Assessing the Immune Tumour Microenvironment (iTME) Using Multiplex Immunoflourescence Histochemistry (mIHC) Demonstrates Close Proximity of Cytotoxic T-Cells to Plasma Cells (PC) in Patients with Newly Diagnosed Multiple Myeloma (NDMM)

Abstract Aim: A dysfunctional iTME facilitates disease progression in MM. Studies have demonstrated the association between the spatial distribution of immune cells and progression of various cancers. Using mIHC we aim to describe quantitative and qualitative changes in CD3+CD8+ T-cells (T cytotoxic) in patients with MGUS, ND and relapsed/refractory MM (RRMM) and assess spatial proximity to PCs. Method: Formalin-fixed, paraffin-embedded trephine sections from pts with MGUS (n=32), NDMM (n=65) and RRMM (n=59) were sequentially stained for CD138, CD3, CD8 and checkpoint receptors (CPs) Tim3, Lag-3 and PD-1 (Figure 1). Halo® image analysis platform was used for cell segmentation and phenotyping, facilitating enumeration of T cytotoxic populations and analysis of proximity to PCs. Descriptive statistics and ordinary one-way ANOVA were applied as appropriate. Results: Patient demographics, disease characteristics, treatment (including prior therapies, where applicable), best response, duration of response, median progression free (PFS) and overall survival (OS) will be presented for all cohorts. There was no difference in BM cellularity or total number of nucleated cells assessed across the cohorts (p=0.16 and p=0.25). PC % was higher in the ND and RRMM compared to MUGS cohort (p<0.001). The average distance between T cytotoxic and PCs was similar between the cohorts (p=0.38), but a higher proportion of T cytotoxic were within 50μm of a PC in the ND cohort (p=0.0036, 90.8±15.8% (ND) vs. 77.6±19.5% (MGUS) and 80.1±25.9% (RR)). The % of unique PCs with a single T cytotoxic within 100μm is higher in patients with MGUS and RRMM than NDMM (p=0.0007). There was no difference in the %CD3+, %CD3+CD8+ or %CD3+ cells expressing CD8 (p=0.22, p=0.62, p=0.48). CP expression on T cytotoxic was similar (Tim3 p=0.46, Lag-3 p=0.35; PD-1 p=0.54) with no difference in dual or triple CP expression. Sub-analyses assessing CP expression patterns and T cytotoxic/PC proximity within individual cohorts based on response to treatment/disease progression are to follow. Conclusion: The infiltration of cytotoxic T cells into tumours is a critical factor in immunotherapy efficacy. Here we clearly demonstrate the feasibility of mIHC to describe the spatial context of the iTME and we plan to implement it for predictive value in future studies of immunotherapies in patients with MM. Figure 1: Bone marrow FFPE trephine section stained with mIHC using the Opal TM workflow demonstrating plasma cells (CD138, green), T cells (CD3, yellow; CD8, pink) and checkpoint receptors (PD-1, orange; Lag-3, magenta; Tim3, light blue) with colocalisation of some signals. Disclosures Harrison: Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene/ Juno/ BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Haemalogix: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Eusa: Consultancy, Honoraria, Speakers Bureau; Terumo BCT: Consultancy, Honoraria. Quach: Janssen/Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; CSL: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Antengene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.