Nonstochastic pairing of immunoglobulin heavy and light chains expressed by chronic lymphocytic leukemia B cells is predicated on the heavy chain CDR3

Abstract

We analyzed the immunoglobulin (Ig) variable heavy (IGHV) and variable light chain genes used by leukemia cells of 258 unrelated patients with chronic lymphocytic leukemia (CLL) found to express unmutated Ig heavy chains (IgH) encoded by a 51p1 allele of IGHV1-69 among 1846 CLL patients examined. We found each had at least 98% homology to an identified germline IGKV or IGLV gene. Within the 258 IgH, we identified heavy chain CDR3 (HCDR3) motifs encoded by certain unmutated IGHD and IGHJ genes with restricted reading frames. Frequent and restricted use of particular IGKV and IGLV genes revealed nonstochastic pairing of disparate Ig light chains (IgL) with IgH that had restricted HCDR3 motifs designated CLL69A, -B, -C, and -D. Eighty-six percent (19/22) of CLL cases that expressed motif CLL69B encoded by IGHD2-2/IGHJ6 had distinctive IgL encoded by IGKV1-39. Similarly, 83% (5/6) of samples with motif CLL69D encoded by IGHD2-2/IGHJ6 expressed IGKV3-11, 100% (25/25) with motif CLL69A encoded by IGHD3-16/IGHJ3 used IGKV3-20, and 77% (10/13) with motif CLL69C encoded by IGHD3-3/IGHJ6 expressed IGLV3-9. This study reveals nonstochastic pairing of IgH with particular IgL that is predicated upon Ig HCDR3 structure, providing compelling evidence for selection of antibodies expressed in CLL by conventional antigens.

Figure 1

Relative expression of IGKV and IGLV genes in subgroups of CLL samples. Values are expressed as a percentage of samples found to use each IGKV or IGLV gene. (A) Comparison of IGKV used by 182 CLL samples in this study that express κ light chains (51p1 CLL), with 179 samples reported by Stamatopoulos et al (κ CLL), and the 89 samples in the latter cohort that express unmutated Ig (κ CLL NM). (B) Comparison of IGLV used by 76 CLL samples in this study that express λ light chains (51p1 CLL), with 97 reported by Stamatopoulos et al (λ CLL), and the 53 samples in the cohort that express unmutated Ig (λ CLL NM). Other IGKV and Other IGLV represent the IGKV and IGLV genes, respectively, that are present in less than 3% of the light chains within each of the 3 groups of CLL samples.

Figure 2

Amino acid sequences of the CDR3 of the nearly identical Ig heavy and light chains. (A) Amino acid sequences of the CDR3 of the nearly identical Ig heavy and light chains expressed by the 19 unrelated CLL patients of subgroup CLL69B. Alignments of the amino acid sequences of the 51p1 encoded heavy chains and IGKV1-39 light chains are shown compared with CLL69B2. Dots indicate homology and dashes indicate no sequence at that position. Listed on the left is the designation for each CLL sample. The germline sequences of the IGHD2-2, IGHJ6, IGKV1-39 and IGKJ4 genes are shown for reference. Underlined letters (X) designate amino acid differences between the germline IGKJ genes relative to IGKJ4. (B) Amino acid sequences of the CDR3 of the nearly identical Ig heavy and light chains expressed by the 5 unrelated CLL patients of subgroup CLL69D. Alignments of the amino acid sequences of the 51p1 encoded heavy chains and IGKV3-11 light chains are shown compared with CLL69D1. Dots indicate homology and dashes indicate no sequence at that position. Listed on the left is the designation for each CLL sample. The germline sequences of the IGHD2-2, IGHJ6, IGKV3-11, and IGKJ3 genes are shown for reference. (C) Amino acid sequences of the CDR3 of the nearly identical Ig heavy and light chains expressed by the 10 unrelated CLL patients of subgroup CLL69C. Alignments of the amino acid sequences of the 51p1 encoded heavy chains and IGLV3-9 light chains are shown compared with CLL69C1. Dots indicate homology and dashes indicate no sequence at that position. Listed on the left is the designation for each CLL sample. The germline sequences of the IGHD3-3, IGHJ6, IGLV3-9, and IGLJ2 genes are shown for reference. (d) Amino acid sequences of the CDR3 of the nearly identical Ig heavy and light chains expressed by the 25 unrelated CLL patients of subgroup CLL69A. Alignments of the amino acid sequences of the 51p1 encoded heavy chains and IGKV3-20 light chains are shown compared with CLL69A1. Dots indicate homology and dashes indicate no sequence at that position. Listed on the left is the designation for each CLL sample. The germline sequences of the IGHD3-16, IGHJ3, IGKV3-20, and IGKJ4 genes are shown for reference. Underlined letters (X) designate amino acid differences between the germline IGKJ genes relative to IGKJ4.