Analysis of the targeting of the hypermutational machinery and the impact of subsequent selection on the distribution of nucleotide changes in human V rearrangements

Abstract

B cells are unique in that they generate and tolerate a high rate of mutations in their antigen receptor genes and employ these mutations as a basis of avidity maturation. The precise role of the mutational machinery versus subsequent selection in determining the frequency and distribution of mutations has not been fully analyzed. To address these issues, the influence of the intrinsic mutational machinery and subsequent selection on the frequency and distribution of mutations in the expressed human immunoglobulin repertoire was analyzed. Analysis of non-productively rearranged VH genes from individual human B cells provided an opportunity to examine the immediate impact of somatic hypermutation without superimposed selective influences. Comparison with the frequency and distribution of mutations in the productively rearranged human VH genes permitted an estimate of the influences of subsequent selection.

Somatic hypermutation targeting to intrinsic hotspots of immunoglobulin genes in follicular lymphoma and multiple myeloma

“…Moreover, mutations in codons contained within the RGYW/WRCY motifs were significantly more frequent in the CDRs than in the FWRs of productive vs non-productive rearrangements. 13 These results were interpreted as strong indicators that the hypermutation mechanism targets the overrepresented RGYW motifs in V genes on both DNA strands and that the resulting replacement mutations are preferentially selected in the productive repertoire.…”

“…23 Our findings regarding the distribution and possible targeting of somatic mutations in rearranged IgV genes of FL and MM conform well with the aforementioned data derived from normal peripheral B cells; for example, the corresponding malignant B cells carrying productive V -J rearrangements and having experienced antigen selection generally exhibit an increased incidence of RGYW targeting in CDRs vs FWRs. 13 The differences observed in favor of tetranucleotide (RGYW and WRCY) targeting in FL-V H vs FL-V and MM-V vs FL-V may implicate differences in the evolution of somatic hypermutation coupled with selection in memory (post-GC) vs GC B cells. [24][25][26][27][28][29][30][31] Interestingly, this pattern of somatic hypermutation targeting to tetranucletides (H Ͼ Ͼ ) as well as the trend for strand-biased targeting only in the CDRs of FL-V H genes (RGYW being significantly more mutated than WRCY) and not in LC V genes recapitulates the temporal pat- tern of Ig gene rearrangements in early B cell ontogeny, where Ig HC genes rearrange first, to be followed by and then LC genes; 32 however, exceptions to this generally occurring pattern of ordered light chain gene rearrangements are known to occur (instead of preceding , in a minority of cases the light chain locus is targeted first by the 'recombinase' machinery).…”

“…A further objective was to identify whether the incidence of mutations was dependent on the actual sequence and location of the nucleotide motifs in the CDRs and framework regions (FWRs). To this purpose, we examined eight highly mutable trinucleotides (AGC, GCT, ATT, AAT, TAC, GTA, AGT and AGA), 13 most of which are part of the RGYW/WRCY motif.…”

Mutational status of IgVH genes in B-cell chronic lymphocytic leukemia and prognosis: percent mutations or antigen-driven selection?

“…1 In a recently published study, Lane et al 2 tested the hypothesis that analysis of IgV H gene mutations according to antigen-driven selection may also influence prognosis of B-CLL patients. In a series of 83 B-CLLs, they found a significant skewing of replacement (R) mutations from framework (FR) to complementarity-determining (CDR) regions of IgV H segments (or silent-S-mutations from CDRs to FRs), as occurs in normal antigen-selected B cells, 3 in about 40% of cases with a non-germ line (GL) IgV H gene configuration. This was obtained by applying the available binomial and/or multinomial statistical models aimed at evaluating the excess/ scarcity of R/S mutations in FR/CDRs.…”

Germinal Center Function in the Spleen during Simian HIV Infection in Rhesus Monkeys

“…An iterative process of selection, expansion, mutation, and further selection culminates in the generation of high-affinity memory B lymphocytes and plasma cells. Specific features of the somatic mutations observed in expressed Igs have been well-characterized (3,4) and are similar in humans and mice. Some disease states are associated with atypical patterns of somatic mutation in expressed Igs (5)(6)(7)(8)(9).…”