B-cell Precursors In Bone Marrow Research Articles

MiR-582 Suppresses the Proliferation of B-Cell Precursor Acute Lymphoblastic Leukemia (BCP-ALL) Cells and Protects Them From Natural Killer Cell-Mediated Cytotoxicity.

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is a malignancy characterized by the aberrant accumulation of immature B-cell precursors in bone marrow and other lymphoid organs. Although several intrinsic regulatory signals participating in BCP-ALL have been clarified, detailed intrinsic and extrinsic mechanisms that regulate BCP-ALL progression have not been fully understood. In the current study, we report that miR-582 is downregulated in BCP-ALL cells compared with normal B cells. Forced overexpression of miR-582 attenuated BCP-ALL cell proliferation and survival. We found that miR-582 overexpression disturbed the mitochondrial metabolism of BCP-ALL cells, leading to less ATP but more ROS production. Mechanistically, we identified PPTC7 as a direct target of miR-582. MiR-582 overexpression inhibited the activity of CoQ10, which is downstream of PPTC7 and played an important positive regulatory role in mitochondrial electron transportation. Finally, we found that overexpression of miR-582 upregulated the expression of immune checkpoint molecule CD276 and reduced NK cell-mediated cytotoxicity against BCP-ALL cells. CD276 blockade significantly increased NK cell-mediated cytotoxicity against miR-582-overexpressing BCP-ALL cells. Together, our research demonstrates that miR-582 acts as a negative regulator of BCP-ALL cells by reducing proliferation and survival, but protects BCP-ALL cells from NK cell-mediated cytotoxicity, suggesting that miR-582 may be a new therapeutic biomarker for BCP-ALL with CD276 blocker.

Impaired Generation of Bone Marrow B Lymphocytes in Mice Deficient in C/EBPβ

AbstractCAAT/enhancer binding proteins (C/EBP) are a family of transcription factors that mediates adipocyte differentiation and the regulation of genes expressed in immune responses and inflammation, such as interleukin-6 (IL-6), IL-8, and granulocyte colony-stimulating factor (G-CSF ). We investigated the role of C/EBPβ (NF-IL6) in the generation of bone marrow B lymphocytes by taking advantage of C/EBPβ−/− mice. We found that the expansion of bone marrow (BM) B lymphocytes was impaired in long-term lymphoid cultures from C/EBPβ−/− mice. Consistent with this finding, the number of BM B cells was decreased in C/EBPβ−/− mice. Both the levels of IL-7 gene expression and bioactive IL-7 from BM stromal cells were decreased in C/EBPβ−/− mice. Furthermore, the proliferative responsiveness of BM B-cell precursors to IL-7 was also reduced as compared to wild-type mice, indicating that C/EBPβ is required for the generation of BM B cells induced by IL-7. Accordingly, IL-7 stimulates the C/EBPβ DNA-binding activity of normal BM pre-B lymphocytes as well as of 70Z/3 pre-B cells. These results point to C/EBPβ as a critical signaling molecule in BM B lymphopoiesis.

Abstract 4499: Cancer targets early B-cell precursors to generate metastasis-promoting Bregs by promoting their premature emigration from the bone marrow and expansion in the circulation

Abstract We previously reported that breast cancer (BC) generates metastasis-promoting regulatory B cells (CD25+ tumor-evoked Bregs). Because phenotypically these cells resembled bone marrow (BM) Rag+ B-cell precursors, such as large Pre-B cells, we hypothesized whether cancer uses them to generate Bregs. To investigate this idea, we used mouse and human BM aspirates, human PBMCs from BC patients, and mice with different orthotopic cancers, such as highly metastatic 4T1 breast cancer cells and EMT6. We report that breast cancer indeed uses BM B-cell precursors to generate Bregs. However, to do this, cancer expresses thymic stromal lymphopoietin (TSLP). Mechanistically, cancer-produced TSLP downregulates surface expression of CXCR4 and α4β1 (VLA-4) of B-cell precursors, thereby impairing their BM retention and increasing their exit into the circulation. TSLP also enables survival and proliferation of these BM emigrants, while other factors such as 5-lipoxygenase metabolites convert them into Bregs. The loss of TSLP expression in cancer cells alone or TSLPR deficiency in B cells not only reduce pre-B cells in the circulation, but also retard lung metastasis. Overall, our data reveal a previously unknown function of cancer-produced TSLP as inducers of premature B-cell precursor emigration from BM to support Breg generation. The results also suggest that the TSLP-pre-B cell axis can be an attractive therapeutic target. Citation Format: Emeline Ragonnaud, Kanako Moritoh, Monica Bodogai, Soizic Garaud, Chen Chen, Xin Wang, Karen Willard-Gallo, Arya Biragyn. Cancer targets early B-cell precursors to generate metastasis-promoting Bregs by promoting their premature emigration from the bone marrow and expansion in the circulation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4499.

The influence of a dosage regimen of dexamethasone on detection of normal B-cell precursors in the bone marrow of children with BCP-ALL at the end of induction therapy

Minimal residual disease (MRD) monitoring by flow cytometry at the end of induction therapy is one of the key ways of a prognosis assessment in patients with acute lymphoblastic leukemia (ALL). In B-cell precursor ALL (BCP–ALL), this method of MRD detection is complicated due to the immunophenotypic similarity between leukemic cells and normal B-cell precursors (BCPs). A decrease in intensity of induction therapy can lead to a more frequent appearance of normal BCPs in the bone marrow, which significantly complicates the MRD monitoring. Aim: to assess the incidence of normal BCPs in bone marrow on the 36th day of induction therapy with two different regimens of glucocorticoid (GC) administration according to ALL-MB 2015 protocol. This study was approved by the Independent Ethical Committee and the Academic Council of Dmitriy Rogachev National Medical Research Center of Pediatric Hematology, Oncology, Immunology Ministry of Healthcare of Russian Federation. The study included 220 patients with BCP-ALL who were randomized to two types of GC-based induction therapy: a continuous administration of dexamethasone (n = 139) and an intermittent regimen with a 1-week dexamethasone therapy stop (n = 81). On the 36th day of induction therapy, MRD and normal BCPs were quantified in bone marrow samples by flow cytometry. On the 36th day of treatment, 43.2% of BCP(+) samples were established in the intermittent-therapy group, and 27.3% in the continuous-therapy group (p = 0.016). Comparison of the BCP level in BCP(+) samples revealed the more equitable distribution of BCPs at different developmental stages in the intermittent-therapy group, meanwhile mainly the immature BCPs in a quantity of less than 0.01% were found in the continuous-therapy group. Reduced-intensity induction therapy for patients with BCP-ALL leads to a noticeable increase of normal BCPs in bone marrow at the end of this treatment stage. A higher rate of BCP(+) bone marrow samples hinder the MRD detection due to the immunophenotypic similarity of BCPs and leukemic cells.

Tumor-Derived Thymic Stromal Lymphopoietin Expands Bone Marrow B-cell Precursors in Circulation to Support Metastasis.

Immature B cells in the bone marrow emigrate into the spleen during adult lymphopoiesis. Here, we report that emigration is shifted to earlier B-cell stages in mice with orthotopic breast cancer, spontaneous ovarian cancer, and possibly in human breast carcinoma. Using mouse and human bone marrow aspirates and mouse models challenged with highly metastatic 4T1 breast cancer cells, we demonstrated that this was the result of secretion of thymic stromal lymphopoietin (TSLP) by cancer cells. First, TSLP downregulated surface expression of bone marrow (BM) retention receptors CXCR4 and VLA4 in B-cell precursors, increasing their motility and, presumably, emigration. Then, TSLP supported peripheral survival and proliferation of BM B-cell precursors such as pre-B-like cells. 4T1 cancer cells used the increased pool of circulating pre-B-like cells to generate metastasis-supporting regulatory B cells. As such, the loss of TSLP expression in cancer cells alone or TSLPR deficiency in B cells blocked both accumulation of pre-B-like cells in circulation and cancer metastasis, implying that the pre-B cell-TSLP axis can be an attractive therapeutic target. SIGNIFICANCE: Cancer cells induce premature emigration of B-cell precursors from the bone marrow to generate regulatory B cells.

Normal variation of bone marrow B-cell precursors according to age - reference ranges for studies in myelodysplastic syndromes in Brazil.

Normal B lymphoid maturation occurs in bone marrow (BM) throughout life, but immature B-cell progenitors (BCPs) are more numerous in children than in adults. To assess the normal values according to age became important as BCPs are decreased in myelodysplastic syndromes and have been considered an important diagnostic and prognostic feature in these clonal disorders. in a multicenter retrospective study from the Brazilian Group of Flow Cytometry we analyzed the variation of BCPs in normal BM according to age and technical peculiarities of each laboratory. We analysed of 45 BM donors and 89 cases examined for elucidation of transitory reactive cytopenias presenting a normal BM immunophenotyping. BCPs were enumerated as CD19+ /CD34+ /CD45dim /CD10+ cells (panel 1) or CD19+ /CD34+ /CD45dim cells (panel 2) among the total nucleated non-erythroid cells and as percentage of CD34+ cells. we included 134 cases. Panel 1 was applied in 88 cases and panel 2 was used in 46. Age range: 10 months to 89 years. In a multiple regression, % BCPs/total nucleated cells was an exponential function of age. Age explained alone 49.4% of the variance, while 'panel used' explained 1.8% and 'laboratory' explained 0.7%. Age explained only 24.9% of the variance of BCPs/CD34+ cells. in normal individuals, BM B-cell precursors varied mainly according to age, but were also dependent on technical peculiarities of operators and equipments. Analysis by phenotype and as percentage of total nucleated cells was more accurate and less susceptible to variation than evaluating % BCPs/total CD34+ cells. © 2017 International Clinical Cytometry Society.

Detailed immunophenotyping of B-cell precursors in regenerating bone marrow of acute lymphoblastic leukaemia patients: implications for minimal residual disease detection.

Flow cytometric detection of minimal residual disease (MRD) in children with B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) requires immunophenotypic discrimination between residual leukaemic cells and B-cell precursors (BCPs) which regenerate during therapy intervals. In this study, EuroFlow-based 8-colour flow cytometry and innovative analysis tools were used to first characterize the immunophenotypic maturation of normal BCPs in bone marrow (BM) from healthy children, resulting in a continuous multiparametric pathway including transition stages. This pathway was subsequently used as a reference to characterize the immunophenotypic maturation of regenerating BCPs in BM from children treated for BCP-ALL. We identified pre-B-I cells that expressed low or dim CD34 levels, in contrast to the classical CD34high pre-B-I cell immunophenotype. These CD34-dim pre-B-I cells were relatively abundant in regenerating BM (11-85% within pre-B-I subset), while hardly present in healthy control BM (9-13% within pre-B-I subset; P=0·0037). Furthermore, we showed that some of the BCP-ALL diagnosis immunophenotypes (23%) overlapped with CD34-dim pre-B-I cells. Our results indicate that newly identified CD34-dim pre-B-I cells can be mistaken for residual BCP-ALL cells, potentially resulting in false-positive MRD outcomes. Therefore, regenerating BM, in which CD34-dim pre-B-I cells are relatively abundant, should be used as reference frame in flow cytometric MRD measurements.

157 - Normal Values of Bone Marrow B-Cell Precursors as a Reference for MDS Studies – A Brazilian Multicenter Investigation

157 - Normal Values of Bone Marrow B-Cell Precursors as a Reference for MDS Studies – A Brazilian Multicenter Investigation

Significance of CD34/CD123 expression in detection of minimal residual disease in B-ACUTE lymphoblastic leukemia in children

Background: MRD is seen as the major cause of disease relapse. So, it gives important feedback about conventional treatment success and helps in selecting therapeutic alternatives. We aimed to compare the expression of CD34/CD123 on normal B-cell precursors in bone marrow (“hematogones”) and on leukemic blasts in B-acute lymphoblastic leukemias (B-ALL) pediatric cases by flowcytometric analysis. Our study conducted on 20 children as a control and 30 B-ALL children cases at diagnosis and after 28days of induction therapy. We found that the less mature hematogones (dim CD45+) that express CD34 lack CD123 expression, whereas the more mature hematogones (moderate CD45+) lack CD34 but always express CD123. In contrast with this discordant pattern of CD34 and CD123 expression in hematogones, blasts in 24 of 30 cases (80%) of B-ALL showed concordant expression pattern of the 2 antigens: 63% (19 of 30) cases expressed both antigens, whereas 17% (5 of 30) expressed neither. Our study concluded that these distinct patterns of CD34/CD123 expression on hematogones (discordant) and B-ALL blasts (concordant) are useful in differentiating small populations of residual blasts from hematogones after induction therapy to detect MRD.

Craig Issue Highlight 2015

Craig Issue Highlight 2015

Improving the differential diagnosis between myelodysplastic syndromes and reactive peripheral cytopenias by multiparametric flow cytometry: the role of B-cell precursors.

BackgroundImmunophenotyping is a valuable ancillary technique for the differential diagnosis between myelodysplastic syndromes (MDS) with low bone marrow (BM) blast counts and a normal karyotype, and reactive peripheral (PB) cytopenias. Our aim was to search for the most important variables for this purpose. We also analyzed the age variation of BM B-cell precursors (BCP) and its differences in reactive and clonal cytopenias.MethodsImmunophenotypic analyzes were performed in BM of 54 patients with MDS (76% with BM blasts <5%) and 35 cases of reactive cytopenias. Healthy allogeneic BM transplantation donors (n = 41) were used as controls. We used a four-color panel of antibodies analyzing 9 granulocytic, 8 monocytic and 6 CD34+ cell features.ResultsAsynchronous shift to the left in maturing granulocytes and increase in CD16+ monocytes were also found in reactive PB cytopenias, but the most important aberrancies in MDS were seen in myeloid CD34+ cells. Decrease in BCP, that is a hallmark of MDS, could also be found in reactive cytopenias, especially in patients >55 years. % BM BCP could be calculated by the formula: (−7.97 × log age) + (4.24 × log % CD34+cells) – (0.22 x nr. alterations CD34+cells) + 0.577. Corrected R2 = 0.467.ConclusionAnalysis of myelomonocytic precursors and CD34+ cells was satisfactory for the differential diagnosis between reactive PB cytopenias and MDS. The most specific alterations were found in CD34+ cells. Comparison of the values obtained with those of normal age-matched controls is recommended.

B-Cell Lymphopoiesis Is Regulated by Cathepsin L

Cathepsin L (CTSL) is a ubiquitously expressed lysosomal cysteine peptidase with diverse and highly specific functions. The involvement of CTSL in thymic CD4+ T-cell positive selection has been well documented. Using CTSLnkt/nkt mice that lack CTSL activity, we have previously demonstrated that the absence of CTSL activity affects the homeostasis of the T-cell pool by decreasing CD4+ cell thymic production and increasing CD8+ thymocyte production. Herein we investigated the influence of CTSL activity on the homeostasis of peripheral B-cell populations and bone marrow (BM) B-cell maturation. B-cell numbers were increased in lymph nodes (LN), spleen and blood from CTSLnkt/nkt mice. Increases in splenic B-cell numbers were restricted to transitional T1 and T2 cells and to the marginal zone (MZ) cell subpopulation. No alterations in the proliferative or apoptosis levels were detected in peripheral B-cell populations from CTSLnkt/nkt mice. In the BM, the percentage and the absolute number of pre-pro-B, pro-B, pre-B, immature and mature B cells were not altered. However, in vitro and in vivo experiments showed that BM B-cell production was markedly increased in CTSLnkt/nkt mice. Besides, BM B-cell emigration to the spleen was increased in CTSLnkt/nkt mice. Colony-forming unit pre-B (CFU pre-B) assays in the presence of BM stromal cells (SC) and reciprocal BM chimeras revealed that both BM B-cell precursors and SC would contribute to sustain the increased B-cell hematopoiesis in CTSLnkt/nkt mice. Overall, our data clearly demonstrate that CTSL negatively regulates BM B-cell production and output therefore influencing the homeostasis of peripheral B cells.

Analysis of the immune system of multiple myeloma patients achieving long-term disease control by multidimensional flow cytometry

Multiple myeloma remains largely incurable. However, a few patients experience more than 10 years of relapse-free survival and can be considered as operationally cured. Interestingly, long-term disease control in multiple myeloma is not restricted to patients with a complete response, since some patients revert to having a profile of monoclonal gammopathy of undetermined significance. We compared the distribution of multiple compartments of lymphocytes and dendritic cells in the bone marrow and peripheral blood of multiple myeloma patients with long-term disease control (n=28), patients with newly diagnosed monoclonal gammopathy of undetermined significance (n=23), patients with symptomatic multiple myeloma (n=23), and age-matched healthy adults (n=10). Similarly to the patients with monoclonal gammopathy of undetermined significance and symptomatic multiple myeloma, patients with long-term disease control showed an expansion of cytotoxic CD8(+) T cells and natural killer cells. However, the numbers of bone marrow T-regulatory cells were lower in patients with long-term disease control than in those with symptomatic multiple myeloma. It is noteworthy that B cells were depleted in patients with monoclonal gammopathy of undetermined significance and in those with symptomatic multiple myeloma, but recovered in both the bone marrow and peripheral blood of patients with long-term disease control, due to an increase in normal bone marrow B-cell precursors and plasma cells, as well as pre-germinal center peripheral blood B cells. The number of bone marrow dendritic cells and tissue macrophages differed significantly between patients with long-term disease control and those with symptomatic multiple myeloma, with a trend to cell count recovering in the former group of patients towards levels similar to those found in healthy adults. In summary, our results indicate that multiple myeloma patients with long-term disease control have a constellation of unique immune changes favoring both immune cytotoxicity and recovery of B-cell production and homing, suggesting improved immune surveillance.

Multidimensional Flow Cytometric (MFC) Analysis of the Immune System of Multiple Myeloma (MM) Patients Achieving Long Term Disease Control

Abstract 810▪FN2▪This icon denotes a clinically relevant abstractIncreasing evidence shows that a small fraction of MM patients (pts) treated with high-dose therapy followed by autologous stem cell transplantation achieve long-term remission. Interestingly, this is not restricted to pts in complete response (CR), since those that revert to a monoclonal gammopathy of undetermined significance (MGUS) profile may also achieve long-term remission, despite the persistence of residual myeloma plasma cells (PCs). These results suggest that in addition to the anti-myeloma therapy, other factors may play a role in the control of the disease.Herein, we used 8-color MFC for detailed characterization of the structural components of the immune system and hematopoietic precursor cells (HPC) in paired bone marrow (BM) and peripheral blood (PB) samples from 26 MM patients in long-term disease control (LTDC): 9 in continuous CR and 17 who reverted to an MGUS profile and that subsequently showed stable disease without treatment for ≥5 years (median of 9 years; range, 5–19). As controls, paired BM and PB samples from 23 newly-diagnosed MGUS and 16 MM pts, together with 10 healthy adults (HA), were studied in parallel. In all BM and PB samples the distribution of the major T- (CD4, CD8, Tregs and γδ), NK- (CD56dim and CD56bright) and B-cell subsets (Pro-B, Pre-B, naïve and memory), in addition to normal PCs, dendritic cell (DC) subsets (plasmacytoid, myeloid and monocytic), monocytes, and CD34+ HPC (myeloid and lymphoid), were studied. The percentage and absolute count of each cell population was analysed in the BM and PB, respectively.Comparison of the two groups of MM pts with LTDC (9 CR vs. 17 MGUS-like) showed similar (p>.05) cellular profiles in PB and BM, except for an increased number of BM and PB normal PCs in CR patients (P≤.04). Consequently, for all subsequent analyses, LTDC myeloma pts were pooled together.When compared to HA, patients with LTDC had increased numbers of CD8 T-cells and CD56dim NK-cells in both the BM and PB (p≤.03 and p≤.01, respectively). Despite this, the distribution of BM and PB CD4, CD8 and γδ T-cells among LTDC patients was similar (p>.05) to that of both newly-diagnosed MM and MGUS cases; in contrast, BM and PB Tregs were significantly decreased vs newly-diagnosed MM (P=.03) and MGUS (P=.04). Regarding B-cells and normal PCs, LTDC patients showed increased numbers of BM B-cell precursors (both Pro-B and Pre-B cells) and normal PCs vs. newly diagnosed MM (P≤.05), but not MGUS, together with increased numbers of naïve B-cells vs. both MM and MGUS pts (P≤.01); all such cell populations returned to levels similar (p>.05) to those of HA. As expected, this also included the number of CD34+ B-cell HPC which was increased among patients who achieved LTDC vs MM (p=.02), at levels similar (p>.05) to those of MGUS and HA.Regarding DC, LTDC patients showed normal DC numbers in PB (but with higher PB myeloid-DC numbers vs. MM; p=.02), in association with decreased numbers of plasmacytoid DC and increased monocytic-DC in the BM vs. HA (p≤.04). No differences were found for the numbers of BM and PB monocytes.In summary, here we investigated for the first time the immune cell profile of MM patients who achieve long-term disease control. Our results show that, as newly-diagnosed MM, patients that achieve long-term disease control also show increased numbers of cytotoxic T-cells and CD56dim NK-cells; however, in contrast to newly-diagnosed MM, among LTDC patients such increase is associated with lower numbers of T-regs and an almost complete recovery of the normal PC, B-cell precursor and naïve B-cell compartments both in BM and PB. Further investigations on the activation and functional status of these cell populations are warranted.MO (%)/SP (cels./μl)HA N= 10MGUS N= 23MM N= 16LTDC-MM N= 26T cells9.588110.6117313113711926CD4+4.85004.6624^6*5085463CD8+3.7∼216∼4.63865.32645.3431TCR γδ.2426.3230.2428.3421Treg.4137.4141^.54*38.3432NK cells.7∼87∼1.51982.11721.6212CD56 dim.65∼79∼1.41922.21681.6202B cells2.81471.8104.97*68*1.9160Pro B.11—.06—.02*—.07—Pre B.6—.4—.08—.23—Naive SP—80—57^—36*—118Normal-PCS.18.9.11.7.008.72*.11.84DCs.3449.3653.6848.558Monocytes2.22472.42853.43023.1315m-DC SP—11—14—8*—12MO-DC.11∼29.2036.434.2837p-DC.2∼4.1.145.112.8.123.8CD34+.9∼1.46.61.1.261.4.431.4Mie-HPC.8∼—.53—.26—.36—Linfo-HPC.1—.07—.03*—.05—*p≤.05 LTDC vs MM: ^ p≤.05 LTDC vs MGUS; ∼ p≤.05 LTDC vs HA Disclosures:Paiva:Jansen-Cillag: Honoraria; Celgene: Honoraria. Martinez:Janssen: Honoraria; Celgene: Honoraria. Maiolino:Centocor Ortho Biotech Research & Development: Research Funding.

Competition Between (Mono)Clonal Plasma Cells and Normal Cells for Potentially Overlapping Bone Marrow Niches Is Associated with a Progressively Altered Cellular Distribution In MGUS Vs. Myeloma

AbstractAbstract 617Disappearance of normal bone marrow (BM) plasma cells (N-PC) predicts malignant transformation of monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM) into symptomatic myeloma (MM). The homing, behavior and survival of N-PC, but also CD34+ hematopoietic stem/precursor cells (HPC), B-cell precursors, and (mono)clonal/aberrant PC (M-PC) largely depends on their interaction with SDF-1 expressing BM stromal cell niches. Accordingly, it can be hypothesized that a certain degree of competition among BM B-cell precursors, CD34+ HPC, and PC exist for the same BM niches. Thus, progressive replacement of normal cells by M-PC could help to explain the occurrence of cytopenias and hypogammaglobulinemia in MM patients. However, this hypothesis has not been investigated in depth neither in MM nor in SMM and MGUS.In this study we analyze by 8-color multiparameter flow cytometry the distribution and competitive migration capacity of B-cell precursors, CD34+ HPC, N-PC and M-PC in the BM and PB of patients with MGUS (n=60), SMM (n=47) and MM (n=87) at diagnosis plus 12 MM cases studied after high-dose therapy/autologous stem cell transplantation (MM POST-HDT/ASCT) vs. healthy adults aged >60 years (HA; n=26).The percentage of BM M-PC as well as the number of M-PC from all BMPC found at diagnosis significantly (p<.001) increased from MGUS to SMM and MM patients. Circulating M-PC were also detected at diagnosis in the PB of MGUS (21%) vs. SMM (69%) and MM (75%) at increasing M-PC counts (p≤.002). Interestingly, PB vs. BM M-PC showed significantly lower amounts of sideward light scatter (p<.001), together with lower levels of CD38 (p=.001), CD40 (p=.006), CD56 (p=.03) and CD138 (p=.02) expression. Focusing on the CXCR4-SDF1 axis, we found that the proportion of CXCR4+ PC slightly decreased (p>.05) from N-PC from HA (42%) to M-PC from MGUS (39%), SMM (37%) and MM (35%) patients at diagnosis, while MM POST-HDT/ASCT cases showed the lowest values (28%). In contrast, plasma levels of SDF-1 increased from HA (1150 pg/mL) to MGUS (1352 pg/mL), SMM (1656 pg/mL) and MM (1778 pg/mL; p=.04 vs. HA) patients, returning to almost normal levels in MM POST-HDT/ASCT (1331 pg/mL). Thus, an inverse correlation trend (r2=.12; p=.05) between the proportion of CXCR4+ PC and SDF-1 plasma levels was found.Concerning the distribution of the normal cell populations, BM pro-B and pre-B cell precursors were significantly decreased in MM (p=.001) patients vs. HA, while it was normal in MGUS (p>.05) and SMM (p>.05). Despite the number of N-PC in the BM was significantly lower among MM and SMM vs. MGUS cases (p<.001), the distribution of circulating N-PC in PB was normal in all three groups of patients (p>.05 vs. HA). Interestingly however, the proportion of CXCR4+ PB N-PC progressively increased from HA (11%) to MGUS (14%), SMM (15%) and MM (21%; p=.05 vs. HA), while MM POST-HDT/ASCT cases showed the lowest median percentage of CXCR4+ PB N-PC (5%).CD34+ HPC were found to be depleted in the BM of MM (0.3%; p=.001) and SMM (0.4%; p=.002) patients vs. HA (0.9%) while MGUS (0.8%) and MM POST-HDT/ASCT (1.1%) patients showed normal CD34+ HPC numbers. Conversely, PB CD34+ HPC progressively increase from HA to MGUS, SMM and MM cases (p=.008 and p=.06 vs. HA, respectively). By contrast, in MM POST-HDT/ASCT patients the number of PB CD34+ HPC returned to normal/lower levels.Ex-vivo competition assays between BM B-cells, PC and CD34+ HPC for SDF-1 induced migration showed that in HA, CD34+ HPC displayed the highest migration potential in the presence of SDF-1, followed by pre-B cell precursors; conversely N-PC barely migrated. No significant differences were found for the migration of all cell populations analyzed between MGUS and SMM patients vs. HA, except for M-PC that showed an impaired migration in the presence of SDF-1. In turn, the migration potential of CD34+ HPC (p=.04), and pre-B cell precursors (p=.02) was markedly reduced in symptomatic MM, particularly at lower SDF-1 concentrations (30nM). Most interestingly, the migration of M-PC from symptomatic MM was markedly increased at both concentrations of SDF-1 used: median of 2.9% and 1.0% for SDF-1 concentrations of 30nM and 70nM, respectively.Overall, these findings provide evidence about the role of progressive competition and replacement of normal BM cells by M-PC in determining transformation of pre-malignant MGUS and SMM into symptomatic MM. Disclosures:No relevant conflicts of interest to declare.

Distinct Expression Patterns of CD123 and CD34 on Normal Bone Marrow B-Cell Precursors (“Hematogones”) and B Lymphoblastic Leukemia Blasts

We compared the expression of CD123, the alpha chain of the interleukin-3 receptor, on normal B-cell precursors in bone marrow ("hematogones") from 75 specimens and on leukemic blasts in 45 newly diagnosed B-acute lymphoblastic leukemias (B-ALL) cases. We found that the less mature hematogones (dim CD45+) that express CD34 lack CD123 expression, whereas the more mature hematogones (moderate CD45+) lack CD34 but always express CD123. In contrast with this discordant pattern of CD34 and CD123 expression in hematogones, blasts in 41 (91%) of 45 cases of B-ALL showed concordant expression of the 2 antigens: 80% (36 of 45) cases expressed both antigens, whereas 11% (5 of 45) expressed neither. We found that these distinct patterns of CD34/CD123 expression on hematogones (discordant) and B-ALL blasts (concordant) remain stable after chemotherapy and are useful in differentiating small populations of residual blasts from hematogones that may be simultaneously present.

Effects of Growth Hormone on the Differentiation of Mouse B-Lymphoid Precursors

Growth hormone (GH) has been known to enhance immune responses directly or through insulin-like growth factor-I (IGF-I). The present study aimed to clarify the roles of GH in the differentiation of B-lineage precursors. In short-term bone marrow cultures, which contained stem cells and early B-lineage cells, GH (10 μg/L) treatment for one day decreased the percentages of stem cells (0.5-fold) and increased those of B-lineage cells (1.4-fold). Furthermore, GH changed the expressions of transcription factors for B cell progenitors differentiation such as paired box gene-5 (Pax-5), immunoglobulin-associated-α (Ig-α)/CD79a, Ig-β/CD79b, and IGF-I. Thus, a physiological concentration of GH stimulated the differentiation of B-lymphoid precursors from bone marrow stem cells. Since mRNAs of both GH and GH receptor were present in stem cells and B-cell precursors in bone marrow, GH may modulate B-lymphoid precursors development in an autocrine or paracrine manner in bone marrows.

Fortifying B cells with CD154: an engaging tale of many hues.

Although the original antibody to what is now defined as CD40 was raised against and shown to react with bladder carcinoma cells, the major insights into the functional attributes of this important receptor molecule – now known to be found on a diverse range of cell types – have arisen from studies on B lymphocytes. This 50 000 MW glycoprotein member of the tumour necrosis factor receptor (TNF-R) family, expressed constitutively at high density throughout B-cell differentiation, provides the focus for T-cell delivered cognate help to the B cell via the capacity to engage its inducible counterstructure – CD154; or ‘CD40 ligand’ (CD40L).1–5 The aim of this article is to review the multiple stages at which the cognate CD40–CD40L pairing might serve to direct and modify the B-cell response with a focus on data generated from human in vitro studies set within an in vivo context gleaned primarily from observations in the mouse. The consequences of engaging CD40 on lymphoma B cells are discussed while, finally, we address how the quantity and quality of the CD154 being offered to its receptor may dictate the functional outcome of the cell in question.

Changes in the B-cell repertoire with age

Changes in the B-cell repertoire during aging include a shift in antibody specificities from foreign to autologous antigens associated with a decline in the activity of conventional B2 compared to B1 lymphocytes. The age-associated increase in B1 lymphocyte number and activity contribute to the increased serum concentration of autoantibodies and the B-cell clonal expansions that develop with age. Aging is also associated with a decreased diversity of the antibody response reflected in the preferential loss of IgG and high affinity antibodies following immunization with a foreign antigen. Many of these changes can be traced to an impaired capacity of T cells to support isotype switching and somatic mutation in the periphery and the generation of a diverse B-cell repertoire from bone marrow B-cell precursors.

Expansion of polyclonal B-cell precursors in bone marrow from children treated for acute lymphoblastic leukemia.

In a series of 12 patients (mean age: 3 years at diagnosis) receiving chemotherapy for acute lymphoblastic leukemia, bone marrow examinations performed during hematopoietic recovery following treatment-induced agranulocytosis or completion of maintenance treatment showed at least 15% of non malignant immature cells which were sometimes hardly distinguishable from leukemic cells. No comparable data was observed in patients treated with G-CSF. The cytological features of these cells as well as their immunophenotyping were defined. Results showed that the majority of cells expressed HLA-DR, CD19, CD10 and cytoplasmic IgM but not the CD34 markers. This predominant and homogeneous pre-B cell population which likely represents the expansion of a minor population detectable in normal bone marrow is phenotypically indistinguishable from leukemic cells. The pattern of IgH gene rearrangements studied by PCR amplification of the CDRIII region showed that these cells were polyclonal. Except in one patient, minimal residual disease was not detected using probes specific for IgH or TCR gene rearrangement of the malignant clone. In children during the hematopoietic recovery after chemotherapy, immature marrow cells in great numbers, even with an highly homogeneous immunophenotype identical to the malignant clone's, are not sufficient for the diagnosis of relapse.