Novel T-Cell Receptor Signature Linked to Plasma Cell Dyscrasias

Introduction: The immune system, particularly T cells, plays a crucial role in the progression and prognosis of multiple myeloma (MM). Early studies utilizing low-resolution techniques, such as flow cytometry with panels of anti-T-cell receptor (TCR) variable-β monoclonal antibodies, consistently reported clonal T cell expansions in peripheral blood and bone marrow aspirates of patients with MM. Notably, clonal T cell expansion has been associated with improved progression-free survival (PFS) and overall survival (OS) in patients with MM, especially those with a low tumor burden, suggesting a potential anti-tumor effect. However, with the advent of next-generation sequencing (NGS) technologies, enabling a higher resolution analysis of the TCR repertoire, this association has not been consistently replicated. This study aims to re-evaluate the T cell repertoire in patients with plasma cell dyscrasias using NGS to investigate the association between T cell clonality, immune response, and clinical outcomes.

Methods: Targeted DNA sequencing of the CDR3 regionTCR beta chain (TCRB) was analyzed from 447 peripheral blood samples collected from 81 patients with monoclonal gammopathy of undetermined significance (MGUS), 55 with high-risk smoldering multiple myeloma (SMM), and 31 with MM. This data was compared to TCRB sequencing from 166 healthy controls from Adaptive Biotechnology’s immuneACCESS database. Patients with SMM were enrolled in a phase 2 nonrandomized controlled trial at the National Institutes of Health Clinical Center, receiving a combination of carfilzomib, lenalidomide, and dexamethasone (KRd) for eight cycles every 28 days, followed by lenalidomide maintenance for two years (NCT01572480). We assessed the stability of TCRB clonality in patients with MGUS over a median interval of 660 days (range, 163-1149 days). Diversity was assessed using the Gini coefficient and a multivariate linear regression analysis adjusted for age. TCRBclustering based on similar CDR3 beta amino acid sequences was performed using ClusTCR. Machine learning models were employed to identify distinct TCRB clusters between healthy individuals and those with plasma cell dyscrasias.

Results: TCRB repertoire diversity did not differ significantly between healthy individuals and patients with MGUS, SMM, or MM after age adjustment. Additionally, the T cell repertoire in MGUS patients remained stable over a median follow-up greater than two years. Furthermore, neither the depth of response to induction therapy in patients with newly diagnosed MM nor the achievement of sustained MRD negativity in patients with high-risk SMM correlated with TCRB diversity. Although significant changes in TCRB repertoire diversity were noted in patients with high-risk SMM during KRd treatment (Wilcoxon signed-rank P value < 0.05), these changes were not associated with clinical outcomes. This suggests that while treatment may influence the T-cell repertoire, these changes in TCRB repertoire diversity do not necessarily translate into a clinically meaningful impact on disease progression or response. Despite the lack of association between overall TCRB diversity and clinical outcomes, our machine learning analysis revealed a high level of accuracy (area under the curve 0.84) in predicting TCRB signatures from differentially abundant TCRB clusters between healthy individuals and those with plasma cell dyscrasias. These clusters exhibited different amino acid properties, suggesting potential differences in antigen recognition.

Conclusions: While our study did not find a significant association between overall T-cell repertoire diversity and clinical outcomes in plasma cell dyscrasias, we identified distinct TCRB clusters that differentiate healthy individuals from those with plasma cell disorders. To our knowledge, this is the largest study to date reporting on the TCRB repertoire in plasma cell dyscrasias and the first to demonstrate that distinct TCRB clusters can differentiate individuals with these disorders from healthy individuals. Further research is needed to unravel the functional implications of these clusters and their potential role in disease development and progression. Our findings highlight the need for continued investigation into the interplay between T-cell responses and disease outcomes.