To reveal the control of C5aR1 expression in macrophages

Introduction
Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy characterized by a dense stroma and immunosuppressive tumor microenvironment (TME), limiting the effectiveness of conventional therapies and immunotherapies. Tumor-associated macrophages (TAMs), particularly the M2-like phenotype, play a pivotal role in immune evasion and tumor progression. The C5a-C5aR1 complement axis in TAMs has been implicated in promoting immunosuppression in various cancers, yet its regulation and role in PDAC remain underexplored. This study aims to elucidate the regulatory mechanisms of C5aR1 expression in macrophages and investigate the effect of C5aR1 depletion on tumor development.

Materials and Methods

We performed genome-wide CRISPR screens in bone marrow-derived macrophages (BMDMs), using C5aR1 expression as a readout. We validated top-ranked genes using single gRNA. We explored the expression of validated hits in published human and mouse PDAC data.

Results and Discussion

Preliminary CRISPR screens revealed three novel genes regulating C5aR1, including Snx13, which appears to control receptor recycling or G protein signalling. Targeting Snx13 reduced C5aR1 expression and demonstrated promising effects on macrophage polarization. In vivo adoptive transfer of C5aR1-deficient BMDMs into PDAC models enhanced CD8+ T cell infiltration and reduced tumor burden. These findings suggest that reprogramming TAMs by targeting C5aR1 and its regulators can shift the TME toward an anti-tumor state. Combining this strategy with immune checkpoint blockade will be tested in the future.

Conclusions
Snx13 is a novel regulator of C5aR1 expression in macrophages. The effect of Snx13 on other receptors and macrophage function needs to be addressed to examine if Snx13 can be used as a target for immunotherapy.