N-Glycosylation of the Ig Receptors Shapes the Antigen Reactivity in Chronic Lymphocytic Leukemia Subset #201.

ABSTRACT

Subset #201 is a clinically indolent subgroup of patients with chronic lymphocytic leukemia defined by the expression of stereotyped, mutated IGHV4-34/IGLV1-44 BCR Ig. Subset #201 is characterized by recurrent somatic hypermutations (SHMs) that frequently lead to the creation and/or disruption of N-glycosylation sites within the Ig H and L chain variable domains. To understand the relevance of this observation, using next-generation sequencing, we studied how SHM shapes the subclonal architecture of the BCR Ig repertoire in subset #201, particularly focusing on changes in N-glycosylation sites. Moreover, we profiled the Ag reactivity of the clonotypic BCR Ig expressed as rmAbs. We found that almost all analyzed cases from subset #201 carry SHMs potentially affecting N-glycosylation at the clonal and/or subclonal level and obtained evidence for N-glycan occupancy in SHM-induced novel N-glycosylation sites. These particular SHMs impact (auto)antigen recognition, as indicated by differences in Ag reactivity between the authentic rmAbs and germline revertants of SHMs introducing novel N-glycosylation sites in experiments entailing 1) flow cytometry for binding to viable cells, 2) immunohistochemistry against various human tissues, 3) ELISA against microbial Ags, and 4) protein microarrays testing reactivity against multiple autoantigens. On these grounds, N-glycosylation appears as relevant for the natural history of at least a fraction of Ig-mutated chronic lymphocytic leukemia. Moreover, subset #201 emerges as a paradigmatic case for the role of affinity maturation in the evolution of Ag reactivity of the clonotypic BCR Ig.