85P - Whole-genome CRISPR screening identifies chemosensor receptors as key regulators of the cancer-macrophage crosstalk

Background

Tumor-associated macrophages (TAMs) are known to support tumor growth and progression in multiple cancers, including prostatic adenocarcinoma (PCa). However, the mechanisms behind macrophage re-education by cancer cells are still mostly unknown. Main aim of this project is to dissect the mechanisms utilised by the tumour to train macrophages in its favour. Our final purpose is to find molecular targets that may be exploited to develop novel immunotherapies or more efficient combinatorial approaches for the treatment of cancer.

Methods

We employed a genome wide CRISPRi screening to tumour-conditioned macrophages, with the aim of identifying targets capable of reverting macrophage activation toward an anti-tumour state. We then validated the results of the library using multiparametric Flow Cytometry analysis and immunofluorescence assays and we employed mouse models of prostate cancer to test in vivo promising targets identified by the screening.

Results

We identified a group of genes that codify for chemosensor receptors and act as regulators of pro-tumoral functions in TAMs. Genetic deletion of selected chemosensors re-educates CD206^bright MHC-II^neg pro-tumoral macrophages and confer to these cells a CD206^negMHC-II^bright pro-inflammatory phenotype. Functionally, chemosensors depleted macrophages (chemKO Macs) supported CD8+ cell proliferation and inhibited migration of tumour cells in vitro. In vivo, administration of chemKO Macs to tumour bearing mice resulted in a reduced tumour growth. Moreover, tumours from mice injected with chemKO Macs showed an altered tumour microenvironment enriched in tumour specific CD8+ CD39+ T cells. Additionally, we detected the expression of the chemosensor receptor OR51E2 on primary human macrophages in vitro and in tumor-infiltrating macrophages in tissues from PCa patients, therefore recapitulating our findings in a human setting. Finally, we identified palmitic acid as a ligand of OR51E2 and we confirmed its expression in human biopsies from PCa patients.

Conclusions

Our results identified novel targets that could be manipulated to re-educate the macrophage compartment in PCa.

Editorial acknowledgement

Clinical trial identification

Legal entity responsible for the study

The authors.

Funding

Associazione Italiana per la Ricerca sul cancro (AIRC).

Disclosure

All authors have declared no conflicts of interest.