Background
Monoclonal B-cell lymphocytosis (MBL) is a precursor condition for chronic lymphocytic leukemia (CLL). The prevalence of MBL is ~5-10% in the adult population over age 50. Previously, we described significant B-cell receptor immunoglobulin heavy chain (BcR IGH) gene repertoire clonality and clonotypic evolution up to 16 years before CLL diagnosis. However,  it is currently unclear whether other B-cell malignancies, such as diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), mantle cell lymphoma (MCL) and multiple myeloma (MM) also present with prediagnostic BcR IGH gene repertoire clonality.

Objectives
Here, we aim to sequence the BcR IGH gene repertoire during early development of DLBCL, FL and MCL in peripheral blood samples drawn up to 19 years prior to diagnosis.

Methods
Study subjects were participants in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. In the current study, buffy coat samples from a total of 732 EPIC participants (104 controls, 135 DLBCL, 125 FL, 25 MCL and 101 MM cases) underwent IGH gene repertoire sequencing using a leader-based IGH assay on an Illumina MiSeq . We additionally included 124 CLL cases and 118 controls from an earlier study. The timing of B-cell malignancy diagnosis ranged from 3 months to 19 years after initial blood sampling. The IGH repertoire was characterized using the ARResT/Interrogate immunoprofiler. Abundance ratio was calculated by dividing the abundance of the dominant clonotype by the mean of the abundance of the clonotypes ranked 3rd-7th, as described previously. The cutoff for clonality was set at an abundance ratio of 10. Associations between IGH gene repertoire clonality and B-cell malignancy risk were evaluated using Cox proportional hazards models adjusted for age at recruitment, sex and study center.

Results
BcR IGH gene repertoire clonality in the peripheral blood was strongly associated with the development of leukemic B-cell malignancies like CLL (HR 8.71[5.7-13.2]) and MCL (HR 10.0[3.5-28.1]).  Associations of IGH gene repertoire clonality with nodal lymphoma’s like DLBCL (HR 1.9[1.0-3.31]) and FL (HR 2.4[1.4-4.2]) were weaker, but remained significant. Lastly, IGH gene repertoire clonality was not significantly associated with MM development (HR 1.4[0.9-2.4]). The median dominant clonotype abundance among clonal MCL cases was 13.7% of the IGH gene repertoire (IQR 6.5%-43.7%), while the median dominant clonotype abundance among clonal FL cases was 9% (IQR 2.3%-19%). Half of clonal MCL cases presented with multiple dominant clonotypes with distinct IGHV/IGHJ gene usage and CDR3 regions, also known as bi- or oligoclonality, a feature that is exceedingly rare for other B-cell malignancies.

Conclusions/Implications  
BcR IGH gene repertoire clonality in the peripheral blood is a risk factor for CLL, MCL, FL and DLBCL development. These results suggest that these B-cell malignancies may be preceded by a prolonged indolent precursor phase, reminiscent of low-count MBL observed for CLL. Unsurprisingly, leukemic B-cell malignancy subtypes are more strongly associated with prediagnostic BcR IGH gene repertoire clonality in the peripheral blood than more localized B-cell malignancy subtypes. These findings suggest that monitoring for individuals with MBL should include screening for progression to B-cell lymphoma subtypes beyond CLL.

Molecular clonality and lymphoma risk.