Attenuated Toxoplasma gondii Stimulates Immunity to Pancreatic Cancer by Manipulation of Myeloid Cell Populations

Cancer Immunol Res. 2015 Aug;3(8):891-901. doi: 10.1158/2326-6066.CIR-14-0235. Epub 2015 Mar 24.


Suppressive myeloid cells represent a significant barrier to the generation of productive antitumor immune responses to many solid tumors. Eliminating or reprogramming suppressive myeloid cells to abrogate tumor-associated immune suppression is a promising therapeutic approach. We asked whether treatment of established aggressive disseminated pancreatic cancer with the immunotherapeutic attenuated Toxoplasma gondii vaccine strain CPS would trigger tumor-associated myeloid cells to generate therapeutic antitumor immune responses. CPS treatment significantly decreased tumor-associated macrophages and markedly increased dendritic cell infiltration of the pancreatic tumor microenvironment. Tumor-resident macrophages and dendritic cells, particularly cells actively invaded by CPS, increased expression of costimulatory molecules CD80 and CD86 and concomitantly boosted their production of IL12. CPS treatment increased CD4(+) and CD8(+) T-cell infiltration into the tumor microenvironment, activated tumor-resident T cells, and increased IFNγ production by T-cell populations. CPS treatment provided a significant therapeutic benefit in pancreatic tumor-bearing mice. This therapeutic benefit depended on IL12 and IFNγ production, MyD88 signaling, and CD8(+) T-cell populations. Although CD4(+) T cells exhibited activated effector phenotypes and produced IFNγ, CD4(+) T cells as well as natural killer cells were not required for the therapeutic benefit. In addition, CD8(+) T cells isolated from CPS-treated tumor-bearing mice produced IFNγ after re-exposure to pancreatic tumor antigen, suggesting this immunotherapeutic treatment stimulated tumor cell antigen-specific CD8(+) T-cell responses. This work highlights the potency and immunotherapeutic efficacy of CPS treatment and demonstrates the significance of targeting tumor-associated myeloid cells as a mechanism to stimulate more effective immunity to pancreatic cancer.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antigens, Neoplasm / immunology
  • CD8-Positive T-Lymphocytes / immunology
  • CD8-Positive T-Lymphocytes / metabolism
  • Cytokines / biosynthesis
  • Disease Models, Animal
  • Female
  • Humans
  • Immunity*
  • Immunomodulation*
  • Interleukin-12 / biosynthesis
  • Lymphocyte Activation / immunology
  • Mice
  • Mice, Knockout
  • Myeloid Cells / immunology*
  • Myeloid Cells / metabolism
  • Neoplasm Invasiveness
  • Pancreatic Neoplasms / genetics
  • Pancreatic Neoplasms / immunology*
  • Pancreatic Neoplasms / mortality
  • Pancreatic Neoplasms / pathology
  • Pancreatic Neoplasms / therapy
  • Protozoan Vaccines / administration & dosage
  • Protozoan Vaccines / immunology
  • T-Lymphocyte Subsets / immunology
  • T-Lymphocyte Subsets / metabolism
  • Toxoplasma / immunology*
  • Tumor Microenvironment / immunology


  • Antigens, Neoplasm
  • Cytokines
  • Protozoan Vaccines
  • Interleukin-12