Mass cytometry identifies expansion of double positive and exhausted T cell subsets in the tumour microenvironment of patients with POEMS syndrome.

We sought to dissect the tumour microenvironment in a small cohort (N = 10) of patients with POEMS at diagnosis and after therapy using mass cytometry. We included 10 MGUS patients as controls. We identified 29 immune cell subsets in the CD45+ and CD3+ compartments. Double positive T cells and PD-1 positive CD4 T cells were expanded and naïve CD4 T cells were decreased in the bone marrow of patients with newly diagnosed/progressing POEMS. These findings provide evidence for possible antigenic-driven selection as a driver of disease pathogenesis in POEMS.