Krull, Jordon

Abstract The role of the bone marrow (BM) microenvironment in regulating the antitumor immune response in Waldenstrom macroglobulinemia (WM) remains limited. Here we transcriptionally and phenotypically profiled non-malignant (CD19− CD138−) BM cells from WM patients with a focus on myeloid derived suppressive cells (MDSCs) to provide a deeper understanding of their role in WM. We found that HLA-DRlowCD11b+CD33+ MDSCs were significantly increased in WM patients as compared to normal controls, with an expansion of predominantly polymorphonuclear (PMN)-MDSCs. Single-cell immunogenomic profiling of WM MDSCs identified an immune-suppressive gene signature with upregulated inflammatory pathways associated with interferon and TNF signaling. Gene signatures associated with an inflammatory and immune suppressive environment were predominately expressed in PMN-MDSCs. In vitro WM PMN-MDSCs demonstrated robust T-cell suppression, and their viability and expansion was notably enhanced by G-CSF and TNFα. Furthermore, BM malignant B-cells attracted PMN-MDSCs to a greater degree than monocytic MDSCs. Collectively, these data suggest that malignant WM B cells actively recruit PMN-MDSCs which promote an immunosuppressive BM microenvironment through a direct T cell inhibition, while release of G-CSF/TNFα in the microenvironment further promotes PMN-MDSC expansion and in turn immune suppression. Targeting PMN-MDSCs may therefore represent a potential therapeutic strategy in patients with WM.