Neutrophils In Human Colorectal Cancer

Neutrophil Granulocytes (N) account for the majority of blood-circulating phagocytes that can infiltrate malignant tissues, including Colorectal Cancer (CRC). However, despite the fact that CRC progression has been linked to the immune contexture of its microenvironment and its microbiome, the phenotypic and functional characteristics of CRC-associated N is largely unknown. Our group has recently demonstrated that CRC infiltration by CD16/FcγRIII+ and Myeloperoxidase (MPO)+ cells, expressing phenotypic features of N, represents an independent favourable prognostic factor in human CRC. T cell derived cytokines, particularly IFN-γ and GM-CSF, have also been associated to favourable CRC prognosis. Interestingly, we found a direct correlation between MPO+ cell infiltration and number of CRC-infiltrating CD3+ cells, suggesting the possibility of a crosstalk between among MPO+ cells and T cells. Based on this observations, we hypothesize that factors present in the tumor microenvironment, including cytokines and CRC-associated microbiota, may account for the phenotypic characteristics of Tumor-associated Neutrophils (TAN) and that TAN may impact on disease progression by modulating intratumoral T cell responses and tumor cell growth. When cultured in the presence of T cell-derived cytokines, including IFN-γ and GM-CSF, peripheral blood N from healthy donors displayed a prolonged viability, even in the presence of strong a microbial challenge. Moreover, N cultured in those conditions were characterized by high surface expression of CD16 and a substantial increase of CD54 expression. These results suggest that cytokines associated with a prolonged CRC survival, could account for the accumulation of live activated CD16+/MPO+ N in CRC tissues. We are currently assessing whether the phenotype of in vitro activated N is also expressed by CD16+/MPO+ cells infiltrating CRC surgical specimens. Since N may also interact with commensals present in the CRC microenvironment, we are investigating whether the beneficial effect of MPO+ cells may relate to their capacity to sense and eliminate CRC-associated, pro-tumorigenic commensals, in particular Fusobacterium nucleatum. Our preliminary observations indicate that F. nucleatum induced a rapid down-modulation of CD16, CD11b, CD62L expression on N and release of ROS. Although N activated by F. nucleatum did not appear to inhibit the growth of CRC cells in vitro, F. nucleatum phagocytosis by CRC-infiltrating N might have an impact on CRC growth in vivo. Collectively, these results suggest that stimuli known to be present in the CRC microenvironment differentially impact on TAN survival and phenotype. The assessment of CRC-infiltrating N ex vivo and in situ is now mandatory to gain mechanistic insights into their positive prognostic value. Citation Format: Valeria Governa, Valentina Mele, Christian Hirt, Raoul Droeser, Luca Quagliata, Luigi Terracciano, Giandomenica Iezzi, Nina Kanna, Giulio Spagnoli, Elisabetta Padovan. Neutrophils in human colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3350. doi:10.1158/1538-7445.AM2015-3350