Wendy G. Nieto

Human peripheral blood B-Cell compartments: A crossroad in B-cell traffic

A relatively high number of different subsets of B‐cells are generated through the differentiation of early B‐cell precursors into mature B‐lymphocytes in the bone marrow (BM) and antigen‐triggered maturation of germinal center B‐cells into memory B‐lymphocytes and plasmablasts in lymphoid tissues. These B‐cell subpopulations, which are produced in the BM and lymphoid tissues, recirculate through peripheral blood (PB), into different tissues including mucosa and the BM, where long‐living plasma cells produce antibodies. These circulating PB B‐cells can be classified according to their maturation stage into i) immature/transitional, ii) naïve, and iii) memory B‐lymphocytes, and iv) plasmablasts/plasma cells. Additionally, unique subsets of memory B‐lymphocytes and plasmablasts/plasma cells can be identified based on their differential expression of unique Ig‐heavy chain isotypes (e.g.: IgM, IgD, IgG, IgA). In the present paper, we review recent data reported in the literature about the distribution, immunophenotypic and functional characteristics of these cell subpopulations, as well as their distribution in PB according to age and seasonal changes. Additional information is also provided in this regard based on the study of a population‐based cohort of 600 healthy adults aged from 20 to 80 years, recruited in the Salamanca area in western Spain. Detailed knowledge of the distribution and traffic of B‐cell subsets through PB mirrors the immune status of an individual subject and it may also contribute to a better understanding of B‐cell disorders related to B‐cell biology and homeostasis, such as monoclonal B‐cell lymphocytosis (MBL).

Combined Patterns of IGHV Repertoire and Cytogenetic/Molecular Alterations in Monoclonal B Lymphocytosis versus Chronic Lymphocytic Leukemia

Background Chronic lymphocytic leukemia (CLL)-like monoclonal B lymphocytosis (MBL) with (MBLhi) or without (MBLlo) absolute B-lymphocytosis precedes most CLL cases,the specific determinants for malignant progression remaining unknown. Methodology/Principal Findings For this purpose, simultaneous iFISH and molecular analysis of well-established cytogenetic alterations of chromosomes 11, 12, 13, 14 and 17 together with the pattern of rearrangement of the IGHV genes were performed in CLL-like cells from MBL and CLL cases. Our results based on 78 CLL-like MBL and 117 CLL clones from 166 subjects living in the same geographical area, show the existence of three major groups of clones with distinct but partially overlapping patterns of IGHV gene usage, IGHV mutational status and cytogenetic alterations. These included a group enriched in MBLlo clones expressing specific IGHV subgroups (e.g. VH3-23) with no or isolated good-prognosis cytogenetic alterations, a second group which mainly consisted of clinical MBLhi and advanced stage CLL with a skewed but different CLL-associated IGHV gene repertoire (e.g. VH1-69), frequently associated with complex karyotypes and poor-prognosis cytogenetic alterations, and a third group of clones with intermediate features, with prevalence of mutated IGHV genes, and higher numbers of del(13q)+ clonal B-cells. Conclusions/Significance These findings suggest that the specific IGHV repertoire and IGHV mutational status of CLL-like B-cell clones may modulate the type of cytogenetic alterations acquired, their rate of acquisition and/or potentially also their clinical consequences. Further long-term follow-up studies investigating the IGHV gene repertoire of MBLlo clones in distinct geographic areas and microenvironments are required to confirm our findings and shed light on the potential role of some antigen-binding BCR specificities contributing to clonal evolution.

Non-CLL-like monoclonal B-Cell lymphocytosis in the general population: Prevalence and phenotypic/genetic characteristics

Monoclonal B‐cell lymphocytosis (MBL) indicates <5 × 109 peripheral blood (PB) clonal B‐cells/L in healthy individuals. In most cases, MBL cells show similar phenotypic/genetic features to chronic lymphocytic leukemia cells—CLL‐like MBL—but little is known about non‐CLL‐like MBL.

Common Infectious Agents and Monoclonal B-Cell Lymphocytosis: A Cross-Sectional Epidemiological Study among Healthy Adults

Background Risk factors associated with monoclonal B-cell lymphocytosis (MBL), a potential precursor of chronic lymphocytic leukaemia (CLL), remain unknown. Methods Using a cross-sectional study design, we investigated demographic, medical and behavioural risk factors associated with MBL. “Low-count” MBL (cases) were defined as individuals with very low median absolute count of clonal B-cells, identified from screening of healthy individuals and the remainder classified as controls. 452 individuals completed a questionnaire with their general practitioner, both blind to the MBL status of the subject. Odds ratios (OR) and 95% confidence interval (CI) for MBL were estimated by means of unconditional logistic regression adjusted for confounding factors. Results MBL were detected in 72/452 subjects (16%). Increasing age was strongly associated with MBL (P-trend<0.001). MBL was significantly less common among individuals vaccinated against pneumococcal or influenza (OR 0.49, 95% confidence interval (CI): 0.25 to 0.95; P-value = 0.03 and OR: 0.52, 95% CI: 0.29 to 0.93, P-value = 0.03, respectively). Albeit based on small numbers, cases were more likely to report infectious diseases among their children, respiratory disease among their siblings and personal history of pneumonia and meningitis. No other distinguishing epidemiological features were identified except for family history of cancer and an inverse relationship with diabetes treatment. All associations described above were retained after restricting the analysis to CLL-like MBL. Conclusion Overall, these findings suggest that exposure to infectious agents leading to serious clinical manifestations in the patient or its surroundings may trigger immune events leading to MBL. This exploratory study provides initial insights and directions for future research related to MBL, a potential precursor of chronic lymphocytic leukaemia. Further work is warranted to confirm these findings.

Molecular and cytogenetic characterization of expanded B-cell clones from multiclonal versus monoclonal B-cell chronic lymphoproliferative disorders

Chronic antigen-stimulation has been recurrently involved in the earlier stages of monoclonal B-cell lymphocytosis, chronic lymphocytic leukemia and other B-cell chronic lymphoproliferative disorders. The expansion of two or more B-cell clones has frequently been reported in individuals with these conditions; potentially, such coexisting clones have a greater probability of interaction with common immunological determinants. Here, we analyzed the B-cell receptor repertoire and molecular profile, as well as the phenotypic, cytogenetic and hematologic features, of 228 chronic lymphocytic leukemia-like and non-chronic lymphocytic leukemia-like clones comparing multiclonal (n=85 clones from 41 cases) versus monoclonal (n=143 clones) monoclonal B-cell lymphocytosis, chronic lymphocytic leukemia and other B-cell chronic lymphoproliferative disorders. The B-cell receptor of B-cell clones from multiclonal cases showed a slightly higher degree of HCDR3 homology than B-cell clones from mono clonal cases, in association with unique hematologic (e.g. lower B-lymphocyte counts) and cytogenetic (e.g. lower frequency of cytogenetically altered clones) features usually related to earlier stages of the disease. Moreover, a subgroup of coexisting B-cell clones from individual multiclonal cases which were found to be phylogenetically related showed unique molecular and cytogenetic features: they more frequently shared IGHV3 gene usage, shorter HCDR3 sequences with a greater proportion of IGHV mutations and del(13q14.3), than other unrelated B-cell clones. These results would support the antigen-driven nature of such multiclonal B-cell expansions, with potential involvement of multiple antigens/epitopes.

Commentary: Comparison of Current Flow Cytometry Methods for Monoclonal B Cell Lymphocytosis Detection

Monoclonal B cell lymphocytosis (MBL) is now recognized as the B‐lymphocyte analogue of a monoclonal gammopathy of unknown significance. MBL can be the precursor of chronic lymphocytic leukemia or associated with non‐Hodgkins lymphoma. It may be associated with an autoimmune abnormality or be related to aging (immunosenescence). The combination of available new fluorochrome‐conjugated monoclonal antibody reagents, multilaser instrumentation, and improved software tools have led to a new level of multicolor analysis of MBL. Presently, several centers, including the University of Salamanca (Spain), Duke University (Durham, NC), Mayo Clinic (Rochester, MN), and the National Cancer Institute (Bethesda, MD) in conjunction with the Genetics and Epidemiology of Familial chronic lymphocytic leukemia Consortium, the Food and Drug Administration (Bethesda, MD), and the Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry (Atlanta, GA) in collaboration with Saint Lukes Hospital (Kansas City, MO), the Università Vita‐Salute San Raffaele in Milan (Italy), and Leeds Teaching Hospital (UK) are all actively conducting studies on MBL. This commentary is an updated summary of the current methods used in these centers. It is important to note the diversity of use in reagents, instruments, and methods of analysis. Despite this diversity, there is a consensus in what constitutes the diagnosis of MBL and its subtypes. There is also an emerging consensus on what the next investigative steps should be. Published 2010 Wiley‐Liss, Inc.

Host virus and pneumococcus-specific immune responses in high-count monoclonal B-cell lymphocytosis and chronic lymphocytic leukemia: implications for disease progression

Patients diagnosed with chronic lymphocytic leukemia (CLL) display a high incidence of infections due to an associated immunodeficiency that includes hypogammaglobulinemia. A higher risk of infections has also been recently reported for high-count monoclonal B-cell lymphocytosis, while no information is available in low-count monoclonal B-cell lymphocytosis. Here, we evaluated the status of the humoral immune system in patients with chronic lymphocytic leukemia (n=58), as well as in low- (n=71) and high- (n=29) count monoclonal B-cell lymphocytosis versus healthy donors (n=91). Total free plasma immunoglobulin titers and specific levels of antibodies against cytomegalovirus, Epstein-Barr virus, influenza and S.pneumoniae were measured by nephelometry and ELISA-based techniques, respectively. Overall, our results show that both CLL and high-count monoclonal B-cell lymphocytosis patients, but not low-count monoclonal B-cell lymphocytosis subjects, present with relatively high levels of antibodies specific for the latent viruses investigated, associated with progressively lower levels of S.pneumoniae-specific immunoglobulins. These findings probably reflect asymptomatic chronic reactivation of humoral immune responses against host viruses associated with expanded virus-specific antibody levels and progressively decreased protection against other micro-organisms, denoting a severe humoral immunodeficiency state not reflected by the overall plasma immunoglobulin levels. Alternatively, these results could reflect a potential role of ubiquitous viruses in the pathogenesis of the disease. Further analyses are necessary to establish the relevance of such asymptomatic humoral immune responses against host viruses in the expansion of the tumor B-cell clone and progression from monoclonal B-cell lymphocytosis to CLL.

Subjects with chronic lymphocytic leukaemia‐like B‐cell clones with stereotyped B‐cell receptors frequently show MDS‐associated phenotypes on myeloid cells

An increasing body of evidence suggests the potential occurrence of antigen encounter by the cell of origin in chronic lymphocytic leukaemia (CLL) and CLL‐like monoclonal B‐cell lymphocytosis (MBL). However, the scenario in which this event might occur remains unknown. In order to gain insight into this scenario we investigated the molecular, cytogenetic and haematological features of 223 CLL‐like (n = 84) and CLL (n = 139) clones with stereotyped (n = 32) versus non‐stereotyped (n = 191) immunoglobulin heavy chain variable region (IGHV) amino acid sequences. Overall, stereotyped CLL‐like MBL and CLL clones showed a unique IGHV profile, associated with higher IGHV1 and lower IGHV3 gene family usage (P = 0·03), longer IGHV complementary determining region 3 (HCDR3) sequences (P = 0·007) and unmutated IGHV (P < 0·001) versus non‐stereotyped clones. Whilst the overall size of the stereotyped B‐cell clones in peripheral blood did not appear to be associated with the CLL‐related cytogenetic profile of B‐cells (P > 0·05), it did show a significant association with the presence of myelodysplastic syndrome (MDS)‐associated immunophenotypes on peripheral blood neutrophils and/or monocytes (P = 0·01). Altogether our results point to the potential involvement of different selection forces in the expansion of stereotyped vs. non‐stereotyped CLL and CLL‐like MBL clones, the former being potentially favoured by an underlying altered haematopoiesis.

Low-count monoclonal B-cell lymphocytosis persists after seven years of follow up and is associated with a poorer outcome

Low-count monoclonal B-cell lymphocytosis is defined by the presence of very low numbers of circulating clonal B cells, usually phenotypically similar to chronic lymphocytic leukemia cells, whose biological and clinical significance remains elusive. Herein, we re-evaluated 65/91 low-count monoclonal B-cell lymphocytosis cases (54 chronic lymphocytic leukemia-like and 11 non-chronic lymphocytic leukemia-like) followed-up for a median of seven years, using high-sensitivity flow cytometry and interphase fluorescence in situ hybridization. Overall, the clone size significantly increased in 69% of low-count monoclonal B-cell lymphocytosis cases, but only one subject progressed to high-count monoclonal B-cell lymphocytosis. In parallel, the frequency of cytogenetic alterations increased over time (32% vs. 61% of cases, respectively). The absolute number of the major T-cell and natural killer cell populations also increased, but only among chronic lymphocytic leukemia-like cases with increased clone size vs. age- and sex-matched controls. Although progression to chronic lymphocytic leukemia was not observed, the overall survival of low-count monoclonal B-cell lymphocytosis individuals was significantly reduced vs. non-monoclonal B-cell lymphocytosis controls (P=0.03) plus the general population from the same region (P≤0.001), particularly among females (P=0.01); infection and cancer were the main causes of death in low-count monoclonal B-cell lymphocytosis. In summary, despite the fact that mid-term progression from low-count monoclonal B-cell lymphocytosis to high-count monoclonal B-cell lymphocytosis and chronic lymphocytic leukemia appears to be unlikely, these clones persist at increased numbers, usually carrying more genetic alterations, and might thus be a marker of an impaired immune system indirectly associated with a poorer outcome, particularly among females.

A systematic approach for peptide characterization of B-cell receptor in chronic lymphocytic leukemia cells

A wide variety of immunoglobulins (Ig) is produced by the immune system thanks to different mechanisms (V(D)J recombination, somatic hypermutation, and antigen selection). The profiling of Ig sequences (at both DNA and peptide levels) are of great relevance to developing targeted vaccines or treatments for specific diseases or infections. Thus, genomics and proteomics techniques (such as Next-Generation Sequencing (NGS) and mass spectrometry (MS)) have notably increased the knowledge in Ig sequencing and serum Ig peptide profiling in a high-throughput manner. However, the peptide characterization of membrane-bound Ig (e.g., B-cell receptors, BCR) is still a challenge mainly due to the poor recovery of mentioned Ig. Herein, we have evaluated three different sample processing methods for peptide sequencing of BCR belonging to chronic lymphocytic leukemia (CLL) B cells identifying up to 426 different peptide sequences (MS/MS data are available via ProteomeXchange with identifier PXD004466). Moreover, as a consequence of the results here obtained, recommended guidelines have been described for BCR-sequencing of B-CLL samples by MS approaches. For this purpose, an in–house algorithm has been designed and developed to compare the MS/MS results with those obtained by molecular biology in order to integrate both proteomics and genomics results and establish the steps to follow when sequencing membrane-bound Ig by MS/MS.