Dissecting the cellular architecture of neuroblastoma bone marrow metastasis using single-cell transcriptomics and epigenomics

The bone marrow (BM) is the third most frequent site of metastasis for solid tumors, creating an unfavorable clinical outcome. It provides a unique microenvironment that promotes growth of tumors, however, the role of different BM cells, their molecular features, and their interactions with tumor cells, are poorly defined. Here, we investigate the BM niche in neuroblastoma (NB), a pediatric cancer of the sympathetic nervous system. NB has been molecularly defined at the primary cancer site, yet, the metastatic site is poorly characterized. We performed single-cell transcriptomics (scRNA-seq) and epigenomic profiling (scATAC-seq) of BM aspirates from 11 subjects spanning three major NB subtypes: patients with MYCN amplification (MNA), ATRX mutations (ATRXmut), and cases that lack these alterations (sporadic): NB cases were then compared to five age-matched and metastasis-free BM (controls), followed by in-depth single cell analyses of tissue diversity and cell-cell interactions. We present the first map of the epigenetic and transcriptomic effects of bone marrow metastases. Our analyses demonstrate that tumor cells in the metastatic niche display plasticity that differs among NB subtypes. NB cells via cell-cell interaction signal to the bone marrow microenvironment, rewiring specifically monocytes, which exhibit M1 and M2 features, marked by activation of pro- and anti-inflammatory programs, and express tumor-promoting factors, reminiscent of tumor-associated macrophages. Our study may provide the basis for a therapeutic approach, targeting tumor-to-microenvironment interactions.