A dysfunctional immune tumour microenvironment facilitates disease progression in multiple myeloma (MM). Using multiplex immunohistochemistry (mIHC), we described the quantitative and qualitative changes in CD3+ CD8+ cytotoxic T-cells and assess their proximity to malignant plasma cells (PCs) in patients with monoclonal gammopathy of undetermined significance (MGUS), newly diagnosed (ND) and relapsed/refractory (RR) MM. Formalin-fixed, paraffin-embedded trephine sections from patients with MGUS (n=32), NDMM (n=65) and RRMM (n=59) were sequentially stained for CD138, CD3, CD8, and checkpoint receptors (CPR) Tim-3, Lag-3, and PD-1. Halo® image analysis platform was used for cell segmentation and phenotyping, facilitating enumeration of cytotoxic T-cells and analysis of proximity to PCs. The percentage of CD8+ cytotoxic T-cells in proximity to PCs is greater in patients with NDMM than patients with RRMM (at 50gm distance 90.8% vs. 81.5%, p=0.038). There is a trend for more CD3+ T-cells in MGUS (p=0.08) but no difference was observed in the prevalence of CD8+ cytotoxic T-cells (p=0.48). Lag-3 is the most common CPR expressed on cytotoxic T-cells in myeloma (p<0.0001), while PD-1 is the most common CPR on CD8 negative T-cells of patients with MGUS and RRMM. Our study is the first to report on the spatial relationship between T-cells and PCs using mIHC on FFPE bone marrow trephine sections from patients with plasma cell dyscrasia. The proximity of Tcells to PCs during early stages of MM, and over-expression of Lag-3, validate the move of immune therapeutic strategies, including T-cell engagers and checkpoint inhibitors to upfront or in early-line treatment of MM.
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