Intraclonal diversification of immunoglobulin light chains in a subset of chronic lymphocytic leukemia alludes to antigen-driven clonal evolution

Abstract

The study of intraclonal diversification (ID) in immunoglobulin (IG) genes offers valuable insight into the role of ongoing interactions with antigen in lymphomagenesis. We recently showed that ID in the IG heavy chain genes of patients with chronic lymphocytic leukemia (CLL) was generally limited; however, intense ID was evident in selected cases, especially those expressing stereotyped IGHV4-34 rearrangements and assigned to subset 4. Here, we report results from a large-scale subcloning study of IG light variable genes, in a total of 1008 subcloned sequences from 56 CLL cases. Multiple analogies were noted between heavy and light chains regarding the occurrence and molecular features of ID. More specifically, the impact of ID on the clonotypic light chains was generally low, with the significant exception of subset 4. Similar to the IGHV4-34 heavy chains of this subset, their partner IGKV2-30 light chains were affected by an active and precisely targeted ID process. Altogether, these findings strengthen the argument that stereotypy in subset 4 extends to stereotyped ID patterns for both heavy and light chains through persistent antigenic stimulation. Furthermore, they strongly suggest that light chains have an active role in the antigen selection process, at least for certain subsets of CLL cases.

Temporal Dynamics of Clonal Evolution in Chronic Lymphocytic Leukemia with Stereotyped IGHV4-34/IGKV2-30 Antigen Receptors: Longitudinal Immunogenetic Evidence

“…We recently investigated intraclonal diversification (ID) within the IG genes of patients with CLL and found that most cases showed no or low levels of ID. In sharp contrast, we reported intense ID within both the heavy and light chain IG genes of patients assigned to subset #4 (29,30).…”

“…Intraclonal diversification in sets of subcloned sequences obtained from the same sample was assessed by examination of sequence variation in the V domain following definitions previously proposed by our group (29,30). In brief, all 'non-ubiquitous' sequence changes from the germline were evaluated in the counts and characterized as follows: (1) Although, the extent of ID varied between cases with, for example, P3020 and P3916 undergoing limited diversification in comparison to several other cases analyzed, most notably P1422 and P2920, overall the incidence and topology of ID in subset #4 over time are suggestive of selection events governed by structural constraints for optimal antigen recognition.…”

“…All amplification reactions were run using the high-fidelity Accuprime Pfx polymerase (Invitrogen) and purified PCR amplicons were subjected to direct sequencing on both strands (16,17,(29)(30)(31). …”

Silenced B-cell receptor response to autoantigen in a poor-prognostic subset of chronic lymphocytic leukemia

“…18 Within stereotyped subsets, similarities between different cases extend from BcR Ig sequences to biological and prognostic features, clinical presentation, and even outcome. For example, patients assigned to subset #4 (IGHV4-34/IGKV2-30) are relatively young at diagnosis, 7 uniformly express mutated IgG-switched Igs with pronounced intraclonal diversifications, [7][8][9]19 display distinctive gene expression and microRNA profiles, [20][21][22] and follow an indolent disease course. 7,23 In contrast, patients belonging to subset #1 (Clan I IGHV/IGKV1(D)-39) uniformly express unmutated BcR Igs, exhibit a distinctive gene expression signature with several differentially expressed transcripts involved in BcR signaling, apoptosis regulation, cell proliferation and oxidative processes, 24 and suffer from a poor prognosis even when compared to other patients with unmutated IGHV genes.…”

“…[1][2][3] From an immunogenetic perspective, perhaps the strongest evidence for antigen involvement is the existence of different subsets of cases with highly similar or 'stereotyped' immunoglobulins (Igs) in their B-cell receptors (BcRs), [4][5][6][7] indicating selection by antigen in CLL ontogeny. 8,9 Several self and exogenous antigens (i.e. non-muscle myosin, vimentin, cofilin, oxLDL, bacterial polysaccharides, fungal β-glycans) are considered to be involved in the initiation and/or progression of CLL, 2,10-13 in synergy with microenvironment factors, [14][15][16][17] that signal via innate immune receptors, such as Toll-like receptors (TLRs).…”