The nature and origin of the B-chronic lymphocytic leukemia cell: a tentative model

CLLU1 as an emerging biomarker in chronic lymphoid leukemia

CLLU1, a disease-specific gene associated with chronic lymphoid leukemia (CLL), is located on chromosome 12q22. Previous studies considered CLLU1 to be a non-coding RNA; however, recent research has discovered that its coding sequence region possesses the potential to encode a short peptide similar to interleukin-4. Remarkably, abnormally elevated expression of CLLU1 has only been detected in chronic lymphoid leukemia among all hematological cancers. High CLLU1 expression often indicates more malignant pathological features and an unfavorable prognosis for patients. Importantly, the expression level of CLLU1 remains unaffected by the passage of time or therapeutic interventions, thus rendering it a novel prognostic marker. This article provides a comprehensive summary of relevant research findings on CLLU1 in the context of CLL prognosis and clinical applications, aiming to guide subsequent theoretical and clinical investigations in this field.

Potential Relevance of B-cell Maturation Pathways in Defining the Cell(s) of Origin for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common, incurable disease of undefined cause. Notably, the normal cell equivalents of CLL cells remain elusive, and it is possible that the disease emanates from several normal B-cell subsets. This article reviews the literature relating to this issue, focusing on recent findings, in particular made through epigenetic analyses that strongly support the disease developing from a normal Ag-experienced and memory cell-like B lymphocyte. It also reports the known pathways whereby normal B lymphocytes mature after antigenic challenge and proposes that this information is relevant in defining the cells of origin of this disease.

Comparison of the mRNA expression profile of B-cell receptor components in normal CD5-high B-lymphocytes and chronic lymphocytic leukemia: a key role of ZAP70

The B‐cell receptor (BCR) signaling pathway is of great importance for B‐cell survival and proliferation. The BCR expressed on malignant B‐CLL cells contributes to the disease pathogenesis, and its signaling pathway is currently the target of several therapeutic strategies. Although various BCR alterations have been described in B‐CLL at the protein level, the mRNA expression levels of tyrosine kinases in B‐CLL compared to that in normal CD5‐high and CD5‐low B‐lymphocytes remain unknown. In the current study, we measured the mRNA expression levels of CD79A, CD79B, LYN, SYK, SHP1, and ZAP70 in purified populations of CD5‐high B‐CLL cells, CD5‐low B‐cells from the peripheral blood of healthy donors, and CD5‐high B‐cells from human tonsils. Here, we report a clear separation in the B‐CLL dataset between the ZAP70‐high and ZAP70‐low subgroups. Each subgroup has a unique expression profile of BCR signaling components that might reflect the functional status of the BCR signaling pathway. Moreover, the ZAP70‐low subgroup does not resemble either CD5‐high B‐lymphocytes from the tonsils or CD5‐low lymphocytes from PBMC (P < 0.05). We also show that ZAP70 is the only gene that is differentially expressed in CD5‐high and CD5‐low normal B‐lymphocytes, confirming the key role of Zap‐70 tyrosine kinase in BCR signaling alterations in B‐CLL.

Aberrant expression of CD8 in B-cell non-Hodgkin lymphoma: a multicenter study of 951 bone marrow samples with lymphomatous infiltration

T-cell antigen expression can be observed in B-cell non-Hodgkin lymphoma (B-NHL). Although CD5 is expressed in B-cell chronic lymphocytic leukemia (B-CLL) and mantle cell lymphoma, the presence of other T-cell antigens is less common. This article reports a retrospective multicenter analysis in which flow cytometry was used to evaluate aberrant CD8 expression on the pathologic B cells of 951 bone marrow samples from patients with various types of B-NHL. In a total of 18 patients, CD8 was coexpressed: 10 had B-CLL; 1, small lymphocytic lymphoma (SLL); 1, marginal zone lymphoma; 1, lymphoplasmacytic lymphoma; 2, diffuse large B-cell lymphoma; and 3, follicular lymphoma. There was a 1.89% overall frequency of CD8 coexpression in which B-CLL/SLL had a higher frequency (3.03%) than did the other B-cell neoplasms (1.18%). Most cases were characterized by a favorable outcome.

The prognostic evaluation of CLLU1 expression levels in 50 Chinese patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the relentless accumulation of monoclonal B cells with the appearance of small mature lymphocytes and a characteristic CD5 and CD19 co-expression immunophenotype. The incidence of CLL is lower in Asian countries than in Western countries, where CLL is the most common leukemia. To investigate CLLU1 expression in CLL and explore the relationship between CLLU1 expression and alternative prognostic markers, we measured CLLU1 expression levels by semiquantitative RT-PCR in a cohort of 50 Chinese patients with CLL. Analyses of IgVH somatic mutational status, ZAP-70 expression, CD38 expression, and chromosomal aberrations were also performed. The expression of CLLU1 mRNA was determined in 26 of the 50 cases (52%), among which 7 at Binet A (7/21, 33.33%) and 19 at Binet B + C (19/29, 65.52%). The expression levels of CLLU1 were significantly increased in B + C CLL patients at Binet stage compared with those at Binet stage A (P = 0.005). Data for the IgVH somatic mutational status were available for 20 patients with known CLLU1 expression. Five (25%) patients, all expressed CLLU1 mRNA, displayed unmutated IgVH gene usage. While in 15 patients (15/20, 75%) with mutated IgVH gene, only 6 were CLLU1 positive. Patients with unmutated IgVH genes expressed higher levels of CLLU1 than did those with IgVH mutations (P < 0.05). Among 24 CD38(+)-CLL cases, 17 (70.83%) were CLLU1 positive, whereas only 9 (34.62%) positive cases were identified in 26 CD38(-)-CLL patients. Thus, the expression of CLLU1 in CD38(+)-CLL was significantly higher than that in CD38(-)-CLL. However, no significant difference of CLLU1 expression was found between ZAP-70(+) (14/22, 63.64%) and ZAP-70(-) (12/28, 42.86%) patients (P > 0.05). We conclude that CLLU1 expression was significantly associated with clinical stages, IgVH somatic mutational status and CD38 expression, and might be an important prognostic factor in CLL patients.

CD5+ B cells with the features of subepithelial B cells found in human tonsils

This study describes a CD5+ B cell that differs from the majority of the CD5+ B cells from human tonsils. This cell, isolated from in vivo activated B cells, expressed activation markers and featured a CD23-, IgMhigh, IgDlow surface phenotype, responded to T cell-independent type-2 antigens in vitro, and was detected in the subepithelial (SE) areas, the tonsil equivalent of the splenic marginal zone (MZ). Most of the cells utilized unmutated Ig VH genes, although cells with mutated genes also were found, a finding confirmed by single-cell studies. Mutated sequences were more frequent in suspensions enriched for CD27+ cells. Repeated VDJ gene sequences were observed in different molecular clones from the same cell suspension, suggesting in situ expansion. These CD5+ B cells seem to share features with previously characterized tonsil CD5- SE B cells and differ from the majority of tonsil CD5+ B cells, which have the surface phenotype of follicular mantle B cells, lack activation markers, do not respond to T cell-independent antigens, and utilize unmutated VH genes. These data are discussed considering the present views on the origin of B cell subset populations and the relationships between MZ and B1 cells.

The normal counterpart to the chronic lymphocytic leukemia B cell

Chronic lymphocytic leukemia (CLL) is characterized by the monoclonal expansion of small mature-looking B cells that accumulate in the blood, marrow, and lymphoid organs, and have a remarkable phenotypic homogeneity. By definition, CLL cells co-express CD5 and CD23 with faint to undetectable amounts of monoclonal surface immunoglobulins (sIg). The concept of phenotypic homogeneity has been reinforced by gene expression profiling data, which suggest that the pathogenesis of CLL has to be associated with a fairly common mechanism of transformation. In recent years the biology of CLL has been enriched by an unprecedented flurry of new observations that are leading to a better understanding of the natural history of the disease. Still CLL cells have so far defied any attempt to satisfactorily answer the simple time-honored question of what their cell of origin is. It is the purpose of this review to discuss the features a cell must possess to be considered with reasonable approximation the normal counterpart of a CLL B cell.

Heterogeneous intracellular expression of B-cell receptor components in B-cell chronic lymphocytic leukaemia (B-CLL) cells and effects of CD79b gene transfer on surface immunoglobulin levels in a B-CLL-derived cell line

B-cell chronic lymphocytic leukaemia (B-CLL) cells display low amounts of surface immunoglobulins (sIg). To investigate the mechanisms underlying this phenomenon, we performed a thorough study of surface and intracellular expression of the B-cell receptor (BCR) components in B-CLL cells using flow cytometry. There was an heterogeneous pattern of expression. Overall, 20 of 22 samples showed reduced sIgM levels, compared with normal B cells. Among them, three (15%) had very low to undetectable intracellular IgM levels and variable amounts of CD79a and CD79b; nine (45%) had low intracellular CD79b levels but appreciable levels of IgM and CD79a; and eight (40%) had relatively normal intracellular levels of all BCR components. To investigate whether surface BCR levels could be controlled by the rate of CD79b synthesis, adenoviral vectors encoding CD79b were generated and used for gene transfer experiments. Delivery of CD79b to non-B cells transfected with IgM and CD79a lead to high-level expression of a functional BCR. Moreover, CD79b gene transfer in a B cell line derived from a B-CLL patient and characterised by low intracellular levels of endogenous CD79b consistently increased sIgM levels. These findings indicate that the phenotype of B-CLL cells in a subset of patients may depend primarily on poor CD79b expression, and suggest that upregulation of CD79b expression may correct the phenotype of these cells.

Immunoglobulin light chain repertoire in chronic lymphocytic leukemia

Immunoglobulin kappa (IGK) and immunoglobulin lambda (IGL) light chain repertoire was analyzed in 276 chronic lymphocytic leukemia (CLL) cases and compared with the relevant repertoires from normal, autoreactive, and neoplastic cells. Twenty-one functional IGKV genes were used in IGKV-J rearrangements of 179 kappa-CLL cases; the most frequent genes were IGKV3-20(A27), IGKV1-39/1D-39(O2/O12), IGKV1-5(L12), IGKV4-1(B3), and IGKV2-30(A17); 90 (50.3%) of 179 IGK sequences were mutated (similarity < 98%). Twenty functional IGLV genes were used in IGLV-J rearrangements of 97 lambda-CLL cases; the most frequent genes were IGLV3-21(VL2-14), IGLV2-8(VL1-2), and IGLV2-14(VL1-4); 44 of 97 IGL sequences (45.4%) were mutated. Subsets with "CLL-biased" homologous complementarity-determining region 3 (CDR3) were identified: (1) IGKV2-30-IGKJ2, 7 sequences with homologous kappa CDR3 (KCDR3), 5 of 7 associated with homologous IGHV4-34 heavy chains; (2) IGKV1-39/1D-39-IGKJ1/4, 4 unmutated sequences with homologous KCDR3, 2 of 4 associated with homologous IGHV4-39 heavy chains; (3) IGKV1-5-IGKJ1/3, 4 sequences with homologous KCDR3, 2 of 4 associated with unmutated nonhomologous IGHV4-39 heavy chains; (4) IGLV1-44-IGLJ2/3, 2 sequences with homologous lambda CDR3 (LCDR3), associated with homologous IGHV4-b heavy chains; and (5) IGLV3-21-IGLJ2/3, 9 sequences with homologous LCDR3, 3 of 9 associated with homologous IGHV3-21 heavy chains. The existence of subsets that comprise given IGKV-J/IGLV-J domains associated with IGHV-D-J domains that display homologous CDR3 provides further evidence for the role of antigen in CLL pathogenesis.

An alternative exon 1 of the CD5 gene regulates CD5 expression in human B lymphocytes

T lymphocytes and a subpopulation of B lymphocytes express the CD5 coreceptor. Its functional importance is evident from the multiple levels and developmental stages of the regulation of its expression. We here report the discovery of a novel regulatory exon upstream of the noncoding region of the CD5 gene in humans. This alternate exon 1 is designated E1B (with the conventional exon 1 renamed E1A) and was shown to regulate the expression of CD5. E1B-containing transcripts existed exclusively in B lymphocytes and encoded a protein that was truncated and retained intracellularly. As a consequence, the amount of E1A-containing transcripts was down-regulated and the membrane CD5 expression was diminished in the presence of E1B-containing transcripts. High levels of E1A transcripts were found in chronic lymphocytic leukemia, and there were no E1A transcripts in 697 pre-B cells, which have no membrane CD5. Introduction of E1B into Jurkat cells reduced their membrane expression of CD5, and sequence analysis revealed that the E1B motif is a defective human endogenous retrovirus. A balance between the 2 alternative exons 1 might be central to the regulation of membrane CD5 in human B cells, and, through CD5-associated SH2-containing phosphatase 1, to the modulation of B-cell antigen receptor-transduced signals.