Batf3-dendritic cells and 4-1BB/4-1BB ligand axis are required at the effector phase within the tumor microenvironment for PD-1/PD-L1 blockade efficacy

The cellular source of positive signals that reinvigorate T cells within the tumor microenvironment (TME) for the therapeutic efficacy of PD-1/PD-L1 blockade has not been clearly defined. We now show that Batf3-lineage dendritic cells (DCs) are essential in this process. Flow cytometric analysis, gene-targeted mice, and blocking antibody studies revealed that 4-1BBL was a major positive costimulatory signal provided by these DCs within the TME, that translated to CD8+ T cell functional reinvigoration and tumor regression. Immunofluorescence and spatial transcriptomics on human tumor samples revealed clustering of Batf3+ DCs and CD8+ T cells, which correlated with anti-PD-1 efficacy. In addition, proximity to Batf3+ DCs within the TME was associated with CD8+ T cell transcriptional states linked to anti-PD-1 response. Our results demonstrate that Batf3+ DCs within the TME are critical for PD-1/PD-L1 blockade efficacy, and indicate a major role for the 4-1BB/4-1BBL axis during this process. Overall design: Spatial transcriptomics (Visium, 10X) was performed on two primary invasive bladder carcinoma samples (B1 and B5) and ten additional primary invasive bladder carcinoma samples at higher resolution (Visium CytAssist, 10X). Samples B12 and B13 were sequenced in the same capture area. These samples were separated based on the tissue coordinates in R. Samples B17 and B18 were obtained from the same tumors as samples B5 and B1, respectively, and were also placed in the same capture area. These data were separated using non-overlapping alignments generated with the Loupe Browser (10X). With the aim to understand how close proximity to Batf3-lineage dendritic cells (DC1s) affect the CD8+ T cells in the tumor microenvironment, the data were used to compare the transcriptome of the spots that contained CD8+ cells (CD8A or CD8B and CD3) that were close or distant from spots that contained DC1s (Batf3, Clec9A or XCR1 and ITGAX).