Novel Approaches in Molecular Characterization of Classical Hodgkin Lymphoma

Abstract

Classical Hodgkin lymphoma (cHL) represents a B-cell lymphoproliferative disease characterized by clonal immunoglobulin gene rearrangements and recurrent genomic aberrations in the Hodgkin Reed-Sternberg cells in a reactive inflammatory background. Several methods are available for the molecular analysis of cHL on both tissue and cell-free DNA isolated from blood, which can provide detailed information regarding the clonal composition and genetic alterations that drive lymphoma pathogenesis. Clonality testing involving the detection of immunoglobulin and T cell receptor gene rearrangements, together with mutation analysis, represent valuable tools for cHL diagnostics, especially for patients with an atypical histological or clinical presentation reminiscent of a reactive lesion or another lymphoma subtype. In addition, clonality assessment may establish the clonal relationship of composite or subsequent lymphoma presentations within one patient. During the last few decades, more insight has been obtained on the molecular mechanisms that drive cHL development, including recurrently affected signaling pathways (e.g., NF-κB and JAK/STAT) and immune evasion. We provide an overview of the different approaches to characterize the molecular composition of cHL, and the implementation of these next-generation sequencing-based techniques in research and diagnostic settings.

Keywords: cell-free DNA; classical Hodgkin lymphoma; clonality assessment; mutation analysis; next-generation sequencing.

Figure 1

Schematic overview of immunoglobulin and T-cell receptor V(D)J gene rearrangements. (a) Immunoglobulin (IG) gene rearrangements generate a B-cell receptor, where IG heavy chain (IGH) genes are represented in blue, while IG kappa (IGK) and IG lambda (IGL) light chain genes are indicated in green. In this figure, only (potentially) productive IGH and IGK gene rearrangements are shown. In case of a non-productive IGK rearrangement, the kappa deleting element will rearrange with an upstream IGK-V gene or the Intron-RSS sequence (not shown in this figure). If both alleles result in a non-productive IGK light chain, the IGL light chain will rearrange, according to a similar process as IGK (not shown in this figure). Please note that the structure of the IGL chain is slightly different compared to the IGK chain shown here, since each IGL constant region is preceded by a single IGL-J gene. (b) V(D)J gene rearrangements of alpha/beta T-cell receptor. TR alpha (TRA) chain is represented in yellow, TR beta (TRB) chain in orange. Gamma/delta T-cell receptors are generated similarly, where TR gamma (TRG) chain undergoes VJ rearrangement similar to TRA, while TR delta (TRD) chain is generated by VDJ rearrangement, like TRB. Please note that the TRD gene cluster is located between the TRA-V and TRA-J gene clusters, as indicated with an asterisk. This TRD gene cluster will be deleted upon TRA gene rearrangements. For both IG and TCR, dark shades represent the constant regions, while the lighter shades correspond to variable regions, which are composed of rearranged V, (D) and J genes.

Figure 2

Schematic overview of the pathways affected by genetic alterations in classical Hodgkin lymphoma. The main affected pathways in the pathogenesis of cHL involve JAK/STAT, NF-κB, PI3K/AKT and immune evasion, caused by inactivating mutations (in red), activating mutations (in green), translocations and overexpression due to gene amplifications. Nuclear–cytoplasmic (e.g., XPO1) transport and epigenetic regulation (e.g., ARID1A) may be disturbed in HRS cells, contributing to oncogenesis.

Figure 3

Schematic overview of EBV-associated gene products in the pathogenesis of classical Hodgkin lymphoma. EBV-associated transcripts and proteins are able to activate pathways and cellular processes that are recurrently affected by mutations in EBV-negative HRS cells. These alterations thereby play an important role in the pathogenesis and survival of EBV-positive HRS cells.