Oligomannose-Type Glycans in the Antigen Binding Site Identify Origin and Prognosis of Diffuse Large B Cell Lymphoma

The acquisition of N-glycosylation sites (AGS) in the complementarity-determining region (CDR) of the tumor immunoglobulin (Ig) is an early clonal requirement of classic follicular lymphoma (FL). In FL, the AGS are occupied by oligomannose-type glycans, which mediate lymphoma Ig interaction with the microenvironmental lectin dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN). This interaction induces a persistent low-level signal, favouring adhesion and ultimately survival and growth of the lymphoma cells in their protected environment. Oligomannose-type glycans can also occupy the CDR-located AGS of a subset of germinal-centre B cell-like (GCB) diffuse large B-cell lymphomas (DLBCL), but the consequences of AGS in DLBCL are less known.

We determined the frequency, distribution, and composition of the glycan structures occupying the AGS in DLBCL using a discovery-validation approach with two large independent international public cohorts (BCC, dataset ID: EGAD00001003783; NCI accession phs001444.v1.p1), following our RNAseq Ig assembly pipeline (Ig-Seq-R) and high-resolution mass-spectrometry. Glycan types were compared to our FL cohort (12 samples) and correlated with DLBCL cell of origin (COO), genetic, clinical characteristics and outcome.

The full IGHV-IGHD-IGHJ-IGHC transcript sequences were obtained from 251 DLBCL of the BCC, and 339 of the NCI cohort. Sample distribution by COO, clinical or molecular features, LymphGen subtype, progression-free survival (PFS) and overall survival (OS) were not different from the extended public cohorts.

AGS were observed in 48-55% GCB-DLBCL, with 84-85% of them located in the CDR. Overall, frequency of CDR-located AGS contrasted dramatically between GCB-DLBCL (41-46%) and activated B-cell like (ABC)-DLBCL (7-10%). Also, within GCB-DLBCL, CDR-located AGS associated mostly with the EZB subtype (68-73%). However, only 66-61% EZB were AGS+ve, all of which were CDR+ve, while the remaining 34-39% had no AGS (AGS-ve EZB).

The glycan structures of the synthetic F(ab)s from 35 AGS+ve DLBCL and 12 FL were analyzed by site-specific mass spectrometry. The DLBCL comprised 12 AGS+ve EZB and 23 AGS+ve non-EZB (14 CDR+ve, 9 located in the framework region). Glycan analysis revealed that all AGS+ve EZB and FL were invariably occupied by oligomannose-type glycans (Ig-Mann+ve DLBCL). In contrast, the other AGS+ve DLBCL were not occupied by oligomannose type glycans. They were either occupied by complex glycans (the remaining non-EZB GCB-DLBCL) or not occupied (preferentially the ABC-DLBCL), irrespective of AGS location. These data indicated that CDR+ve EZB Ig were universally and exclusively Ig-Mann+ve DLBCL, share the COO of FL, and have likely been influenced by an environmental driver distinct from the other GCB-DLBCL and ABC-DLBCL.

We compared the clinical behavior of Ig-Mann+ve DLBCL versus other DLBCL subtypes including AGS-ve EZB and the other non-EZB GCB-DLBCL and ABC-DLBCL. In both the BCC and NCI cohorts, Ig-Mann+ve DLBCL status identified the subset with the worst PFS and OS of all GCB-DLBCL, not different from ABC-DLBCL (Figure 1A). This contrasted with the other GCB-DLBCL (AGS-ve/EZB and AGS+ve/non-EZB), which all shared an extremely good PFS and OS (Figure 1A). Univariate and multivariate analyses revealed that Ig-Mann+ve status was an independent prognostic factor for PFS and OS (Figure 1B).

Gene expression profile analysis revealed that Ig-Mann+ve status associated with an enrichment of MYC, PI3K-Akt-mTORC1, pro-survival, and cell cycle pathways, while proinflammatory and apoptotic pathways were decreased in the Ig-Mann+ve DLBCL compared to AGS-ve/EZB and AGS+ve/non-EZB, independently of MYC translocations and double-hit signature.

These data indicate identical COO of a EZB subset with FL cells, and point to a highly selective chronic environmental pressure on Ig-Mann+ve DLBCL negatively affecting patients survival. The combination of Ig gene analysis with the lymphGen classification can predict Ig glycan structure and provide a new fundamental approach to identifying the most aggressive GCB-DLBCL subtype, and the precise environmental tumour interaction (DC-SIGN:Ig-Mann) to intercept therapeutically early in the natural history of Ig-Mann+ve DLBCL.