Saung et al. investigated CSF-1R within lymphoid aggregates that were induced in surgically resected human pancreatic ductal adenocarcinoma (PDAC) treated with neoadjuvant GVAX, a GM-CSF-secreting cell vaccine. High CSF-1R levels were associated with immunosuppressive myeloid infiltrate and immature DCs. In a therapeutic mouse model of metastatic PDAC, one cycle of anti-CSF-1R Ab pre- and post- GVAX + anti-PD-1 treatment enhanced CD137 (4-1BB) and OX40 expression on infiltrating T cells and improved day 23, but not overall, survival. A higher fraction of CD8+PD-1+CD137+ cells expressed IFNγ compared to CD137- cells.
BACKGROUND: The pancreatic cancer vaccine, GVAX, induces novel lymphoid aggregates in the otherwise immune quiescent pancreatic ductal adenocarcinoma (PDAC). GVAX also upregulates the PD-1/PD-L1 pathway, and a pre-clinical model demonstrated the anti-tumor effects of combination GVAX and anti-PD-1 antibody therapy (GVAX/alphaPD-1). Resistance to GVAX was associated with an immune-suppressive myeloid cell infiltration, which may limit further therapeutic gains of GVAX/alphaPD-1 therapy. The expression of CSF-1R, a receptor important for myeloid cell migration, differentiation and survival, and the effect of its therapeutic blockade in the context of GVAX in PDAC has not been investigated. METHODS: Lymphoid aggregates appreciated in 24 surgically resected PDAC from patients who received one dose of neoadjuvant GVAX were analyzed with multiplex immunohistochemistry. Flow cytometry analysis of tumor infiltrating T-cells in a murine model of PDAC was performed to investigate the therapeutic effects and mechanism of anti-CSF-1R/anti-PD-1/GVAX combination immunotherapy. RESULTS: High CSF-1R expression in resected PDAC from patients who received neoadjuvant GVAX was associated with a higher myeloid to lymphoid cell ratio (p < 0.05), which has been associated with poorer survival. This higher CSF-1R expression was associated with a higher intra-tumoral infiltration of immature dendritic cells (p < 0.05), but not mature dendritic cells (p = 0.132). In the pre-clinical murine model, administering anti-CSF-1R antibody prior to and after GVAX/alphaPD-1 ("pre/post-alphaCSF-1R + alphaPD-1 + GVAX") enhanced the survival rate compared to GVAX/alphaPD-1 dual therapy (p = 0.005), but administering anti-CSF-1R only before GVAX/alphaPD-1 did not (p = 0.41). The "pre/post-alphaCSF-1R + alphaPD-1 + GVAX" group also had higher intra-tumoral infiltration of PD-1 + CD8+ and PD-1 + CD4+ T-cells compared to alphaPD-1/GVAX (p < 0.001). Furthermore, this regimen increased the intra-tumoral infiltration of PD-1 + CD137 + CD8+, PD-1 + CD137 + CD4+ and PD-1 + OX40 + CD4+ T-cells (p < 0.001). These PD-1 + CD137 + CD8+ T-cells expressed high levels of interferon-gamma (median 80-90%) in response to stimulation with CD3/CD28 activation beads, and this expression was higher than that of PD-1 + CD137-CD8+ T-cells (p < 0.001). CONCLUSIONS: The conversion of exhausted PD-1+ T-cells to CD137+ activated effector T-cells may contribute to the anti-tumor effects of the anti-CSF-1R/anti-PD-1/GVAX combination therapy. Anti-CSF-1R antibody with anti-PD-1 antibody and GVAX have the potential be an effective therapeutic strategy for treatment of PDAC.
