During the two years of the Marie Curie fellowship I have worked on two complementary projects.
I. Effect of metastatic breast cancer cells on the inflammatory response
An efficient immune response requires the sensing of danger by the immune system. Within tumours, this danger signal is the presence of extracellular nucleic acids released upon chemo or radiotherapy and in DNA-rich neutrophil extracellular traps (NETs) released by neutrophils under some circumstances. The sensing of nucleic acid by cells leads to the production of type I interferons (IFN-I), a family of cytokines that has been shown to have strong anti-tumour and anti-metastatic properties.
My work has revealed that human metastatic breast cancer cells induce the formation of DNA-rich NETs by neutrophils. NETs have previously been shown to favor the metastatic potential of cancer cells. Interestingly, the recognition of nucleic acids in NETs by key immune cells, dendritic cells (DCs), is suppressed by metastatic cancer cells. The absence of IFN-I production leads to the failure of an anti-tumour immune response and potentiates metastasis. Thus tumour cells use a double-pronged approach to propagate, by inducing metastasis-favorable NETs on one hand while suppressing their detection by immune cells on the other hand.
I have further characterized that the suppression of nucleic acid recognition is mediated by soluble proteins secreted by tumour cells that bind to free nucleic acid shielding them from sensing by the myriad receptors present in DCs. The identification of these suppressive proteins reveal novel therapeutic targets to increase nucleic acid-sensing.
Identification of target nucleic acid-binding proteins will be the basis of a patent application providing us with the opportunity to collaborate with pharmaceutical companies to generate specific drugs.
II. Effect of tumour-associated fibroblasts on disease burden and immune cell infiltration
Fibroblasts infiltrate tumours and form the supporting stroma. Cancer-associated fibroblasts (CAFs) have been linked to the progression of disease and metastasis. CAFs keep cytotoxic T cells out of the tumour while their selective ablation leads to tumour regression. Few studies have focused on the role of CAFs on other cells of the immune system. Particularly, the impact on the infiltration and function of DCs remains unknown. The present work attempts to shed light on the effect of CAFs on DC subsets.
In primary human clear cell Renal Cell carcinomas (ccRCC), we found that a sub-population of fibroblasts where enriched within and around the tumour. The presence of these CAFs co-related with the severity of the disease. Furthermore, systematic multi-panel flow cytometry analysis of ccRCC’s revealed that a key DC subset, CD141+ DCs, failed to enter the tumour. Absence of CD141+ cells co-related to the presence of the CAF subset around the tumour suggesting that CAFs may be responsible for the block in entry. At present, we are performing deep sequencing analysis of sorted fibroblasts to ascertain factors that could be responsible for this blockade. Targeting these factors would enable entry of DCs into the tumour where they could efficiently sample tumour antigens and mount a specific immune response.
Results from both projects are part of grant applications for further funding to continue the research. Publication of the results are underway in scientific journals of high impact. Both projects reveal novel pathways of immune suppression; the secretion of nucleic acid-binding soluble proteins and the impact of fibroblasts on the infiltration of DCs into tumours. The publication of these results will open paths for further investigation into similar mechanisms not only during carcinogenesis but also in infectious diseases and autoimmunity.
