Follicular lymphoma B cells undergo continuous somatic hypermutation (SHM) of their immunoglobulin variable region genes, generating a heterogeneous tumor population. SHM introduces DNA sequences encoding N-glycosylation sites asparagine-X-serine/threonine (N-gly sites) within the V-region that are rarely found in normal B-cell counterparts. Unique attached oligomannoses activate B-cell receptor signaling pathways after engagement with calcium-dependent lectins expressed by tissue macrophages. This novel interaction appears critical for tumor growth and survival. To elucidate the significance of N-gly site presence and loss during ongoing SHM, we tracked site behavior during tumor evolution and progression in a diverse group of patients through next-generation sequencing. A hierarchy of subclones was visualized through lineage trees based on SHM semblance between subclones and their discordance from the germline sequence. We observed conservation of N-gly sites in more than 96% of subclone populations within and across diagnostic, progression, and transformation events. Rare N-gly-negative subclones were lost or negligible from successive events, in contrast to N-gly-positive subclones, which could additionally migrate between anatomical sites. Ongoing SHM of the N-gly sites resulted in subclones with different amino acid compositions across disease events, yet the vast majority of resulting DNA sequences still encoded for an N-gly site. The selection and expansion of only N-gly-positive subclones is evidence of the tumor cells’ dependence on sites, despite the changing genomic complexity as the disease progresses. N-gly sites were gained in the earliest identified lymphoma cells, indicating they are an early and stable event of pathogenesis. Targeting the inferred mannose-lectin interaction holds therapeutic promise.

CD180 is a toll-like receptor that is highly expressed in complex with the MD-1 satellite molecule on the surface of B cells. In chronic lymphocytic leukaemia (CLL) however, the expression of CD180 is highly variable and overall, significantly reduced when compared to normal B cells. We have recently shown that reduced CD180 expression in CLL lymph nodes is associated with inferior overall survival. It was therefore important to better understand the causes of this downregulation through investigation of CD180 at the transcriptional and protein expression levels. Unexpectedly, we found CD180 RNA levels in CLL cells (n = 26) were comparable to those of normal B cells (n = 13), despite heterogeneously low expression of CD180 on the cell surface. We confirmed that CD180 RNA is translated into CD180 protein since cell surface CD180-negative cases presented with high levels of intracellular CD180 expression. Levels of MD-1 RNA were, however, significantly downregulated in CLL compared to normal controls. Together, these data suggest that changes in CD180 cell surface expression in CLL are not due to transcriptional downregulation, but defective post-translational stabilisation of the receptor due to MD-1 downregulation.

The British Journal of Haematology publishes original research papers in clinical, laboratory and experimental haematology. The Journal also features annotations, reviews, short reports, images in haematology and Letters to the Editor.

Follicular lymphoma (FL) is a heterogeneous and incurable disease. One of the hallmark features of FL cells is the introduction of N-glycosylation (N-gly) amino acid sequence motifs into the immunoglobulin variable (IgV) region through ongoing somatic hypermutation (SHM) in the early stages of lymphoma development. These N-gly motifs, containing oligomannoses, are rarely found in healthy B cells but evidently play a crucial role in the clonal evolution and survival of FL cells in the hostile environment of germinal centers. The random nature of the ongoing SHM in FL occasionally results in the loss of productive immunoglobulin (Ig) genes or the elimination of N-gly motifs in productive genes. Such events typically lead to clonal deletion, as demonstrated by the longitudinal analysis of FL samples. However, rare N-gly-negative subclones demonstrate prolonged survival with evidence of ongoing SHM, giving rise to new N-gly-negative subclones before eventual deletion. This observation suggests the presence of specific mechanisms supporting their survival and proliferation. This perspective examines the current literature and explores whether a detailed transcriptomic and functional comparison of FL subclones characterized by different N-gly statuses, with a particular focus on N-gly-negative subclones, will lead to a comprehensive understanding of both N-gly-dependent and independent pro-survival and proliferative transcriptional signatures. Specifically, it aims to deepen our understanding of FL pathobiology and identify novel therapeutic targets for better disease management.