Targeting CXCL12 from FAP-expressing carcinoma-associated fibroblasts synergizes with anti-PD-L1 in pancreas cancer

An autochthonous model of pancreatic ductal adenocarcinoma (PDA) permitted the analysis of why immunotherapy is ineffective in this human disease. Despite finding that PDA-bearing mice had cancer cell-specific CD8+ T cells, the mice, like human PDA patients, did not respond to two immunological checkpoint antagonists that promote the function of T cells, a-CTLA-4 and a-PD-L1. Immune control of PDA growth was achieved, however, by depleting carcinoma-associated fibroblasts (CAFs) that express Fibroblast Activation Protein (FAP). The depletion of the FAP+ stromal cell also uncovered the anti-tumor effects of a-CTLA-4 and a-PD-L1, indicating that its immune suppressive activity accounts for the failure of these T cell checkpoint antagonists. Three findings suggested that CXCL12 explained the overriding immunosuppression by the FAP+ cell: T cells were absent from regions of the tumor containing cancer cells; cancer cells were coated with the chemokine, CXCL12; and the FAP+ CAF was the principle source of CXCL12 in the tumor. Administering AMD3100, a CXCL12 receptor (CXCR4) inhibitor, induced rapid T cell accumulation among cancer cells, and acted synergistically with a-PD-L1 to selectively and greatly diminish cancer cells, identified by their loss-of-heterozygosity (LOH) of Trp53. The residual tumor was comprised only of pre-malignant epithelial cells and inflammatory cells. Thus, a single protein, CXCL12, from a single stromal cell type, the FAP+ CAF, may direct tumor immune evasion in a model of human PDA. Overall design: FAP+ cells were sorted from pancreatic ductal adenocarcinoma. Cells were isolated in duplicate experiments and these were analysed separately. These were compared separately to previously published publicly available CD4+ T-cell subset data (C57BL/6 mice and Foxp3-RFP mice (Line 8374) GEO accession GSE20898), and previously published FAP+ cell datasets (transgenic albino (Tyr-/-) C57BL/6 mouse, GEO accession GSE39438).

4

Feig C, Jones JO, Kraman M, Wells RJ, Deonarine A, Chan DS, Connell CM, Roberts EW, Zhao Q, Caballero OL, Teichmann SA, Janowitz T, Jodrell DI, Tuveson DA, Fearon DT