A Listeria Vaccine and Depletion of T-Regulatory Cells Activate Immunity Against Early Stage Pancreatic Intraepithelial Neoplasms and Prolong Survival of Mice

Abstract

BACKGROUND & AIMS Premalignant lesions and early stage tumors contain immunosuppressive microenvironments that create barriers for cancer vaccines. KrasG12D/+;Trp53R172H/+;Pdx-1-Cre (KPC) mice, which express an activated form of Kras in pancreatic tissues, develop pancreatic intraepithelial neoplasms (PanIN) that progress to pancreatic ductal adeno-carcinoma (PDA). We used these mice to study immune suppression in PDA. METHODS We immunized KPC and KrasG12D/+;Pdx-1-Cre mice with attenuated intracellular Listeria monocytogenes (which induces CD4+ and CD8+ T-cell immunity) engineered to express KrasG12D (LM-Kras). The vaccine was given alone or in sequence with an anti-CD25 antibody (PC61) and cyclophosphamide, to deplete T-regulatory (Treg) cells. Survival times were measured; pancreatic and spleen tissues were collected and analyzed by histologic, flow cytometry, and immunohistochemical analyses. RESULTS Interferon γ-mediated, CD8+ T-cell responses were observed in KPC and KrasG12D/+;Pdx-1-Cre mice given LM-Kras, but not in unvaccinated mice. Administration of LM-Kras to KPC mice 4–6 weeks old (with early stage PanINs), depleted of Treg cells, significantly prolonged survival and reduced PanIN progression (median survival, 265 days), compared with unvaccinated mice (median survival, 150 days; P = .002), mice given only LM-Kras (median survival, 150 days; P = .050), and unvaccinated mice depleted of Treg cells (median (medium survival, 170 days; P = .048). In 8- to 12-week-old mice (with late-stage PanINs),¼LM-Kras, alone or in combination with Treg cell depletion, did not increase survival time or slow PanIN progression. The combination of LM-Kras and Treg cell depletion reduced numbers of Foxp3+CD4+ T cells in pancreatic lymph nodes, increased numbers of CD4+ T cells that secrete interleukin 17 and interferon g, and caused CD11b+Gr1+ cells in the pancreas to acquire an immunostimulatory phenotype. CONCLUSIONS Immunization of KPC mice with Listeria monocytogenes engineered to express KrasG12D, along with depletion of Treg cells, reduces progression of early stage, but not late-stage, PanINs. This approach increases infiltration of the lesion with inflammatory cells. It might be possible to design immuno-therapies against premalignant pancreatic lesions to slow or prevent progression to PDA.

Bruton Tyrosine Kinase–Dependent Immune Cell Cross-talk Drives Pancreas Cancer

“…Although one prior study linked the Class IA PI3Ks to BTK activation in B cells, recent studies have reported that these proteins regulate similar but distinct signaling pathways in B cells (33, 34). Our studies instead reveal the selective role of the Class IB PI3K isoform PI3Kγ in regulating BTK to control the macrophage response to the tumor microenvironment.…”

Exclusion of T Cells From Pancreatic Carcinomas in Mice Is Regulated by Ly6Clow F4/80+ Extratumoral Macrophages

“…Because PDAC development is associated with the emergence of immunosuppressive cell populations including Tregs and myeloid cells 14-16 , we hypothesized that systemic immunosuppression present within tumor-bearing KPC mice may inhibit the ability of Gem+FGK to induce T cell dependent anti-tumor immunity. To examine this hypothesis, we implanted KPC-derived tumor cell lines into syngeneic KPC mice with spontaneous pancreatic tumors (Figure 2A).…”

CD40 Stimulation Obviates Innate Sensors and Drives T Cell Immunity in Cancer

“…For example, FAP + stromal cells in PDA regulate T cell infiltration to PDA via CXCL12/CXCR4 (Feig et al, 2013), but FAP + stromal cells in the KPC model are CD40-negative, and FAP + cell depletion (or CXCR4 inhibition) does not negatively impact T Regs in the way αCD40/chemotherapy does in the same KPC model. Vaccination with recombinant antigen-expressing Listeria is another powerful method to generate anti-PDA T cells (Keenan et al, 2014) but appears to rely on STING activation (Jin et al, 2013; Woodward et al, 2010), unlike αCD40. Other treatments that can mediate T cell responses against PDA include GVAX vaccination (Le et al, 2015; Soares et al, 2015), adoptive transfer of antigen-receptor engineered T cells (Stromnes et al, 2015), and CSF-1R inhibition (Zhu et al, 2014).…”