Investigating the significance of acquired glycosylation in the surface immunoglobulin of B-cell lymphomas

Abstract

The surface immunoglobulin (sIg) variable regions of follicular lymphoma (FL) are characterised by the presence of acquired N-glycosylation sites (AGS), introduced during somatic hypermutation primarily in the complementarity determining regions (CDRs). These CDR-located AGS are acquired early during disease progression, are maintained throughout disease progression, and are occupied by oligomannose-type glycans (sIg-Mann). These interact with the C-type lectin dendritic cell-specific ICAM-3-grabbing non-integrin (DC-SIGN), expressed in the FL microenvironment on IL-4-polarised macrophages and CD21+ follicular dendritic cells. This interaction promotes antigen-independent, low-level signalling, through B-cell receptor (BCR)-associated kinases, and protects FL cells from antigenic stimulation. CDR-located AGS have also been identified in a subset of germinal centre B cell-like (GCB) diffuse large B-cell lymphoma (DLBCL), but the consequences of AGS in DLBCL have been less studied.
We used several large international public RNAseq cohorts, to study the prevalence, distribution and composition of glycans occupying AGS first in FL, and in DLBCL, using the IgSeqR IG assembly pipeline and liquid-chromatography mass spectrometry. The glycan types were correlated with genetic characteristics and clinical outcomes. The consequences of DC-SIGN engagement of sIg-Mann were also investigated further in vitro.
AGS were identified in 66-80% of FL cases, and the majority (90-96%) were located in the CDRs (CDR+ve FL). Mass-spectrometry revealed that CDR-located glycans were occupied by oligomannose-type glycans, while all AGS located in the framework regions (FR) were complex or unoccupied. CDR+ve cases associated with the BCL2 translocation, while those cases with no BCL2 translocation associated more with no AGS or FR-located AGS. The engagement of DC-SIGN to sIg-Mann on FL cells promoted FL adhesion to integrin receptor vascular cell adhesion molecule (VCAM)-1, and disrupted chemokine mediated migration.
In DLBCL, AGS were identified in 48-55% GCB-DLBCL, with 84-85% in the CDR. CDR-located AGS associated mostly with EZB-DLBCL (61-66% of EZB DLBCL were CDR+ve). Studying the glycan structures revealed, similar to FL, all CDR+ve EZB cases were occupied by oligomannose-type glycans, while all other AGS in DLBCL were either occupied by complex glycans or were unoccupied; Mann+ve glycans are a therefore a shared feature of FL and CDR+ve EZB (Mann+ve) DLBCL, both defined by BCL2 translocation. Mann+ve DLBCL had worse clinical outcomes compared to other GCB-DLBCL and was an independent prognostic factor for worse outcomes.
Overall, these data show Mann+ve AGS are a shared feature of FL and a subset of DLBCL, and Mann+ve lymphomas have worse clinical outcomes compared to their Mann-ve counterparts. Their interaction with DC-SIGN promotes FL cell retention within the lymph node and reveals the major interaction to disrupt for the therapeutic intervention of Mann+ve lymphomas.

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Identifiers

ORCID for Dylan James Tatterton: orcid.org/0000-0002-1453-7496

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