The stromal composition of malignant lymphoid aggregates in bone marrow: variations in architecture and phenotype in different B-cell tumours

Identification of novel myelodysplastic syndromes prognostic subgroups by integration of inflammation, cell-type composition, and immune signatures in the bone marrow

Mutational profiles of myelodysplastic syndromes (MDS) have established that a relatively small number of genetic aberrations, including SF3B1 and SRSF2 spliceosome mutations, lead to specific phenotypes and prognostic subgrouping. We performed a multi-omics factor analysis (MOFA) on two published MDS cohorts of bone marrow mononuclear cells (BMMNCs) and CD34 + cells with three data modalities (clinical, genotype, and transcriptomics). Seven different views, including immune profile, inflammation/aging, retrotransposon (RTE) expression, and cell-type composition, were derived from these modalities to identify the latent factors with significant impact on MDS prognosis. SF3B1 was the only mutation among 13 mutations in the BMMNC cohort, indicating a significant association with high inflammation. This trend was also observed to a lesser extent in the CD34 + cohort. Interestingly, the MOFA factor representing the inflammation shows a good prognosis for MDS patients with high inflammation. In contrast, SRSF2 mutant cases show a granulocyte-monocyte progenitor (GMP) pattern and high levels of senescence, immunosenescence, and malignant myeloid cells, consistent with their poor prognosis. Furthermore, MOFA identified RTE expression as a risk factor for MDS. This work elucidates the efficacy of our integrative approach to assess the MDS risk that goes beyond all the scoring systems described thus far for MDS.

Bone Marrow Lymphoid Niche Adaptation to Mature B Cell Neoplasms

B-cell non-Hodgkin lymphoma (B-NHL) evolution and treatment are complicated by a high prevalence of relapses primarily due to the ability of malignant B cells to interact with tumor-supportive lymph node (LN) and bone marrow (BM) microenvironments. In particular, progressive alterations of BM stromal cells sustain the survival, proliferation, and drug resistance of tumor B cells during diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and chronic lymphocytic leukemia (CLL). The current review describes how the crosstalk between BM stromal cells and lymphoma tumor cells triggers the establishment of the tumor supportive niche. DLBCL, FL, and CLL display distinct patterns of BM involvement, but in each case tumor-infiltrating stromal cells, corresponding to cancer-associated fibroblasts, exhibit specific phenotypic and functional features promoting the recruitment, adhesion, and survival of tumor cells. Tumor cell-derived extracellular vesicles have been recently proposed as playing a central role in triggering initial induction of tumor-supportive niches, notably within the BM. Finally, the disruption of the BM stroma reprogramming emerges as a promising therapeutic option in B-cell lymphomas. Targeting the crosstalk between BM stromal cells and malignant B cells, either through the inhibition of stroma-derived B-cell growth factors or through the mobilization of clonal B cells outside their supportive BM niche, should in particular be further evaluated as a way to avoid relapses by abrogating resistance niches.

Role of the Bone Marrow Niche in Supporting the Pathogenesis of Lymphoid Malignancies

While the bone marrow (BM) microenvironment is the primary location for nurturing the multipotent hematopoietic stem cells and developing the blood cells of either myeloid or lymphoid origin under normal physiological conditions, it could provide a supportive milieu for the proliferation of blood cancer cells. In fact, the multiple and complex direct cell-to-cell or indirect soluble factors-mediated interactions taking place among the BM cells of different origins are shown to play a significant role in tumorigenesis of hematological cancers. In the current review, we focus on lymphoid malignancies and highlight the novel insights surrounding the role of both cellular as well as non-cellular BM compartments in modulating hematopoiesis and promoting growth and proliferation of cancer cells across a variety of aggressive and indolent lymphoid malignancies, including diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma, and Waldenstrom Macroglobulinemia. We also discuss the mechanisms of potential intervention and discuss their therapeutic impact in clinical settings.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

Extracellular vesicles shed by follicular lymphoma B cells promote polarization of the bone marrow stromal cell niche

Follicular lymphoma (FL) originates in the lymph nodes (LNs) and infiltrates bone marrow (BM) early in the course of the disease. BM FL B cells are characterized by a lower cytological grade, decreased proliferation, and a specific phenotypic and subclonal profile. Mesenchymal stromal cells (MSCs) obtained from FL BM display a specific gene expression profile (GEP), including enrichment for a lymphoid stromal cell signature, and an increased capacity to sustain FL B-cell growth. However, the mechanisms triggering the formation of the medullar FL permissive stromal niche have not been identified. In the current work, we demonstrate that FL B cells produce extracellular vesicles (EVs) that can be internalized by BM-MSCs, making them more efficient to support FL B-cell survival and quiescence. Accordingly, EVs purified from FL BM plasma activate transforming growth factor β–dependent and independent pathways in BM-MSCs and modify their GEP, triggering an upregulation of factors classically associated with hematopoietic stem cell niche, including CXCL12 and angiopoietin-1. Moreover, we provide the first characterization of BM FL B-cell GEP, allowing the definition of the landscape of molecular interactions they could engage with EV-primed BM-MSCs. This work identifies FL-derived EVs as putative mediators of BM stroma polarization and supports further investigation of their clinical interest for targeting the crosstalk between BM-MSCs and malignant B cells.

Role of the microenvironment across histological subtypes of NHL

Recent progress in next-generation sequencing strategies has revealed the genetic landscape of B-cell non-Hodgkin lymphoma, but the tumor microenvironment is increasingly recognized as crucial to sustaining malignant B-cell survival and growth, subclonal evolution, and drug resistance. The tumor niche is made up of a dynamic and organized network of strongly heterogeneous immune and stromal cell subsets characterized by specific phenotypic, transcriptomic, and functional features. Nonmalignant cell recruitment and plasticity are dictated by lymphoma B cells, which convert their surrounding microenvironment into a supportive niche. In addition, they are also influenced by the crosstalk between the various components of this niche. In agreement with this, the B-cell lymphoma subtype is a key determinant of the organization of the tumor niche, but genetic alteration patterns, tumor localization, stage of the disease, and treatment strategy may also modulate its composition and activity. Moreover, the complex set of bidirectional interactions between B cells and their microenvironment has been proposed as a promising therapeutic target with the aim of reinforcing antitumor immunity and/or of abbrogating the lymphoma-promoting signals delivered by the tumor niche.

IL-4/CXCL12 loop is a key regulator of lymphoid stroma function in follicular lymphoma

FL-infiltrating stromal cells overexpress CXCL12, which triggers FL B-cell migration, adhesion, and activation. Polarization into CXCL12hi stroma involves IL-4+ TFH cells, unlike malignant B cells, revealing an indirect protumoral activity of FL-TFH cells.

Haematological malignancies: at the forefront of immunotherapeutic innovation

The recent successes of cancer immunotherapies have stimulated interest in the potential widespread application of these approaches; haematological malignancies have provided both initial proofs of concept and an informative testing ground for various immune-based therapeutics. The immune-cell origin of many of the blood malignancies provides a unique opportunity both to understand the mechanisms of cancer immune responsiveness and immune evasion, and to exploit these mechanisms for therapeutic purposes.

Shaping of the tumor microenvironment: Stromal cells and vessels

Lymphomas develop and progress in a specialized tissue microenvironment such as bone marrow as well as secondary lymphoid organs such as lymph node and spleen. The lymphoma microenvironment is characterized by a heterogeneous population of stromal cells, including fibroblastic reticular cells, nurse-like cells, mesenchymal stem cells, follicular dendritic cells, and inflammatory cells such as macrophages, T- and B-cells. These cell populations interact with the lymphoma cells to promote lymphoma growth, survival and drug resistance through multiple mechanisms. Angiogenesis is also recognized as an important factor associated with lymphoma progression. In recent years, we have learned that the interaction between the malignant and non-malignant cells is bidirectional and resembles, at least in part, the pattern seen between non-neoplastic lymphoid cells and the normal microenvironment of lymphoid organs. A summary of the current knowledge of lymphoma microenvironment focusing on the cellular components will be reviewed here.

The tumour microenvironment in B cell lymphomas

B cell lymphomas are cancers that arise from cells that depend on numerous highly orchestrated interactions with immune and stromal cells in the course of normal development. Despite the recent focus on dissecting the genetic aberrations within cancer cells, it has been increasingly recognized that tumour cells retain a range of dependence on interactions with the non-malignant cells and stromal elements that constitute the tumour microenvironment. A fundamental understanding of these interactions gives insight into the pathogenesis of most B cell lymphomas and, moreover, identifies novel therapeutic opportunities for targeting oncogenic pathways, both now and in the future.

A quality improvement assessment of multiple, concurrent flow cytometry analyses at a tertiary care center

INTRODUCTION

The utility of flow cytometry (FC) in diagnosis and staging of hematologic malignancy is controversial. Often, multiple specimens from the same patient are processed concurrently for FC analyses, alongside tissue for histomorphologic diagnosis.

METHODS

To assess the diagnostic utility of multiple, concurrent FC analyses, a 10-year retrospective review of cases with ≥2 concurrent specimens (from the same patient) submitted for FC was conducted. Light microscopic (LM) diagnoses were compared to FC findings, and the contribution of FC results to final diagnoses was examined.

RESULTS

Of 4058 specimens (predominantly lymph nodes, bone marrows, and oropharyngeal tissues) submitted for FC analyses, 129 (3.2%) represented cases with multiple (average: 2.19) concurrent FC analyses. All were accompanied by tissues and/or aspirates for LM examination. In 115 (89.1%) cases, multiple FC analyses were performed prior to morphologic examination. In 87.0% of those cases, ≥1 FC result(s) aligned with LM findings. In 15 (13.0%) cases where FC results differed from morphologic diagnoses, 86.7% (13/15) failed to detect an abnormal cell population by FC in the presence of a hematologic malignancy by LM. In one case (0.9%), FC detected a lymphoma, without morphologic evidence by LM.

CONCLUSIONS

Overall, multipart FC failed to demonstrate a significant contribution in initial diagnoses of hematologic malignancies compared with analysis of a single specimen.

The yin and the yang of follicular lymphoma cell niches: role of microenvironment heterogeneity and plasticity

Follicular lymphoma (FL) results from the malignant transformation of germinal center B cells and is characterized by recurrent genetic alterations providing a direct growth advantage or facilitating interaction with tumor microenvironment. In agreement, accumulating evidences suggest a dynamic bidirectional crosstalk between FL B cells and surrounding non-malignant cells within specialized tumor niches in both invaded lymph nodes and bone marrow. Infiltrating stromal cells, macrophages, and T/NK cell subsets either contribute to anti-tumor immune response, or conversely form a tumor supportive network promoting FL B cell survival, growth, and drug resistance. This review depicts the phenotypic heterogeneity and functional plasticity of the most important FL cell partners and describes their complex interplay. We also unravel how malignant B cells recruit and subvert accessory immune and stromal cells to trigger their polarization toward a supportive phenotype. Based on these observations, innovative therapeutic approaches have been recently proposed, in order to benefit from local anti-tumor immunity and/or to selectively target the protective cell niche.

Stromal cell contribution to human follicular lymphoma pathogenesis

Follicular lymphoma (FL) is the prototypical model of indolent B cell lymphoma displaying a strong dependence on a specialized cell microenvironment mimicking normal germinal center. Within malignant cell niches in invaded lymph nodes and bone marrow, external stimuli provided by infiltrating stromal cells make a pivotal contribution to disease development, progression, and drug resistance. The crosstalk between FL B cells and stromal cells is bidirectional, causing activation of both partners. In agreement, FL stromal cells exhibit specific phenotypic, transcriptomic, and functional properties. This review highlights the critical pathways involved in the direct tumor-promoting activity of stromal cells but also their role in the organization of FL cell niche through the recruitment of accessory immune cells and their polarization to a B cell supportive phenotype. Finally, deciphering the interplay between stromal cells and FL cells provides potential new therapeutic targets with the aim to mobilize malignant cells outside their protective microenvironment and increase their sensitivity to conventional treatment.

Mesenchymal stromal cells orchestrate follicular lymphoma cell niche through the CCL2-dependent recruitment and polarization of monocytes

Accumulating evidence indicates that infiltrating stromal cells contribute directly and indirectly to tumor growth in a wide range of cancers. In follicular lymphoma (FL), malignant B cells are found admixed with heterogeneous lymphoid-like stromal cells within invaded lymph nodes and BM. In addition, mesenchymal stromal cells (MSCs) support in vitro FL B-cell survival, in particular after their engagement toward lymphoid differentiation. We show here that BM-MSCs obtained from patients with FL (FL-MSCs) display a specific gene expression profile compared with MSCs obtained from healthy age-matched donors (HD-MSCs). This FL-MSC signature is significantly enriched for genes associated with a lymphoid-like commitment. Interestingly, CCL2 could be detected at a high level within the FL-cell niche, is up-regulated in HD-MSCs by coculture with malignant B cells, and is overexpressed by FL-MSCs, in agreement with their capacity to recruit monocytes more efficiently than HD-MSCs. Moreover, FL-MSCs and macrophages cooperate to sustain malignant B-cell growth, whereas FL-MSCs drive monocyte differentiation toward a proangiogenic and lipopolysaccharide-unresponsive phenotype close to that of tumor-associated macrophages. Altogether, these results highlight the complex role of FL stromal cells that promote direct tumor B-cell growth and orchestrate FL-cell niche, thus emerging as a potential therapeutic target in this disease.

Notch-3 and Notch-4 signaling rescue from apoptosis human B-ALL cells in contact with human bone marrow-derived mesenchymal stromal cells

Although many literature data are available on the role of Notch signaling in T-cell acute lymphoblastic leukemia (ALL) biology, the importance of this molecular pathway in the development of B-lineage ALL (B-ALL) cells in the BM microenvironment is unknown so far. In this study, we used anti-Notch molecules neutralizing Abs and γ-secretase inhibitor (GSI) XII to investigate the role of the Notch signaling pathway in the promotion of human B-ALL cell survival in presence of stromal cell support. The treatment with combinations of anti-Notch molecule neutralizing Abs resulted in the decrease of B-ALL cell survival, either cultured alone or cocultured in presence of stromal cells from normal donors and B-ALL patients. Interestingly, the inhibition of Notch-3 and -4 or Jagged-1/-2 and DLL-1 resulted in a dramatic increase of apoptotic B-ALL cells by 3 days, similar to what is obtained by blocking all Notch signaling with the GSI XII. Our data suggest that the stromal cell-mediated antiapoptotic effect on B- ALL cells is mediated by Notch-3 and -4 or Jagged-1/-2 and DLL-1 in a synergistic manner.

The bone marrow stroma in hematological neoplasms--a guilty bystander

In the setting of hematological neoplasms, changes in the bone marrow (BM) stroma might arise from pressure exerted by the neoplastic clone in shaping a supportive microenvironment, or from chronic perturbation of the BM homeostasis. Under such conditions, alterations in the composition of the BM stroma can be profound, and could emerge as relevant prognostic factors. In this Review, we delineate the multifaceted contribution of the BM stroma to the pathobiology of several hematological neoplasms, and discuss the impact of stromal modifications on the natural course of these diseases. Specifically, we highlight the involvement of BM stromal components in lymphoid and myeloid malignancies, and present the most relevant processes responsible for remodeling the BM stroma. The role of bystander BM stromal elements in the setting of hematological neoplasms is discussed, strengthening the rationale for treatment strategies that target the BM stroma.

The stromal composition of mast cell aggregates in systemic mastocytosis

Systemic mastocytosis is a stem cell disorder characterized histologically by the presence of multifocal compact aggregates of mast cells in at least one extracutaneous organ with or without evidence of skin lesions. The mast cell aggregates are accompanied by fibrosis, which is often significant. However, in spite of its frequent occurrence and severity, little is known about its characteristics. In this study, we evaluated the composition of the fibrotic mast cell aggregates by studying eight bone marrow biopsies and two spleens involved by systemic mastocytosis, and compared the findings with those observed in other fibrotic bone marrow disorders such as primary myelofibrosis and metastatic malignancy. Histochemistry and immunohistochemistry were used to evaluate: (a) extracellular matrix (reticulin, trichrome, collagen IV, laminin); (b) stromal reticulum cells (low-affinity nerve growth factor receptor); (c) presence of myofibroblastic differentiation (smooth muscle actin) and (d) microvessel density (CD34). We found that all cases showed marked reticulin and collagen fibrosis. However, unlike primary myelofibrosis and metastatic malignancy, which are usually associated with increased low-affinity nerve growth factor receptor positivity, its expression was low in all cases of systemic mastocytosis. Myofibroblastic differentiation was only focally detected in two of eight bone marrow biopsies. In all cases, the systemic mastocytosis lesions were largely devoid of type IV collagen and laminin. The latter findings were in contrast with those seen in cases of primary myelofibrosis and metastatic malignancy where smooth muscle actin, collagen IV and laminin were expressed in most cases. Also in contrast with the other two conditions, only minimal vascularity was detectable within the fibrotic mast cell lesions. These findings indicate that systemic mastocytosis exhibits a distinct pattern of stromal change, and suggest that the fibrogenetic mechanism in systemic mastocytosis is most likely different from that of other bone marrow neoplasms which are also associated with fibrosis.

CD40 ligand protects from TRAIL-induced apoptosis in follicular lymphomas through NF-kappaB activation and up-regulation of c-FLIP and Bcl-xL

The TNF family member TRAIL is emerging as a promising cytotoxic molecule for antitumor therapy. However, its mechanism of action and the possible modulation of its effect by the microenvironment in follicular lymphomas (FL) remain unknown. We show here that TRAIL is cytotoxic only against FL B cells and not against normal B cells, and that DR4 is the main receptor involved in the initiation of the apoptotic cascade. However, the engagement of CD40 by its ligand, mainly expressed on a specific germinal center CD4(+) T cell subpopulation, counteracts TRAIL-induced apoptosis in FL B cells. CD40 induces a rapid RNA and protein up-regulation of c-FLIP and Bcl-x(L). The induction of these antiapoptotic molecules as well as the inhibition of TRAIL-induced apoptosis by CD40 is partially abolished when NF-kappaB activity is inhibited by a selective inhibitor, BAY 117085. Thus, the antiapoptotic signaling of CD40, which interferes with TRAIL-induced apoptosis in FL B cells, involves NF-kappaB-mediated induction of c-FLIP and Bcl-x(L) which can respectively interfere with caspase 8 activation or mitochondrial-mediated apoptosis. These findings suggest that a cotreatment with TRAIL and an inhibitor of NF-kappaB signaling or a blocking anti-CD40 Ab could be of great interest in FL therapy.

Development of human lymph nodes and Peyer's patches

In contrast to our understanding of murine lymphoid organogenesis, detailed knowledge on the mechanisms of human lymph node development is virtually lacking. This is mainly due to the obvious difficulties that accompany research using human fetal organs. In this review we will highlight current knowledge on human lymph node and Peyer's patch development and will temporally align observations made in humans with data available from murine studies. In the final paragraphs we will put this knowledge in the context of human malignancies in which interactions between lymphocytes and stroma, resembling those seen in lymphoid organs, are recapitulated.

Bone marrow fibroblasts induce expression of PI3K/NF-kappaB pathway genes and a pro-angiogenic phenotype in CLL cells

Microarray-based gene expression profiling (GEP) was used to study how stroma modulates the survival of CLL cells in an in vitro coculture model employing the murine fibroblast cell line M2-10B4. CLL cells cultured in direct contact with the stromal layer (STR) showed a significantly better survival than cells cultured in transwell (TW) inserts above the M2-10B4 cells. STR as compared to TW conditions induced a significant up-regulation of PI3K/NF-kappaB pro-survival pathway genes and mediated a pro-angiogenetic switch in the CLL cells by up-regulation of vascular endothelial growth factor (VEGF) and osteopontin (OPN) and down-regulation of the anti-angiogenetic molecule thrombospondin-1 (TSP-1).

Follicular Lymphoma in Staging Bone Marrow Specimens: Correlation of Histologic Findings With the Results of Flow Cytometry Immunophenotypic Analysis

Context.—Bone marrow (BM) examination is part of the staging workup of lymphoma patients. Few studies have compared BM histologic findings with results of flow cytometric immunophenotyping analysis in follicular lymphoma (FL) patients.

Objective.—To correlate histologic findings with immunophenotypic data in staging BM biopsy and aspiration specimens of FL patients.

Design.—Bone marrow biopsy specimens of untreated FL patients were reviewed. Histologic findings were correlated with 3-color flow cytometric immunophenotyping results on corresponding BM aspirates.

Results.—Bone marrow biopsy specimens (with or without aspirates) of 114 patients with histologic evidence of FL in BM were reviewed. There were 76 bilateral and 38 unilateral biopsies performed, resulting in 190 specimens: 187 involved by FL and 3 negative (in patients with a positive contralateral specimen). The extent of BM involvement was <5% in 32 (17.1%), ≥5% and ≤25% in 102 (54.6%), >25% and ≤50% in 27 (14.4%), and >50% in 26 (13.9%) specimens. The pattern of involvement was purely paratrabecular in 81 (43.3%), mixed in 80 (42.8%), and purely nonparatrabecular in 26 (13.9%). Immunophenotyping was only performed unilaterally, on BM aspirates of 92 patients, and was positive for a monoclonal B-cell population in 53 (57.6%) patients. Immunophenotyping was more often negative when biopsy specimens showed FL with a purely paratrabecular pattern. For comparison, we assessed 163 FL patients without histologic evidence of FL in BM also analyzed by flow cytometric immunophenotyping. A monoclonal B-cell population was identified in 5 patients (3%).

Conclusions.—Our data suggest that 3-color flow cytometric immunophenotyping adds little information to the evaluation of staging BM specimens of FL patients.

Human mesenchymal stem cells isolated from bone marrow and lymphoid organs support tumor B-cell growth: role of stromal cells in follicular lymphoma pathogenesis

Accumulating evidence indicates that the cellular microenvironment plays a key role in follicular lymphoma (FL) pathogenesis, both within tumor lymph nodes (LNs) and in infiltrated bone marrow where ectopic LN-like reticular cells are integrated within malignant B-cell nodular aggregates. In normal secondary lymphoid organs, specific stromal cell subsets provide a highly specialized microenvironment that supports immune response. In particular, fibroblastic reticular cells (FRCs) mediate immune cell migration, adhesion, and reciprocal interactions. The role of FRCs and their postulated progenitors, that is, bone marrow mesenchymal stem cells (MSCs), in FL remains unexplored. In this study, we investigated the relationships between FRCs and MSCs and their capacity to sustain malignant B-cell growth. Our findings strongly suggest that secondary lymphoid organs contain MSCs able to give rise to adipocytes, chondrocytes, osteoblasts, as well as fully functional B-cell supportive FRCs. In vitro, bone marrow-derived MSCs acquire a complete FRC phenotype in response to a combination of tumor necrosis factor-alpha and lymphotoxin-alpha1beta2. Moreover, MSCs recruit primary FL cells that, in turn, trigger their differentiation into FRCs, making them able to support malignant B-cell survival. Altogether, these new insights into the cross talk between lymphoma cells and their microenvironment could offer original therapeutic strategies.

Bone Marrow Biopsy Involvement by Non-Hodgkin's Lymphoma

To evaluate the features of bone trephine biopsy involvement by non-Hodgkin lymphoma, 450 specimens were evaluated for percentage of marrow involvement, pattern of involvement, presence of germinal centers or follicular structures, and discordance with other involved sites. A subset of 197 cases was evaluated for evidence of concurrent peripheral blood involvement. Follicular grade 1 lymphoma (30.4%) was the most common type to involve the marrow, followed by diffuse large B-cell lymphoma (16.0%), mantle cell lymphoma (9.3%), low-grade B-cell lymphoma, not otherwise specified (8.7%), lymphoplasmacytic lymphoma (8.4%), follicular grade 2 lymphoma (7.1%), and mature T- and NK-cell lymphomas (6.4%). A mixed pattern of infiltration was most common, followed by paratrabecular, nodular, diffuse, and interstitial patterns. Greater than 90% of follicular lymphomas had at least a focal paratrabecular infiltration pattern, but this pattern was also seen with other lymphoma types. Interstitial disease infiltration tended to correlate with lymphoplasmacytic lymphoma but was also not specific. The presence of germinal centers or follicular structures was associated with follicular lymphoma in 88% of cases. Discordance between the bone marrow morphology and other tissue sites was observed in 24.9% of cases and was most often seen with follicular or diffuse large B-cell lymphoma. Peripheral blood involvement by lymphoma was observed in 29% of cases, found in all disease groups except for follicular grade 3 lymphoma. This study highlights the frequency of different lymphoma patterns in the marrow, limitations of primary lymphoma classification on biopsy material alone, and the relative frequency of marrow discordance and peripheral blood involvement by marrow lymphoma.

Inhibition of PI3K, mTOR and MEK signaling pathways promotes rapid apoptosis in B-lineage ALL in the presence of stromal cell support

Bone marrow stromal cells are essential for the differentiation, survival and proliferation of normal and leukemic human B-lineage cells. Leukemic cells require stromal cell support for optimal proliferation and apoptotic resistance. Stromal cell contact can promote resistance to chemotherapeutic agents. In this study, we have made use of small molecular weight inhibitors and an established stromal cell-dependent pre-B-ALL cell line, BLIN-2, to investigate the role of the MAP kinase, PI3K/Akt, JAK/STAT and mTOR pathways in the promotion of leukemic cell growth in the presence of stromal cell support. Treatment with PI3K+JAK, PI3K+MEK, or MEK+JAK inhibitor combinations resulted in an inhibition of proliferation as measured by DNA synthesis. However, only inhibition of both PI3K and MEK or both mTOR and MEK resulted in a dramatic increase in the number of annexinV(+)/PI(+) apoptotic events within a 24 h period. Our data suggest that stromal cell-mediated apoptotic protection in B-lineage ALL is mediated by PI3K/mTOR and MEK via a synergistic mechanism(s).

In vitro functional defects of bone marrow-derived CD34+ progenitors from newly diagnosed mature B-cell malignancies with bone marrow tumor involvement

OBJECTIVE

We hypothesized that the presence of tumor cells in bone marrow (BM) could alter hematopoietic progenitor cell functions. Therefore, we evaluated phenotypic and in vitro functional properties of BM-derived CD34+ progenitors issued from untreated and newly diagnosed patients presenting a mature B-lymphoproliferative disorder (LPD) involving the BM (Inv+).

PATIENTS AND METHODS

In vitro proliferation and differentiation capacities of primitive and committed progenitors were evaluated by cobblestone area-forming cell (CAFC) and colony-forming cell (CFC) assays, and ex vivo cell expansion. Migratory capacities of CD34+ cells were explored by chemotaxis assays using a CXCL12alpha gradient.

RESULTS

Our results showed that CD34+ cells from Inv+ patients overexpressed CD117 and had a significant decrease of week-3 and -6 CAFC, and CFC frequencies, compared to cells obtained from healthy volunteers and LPD patients without BM involvement (Inv-). In addition, progenitors from Inv+ patients maintained a significantly decreased CFC capacity after ex vivo cell expansion, compared to healthy volunteers. However, the former cells held their migratory capacity in response to CXCL12alpha.

CONCLUSION

Functional defects of primitive and committed CD34+ progenitors detected among LPD patients with BM tumor involvement suggest either that tumor cells may induced bystander effects on progenitors or that "unusual" CD34+ cells may exist in the BM that could belong to the proliferating tumor tissue.

In vitro assessment of bone marrow endothelial colonies (CFU-En) in non-Hodgkin's lymphoma patients undergoing peripheral blood stem cell transplantation

The distribution and functional characteristics of in vitro bone marrow (BM) endothelial colonies (CFU-En) were studied in 70 non-Hodgkin's lymphoma (NHL) patients in different phases of the disease to explore the association between CFU-En growth and angiogenesis, and between the number of CFU-En and the presence of hematopoietic and mesenchymal progenitor cells. The mean number of CFU-En/10(6) BM mononuclear cells seen in remission patients was significantly higher than that seen in newly diagnosed patients (P=0.04), and in normal subjects (P=0.008). Patients with low-grade NHL in remission displayed a higher CFU-En value compared with high-grade NHL (P=0.04). In the autograft group (40 patients), a significant reduction of CFU-En number was detected in the first 4-6 months after transplantation. In remission patients, the CFU-En number positively correlated with the incidence of BM colony-forming unit granulocyte-macrophage (CFU-GM) (P=0.013) and CFU-multilineage (CFU-GEMM) hematopoietic colonies (P=0.044). These in vitro data show that CFU-En numbers increase following standard-dose chemotherapy, thus providing a rationale for further investigating the effects of different cytostatic drugs on BM endothelial cells growth and function.

Dissolution of the lymphoid follicle is a feature of the HHV8+ variant of plasma cell Castleman's disease

The plasma cell variant of Castleman's disease (PCD) may occur in a variety of clinical settings. One recently delineated type of PCD is caused by human herpesvirus 8 (HHV8) infection. Lymph nodes from 25 patients with PCD, including six HHV8+ and 19 HHV8- cases, were studied. Three patients with HHV8+ PCD were also infected with human immunodeficiency virus-1. Features common to all cases were interfollicular plasmacytosis and variably hyperplastic and regressed follicle germinal centers. Features associated only with HHV8+ PCD included follicle dissolution resulting from blurring of the mantle zone boundary (p = 0.0001), presence of atypical plasma cells and immunoblasts within these areas (p = 0.0006), and more prominent interfollicular vascular proliferation than in HHV8- PCD. HHV8+ cells were predominantly immunoblasts and small lymphocytes that were highly enriched in the mantle zones of altered follicles. These areas showed a predominance of plasmacytoid forms expressing lambda light chain in four of six cases. The extrafollicular fibroblastic network surrounding altered germinal centers demonstrated marked upregulation of low-affinity nerve growth factor receptor in five of five HHV8+ cases but in only two of 10 HHV8- cases. We conclude that HHV8+ PCD is distinctive histologically because of the accumulation of infected lymphocytes in the mantle zone leading to progressive dissolution of the germinal center and altered regulation of the surrounding stroma.