Transcriptional and chromatin accessibility landscapes of hematopoiesis in a mouse model of breast cancer.

Increased myeloid lineage production, termed myeloid skewing, leading to decreased tumor immunity, is a hallmark of aberrant hematopoiesis associated with cancer. It is believed that myeloid skewing may occur at the hematopoietic stem and progenitor cells (HSPCs) level to elicit hematopoietic changes. However, our understanding of the underlying molecular mechanisms remains incomplete. Here, we characterize the transcriptional and chromatin accessibility landscapes of bone marrow and splenic hematopoietic progenitors in the MMTV-PyMT mouse model of breast cancer using single-cell ATAC + RNA sequencing. We show that HSPCs in the bone marrow (BM) of the tumor-bearing mice show a modest upregulation of the myeloid-bias transcriptional signature without significant chromatin accessibility changes. By contrast, dendritic cell (DC) progenitors exhibit the most prominent transcriptional and chromatin changes, showing a signature of STAT3, CEBP, and non-DC myeloid gene activation. Compared to BM, splenic HSPCs exhibit a Notch signaling signature associated with erythroid commitment rather than further upregulation of the myeloid-bias signature. In addition, we also identify a cluster of splenic HSPCs in tumor-bearing animals with a transcriptional signature of mobilization. Our paired chromatin data suggest that AP-1 factors play a crucial role in driving this HSPC mobilization signature. Overall, we provide a comprehensive dataset for understanding the hematopoietic consequences of cancer.