Monoclonal B-cell lymphocytosis in a hospital-based UK population and a rural Ugandan population: a cross-sectional study

Progression and transformation of chronic lymphocytic leukemia/small lymphocytic lymphoma and B-cell prolymphocytic leukemia: Report from the 2021 SH/EAHP Workshop

OBJECTIVES

Session 3 of the 2021 Workshop of the Society for Hematopathology/European Association for Haematopathology examined progression and transformation of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and B-cell prolymphocytic leukemia (B-PLL).

METHODS

Thirty-one cases were reviewed by the panel. Additional studies such as immunohistochemistry and molecular genetic testing, including whole-exome sequencing and expression profiling, were performed in select cases.

RESULTS

Session 3 included 27 CLL/SLL cases and miscellaneous associated proliferations, 3 cases of B-PLL, and 1 case of small B-cell lymphoma. The criteria for -accelerated CLL/SLL are established for lymph nodes, but extranodal disease can be diagnostically challenging. Richter transformation (RT) is a broad term and includes true transformation from original CLL/SLL clone(s) and clonally unrelated neoplasms. The morphologic, immunophenotypic, and genetic spectrum is diverse with classical and highly unusual examples. T-cell proliferations can also be encountered in CLL/SLL. B-cell prolymphocytic leukemia is a rare, diagnostically challenging disease due to its overlaps with other lymphoid neoplasms.

CONCLUSIONS

The workshop highlighted complexity of progression and transformation in CLL/SLL and B-PLL, as well as diagnostic caveats accompanying heterogeneous presentations of RT and other manifestations of disease progression. Molecular genetic studies are pivotal for diagnosis and determination of clonal relationship, and to predict response to treatment and identify resistance to targeted therapy.

Abnormalities by Multicolor Flow Cytometry for Detection of Minimal Residual Disease in Recipients of Allo-HSCT Originating from Donors: A Cohort Study

Objective

In minimal residual disease (MRD) analysis after allogeneic hematopoietic stem cell transplantation (allo-HSCT), abnormal immunophenotyping is commonly considered as evidence of a secondary recurrence or complications, leading to overtreatment. We aimed to confirm whether such phenotypic abnormality might originate from donors using multicolor flow cytometry (MFC).

Materials and Methods

The MRD of bone marrow specimens of 3395 patients who had received allo-HSCT were analyzed using the conventional two-tube, eight-color MFC panel. The frequencies of abnormal immunophenotypes were also evaluated in three groups of patients without malignancies.

Results

The frequency of new abnormal polymorphisms was 0.088% (3/3395) among patients who received allo-HSCT. The abnormal cells seen in three patients in complete remission were Fcγ receptor IIIB (FcγRIIIB) gene deletion (CD16- neutrophils), CD2-CD159a-CD159c⁺ natural killer (NK) cells, and monoclonal B lymphocytosis (MBL), respectively. In addition, abnormal T-cells (CD4⁺CD8⁺) were detected in one donor before allo-HSCT. Identical abnormalities were found in the peripheral blood of the corresponding donors of the three patients via MFC. Among the individuals without malignancies, the incidence of FcγRIIIB deletion was 0.2% (11/5256), that of NK cells with the absence of CD2 and single-positive CD159c was 0.05% (1/2000), that of monoclonal CD4/CD8 double-positive T-cells was 0.05% (1/2000), and that of MBL was 1.3% (14/1100). The frequency of NK cells with the absence of CD2 was 1.3% (1/79) and with CD8^dim was 14% (11/79) in NK cell lymphoma. The following abnormalities could be identified by the two-tube, eight-color MFC panel: cκ/cλ/CD19/CD5/CD20/ CD38/CD45/CD56 (adding CD10 and CD34 as the ninth and tenth colors) and CD16⁺CD56/CD5/CD3/CD7/CD4/CD8/CD2/CD45 (adding CD117 as the ninth color).

Conclusion

Abnormalities in recipients of allo-HSCT detected by MRD analysis may originate from their donors. Screening of donor specimens with a suitable two-tube, eight- to ten-color MFC panel may be a promising method for minimizing misdiagnoses.

Age- and Sex-Matched Normal Leukocyte Subset Ranges in the General Population Defined with the EuroFlow Lymphocyte Screening Tube (LST) for Monoclonal B-Cell Lymphocytosis (MBL) vs. Non-MBL Subjects

Reference ranges of blood-circulating leukocyte populations by, e.g., age and sex, are required for monitoring immune-cell kinetics. Most previous reports in which flow cytometry has been used to define the reference ranges for leukocyte counts included a limited number of donors and/or cell populations and/or did not consider age and sex simultaneously. Moreover, other factors not previously considered in the definition of normal ranges, such as the presence of chronic-lymphocytic-leukemia (CLL)-like low-count monoclonal B-cell lymphocytosis (MBLlo), might also be associated with an altered distribution of leukocytes in blood in association with an immunodeficiency and increased risk of infection and cancer. Here, we established reference cell-count ranges for the major populations of leukocytes in blood of non-MBL and MBLlo adult Caucasians matched by age and sex using the EuroFlow Lymphocyte Screening Tube (LST). A total of 706 Caucasian adult donors—622 non-MBL and 84 MBLlo—were recruited from the general population. Among non-MBL donors, the total leukocyte, neutrophil, basophil dendritic cell and monocyte counts remained stable through adulthood, while the absolute numbers of T- and B-cell populations and plasma cells decreased with age. The number of eosinophils and NK-cell increased over time, with clear differences according to sex for certain age ranges. In MBLlo subjects, few differences in the absolute cell counts by age (vs. non-MBL) were observed, and MBLlo men and women showed similar trends to non-MBL subjects except for the B-cell count drop observed in >70 y-men, which was more pronounced in MBLlo vs. non-MBL controls. Building robust age- and sex-matched reference ranges for the most relevant immune-cell populations in the blood of non-MBL donors is essential to appropriately identify an altered immune status in different clinical settings and highlight the altered immune-cell profiles of MBLlo subjects.

Monoclonal B-cell Lymphocytosis - a review of diagnostic criteria, biology, natural history, and clinical management

Since first described almost two decades ago, there has been significant evolution in our definition and understanding of the biology and implications of monoclonal B-cell lymphocytosis (MBL). This review provides an overview of the definition, classification, biology, and natural history of MBL, mainly focused on the dominant CLL-like phenotype form of MBL. The increasingly recognized implications of MBL with respect to immune dysfunction are discussed, particularly in view of the COVID-19 pandemic, along with management recommendations for MBL in the clinic.

Old and New Facts and Speculations on the Role of the B Cell Receptor in the Origin of Chronic Lymphocytic Leukemia

The engagement of the B cell receptor (BcR) on the surface of leukemic cells represents a key event in chronic lymphocytic leukemia (CLL) since it can lead to the maintenance and expansion of the neoplastic clone. This notion was initially suggested by observations of the CLL BcR repertoire and of correlations existing between certain BcR features and the clinical outcomes of single patients. Based on these observations, tyrosine kinase inhibitors (TKIs), which block BcR signaling, have been introduced in therapy with the aim of inhibiting CLL cell clonal expansion and of controlling the disease. Indeed, the impressive results obtained with these compounds provided further proof of the role of BcR in CLL. In this article, the key steps that led to the determination of the role of BcR are reviewed, including the features of the CLL cell repertoire and the fine mechanisms causing BcR engagement and cell signaling. Furthermore, we discuss the biological effects of the engagement, which can lead to cell survival/proliferation or apoptosis depending on certain intrinsic cell characteristics and on signals that the micro-environment can deliver to the leukemic cells. In addition, consideration is given to alternative mechanisms promoting cell proliferation in the absence of BcR signaling, which can explain in part the incomplete effectiveness of TKI therapies. The role of the BcR in determining clonal evolution and disease progression is also described. Finally, we discuss possible models to explain the selection of a special BcR set during leukemogenesis. The BcR may deliver activation signals to the cells, which lead to their uncontrolled growth, with the possible collaboration of other still-undefined events which are capable of deregulating the normal physiological response of B cells to BcR-delivered stimuli.

Ethnic and geographic diversity of chronic lymphocytic leukaemia

East Asians, Asian Indians and Amerindians have a five to ten-fold lower age-adjusted incidence rate (AAIR) of chronic lymphocytic leukaemia (CLL) compared with persons of predominately European descent. The data we review suggest a genetic rather than environmental basis for this discordance. All these populations arose from a common African Black ancestor but different clades have different admixture with archaic hominins including Neanderthals, Denisovans and Homo erectus, which may explain different CLL incidences. There are also some differences in clinical laboratory and molecular co-variates of CLL between these populations. Because the true age-adjusted incidence rate in African Blacks is unknown it is not possible to determine whether modern Europeans acquired susceptibility to CLL or the other populations lost susceptibility and/or developed resistance to developing CLL. We also found other B-cell lymphomas and T- and NK-cell cancers had different incidences in the populations we studied. These data provide clues to determining the cause(s) of CLL.

Screening for monoclonal B-lymphocyte expansion in a hospital-based Chinese population with lymphocytosis: an observational cohort study

OBJECTIVES

Screening of monoclonal B-cell lymphocytosis (MBL) has improved the early detection of B-cell lymphoproliferative disorders (B-LPDs). This study was designed to find the most cost-effective way to screen for asymptomatic B-LPD.

DESIGN

Observational study.

SETTING

A lymphocytosis screening project was conducted at a large-scale hospital among the Chinese population.

PARTICIPANTS

For 10 consecutive working days in 2018, 22 809 adult patients who received a complete blood count (CBC) were reviewed. These patients were selected from the outpatient, inpatient and health examination departments of a National Medical Centre in China.

RESULTS

A total of 254 patients (1.1%, 254/22 809) were found to have lymphocytosis (absolute lymphocyte count (ALC) >3.5×10⁹/L). Among them, a population of circulating monoclonal B-lymphocytes were detected in 14 patients, with 4 having chronic lymphocytic leukaemia (CLL) and 10 having MBL, indicating an overall prevalence of 5.5% for B-LPD (3.9% for MBL). The prevalence of CLL among the elderly patients with lymphocytosis (≥60 years) was determined to be 4.3% (4/92). In the patients over 60 years of age, the prevalence of MBL was found to be 8.7%. CD5 (-) non-CLL-like MBL was observed to be the most common subtype (8, 80%), followed by CLL-like phenotype (1, 10.0%) and atypical CLL phenotype (1, 10.0%). The receiver operating characteristic curve analysis for the CBC results revealed that the ALC of 4.7×10⁹/L may serve as the optimal and cost-effective cut-off for screening for early-stage asymptomatic B-LPD.

CONCLUSION

In Chinese patients with lymphocytosis, there was a relatively high proportion of patients with CLL among individuals over 60 years of age. MBL is an age-related disorder. Non-CLL-like MBL was the most common MBL subtype, almost all of whom displayed a pattern of 'marginal zone lymphoma (MZL)-like' MBL. Lymphocytosis screening among the elderly would be effective in the detection of B-LPD and MBL.

Prevalence and Immunophenotypic Characteristics of Monoclonal B-Cell Lymphocytosis in Healthy Korean Individuals With Lymphocytosis

Epidemiological studies of monoclonal B-cell lymphocytosis (MBL) have been conducted in limited geographical regions. Little is known about the prevalence of MBL in Asia. We investigated the prevalence and immunophenotypic characteristics of MBL in Koreans who had idiopathic lymphocytosis (lymphocyte count >4.0×10⁹/L) and were ≥40 years of age. A total of 105 leftover peripheral blood samples met these criteria among those from 73,727 healthy individuals who visited the Health Promotion Center, Samsung Medical Center, Korea, from June 2018 to August 2019. The samples were analyzed using eight-color flow cytometry with the following monoclonal antibodies: CD45, CD5, CD10, CD19, CD20, CD23, and kappa and lambda light chains. The overall prevalence of MBL in the study population was 2.9% (3/105); there was one case of chronic lymphocytic leukemia (CLL)-like MBL (CD5⁺CD23⁺), one case of atypical CLL-like MBL (CD5⁺CD23⁻), and one case of CD5⁻MBL with a lambda restriction pattern. This is the first study on the MBL prevalence in an East Asian population, and it reveals a relatively low prevalence of MBL in healthy Korean individuals with lymphocytosis.

Monoclonal B-cell lymphocytosis

Flow cytometry diagnostic practices can detect very low levels of clonal B cells in the peripheral blood. In the absence of clinical symptoms, cytopenia or organomegaly, the small clones may correspond to monoclonal B-cell leukemia (MBL) diagnosis. Most MBLs harbor a chronic lymphocytic leukemia (CLL) phenotype (e.g., CD5⁺, CD23⁺) and are referred to as CLL-type MBL. The two other types are atypical CLL-type MBL and non-CLL-type MBL. In addition to the phenotypical classification, the clonal B count is a major issue because of the impact on the prognosis and the risk of progression in CLL. It allows for the discrimination of two distinct types: high-count (HC) MBL and low-count (LC)-MBL based on a cutoff value of 0.5 × 10⁹/L clonal B cells. LC MBL appears to be very stable over time and is probably related to immunosenescence. Conversely, HC MBL could be a premalignant state before the occurrence of CLL.