using CTLA-4 blockade. Cancer Res. 2000;
41. Mackall CL, Hakim FT, Gress RE. Restoration of
T-cell homeostasis after T-cell depletion. Semin
42. Gattinoni L, et al. Removal of homeostatic cytokine
sinks by lymphodepletion enhances the efficacy of
adoptively transferred tumor-specific CD8+ T cells.
J Exp Med. 2005;202(7):907–912.
43. Leonard JP, et al. Effects of single-dose interleu-
kin-12 exposure on interleukin-12-associated
toxicity and interferon-gamma production. Blood.
44. Gollob JA, et al. Phase I trial of concurrent
twice-weekly recombinant human interleukin-
12 plus low-dose IL-2 in patients with melano-
ma or renal cell carcinoma. J Clin Oncol. 2003;
45. Kilinc MO, et al. Reversing tumor immune suppres-
sion with intratumoral IL-12: activation of tumor-
associated T effector/memory cells, induction of T
suppressor apoptosis, and infiltration of CD8+ T
effectors. J Immunol. 2006;177(10):6962–6973.
46. Rosenberg SA, et al. Gene transfer into humans--
immunotherapy of patients with advanced mela-
noma, using tumor-infiltrating lymphocytes modi-
fied by retroviral gene transduction. N Engl J Med.
47. Morecki S, et al. Retrovirus-mediated gene transfer
into CD4+ and CD8+ human T cell subsets derived
from tumor-infiltrating lymphocytes and periph-
eral blood mononuclear cells. Cancer Immunol
48. Blaese RM, et al. T lymphocyte-directed gene thera-
py for ADA- SCID: initial trial results after 4 years.
49. Dighe AS, Richards E, Old LJ, Schreiber RD.
Enhanced in vivo growth and resistance to rejection
of tumor cells expressing dominant negative IFN
gamma receptors. Immunity. 1994;1(6):447–456.
50. Morgan RA, et al. Cancer regression in patients after
transfer of genetically engineered lymphocytes.
51. June CH, Blazar BR, Riley JL. Engineering lympho-
cyte subsets: tools, trials and tribulations. Nat Rev
52. Hwu P, Rosenberg SA. The genetic modification
of T cells for cancer therapy: an overview of labo-
ratory and clinical trials. Cancer Detect Prev. 1994;
53. Brenner MK, Heslop HE. Adoptive T cell therapy of
cancer. Curr Opin Immunol. 2010;22(2):251–257.
54. Barrett AJ, Le Blanc K. Immunotherapy prospects for
acute myeloid leukaemia. Clin Exp Immunol. 2010;
55. Sadelain M. T-cell engineering for cancer immuno-
therapy. Cancer J. 2009;15(6):451–455.
56. Wagner SN, et al. Intracutaneous genetic immuniza-
tion with autologous melanoma-associated antigen
Pmel17/gp100 induces T cell-mediated tumor protec-
tion in vivo. J Invest Dermatol. 2000;115(6):1082–1087.
57. Overwijk WW, et al. Tumor regression and auto-
immunity after reversal of a functionally tolerant
state of self-reactive CD8+ T cells. J Exp Med. 2003;
58. Kerkar SP, et al. Genetic engineering of murine
CD8+ and CD4+ T cells for preclinical adop-
tive immunotherapy studies. J Immunother. 2011;