RNA-Seq analysis to compare myeloid cells from PD-L1-LysMCre mice with littermate Wild-type controls

Programmed death-ligand 1 (PD-L1) is predominantly expressed in the antigen-presenting cells (APCs) that are originated and abundant in bone marrow. The roles of PD-L1 in bone cell differentiation and cancer bone metastasis remain unclear. Here we show that PD-L1 antibody or PD-L1 conditional knockout in the hematopoietic or myeloid lineage suppresses osteoclast differentiation in vitro and in vivo. Bone metastases of breast cancer and melanoma are diminished by PD-L1 antibody or PD-L1 deletion in the myeloid lineage. Transcriptional profiling of bone marrow cells reveals that PD-L1 deletion in the myeloid cells up-regulates immune stimulatory genes, leading to increased macrophage M1 polarization, decreased M2 polarization, enhanced IFN? signaling, and elevated T cell recruitment and activation. All these alterations result in heightened anti-tumor immunity in the cancer microenvironment. Our findings support PD-L1 antibody as a potent therapy for bone metastasis of breast cancer and melanoma by simultaneously suppressing osteoclast and enhancing immunity. Examination of mRNA profiles of myeloid cells from mice with PD-L1 wild-type (WT) or lysozyme-Cre (LysMCre) mediated PD-L1 conditional knockout by deep sequencing, in biological triplicate, using Illumina HiSeq 2500