Immunological aspects in chronic lymphocytic leukemia (CLL) development

• Published in: Annals of hematology Vol. 91; no. 7; pp. 981 - 996
• Main Authors: García-Muñoz, Ricardo, Roldan Galiacho, Verónica, Llorente, Luis
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2012; Springer Nature B.V
• Subjects: Anergy; Animals; Apoptosis; Autoantigens; B-Lymphocytes - immunology; B-Lymphocytes - metabolism; B-Lymphocytes - physiology; Biomarkers, Tumor - analysis; Biomarkers, Tumor - genetics; Biomarkers, Tumor - physiology; Bone marrow; CD5 antigen; Cell activation; Cell Differentiation - genetics; Cell Differentiation - immunology; Cell survival; Cell Transformation, Neoplastic - genetics; Cell Transformation, Neoplastic - immunology; Chronic lymphatic leukemia; Development; Gene Expression Profiling; Germinal centers; Hematology; Humans; Immune Tolerance - genetics; Immune Tolerance - physiology; Immunoglobulins; Immunological aspects; Leukemia, Lymphocytic, Chronic, B-Cell - diagnosis; Leukemia, Lymphocytic, Chronic, B-Cell - etiology; Leukemia, Lymphocytic, Chronic, B-Cell - immunology; Lymphocytes B; Malignancy; Medicine & Public Health; Models, Biological; Neoplastic Stem Cells - immunology; Neoplastic Stem Cells - physiology; Oncology; Pathogens; Review; Review Article; somatic hypermutation; Somatic Hypermutation, Immunoglobulin - genetics; Somatic Hypermutation, Immunoglobulin - physiology; Surface markers; Self-reactive B cells; Anergy; Clonal deletion; Receptor editing; Receptor revision; Memory B cell checkpoints; CD5+ expression
• ISSN: 0939-5555; 1432-0584; 1432-0584
• DOI: 10.1007/s00277-012-1460-z

Chronic lymphocytic leukemia (CLL) is unique among B cell malignancies in that the malignant clones can be featured either somatically mutated or unmutated IGVH genes. CLL cells that express unmutated immunoglobulin variable domains likely underwent final development prior to their entry into the germinal center, whereas those that express mutated variable domains likely transited through the germinal center and then underwent final development. Regardless, the cellular origin of CLL remains unknown. The aim of this review is to summarize immunological aspects involved in this process and to provide insights about the complex biology and pathogenesis of this disease. We propose a mechanistic hypothesis to explain the origin of B-CLL clones into our current picture of normal B cell development. In particular, we suggest that unmutated CLL arises from normal B cells with self-reactivity for apoptotic bodies that have undergone receptor editing, CD5 expression, and anergic processes in the bone marrow. Similarly, mutated CLL would arise from cells that, while acquiring self-reactivity for autoantigens—including apoptotic bodies—in germinal centers, are also still subject to tolerization mechanisms, including receptor editing and anergy. We believe that CLL is a proliferation of B lymphocytes selected during clonal expansion through multiple encounters with (auto)antigens, despite the fact that they differ in their state of activation and maturation. Autoantigens and microbial pathogens activate BCR signaling and promote tolerogenic mechanisms such as receptor editing/revision, anergy, CD5+ expression, and somatic hypermutation in CLL B cells. The result of these tolerogenic mechanisms is the survival of CLL B cell clones with similar surface markers and homogeneous gene expression signatures. We suggest that both immunophenotypic surface markers and homogenous gene expression might represent the evidence of several attempts to re-educate self-reactive B cells.