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    Myeloma Genomics and Microenvironment and immune profiling

    T-cell receptor repertoire analysis of blood and bone marrow samples from multiple myeloma patients

    P-192: T-cell receptor repertoire analysis of blood and bone marrow samples from multiple myeloma patients

    Thursday, September 26, 2024
    Introduction: The collection of bone marrow (BM) aspirates from multiple myeloma (MM) patients is the gold-standard method for evaluating both disease burden and for studying the BM microenvironment. The development of liquid biopsy and blood-based approaches may provide a minimally invasive strategy for monitoring disease, clinical response, and for biomarker discovery. As T-cell targeted therapies are being advanced as earlier lines of therapy in MM, we explored the utility of peripheral blood mononuclear cells (PBMC) as a surrogate tissue for BM immune microenvironment, and specifically T-cells.

    Methods: Baseline and longitudinal visit matched patient-derived samples were obtained from subjects enrolled in the MMRF CoMMpass trial (36 subjects; 91 BM and 100 PBMC samples) and PBMC samples from the MMRF CureCloud study (14 subjects). For bulk TCR focused analyses, subject and visit matched PBMC and BM (CD138-negative BMMC) genomic DNA (gDNA) samples were sequenced using the Adaptive Immunosequencing (Adaptive Biotechnologies, Seattle, WA) to quantitatively profile the TCR (TCRb) repertoire. For single cell analyses (paired scRNAseq/scTCRseq), aliquots of cryopreserved PBMCs were thawed and evenly divided for, (i) selective T-cell enrichment (cocktail of non-T cell targeted magnetic beads) and (ii) no T-cell enrichment, prior to gene expression profiling using the 10X Chromium Next GEM 5’ V2 kit.

    Results: TCRb sequences from visit matched, longitudinal, BM and PBMC samples exhibit overlapping profiles and characteristics. TCR repertoire diversity, clonality and richness (dynamics) over time and therapy were highly similar between BM and PBMC samples.



    Single cell T-cell analyses of PBMCs revealed that T-cell enrichment (TCE) captured a broader diversity of T-cell clones. TCE increased the proportion of T-cells analyzed in the samples to 75% vs 40% in unenriched PBMC. While TCE had no impact on transcript-level expression profiles, T-cell subtypes remained consistent between these two processes. Moreover, we observed a higher abundance of functional subsets of CD8 and CD4 T-cells in TCE samples. Additionally, when mapping TCR clone specificity to common large-scale TCR-epitope databases such as vdjDB or immuneCODE we observed that TCE significantly enhanced the identification of both rare and antigen-specific clones compared to samples without enrichment.

    Conclusions: We confirm that the TCR repertoire in blood and BM are conserved with similar dynamics suggesting that blood could be a possible surrogate to monitor T-cell functional status in the BM of MM patients (contingent ddon therapy). We also demonstrate shared TCR diversity and clonality between PBMC and BM. Detailed single cell analyses of TCE samples identifies rare clonotypes which may be of clinical significance. Future analyses will explore the relationship between T-cell/TCR clonality and diversity associated with specific therapies in matched PBMC and BM samples.