The Hydropathy Index of the HCDR3 Region of the B-Cell Receptor Identifies Two Subgroups of IGHV-Mutated Chronic Lymphocytic Leukemia Patients With Distinct Outcome.

Arancha Rodríguez-Caballero,Ignacio Criado,Guillermo Oliva Ariza,Alberto Orfao,Julia Almeida,María Pérez Caro,Andrés C García-Montero,Ana Bela Sarmento-Ribeiro,Francesco Forconi,Marcos González Díaz,Miguel Alcoceba,Carlos Prieto,Blanca Fuentes Herrero

doi:10.3389/fonc.2021.723722

Abstract

The HCDR3 sequences of the B-cell receptor (BCR) undergo constraints in length, amino acid use, and charge during maturation of B-cell precursors and after antigen encounter, leading to BCR and antibodies with high affinity to specific antigens. Chronic lymphocytic leukemia consists of an expansion of B-cells with a mixed immature and “antigen-experienced” phenotype, with either a mutated (M-CLL) or unmutated (U-CLL) tumor BCR, associated with distinct patient outcomes. Here, we investigated the hydropathy index of the BCR of 138 CLL patients and its association with the IGHV mutational status and patient outcome. Overall, two clearly distinct subgroups of M-CLL patients emerged, based on a neutral (mean hydropathy index of -0.1) vs. negatively charged BCR (mean hydropathy index of -1.1) with molecular features closer to those of B-cell precursors and peripheral/mature B-cells, respectively. Despite that M-CLL with neutral HCDR3 did not show traits associated with a mature B-cell repertoire, important differences in IGHV gene usage of tumor cells and patient outcome were observed in this subgroup of patients once compared to both U-CLL and M-CLL with negatively charged HCDR3 sequences. Compared to M-CLL with negatively charged HCDR3 sequences, M-CLL with neutral HCDR3 sequences showed predominance of men, more advanced stages of the disease, and a greater frequency of genetic alterations—e.g., del(17p)—together with a higher rate of disease progression and shorter time to therapy (TTT), independently of other prognostic factors. Our data suggest that the hydropathy index of the HCDR3 sequences of CLL cells allows the identification of a subgroup of M-CLL with intermediate prognostic features between U-CLL and the more favorable subgroup of M-CLL with a negatively charged BCR.

Highlights

Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in adults in the Western world, which is characterized by an expansion of mature-appearing CD5+CD20lo B-cells showing an antigen-experienced CD27+, IgM+, and/or IgD+ unswitched phenotype, in association with either an unmutated (U-CLL) or mutated (M-CLL) B-cell receptor (BCR) [1]
A similar frequency of CLL patients with neutral (GS ≥ -0.5) and negatively charged (GS < -0.5) HCDR3 amino acid sequences was observed in our cohort: 65/138 (47%) vs. 73/138 (53%) CLL patients (p = 0.46), respectively (Figure 1)
CLL patients with neutral HCDR3 sequences showed a significant predominance of men vs. women (72% vs. 47%, p = 0.002), together with a lower percentage of Rai stage 0 (46% vs. 74%, p = 0.01) and Binet stage A cases (57% vs. 79%, p = 0.006), a higher proportion of cases with thrombocytopenia (21% of cases vs. 7%, p = 0.01), a lower proportion of M-CLL cases (46% vs. 66%, p = 0.02), and a lower median percentage of IGHV mutations (1% vs. 4%, p = 0.04) with longer HCDR3 sequences compared to CLL patients with negatively charged HCDR3 (Table 1)

Summary

Introduction

Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in adults in the Western world, which is characterized by an expansion of mature-appearing CD5+CD20lo B-cells showing an antigen-experienced CD27+, IgM+, and/or IgD+ unswitched phenotype, in association with either an unmutated (U-CLL) or mutated (M-CLL) B-cell receptor (BCR) [1]. Most CLL patients show stable disease with a variable number of tumor B-cells in blood (always >5,000 cells/ml) and bone marrow (BM), in the absence of organomegalies, and they do not require active therapy [2]. A significant fraction of patients shows more advanced disease already at diagnosis or they experience disease progression during followup, which translates into the need for active cytotoxic therapy [3]. The mutational status of the immunoglobulin (IG) heavy-chain variable (IGHV) genes that code for the BCR, together with disease stage and tumor cytogenetics, has emerged among other variables, as relevant prognostic factors in CLL [4]. M-CLL patients have a heterogeneous outcome [6, 7]

Methods

Results

Conclusion