IGHV gene insertions and deletions in chronic lymphocytic leukemia: “CLL‐biased” deletions in a subset of cases with stereotyped receptors

Abstract

Nucleotide insertions/duplications or deletions in immunoglobulin heavy chain genes have been found in 24/760 patients (3.15%) with chronic lymphocytic leukemia (CLL). In 21/24 cases, the inserted/duplicated or lost nucleotides occurred in multiples of 3; therefore, the original reading frame was maintained and a potentially intact receptor was coded. The pattern and location of insertions/duplications or deletions in CLL and their restriction to mutated IGHV rearranged genes strongly suggests that they resulted from somatic hypermutation. Their incidence in CLL is consistent with previous reports in normal, auto-reactive and neoplastic human B cells, thus seemingly indicating that these modifications generally arise without any particular disease-specific associations. A striking exception to this rule was identified in CLL IGHV3-21-expressing cases: one amino acid was deleted from the CDR2 region in 16/63 (25.4%) mutated CLL IGHV3-21 sequences (including public database-derived IGHV3-21 CLL cases + the present series) vs. only 2/257 (0.78%) public database-derived mutated non-CLL IGHV3-21 sequences; 15/16 CLL IGHV3-21 sequences carrying this deletion belonged to a subset with unique, shared HCDR3 and light chain CDR3 motifs. This finding further supports the idea of selective antigenic pressures playing a pathogenetic role in some CLL cases.

Immunoglobulin sequence analysis and prognostication in CLL: guidelines from the ERIC review board for reliable interpretation of problematic cases

“…8 Among 4154 cases with CLL from collaborating institutions in France, Greece, Italy, The Netherlands, Sweden and the United Kingdom, unproductive rearrangements were detected in 377 (9.1%) cases ( Table 1). As expected, they were significantly more frequent when genomic DNA (gDNA) rather than complementary DNA (cDNA) was used as the starting material (351/2526 (13.9%) vs 26/1628 (1.6%) cases) and, in the vast majority of cases (350/377, 92.8%), a productive rearrangement was also present.…”

Immunoglobulin gene sequence analysis in chronic lymphocytic leukemia: updated ERIC recommendations

“…The following issues merit special consideration:

Cases with a single unproductive rearrangement, apparent double rearrangements or lacking VH CDR3 anchors (overall frequency: ~3% of cases). 28 In these instances, the report should include a relevant statement, depending on the particular type of ‘issue’, following the published ERIC recommendations for reliable interpretation of problematic cases 28, 30 and/or by consulting the online ERIC Review Board (www.ericll.org/services/).

Cases with IGHV gene rearrangements with ‘borderline’ identity to the closest germ line counterpart.

…”

“…28 In these instances, the report should include a relevant statement, depending on the particular type of ‘issue’, following the published ERIC recommendations for reliable interpretation of problematic cases 28, 30 and/or by consulting the online ERIC Review Board (www.ericll.org/services/). …”

ERIC recommendations on IGHV gene mutational status analysis in chronic lymphocytic leukemia

“…20 One has also to keep in mind that nucleotide insertions/duplications or deletions in IGH genes may occur in up to 3% of CLL sequences. 23 This does not allow a proper alignment using both V-QUEST and DNA plot, hampering a correct analysis. In contrast, the recognition of extra or missing nucleotide is possible with Ig BLAST.…”