Receptor editing in CLL Subset #201

Subset #201 is a clinically indolent subset of patients with chronic lymphocytic leukemia (CLL) defined by the expression of stereotyped, mutated IGHV4-34/IGLV1-44 B cell receptor immunoglobulin (BcR IG). It is characterized by recurrent somatic hypermutations (SHM) that frequently lead to the creation and/or disruption of novel N-glycosylation sites within the IG heavy and light chain variable domains. In order to understand the relevance of this observation, we studied the subclonal architecture of the BcR IG repertoire in subset #201 using next generation sequencing and also profiled the antigen reactivity of the clonotypic BcR IG expressed as recombinant monoclonal antibodies (rmAbs). We found that almost all cases of subset #201 carry SHMs potentially affecting N-glycosylation at the clonal and/or subclonal level and provide evidence for N-glycan occupancy in SHM-induced novel N-glycosylation sites. These particular SHMs impact on (auto)antigen recognition, as indicated by comparisons between the authentic rmAbs and germline revertants of SHMs introducing novel N-glycosylation sites. Finally, we report that at least a fraction of the lambda expressing subset #201 clones carry productive, non-expressed IGKV-IGKJ gene rearrangements and that (auto)antigen reactivity differs between the authentic subset #201 rmAbs and #201 rmAbs where the authentic heavy chain was paired with the productive, non-expressed IGKV-IGKJ gene rearrangement. On these grounds, N-glycoslylation appears as relevant for the natural history of at least a fraction of mutated (M)-CLL. Moreover, subset #201 emerges as a paradigmatic case for the role of receptor editing in the evolution of antigen reactivity of the clonotypic BcR IG.