Somatic hypermutation analysis in follicular lymphoma provides evidence suggesting bidirectional cell migration between lymph node and bone marrow during disease progression and relapse

Abstract

ABSTRACTdeveloped algorithm to describe clonal hierarchy and migration patterns more thoroughly. Methods Patients, histology, and immunohistochemistryThis study comprised three patients with synchronous LN and BM infiltration by FL at presentation. Biopsies were performed during the diagnostic and staging procedures. The selection criteria were the diagnosis of FL according to the fourth edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues.1 Clinical information was obtained from the patients' medical records. Material was collected from patients after their informed consent in accordance with the Declaration of Helsinki. The study was approved by the responsible institutional ethic boards. Further details are provided in the Online Supplementary Methods. Sequence analysis of IgV H genes and definition of mutational patternsDNA from the IgV H gene segments was extracted and amplified as described elsewhere. 23,24 Cloning, sequencing, and the mutational analysis of the obtained segments are described in detail in the Online Supplementary Methods. Delineation of tumor cell evolution by construction of pedigreesFor each patient and each compartment (LN and BM separately), the mutational patterns of IgV H gene segments were arranged in an ascending order of mutations to illustrate the mutational hierarchy of intraclonal sequence heterogeneity. Consequently, mutational patterns of early clones with few mutations had to be included in successor clones. When direct transition of one mutation pattern into that of successor clones with higher mutation loads was not observable, hypothetical predecessor clones (HPC) were introduced to retrace the evolution of sequenced clones back to the determined initial V H DJ H gene rearrangement (wild-type sequence). Accordingly, compartment-specific pedigrees were constructed. Thereafter, a third "summary-pedigree" comprising all sequenced clones was constructed, to evaluate the possibility of inter-compartmental exchange between LN and BM. Generation of hypothetical predecessor clones and delineation of migration probabilityFor each sequenced FL population (i.e. LN, BM, and LN and BM together) the pool of possible HPC was derived from mutations shared by at least two sequenced clones. To select the most appropriate predecessor clones from the abundance of generated HPC, the probability measurement was introduced (Figure 1). Only HPC with the highest probability measurement values were introduced until the evolution of sequenced clones could be retraced to the "wild-type sequence". Already established clone groups could not be disrupted by HPC with lower probability measurement values. These calculations resulted in a LN, a BM and an inter-compartment pedigree. If HPC of the inter-compartment pedigree displayed a higher probability measurement value than the corresponding LN or BM counterparts, inter-compartment migration was considered. The LN or BM allocation of these inter-compartment HPC was directed by the LN or BM affiliation of the majority of ev...

BCL2 mutation spectrum in B‐cell non‐Hodgkin lymphomas and patterns associated with evolution of follicular lymphoma

“…Deregulated BCL2 expression likely confers resistance to apoptosis and allows the acquisition of further aberrations required for the full malignant transformation and FL progression . In addition, recent analysis of IgH gene mutations in specimens from lymph nodes and the bone marrow from three FL patients suggests bidirectional cell migration between the two compartments during disease progression and relapse, further substantiating the complexity of FL evolution .…”

Origin and migration of follicular lymphoma cells

“…Extensive mutation analysis of original lymphoma samples and their paired samples taken during late relapses might also be informative. 17 These authors suggest that relatively fewer mutated FL cells may find a niche in the bone marrow. These cells may be relatively quiescent and in consequence escape the effect of chemotherapy, and may repopulate the body after therapy ("founder cells").…”

Dramatic increase in gene mutational burden after transformation of follicular lymphoma into TdT+ B-lymphoblastic leukemia/lymphoma

“…3). This high level of SHM can be found in FLs (Gagyi et al 2008;Wartenberg et al 2013;Carlotti et al 2015).…”

“…Given that the B-ALL/LBL clearly emerged from the FL as evidenced by the fluorescence in situ hybridization (FISH) and WES data (please see the paragraphs below), this lack of an identifiable dominant clone at the B-ALL/LBL stage likely stems from the extreme SHM upon the disease progression. SHM in advanced FL or, in particular, transformed to diffuse large B-cell lymphoma can be very extensive (Wartenberg et al 2013;Carlotti et al 2015), even involving non-Ig gene loci (Pasqualucci et al 2001;Rossi et al 2006). Accordingly, lineage tracing of the dominant FL rearrangement in our case showed that some B-ALL/LBL clones were identified in distal portions and even in distinct branches of the FL lineage tree (Fig.…”