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. 2015 Jul;149(1):201-10.
doi: 10.1053/j.gastro.2015.04.010. Epub 2015 Apr 14.

Exclusion of T Cells From Pancreatic Carcinomas in Mice Is Regulated by Ly6C(low) F4/80(+) Extratumoral Macrophages

Gregory L Beatty  1 , Rafael Winograd  2 , Rebecca A Evans  2 , Kristen B Long  3 , Santiago L Luque  3 , Jae W Lee  3 , Cynthia Clendenin  4 , Whitney L Gladney  3 , Dawson M Knoblock  3 , Patrick D Guirnalda  3 , Robert H Vonderheide  5
Affiliations

Exclusion of T Cells From Pancreatic Carcinomas in Mice Is Regulated by Ly6C(low) F4/80(+) Extratumoral Macrophages

Gregory L Beatty et al. Gastroenterology. 2015 Jul.

Abstract

Background & aims: Immunotherapies that induce T-cell responses have shown efficacy against some solid malignancies in patients and mice, but these have little effect on pancreatic ductal adenocarcinoma (PDAC). We investigated whether the ability of PDAC to evade T-cell responses induced by immunotherapies results from the low level of immunogenicity of tumor cells, the tumor's immunosuppressive mechanisms, or both.

Methods: Kras(G12D/+);Trp53(R172H/+);Pdx-1-Cre (KPC) mice, which develop spontaneous PDAC, or their littermates (controls) were given subcutaneous injections of a syngeneic KPC-derived PDAC cell line. Mice were then given gemcitabine and an agonist of CD40 to induce tumor-specific immunity mediated by T cells. Some mice were also given clodronate-encapsulated liposomes to deplete macrophages. Tumor growth was monitored. Tumor and spleen tissues were collected and analyzed by histology, flow cytometry, and immunohistochemistry.

Results: Gemcitabine in combination with a CD40 agonist induced T-cell-dependent regression of subcutaneous PDAC in KPC and control mice. In KPC mice given gemcitabine and a CD40 agonist, CD4(+) and CD8(+) T cells infiltrated subcutaneous tumors, but only CD4(+) T cells infiltrated spontaneous pancreatic tumors (not CD8(+) T cells). In mice depleted of Ly6C(low) F4/80(+) extratumoral macrophages, the combination of gemcitabine and a CD40 agonist stimulated infiltration of spontaneous tumors by CD8(+) T cells and induced tumor regression, mediated by CD8(+) T cells.

Conclusions: Ly6C(low) F4/80(+) macrophages that reside outside of the tumor microenvironment regulate infiltration of T cells into PDAC and establish a site of immune privilege. Strategies to reverse the immune privilege of PDAC, which is regulated by extratumoral macrophages, might increase the efficacy of T-cell immunotherapy for patients with PDAC.

Keywords: Lymphocyte; Pancreatic Cancer Treatment; Tolerance; Tumor Microenvironment.

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Figures

Figure 1
Figure 1. Gemcitabine and a CD40 agonist synergize to induce T cell-dependent tumor regression in a transplantable model of pancreatic carcinoma
(A) Healthy PC littermates were implanted subcutaneously on day 0 with a KPC-derived tumor cell line. On day 13, mice were treated with Gemcitabine (Gem) at 120 mg/kg or PBS followed 48 hours later by intraperitoneal injection of FGK45 or control IgG2a (each 100 μg). (B) Waterfall plot of tumor response for each animal (n>6 per group) determined by change in tumor volume measured 14 days after treatment. Gem/FGK45 vs PBS/IgG2a, P=0.005, Fisher's exact test. (C) Overall survival curves of the four experimental groups (n ≥ 6 per group). Gem/FGK45 vs PBS/IgG2a, P=0.0001, Gem/FGK45 vs PBS/FGK45, P=0.04; log-rank test. (D) Whisker plots showing quantification by immunohistochemistry of CD3, CD4, and CD8 cell infiltrates into tumors 14 days after the indicated treatment is shown (n = 4 per group). CD3, *P=0.018; CD4, *P=0.044; CD8, *P=0.022, **P=0.005, Student's t test (E) Healthy PC littermates (n ≥ 6 per group) were implanted and treated as in (A) with cohorts of mice also receiving depleting antibodies for CD4 (GK1.5) and CD8 (2.43) cells before and during treatment. Waterfall plot of tumor response determined by change in tumor volume is shown. Gem/FGK45 vs Gem/FGK45/GK1.5, P=0.001; Gem/FGK45 vs Gem/FGK45/2.43, P=0.015; Fisher's exact test.
Figure 2
Figure 2. Anti-tumor T cell immune responses can be induced in mice with spontaneously arising pancreatic carcinoma
(A) KPC mice with ultrasound confirmed tumors were implanted subcutaneously with a KPC-derived tumor cell line on day -12. On day 0, mice were treated with Gemcitabine (Gem) at 120 mg/kg or PBS followed 48 hours later by intraperitoneal injection of FGK45 or control IgG2a (each 100 · g). (B) Tumor growth curves of subcutaneously implanted tumors in mice (n = 3 per group) treated with control (PBS + IgG2a) versus gemcitabine plus FGK45 (Gem + FGK45). (C) Quantification of cellular infiltrates into tumors detected by immunohistochemistry 14 days after the indicated treatment (n = 4 per group, CD3, P=0.045; CD4, P=0.002; CD8, P=0.043; Foxp3, P=0.482; Student's t test). (D) Images showing hematoxylin & eosin (H&E) staining and immunohistochemistry for CD3, CD4, CD8, and Foxp3 expressing cells in subcutaneously growing tumors from mice 14 days after the indicated treatment.
Figure 3
Figure 3. T cells can penetrate the desmoplastic stromal reaction associated with pancreatic carcinoma
(A) On day 0, explanted PDAC tissue was reimplanted subcutaneously into KPC mice with ultrasound confirmed spontaneous PDAC tumors. Mice were treated on day 13 with Gemcitabine (Gem) at 120 mg/kg or PBS followed 48 hours later by intraperitoneal injection of FGK45 or control IgG2a (each 100 · g). (B) Representative H&E images of tumor tissue from (i) a KPC-derived tumor cell line implanted subcutaneously into a healthy PC littermate, (ii) a spontaneously arising PDAC tumor in a KPC mouse, and (iii) an explanted tumor from a KPC mouse grown subcutaneously in a healthy PC littermate. (C) Shown is the percent change in volume relative to baseline of explant tumors at 14 days after the indicated treatment. Each dot represents a single animal (Gemcitabine/FGK45 vs Control, P=0.003, Mann-Whitney U). (D) Quantification of cellular infiltrates into responding explant tumors detected by immunohistochemistry 14 days after the indicated treatment (n = 4 per group) *P<0.05, **P<0.01, ***P<0.005, Student's t test. (E) Quantification of cellular infiltrates into the spontaneous primary pancreatic tumor detected by immunohistochemistry 14 days after the indicated treatment (n = 4 per group) *P<0.05, **P<0.01, Student's t test.
Figure 4
Figure 4. Macrophages regulate T cell immunosurveillance in spontaneous pancreatic carcinoma
(A) KPC mice with ultrasound confirmed tumors were treated with Gemcitabine (Gem) at 120 mg/kg or PBS followed 48 hours later by intraperitoneal injection of FGK45 or control IgG2a (each 100 μg). A cohort of mice also received clodronate encapsulated liposomes (CEL). (B) Images showing H&E and CD3 staining of spontaneous primary pancreatic tumors from mice treated with control, Gem + FGK45, CEL, and Gem + FGK45 + CEL. (C) Images showing CD4 (i), CD8 (ii), and Foxp3 (iii) staining of spontaneous primary pancreatic tumors from mice treated with Gem + FGK45 + CEL. (D) Quantification of (C) CD3+ (D) CD4+, and (E) CD8+ cellular infiltrates detected by immunohistochemistry is shown (n = 4 per group). *, P<0.05; ***, P<0.001; unpaired 2-tailed t-test determined from 4-6 images per mouse. (E) Serum cytokine levels detected 14 days after treatment. For Gem/FGK45 vs Gem/FGK45/CEL, IL-17A, P=0.01; IFN-γ, P=0.008, IL-4, P=0.008; IL-5, P=0.04; IL-2, P=0.12, Student's t test.
Figure 5
Figure 5. A dual role for macrophages in regulating tumor regression in pancreatic carcinoma
KPC mice with ultrasound confirmed tumors were treated with Gemcitabine (Gem) at 120 mg/kg or PBS followed 48 hours later by intraperitoneal injection of FGK45 or control IgG2a (each 100 μg). Cohorts of mice also received clodronate encapsulated liposomes (CEL) or depleting antibodies for CD8 (2.43). (A) Shown is the percent change in volume relative to baseline of spontaneously arising tumors in KPC mice at 14 days after the indicated treatment. Each dot represents a single animal (Gem/FGK45/CEL vs Gem/FGK45/CEL/2.43, P=0.005, Student's t test). (B) A summary of tumor regression experiments performed with KPC mice in this manuscript is plotted in the context of previous experiments investigating therapy with FGK45. Previously published experiments are included for comparison purposes and are from a previous study . Absolute numbers of tumor regressions/total number of mice treated is shown next to the bar for each experiment.
Figure 6
Figure 6. Phenotype of macrophages that regulate T cell immunosurveillance in spontaneous pancreatic carcinoma
(A) Immunofluorescence images (with high magnification insets) showing DiI-liposome (red) uptake within (i) spleen, (ii) peritumoral lymph node, and (iii) tumor in a KPC mouse 24 hours after intraperitoneal injection of DiI-liposomes. Nuclei are stained with DAPI (blue). Scale bars, 20 μm. (B) A representative lymph node adjacent to tumor showing (i) F4/80+ macrophages (green), (ii) DiI-liposomes (red), and (iii) merged images revealing DiI-liposome uptake by F4/80+ macrophages. Scale bars, 20 μm. (C) Uptake of DiI liposomes by myeloid cells expressing F4/80, Ly6C, and Ly6G markers versus CD3+ T cells was quantified in KPC mice by flow cytometry. Gating strategy is shown in Supplementary Figure 8. *P<0.05, Student's t test. (D) Mean fluorescence intensity (MFI) for surface molecules present on CD45+ CD3neg CD11b+ Ly6Gneg F4/80+ Ly6Clow cells in KPC (blue) vs control (white) mice. *P<0.05, **P<0.005, Student's t test.
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