IGHV sequencing reveals acquired N-glycosylation sites as a clonal and stable event during follicular lymphoma evolution

• Published in: Blood 2020-03, Vol.135 (11), p.834-844
• Main Authors: Odabashian, Mariette, Carlotti, Emanuela, Araf, Shamzah, Okosun, Jessica, Spada, Filomena, Gribben, John G., Forconi, Francesco, Stevenson, Freda K., Calaminici, Mariarita, Krysov, Sergey
• Format: Article
• Language: English
• Subjects: Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - metabolism; Clonal Evolution - genetics; Gene Rearrangement; Glycosylation; High-Throughput Nucleotide Sequencing; Humans; Immunoglobulin Variable Region - genetics; Immunoglobulin Variable Region - metabolism; Lymphoid Neoplasia; Lymphoma, Follicular - etiology; Lymphoma, Follicular - metabolism; Lymphoma, Follicular - pathology; Recurrence
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.2019002279

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. •N-glycosylation sites are acquired early in disease and persist during tumor progression, despite therapy.•Scarcity of N-glycosylation sites-negative subclones and their loss during progression suggest positive clones expand preferentially. [Display omitted]