Higher-order immunoglobulin repertoire restrictions in CLL: the illustrative case of stereotyped subsets 2 and 169

Abstract

Chronic lymphocytic leukemia (CLL) major stereotyped subset #2 (IGHV3-21/IGLV3-21, ~2.5% of all CLL) is an aggressive disease variant, irrespective of the somatic hypermutation (SHM) status of the clonotypic IGHV gene. Minor stereotyped subset #169 (IGHV3-48/IGLV3-21, ~0.2% of all CLL) is related to subset #2 as it displays a highly similar variable antigen-binding site. We further explored this relationship through next-generation sequencing and crystallographic analysis of the clonotypic B cell receptor immunoglobulin (BcR IG). Branching evolution of the predominant clonotype through intraclonal diversification (ID) in the context of ongoing SHM was evident in both heavy and light chain genes of both subsets. Molecular similarities between the two subsets were highlighted by the finding of shared SHMs within both the heavy and the light chain genes in all analyzed cases at either clonal or subclonal level. Particularly noteworthy in this respect was a ubiquitous SHM at the linker region between the variable and the constant domain of the IGLV3-21 light chains, previously reported as critical for IG homotypic interactions underlying cell-autonomous signaling capacity. Notably, crystallographic analysis revealed that the IGLV3-21-bearing CLL subset #169 IG retains the same geometry and contact residues for the homotypic intermolecular interaction observed in subset #2, including the SHM at the linker region, and from a molecular standpoint belong to a common structural mode of autologous recognition. Collectively, our findings document that stereotyped subsets #2 and #169 are very closely related, displaying shared IG features that can be explained only in the context of shared functional selection.

Consistent B Cell Receptor Immunoglobulin Features Between Siblings in Familial Chronic Lymphocytic Leukemia

“…We confirmed the somatic R110 mutation and germline configuration of the K16 and YDSD motifs in all four members of family 3 (Supplementary Figure 1). Regarding the heavy chain, two family members (3B and 3C) belonged to the closely related and clinically aggressive subsets #2 and #169, respectively (44). The respective IGHV genes of these heavy chain stereotypic CLL subsets, IGHV3-21 and IGHV3-48, were 97% identical.…”

Distinctive Signaling Profiles With Distinct Biological and Clinical Implications in Aggressive CLL Subsets With Stereotyped B-Cell Receptor Immunoglobulin

“…The clonotypic IGHV3-21 genes bear a variable SHM load, with most cases (~60%-65%) classified as M-CLL (23,25). The SHM patterns in both the heavy and light chains of subset #2 supported antigen pressure, with some SHMs revealed as critical for self-association leading to cell-autonomous signaling (36,46). Relevant to mention, we recently demonstrated that stereotyped subset #169, a minor CLL subset (~0.2% of all CLL), bears striking immunogenetic but also biological and clinical similarities to subset #2 (25).…”

“…Uniquely among B-cell malignancies, CLL has been found to display an alternative mode of cell activation that is independent of antigen and results from homotypic interactions between two different BcR IG molecules ( 34 ). Studies from our group have dissected the molecular basis of cell-autonomous signaling in CLL, revealing distinct modes of homotypic interactions in different CLL subsets ( 36 , 46 ). Particularly for subsets #2 and #169, it has been demonstrated that BcR–BcR interactions critically rely on light chain-mediated contacts, with a specific mutation from the germline sequence in the linker region between the variable and the constant domain of the light chains, namely, the substitution of arginine for glycine (termed R110) in the clonotypic light chain encoded by the IGLV3-21*01 allele (IGLV3-21 R110 ), identified as key to the capacity for homodimerization underlying cell-autonomous signaling ( 36 , 46 ).…”

“…Moreover, accumulating evidence indicates that patients assigned to the same stereotyped subset display consistent antigenic recognition profiles ( 26 ) as well as similar landscapes of antigen reactivity ( 27 ), BcR IG 3D structure ( 28 ), genomic aberrations ( 29 ), gene expression ( 30 ), epigenetic modifications ( 31 ), Toll-like receptor signaling ( 32 , 33 ), and “classic” ( 27 ) and cell-autonomous BcR signaling ( 34 ), among others. Moreover, BcR IG stereotypy defines subgroups with shared clinical features and similar outcome ( 9 , 25 , 35 , 36 ).…”

Ανάλυση Του Μηχανισμού Της Σωματικής Υπερμεταλλαξιγένεσης Στα Γονίδια Των Ανοσοσφαιρινών Με Μεθοδολογία Αλληλούχησης Μεγάλης Κλίμακας Σε Ασθενείς Με Λεμφοϋπερπλαστικά Νοσήματα

“…Τα δύο υποσύνολα είναι πολύ όμοια και σε γενετικό επίπεδο, καθώς φέρουν σε εξίσου μεγάλη συχνότητα μεταλλάξεις στο γονίδιο SF3B1 (45% στο υποσύνολο #2, 43% στο υποσύνολο #169) 60,101 . Η ελαφριά αλυσίδα του υποσυνόλου #169 κωδικοποιείται επίσης από το γονίδιο IGLV3-21, έχει την ίδια δομή και φέρει την ίδια αλλαγή στο σημείο σύνδεσης της σταθερής και της μεταβλητής περιοχής με το υποσύνολο #2 87,107 .…”