Combinational targeting CCL7 and Flt3L to promote the expansion and infiltration of cDC1 in tumors enhances T cell activation and anti-PD-1 therapy [Dendritic Cell]
Immune checkpoint inhibitors (ICIs) represented by anti-PD-1/PD-L1 antibodies have been widely applied for various cancers and the response rate to ICIs is closely associated with the tumor immune microenvironment (TIME). Here, we show that combinational targeting CCL7 and Fms-like tyrosine kinase 3 ligand (Flt3L) increases the infiltration and expansion of conventional type 1 dendritic cells (cDC1s) in tumor sites and enhances the T cell antitumor responses and the efficacy of anti-PD-1 therapy in subcutaneous tumor models and spontaneous KrasG12D non-small cell lung cancer (NSCLC) models. We demonstrate that the fusion protein PD-1Ab7 in which CCL7 is fused with the single chain fragment variable region of anti-PD-1 antibody (PD-1Ab) exhibits superior antitumor activities compared to PD-1Ab. Mechanistically, PD-1Ab7 promotes antitumor immunity by increasing the infiltration of cDC1s and the activation of T cells, which is severely compromised by depletion of Zbtb46+ cDCs or inhibition of the CCL7 receptor CCR2. Furthermore, complementation of Flt3L sensitizes the ICI-resistant tumors to PD-1Ab7 and synergizes with PD-1Ab7 to inhibit tumor progression. These findings highlight the essential roles of PD-1Ab-based chemokine fusion strategy in targeting cDC1s and T cells for cancer prevention and provide therapeutic lead molecules for antitumor immunotherapy. Overall design: Comparative gene expression profiling analysis of RNA-seq data in cDC1s sorted from tumor-burdened lungs of  KrasLSL-G12D/+Tp53fl/fl NSCLC mouse treated with Flt3L plus PD-1Ab7,PD-1Ab7,PD-1Ab,and PBS.