Background Pancreatic ductal adenocarcinoma (PDAC) is resistant to immune checkpoint inhibition. One of the major resistance mechanisms is attributed to myeloid cells as an immunosuppressive element within the stroma of PDAC. It has been reported that focal adhesion kinase inhibitor (FAKi) can suppress immunosuppressive myeloid cells such as tumor associated macrophages (TAMs) and myeloid derived suppressor cells (MDSC), consequently sensitizing tumor to anti-PD1 antibody in mouse models of PDAC. Our group has previously shown in a murine model that targeting the stroma via PEGylated recombinant human hyaluronidase (PEGPH20) enhanced the anti-tumor activity of the whole cell vaccine (GVAX) by targeting CXCR4-expressing myeloid cells and led to an increase in infiltration of CCR7- effector memory T cell subsets. Here, we evaluate the hypothesis that FAK expressing myeloid cell subsets modulate T cell infiltration in human PDAC and FAKi can synergize with PEGPH20 by targeting myeloid cells in PDAC.
Material and Methods Resected human PDAC tissue specimens treated with GVAX and anti-PD1 therapy was used to assess FAK expression in myeloid cell subsets and its impact on T cell infiltration. A sequential staining and stripping multiplex IHC technique that incorporates 28 myeloid and lymphoid biomarkers, as well as phosphorylated FAK (pFAK) combined with computational image processing was used to assess myeloid cell populations, T cell infiltration and FAK expression.
An established murine model of metastatic PDAC treated with and without anti-PD1 therapy was used to assess the synergy and immune-modulating effect of FAKi and stromal degradation of hyaluronan via PEGPH20.
Results In human PDAC, FAK is widely expressed in TAMs and neutrophils. Increased FAK expression is associated with increased CXCR4 expression. Lower pFAK density in neutrophils and M2 TAMs, but not lower pFAK density in M1 TAMs, is associated with higher CD8+ T cell infiltration.
FAKi and combination of FAKi with anti-PD1 extends survival in the mouse metastasis model of PDAC. Adding PEGPH20 to FAKi and anti-PD1 antibody significantly prolonged survival in this model. Comparing to the combination of FAKi and anti-PD1 antibody, adding PEGPH20 significantly decreased the number of CXCR4-expressing myeloid cells in the tumor microenvironment (TME) of PDAC and consequently led to an increase in the amount of CCR7+ central memory T cells. Additionally, the amount of G-MDSCs, inflammatory resident monocytes and PDL1 expressing myeloid cells in the TME of PDAC, was also decreased in PDAC treated with the triple combination of PEGPH20, FAKi and anti-PD1 antibody compared to FAKi and anti-PD1 antibody.
Conclusion FAK is widely expressed in myeloid cell populations, directly correlated with CXCR4 expression and decreased FAK expression in a myeloid (M2 TAMs, neutrophil) inflamed stroma is associated with infiltration of effector CD8 T cells in human PDAC. Stromal degradation of hyaluronan via PEGPH20 combined with FAKi and anti-PD1 antibody further depletes immunosuppressive cells in the TME including G-MDSCs, inflammatory resident monocytes and PDL1 expressing myeloid cells and appears to target the CXCR4 pathway through PEGPH20. These findings support testing the combination of FAKi and anti-PD1 antibody with agents targeting CXCR4 directly or indirectly by PEGPH20 in human PDAC.
Disclosure Information A. Osipov: None. L. Zheng: None.
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