Colorectal Cancer . Immune Contexture . T cells . Stromal Cells . Chemokines Gut Microbiota

Cancer Immunotherapy

Tumor-host interactions in human colorectal cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death. Non-transformed cells in CRC microenvironment, including tumor-associated mesenchymal stromal cells (TASCs) and immune cells, have been recognized to play key roles in disease progression. Whereas infiltration by specific immune cell types is significantly associated with prolonged patient survival, TASC abundance predicts unfavorable prognosis. Mechanisms leading to recruitment of these cell populations and underlying their effects on clinical outcome remain to be clarified. CRC arises in an environment populated by the gut microflora. Commensal bacteria translocate across the dysfunctional neoplastic epithelium into the lamina propria, thus possibly stimulating stromal and immune cells. The potential impact of these events on tumor development and progression remains to be fully elucidated.We are interested in investigating interactions occurring between tumor, stromal and immune system in CRC and their modulation by the gut microflora. Understanding the complex network of tumor-host interactions in CRC may allow the identification of novel prognostic biomarkers and potential new areas of therapeutic intervention.

Main Projects

  • Role of CRC infiltrating IL-17-producing T cells: Phenotypes and prognostic relevance of tumor infiltrating IL-17-producing T cells (Th17) in CRC are still debated. Upon ex vivo analysis, and in vitro and in vivo experiments we found that CRC infiltrating Th17 are polyfunctional effector cells able to produce, in addition toIL-17, a spectrum of cytokine/chemokines ultimately leading to recruitment of beneficial CD8+ T cells and neutrophils. Our study reveals a positive role played by tumor infiltrating Th17 in CRC, thus calling for caution when envisaging novelIL-17/Th17 targeted therapies.
  • Monocytes-Th17 cells crosstalk: Monocytes (Mo) promote differentiation of naïve cells into Th17. However, their impact on pre-differentiated Th17 cells, suchthose infiltrating CRCs, is unknown. We assessed the ability of classical (cMo) and non-classical monocytes (ncMo) to promote expansion of memory Th17cells in vitro. We found that in the absence of microbial stimulation ncMo are more efficient stimulators of Th17 than cMo, and their ability is counteracted byLFA-1/ICAM-1 interaction. These data highlight ncMo as potential new therapeutic targets in IL-17-mediated inflammation.
  • Immune cell recruitment into CRC: Chemotactic factors leading to CRC infiltration by beneficial immune cells are still unclear. Upon ex vivo analysis of humanCRC specimens, we identified a panel of chemokine genes underlying tumor infiltration by favorable immune cell subsets. Stimulation of CRC cells by gut microbiota markedly enhanced the expression of these chemokines in vitro and invivo, and led to increased T cell recruitment into tumor xenografts. Importantly,in human CRC specimens, bacterial loads correlated with chemokine expression levels and extent of T cell infiltration. Our findings identify the gut microbiotaas critical modulator of immune cell trafficking into CRCs.
  • Impact of TASCs on CRC progression: Mechanisms underlying the negative prognostic significance of TASCs in CRC are not fully understood. By in vitro and invivo experiments, we found that upon tumor conditioning, TASCs acquire surface TGF-β expression and induce epithelial-to-mesenchymal transition (EMT)in CRC cells (see Figure 1). This results in higher numbers of circulating tumor cells, ultimately leading to increase metastasis formation. These data reveal a novel mechanism of tumor-stroma interaction and may suggest novel therapeutic interventions.
  • 3D culture models for primary CRC tissues: In collaboration with the Tissues Engineering group, we developed an innovative 3D system, based on a perfused bioreactor,for culturing freshly isolated CRC specimens. This system proved capable of preserving all components of CRC microenvironment, including tumor, mesenchymal and immune cells, up to five days, and might therefore be suitable for testing the efficacy of innovative anti-cancer compounds targeting the tumor or the tumor-associated stroma.

Figure 1: Tumor-stroma crosstalk in CRC. A. TASCs co-cultured with CRC cells (TASC +CRC) express membrane-bound TGF-β, as revealed by Imagestream analysis. B and C. CRC cells (green) co-cultured with TGF- β-expressing TASCs (CRC+TASC) undergo epithelial–to-mesenchymal transition, as indicated by the acquisition of elongated shape (B, see arrows) and by downregulation of Ecadherin and upregulation of N-cadherin, detected upon Imagestream analysis (C).