Chemotactic factors underlying tumor infiltration by immunocompetent cells in human colorectal cancer

Colorectal cancer (CRC) is a common digestive tract malignancy and a major cause of cancer mortality. Several studies have convincingly shown that CRC infiltration by immunocompetent cells and, in particular, cytotoxic CD8+ T cells (CTLs), IFN-γ-producing T-helper 1 cells (Th1), Foxp3+ regulatory T cells (Tregs), and CD16+ MPO+ neutrophils, is significantly associated with prolonged patient survival. However, the chemotactic factors driving these cell populations into the tumor site, their cellular sources and their microenvironmental triggers remain to be elucidated. During my PhD training I have investigated the chemokine/chemokine receptor network promoting CRC infiltration by immune cells associated to favorable prognosis. In particular, I addressed: 1. The expression of immune cell markers and their correlation with chemokine expression in primary CRC tissues; 2. The identification of chemokine receptors relevant for CRC infiltration by beneficial immune cells; 3. The chemokine sources in CRC; 4. The microenvironmental stimuli triggering chemokine production in CRC tissues; 5. The effects of chemokine production on immune cell recruitment into CRC. The expression of a panel of genes encoding 39 chemokines and 7 markers specific for defined immune cell populations was assessed by quantitative PCR array in 62 samples of freshly excised primary CRC and autologous healthy colonic tissue. Correlations between expression of chemokine genes and immune cell markers were then evaluated. Furthermore, chemokine receptor profiles were analysed by flow cytometry on cell suspensions obtained upon digestion of clinical specimens or on corresponding cell populations from autologous peripheral blood. Based on chemokine receptor expression on tumor infiltrating cells and correlations between expression of chemokines and immune cell markers, I could identify for each immune cell subset a putative “chemokine signature”: 1) CCL3, CCL5, CCL8 CXCL9, CXCL10 and CXCL12, associated with recruitment of cytotoxic CTLs; 2) CCL5, CCL22, ...