CLL stereotyped B-cell receptor immunoglobulin sequences are recurrent in the B-cell repertoire of healthy individuals: Apparent lack of central and early peripheral tolerance censoring

Stereotyped B-Cell Receptor Immunoglobulins in B-Cell Lymphomas

Thorough examination of clonotypic B-cell receptor immunoglobulin (BcR IG) gene rearrangement sequences in patients with mature B-cell malignancies has revealed significant repertoire restrictions, leading to the identification of subsets of patients expressing highly similar, stereotyped BcR IG. This discovery strongly suggests selection by common epitopes or classes of structurally similar epitopes in the development of these tumors. Initially observed in chronic lymphocytic leukemia (CLL), where the stereotyped fraction accounts for a substantial fraction of patients, stereotyped BcR IGs have also been identified in other mature B-cell malignancies, including mantle cell lymphoma (MCL) and splenic marginal zone lymphoma (SMZL).Further comparisons across different entities have indicated that stereotyped IGs are predominantly "disease-biased," indicating distinct immune pathogenetic trajectories. Notably, accumulating evidence suggests that molecular subclassification of mature B-cell malignancies based on BcR IG stereotypy holds biological and clinical relevance. Particularly in CLL, patients belonging to the same subset due to the expression of a specific stereotyped BcR IG exhibit consistent biological backgrounds and clinical courses, especially for major and extensively studied subsets. Therefore, robust assignment to stereotyped subsets may aid in uncovering mechanisms underlying disease initiation and progression, as well as refining patient risk stratification. In this chapter, we offer an overview of recent studies on BcR IG stereotypy in mature B-cell malignancies and delineate past and present methodological approaches utilized for the identification of stereotyped BcR IG.

EXPRESSION OF IMMUNOGLOBULIN LIGHT CHAIN GENES IN STEREOTYPED CASES FROM UKRAINIAN COHORT OF CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS

BACKGROUND

Analysis of immunoglobulin heavy chain gene (IGHV) rearrangements expressed in chronic lymphocytic leukemia (CLL) cells has provided insights into the B-cell receptor (BCR) repertoire in CLL. In more than 40% of CLL patients, (quasi)identical or stereotyped BCR is expressed. The recent data point at the non-stochastic expression of immunoglobulin light lambda (IGLV) or kappa (IGKV) chains as well. Several pairs of IGHV and IGK/LV have been described for some major stereotyped subsets, but most subsets have not been characterized.

AIM

To study the IGK/LV gene expression in stereotyped CLL cases.

MATERIALS AND METHODS

Analysis was performed in a group of 105 CLL patients with stereotyped BCR. The cases with stereotyped BCRs were identified according to Agathangelidis et al. (2021). The IGHV and IGK/LV gene expressions were studied by a polymerase chain reaction followed by direct sequencing.

RESULTS

The expression of the IGK/LV genes in the most presented major stereotyped subsets (#1, #2, #3C3, #4, #6, #28а) was in agreement with the data reported by other authors. For the cases of subsets #5b, #9D1, #9D4, #16, #50, #59, and #77, differences were found. The new data on the IGK/LV gene expression in 55 minor clusters were presented. A number of patterns of the IGK/LV gene expression depending on the phylogenetic clan and mutational status of the IGHV genes have been described.

CONCLUSION

The non-stochastic distribution of the IGKV/LV gene expression in the individual stereotyped subsets was confirmed. Taking into account the complementary role of the light chains in antigen recognition by the clonotypic BCRs, it was suggested that the subsets with the heterogeneous IGK/LV expression might be reclassified and divided into separate subgroups based on the IGHV and IGK/LV association.

B-cell receptor immunoglobulin stereotypy in chronic lymphocytic leukemia: Key to understanding disease biology and stratifying patients

Sequence convergence, otherwise stereotypy, of B-cell receptor immunoglobulin (BcR IG) from unrelated patients is a distinctive feature of the IG gene repertoire in chronic lymphocytic leukemia (CLL) whereby patients expressing a particular BcR IG archetype are classified into groups termed stereotyped subsets. From a biological perspective, the fact that a considerable fraction (∼41%) of patients with CLL express (quasi)identical or stereotyped BcR IG underscores the key role of antigen selection in the natural history of CLL. From a clinical perspective, at odds with the pronounced heterogeneity of CLL at large, patients belonging to the same stereotyped subset display consistent clinical presentation and outcome, including response to treatment, likely as a reflection of consistent biological background. Many major stereotyped subsets were recently shown to have satellites, that is, smaller subsets that are immunogenetically similar. Preliminary evidence supports that this similarity extends to shared biological and even clinical features, with important implications for patient stratification. Consequently, BcR IG stereotypy emerges as a powerful tool for dissecting the heterogeneity of CLL toward refined risk stratification and, eventually, more precise therapeutic interventions.