B-lymphoproliferative Disorder Research Articles

A Meningioma Mimic and Distinct Subtype of Primary Central Nervous System Lymphoma: Primary Dural Lymphoma

Primary central nervous system lymphoma (PCNSL) is an aggressive form of extranodal non-Hodgkin lymphoma that arises in the brain parenchyma, eyes, meninges, or spinal cord in the absence of systemic disease. Primary dural lymphoma (PDL), in contrast, arises from the dura mater of the brain. PDL is usually a low-grade B-cell marginal zone lymphoma (MZL), whereas other types of PCNSL are usually high-grade large B-cell lymphoma. This specific pathological subtype has important therapeutic and prognostic implications, making PDL a distinct subtype of PCNSL. Herein, we report a case of PDL in an African American patient, in her late thirties, who presented to our emergency room with chronic headaches. An emergent magnetic resonance imaging (MRI) of the brain showed a dural-based homogeneously enhancing extra-axial mass along the left hemisphere, which was contained within the anterior and parietal dural mater. A surgical specimen was collected after an emergency debulking procedure. The flow cytometry, done on the surgical specimen obtained, was positive for CD19+, CD20+, and CD22+, but negative for CD5- and CD10-. These findings were consistent with a clonal B-lymphoproliferative disorder. The surgical pathology specimen immunohistochemistry was positive for CD20+ and CD45+, but negative for Bcl-6Cyclin D1- and CD56-. The Ki67 was 10-20%. These findings were consistent with extranodal MZL. Given the location and pathology, the patient was diagnosed with PDL. Due to MZL's indolent nature, location outside the blood-brain barrier, and known efficacy to bendamustine-rituximab (BR), we decided to treat our patient with BR. She completed six cycles without major complications, and her post-therapy brain MRI showed complete remission (CR). Our case adds to the sparse literature about PDL and highlights the efficacy of BR systemic chemotherapy on MZLs.

Concomitant essential thrombocythemia and mature B-lymphoproliferative disorder in a patient

Concomitant essential thrombocythemia and mature B-lymphoproliferative disorder in a patient

IgG cryoglobulinemia.

Mixed Cryoglobulinemia is the most well-known Hepatitis C Virus (HCV)-associated extrahepatic manifestation. MC is both an autoimmune and B-lymphoproliferative disorder. Cryoglobulins (CGs) are classified into three groups according to immunoglobulin (Ig) composition: type I is composed of one isotype or Ig class. Type II and type III mixed CGs are immune complexes composed of polyclonal IgGs acting as autoantigens and mono, polyclonal or oligoclonal IgM with rheumatoid factor activity. IgG1 and IgG3 are the predominant subclasses involved. This study shows the simultaneous presence of IgG-RF and IgG3, supporting the hypothesis of an involvement of this subclass in the initiation of early stages of CGs. We describe a case series of six HCV-positive patients, all of whom had peripheral neuropathy and transient ischemic attacks, presenting cryoprecipitates formed by IgG3 and IgG1. Cryoprecipitate IgG subclass research was carried out by immunofixation electrophoresis by using antisera against IgG1, IgG2, IgG3, and IgG4. Our six patients presented with an immunochemical pattern characterized by the mere presence of IgG1 and IgG3 subclasses with probable RF activity and one of these six patients exhibited monoclonal IgG3 in his cerebrospinal fluid. We can hypothesize that the IgG passage through the blood-brain barrier could have contributed to the cause of TIAs, through a mechanism involving the precipitation of circulating immune complexes formed by the two subclasses in the intrathecal vessels.

CD73, a potential diagnostic marker in Egyptian patients with chronic lymphocytic leukemia

Objective This work aimed to study CD73 expression in chronic lymphocytic leukemia (CLL) patients and its correlation with other disease characteristics. Background CLL is a common B-lymphoproliferative disorder, which can be diagnosed in most cases by morphology and flowcytometry. It displays heterogeneity in clinical presentation, course, and response to treatment, which is likely due to the diversity of the biological nature of the disease. Diagnostic difficulty might arise in some patients due to atypical morphology and/or immunophenotype. CD73 is an extracellular enzyme that hydrolyses adenosine monophosphate to adenosine and is expressed on a subset of T and B lymphocytes. A number of studies have shown CD73 as a contributing factor in the multistep process of carcinogenesis by inducing favorable environment for tumor growth. However, it was shown in some studies to induce apoptosis. Patients and methods CD73 expression on both B and T lymphocytes was measured in 25 cases of newly diagnosed CLL and 15 healthy controls. The levels of expression were correlated to other disease characteristics. Results CD73 expression on CD19 + B lymphocytes was significantly lower in CLL patients compared with controls (mean 3.74 vs. 29.35%, respectively, P Conclusion CD73 expression is a potential diagnostic marker in CLL. This can be particularly relevant in cases with atypical immunophenotype using the current CLL scoring system. CD73 may have a role in CLL pathogenesis as low expression can lead to failure of termination of immune response with subsequent proliferation and clonal expansion of the involved clone.

Epstein-Barr Virus-positive Diffuse Large B-cell Lymphoma of the Elderly Complicated by the Onset of Acute Myeloid Leukemia

We herein describe the case of a 62-year-old woman who presented with anemia and an 8-month history of weight loss. Bone marrow aspiration showed increased myeloblasts. The histopathology findings of biopsy specimens of the right cervical lymph node and intestinal mass indicated B-lymphoproliferative disorder (B-LPD) with Hodgkin lymphoma-like morphologic features and polymorphous diffuse large B-cell lymphoma (DLBCL), respectively. In addition, both types of lymphoma cells were positive for Epstein-Barr virus (EBV)-encoded small RNA-1. The patient was diagnosed with EBV-associated B-LPD and simultaneous acute myeloid leukemia (AML). This is the first case of a patient diagnosed with simultaneous EBV-positive DLBCL of the elderly and AML.

The Absence of a Microbiota Enhances TSLP Expression in Mice with Defective Skin Barrier but Does Not Affect the Severity of their Allergic Inflammation

Evidence is accumulating to suggest that our indigenous microbial communities (microbiota) may play a role in modulating allergic and immune disorders of the skin (Gallo and Nakatsuji, 2011; Macia et al., 2012). To examine the link between the microbiota and atopic dermatitis, we examined a mouse model of defective cutaneous barrier function with an atopic dermatitis-like disease due to loss of Notch signaling. Comparisons of conventionally-raised (CONV-R) and germ-free (GF) mice revealed a similar degree of allergic skin inflammation, systemic atopy, and airway hypersensitivity. GF mutant animals expressed significantly higher levels of thymic stromal lymphopoietin (TSLP), a major proinflammatory cytokine released by skin with defective barrier function, resulting in a more severe B-lymphoproliferative disorder that persisted into adulthood. These findings suggest a role for the microbiota in ameliorating stress signals released by keratinocytes in response to perturbation in cutaneous barrier function.

Immunophenotypic Analysis of CD103+ B-Lymphoproliferative Disorders

CD103 is characteristically expressed in hairy cell leukemia (HCL), a B-lymphoproliferative disorder highly responsive to treatment with purine analogs. Other CD103+ diseases are rare and do not respond well to the same therapy, including HCL variant (HCLv) and splenic marginal zone B-cell lymphoma (SMZL) variants. We analyzed 215 cases of CD103+ B-lymphoproliferative disorders to further delineate their immunophenotypic features. Flow cytometric analysis revealed that 78.6% of all cases expressed CD25 and CD103, characteristic of classical HCL. Cases analyzed immunohistochemically were also invariably positive for annexin-A1; a subset coexpressed CD10 (33/169 [19.5%]) or BCL1 (26/65 [36.9%]). In contrast, 21.4% of cases lacked CD25, a subset of which was analyzed and was invariably negative for annexin-A1, CD10, and BCL1. The CD25- cases had variable morphologic features ranging from HCLv and SMZL to prolymphocytic leukemia and diffuse large B-cell lymphoma. Clinically, patients with CD25- disease tended to be older (P= .001), typically had leukocytosis (P= .014), and did not respond well to cladribine or pentostatin. We suggest categorizing CD103+ B-lymphoproliferative disorders into 2 groups. While HCL coexpresses CD25 and annexin-A1, diseases lacking CD25 and annexin-A1 behave clinically differently and can be separated from HCL on diagnosis.

Correction: Notch-Deficient Skin Induces a Lethal Systemic B-Lymphoproliferative Disorder by Secreting TSLP, a Sentinel for Epidermal Integrity

Correction: Notch-Deficient Skin Induces a Lethal Systemic B-Lymphoproliferative Disorder by Secreting TSLP, a Sentinel for Epidermal Integrity

O4-03-06: Notch or gamma-secretase-deficient skin creates an environment inducing a lethal systemic B-lymphoproliferative disorder by overproducing TSLP, a sentinel for epidermal integrity

O4-03-06: Notch or gamma-secretase-deficient skin creates an environment inducing a lethal systemic B-lymphoproliferative disorder by overproducing TSLP, a sentinel for epidermal integrity

When Skin Damage Causes Death

Our skin routinely shields us from microbes, allergens, and other environmental assaults, a yeoman's service we often take for granted—until that barrier is breached. In response to injury, be it a simple cut or a deep wound, keratinocytes, the cells that form the epidermal layer, proliferate and dispatch chemical messengers to enlist the healing services of immune cells. But new research shows that sometimes damaged skin can send the wrong message to its immune cell partners. Rather than recruiting immune cells to repair a wound, Raphael Kopan and colleagues report, defective skin can trigger a systemic, ultimately fatal immune response. As a self-renewing tissue with four distinct layers of specialized keratinocytes, the epidermis must constantly generate new cells to replace the many thousands that die each day. Both rejuvenation and wound repair require the support of a new pool of specialized cells, a process that is mediated by the Notch signaling pathway, an ancient intercellular communication system found in most multicellular animals. To remain healthy, skin must maintain a delicate balance between cell differentiation and growth. Interfering with differentiation—by impairing the Notch pathway, for example—can cause serious defects in the epidermal barrier and lead to inflammatory skin disorders like psoriasis or atopic dermatitis, a type of eczema. The source of new cells comes from the innermost, basal, skin layer, which harbors a population of stem cells that continually divide to generate the cells that will eventually populate the other layers. Notch appears to operate in one way to suppress basal cell proliferation and promote keratinocyte differentiation, while using a different mode to ensure a dynamic equilibrium between differentiation and growth. Dramatic expansion of pre- and immature B cells in peripheral blood is the hallmark of B-lymphoproliferative disorder, caused by defective skin differentiation seen in the newborn mice lacking Notch signaling in their skin. The inset shows a lymphoblast. ... To investigate Notch's role in skin homeostasis and barrier formation, Kopan and colleagues used a protocol that removes multiple genes in the Notch pathway in keratinocytes during a narrow window of embryonic development in mice, when the blood system is forming. Most mice with no trace of Notch signaling in their skin developed chronic barrier formation defects akin to those seen in atopic dermatitis, and died about three weeks after birth. They also had extremely high levels of B cells, the white blood cells that produce antibodies to fight infection. Paralleling the loss of Notch signaling, the researchers saw an increase in the expression of a cytokine called thymic stromal lymphopoietin (TSLP), in direct proportion to the severity of defects in cell differentiation and barrier formation. The spike in TSLP levels in turn triggered an abnormal expansion of pre- and immature B cells in peripheral tissues (B cell development in normal embryos is restricted to the fetal liver), leading to dangerously high levels of B cells, a condition known as B-lymphoproliferative disorder (B-LPD). In severe cases, the B cells ultimately infiltrate several organs in the mice, which results in death. TSLP, which has been implicated in atopic dermatitis, can stimulate the development of the fetal pre-B cells (but not adult pre-B cells) in test tubes. This study confirms that exposure to high levels of TSLP during embryonic development can trigger a massive expansion of pre- and immature B cells, causing B-LPD and death. The finding that localized skin defects can cause a fatal systemic disease reveals a surprising, complex interaction between the immune system and the skin, and suggests many new questions to explore. Kopan and colleagues want to know, for example, how keratinocytes detect the severity of skin damage and translate this information into TSLP output. With a better understanding of the mechanisms underlying this skin–immune system connection, investigators may be able to develop new therapies to treat a wide range of incurable autoimmune-related skin disorders, including atopic dermatitis, an often debilitating condition that commonly affects children.

Notch-Deficient Skin Induces a Lethal Systemic B-Lymphoproliferative Disorder by Secreting TSLP, a Sentinel for Epidermal Integrity

Epidermal keratinocytes form a highly organized stratified epithelium and sustain a competent barrier function together with dermal and hematopoietic cells. The Notch signaling pathway is a critical regulator of epidermal integrity. Here, we show that keratinocyte-specific deletion of total Notch signaling triggered a severe systemic B-lymphoproliferative disorder, causing death. RBP-j is the DNA binding partner of Notch, but both RBP-j–dependent and independent Notch signaling were necessary for proper epidermal differentiation and lipid deposition. Loss of both pathways caused a persistent defect in skin differentiation/barrier formation. In response, high levels of thymic stromal lymphopoietin (TSLP) were released into systemic circulation by Notch-deficient keratinocytes that failed to differentiate, starting in utero. Exposure to high TSLP levels during neonatal hematopoiesis resulted in drastic expansion of peripheral pre- and immature B-lymphocytes, causing B-lymphoproliferative disorder associated with major organ infiltration and subsequent death, a previously unappreciated systemic effect of TSLP. These observations demonstrate that local skin perturbations can drive a lethal systemic disease and have important implications for a wide range of humoral and autoimmune diseases with skin manifestations.

AntiCD20 monoclonal antibody-based radioimmunotherapy of relapsed chemoresistant aggressive post-transplantation B-lymphoproliferative disorder in heart-transplant recipient

AntiCD20 monoclonal antibody-based radioimmunotherapy of relapsed chemoresistant aggressive post-transplantation B-lymphoproliferative disorder in heart-transplant recipient

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

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+). 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. 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. 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.

Treatment of B-lymphoproliferative disorder with a monoclonal anti–interleukin-6 antibody in 12 patients: a multicenter phase 1-2 clinical trial

Severe T-cell immunodeficiency after solid organ or bone marrow transplantation may result in the uncontrolled outgrowth of latently Epstein-Barr virus-infected B cells, leading to B-lymphoproliferative disorder (BLPD). Given the potentially important pathogenic role of IL-6 in BLPD, it was tested whether the in vivo neutralization of IL-6 by a monoclonal anti-IL-6 antibody could contribute to the control of BLPD. Safety and efficacy were assessed in 12 recipients of transplanted organs who had BLPD refractory to the reduction of immunosuppression over 8 days. Five patients received 0.4 mg/kg per day. The next 7 patients received 0.8 mg/kg per day. Treatment was scheduled to last 15 days. It was completed in 10 patients, and in the other 2 patients was discontinued early (days 10 and 13, respectively) because of disease progression. Treatment tolerance was good, and no major side effects were observed. High C-reactive protein levels were found in 9 patients before treatment but were normalized under treatment in all patients, demonstrating efficient IL-6 neutralization. Complete remission (CR) was observed in 5 patients and partial remission (PR) in 3 patients. Relapse was observed in 1 of these 8 patients in whom remission was observed. This relapse was unresponsive to treatment. Disease was stable in 1 patient, but it progressed in 3 patients. Seven patients are alive and well. Two patients died because of disease progression, and 3 patients died while in CR (chronic rejection in 2 patients and BLPD sequelae in 1 patient). These data suggest that the anti-IL-6 antibody is safe and should be further explored in the treatment of BLPD.

Foiling IL-6 to treat B-lymphoproliferative disorder

Approximately 21 000 solid organ transplantations are performed annually in the United States. These transplantations offer hope to those about to die of a failing heart, a hepatitis C–ravaged liver, or severe chronic obstructive pulmonary disease, or they improve the quality of life for those

Expression of interferon consensus sequence binding protein (ICSBP) is downregulated in Bcr-Abl-induced murine chronic myelogenous leukemia-like disease, and forced coexpression of ICSBP inhibits Bcr-Abl-induced myeloproliferative disorder.

Chronic myelogenous leukemia (CML) is a clonal myeloproliferative disorder resulting from the neoplastic transformation of a hematopoietic stem cell. The majority of cases of CML are associated with the (9;22) chromosome translocation that generates the bcr-abl chimeric gene. Alpha interferon (IFN-alpha) treatment induces hematological remission and prolongs life in 75% of CML patients in the chronic phase. It has been shown that mice deficient in interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family, manifest a CML-like syndrome. We have shown that expression of Bcr-Abl in bone marrow (BM) cells from 5-fluorouracil (5-FU)-treated mice by retroviral transduction efficiently induces a myeloproliferative disease in mice resembling human CML. To directly test whether icsbp can function as a tumor suppressor gene, we examined the effect of ICSBP on Bcr-Abl-induced CML-like disease using this murine model for CML. We found that expression of the ICSBP protein was significantly decreased in Bcr-Abl-induced CML-like disease. Forced coexpression of ICSBP inhibited the Bcr-Abl-induced colony formation of BM cells from 5-FU-treated mice in vitro and Bcr-Abl-induced CML-like disease in vivo. Interestingly, coexpression of ICSBP and Bcr-Abl induced a transient B-lymphoproliferative disorder in the murine model of Bcr-Abl-induced CML-like disease. Overexpression of ICSBP consistently promotes rather than inhibits Bcr-Abl-induced B lymphoproliferation in a murine model where BM cells from non-5-FU-treated donors were used, indicating that ICSBP has a specific antitumor activity toward myeloid neoplasms. We also found that overexpression of ICSBP negatively regulated normal hematopoiesis. These data provide direct evidence that ICSBP can act as a tumor suppressor that regulates normal and neoplastic proliferation of hematopoietic cells.

Humanized anti-CD20 monoclonal antibody (Rituximab) in post transplant B-lymphoproliferative disorder: A retrospective analysis on 32 patients

B-lymphoproliferative post-transplant disorder (BLPD) is a severe complication of organ and bone marrow transplantation. The reduction of immuno-suppressive therapy or surgery for localized disease may cure some BLPDs. Other therapeutic approaches such as chemotherapy and antiviral drugs are toxic and of limited efficacy. Adoptive immunotherapy with donor T-cell infusions has yielded promising results but is, at the present time, easily applicable only in bone marrow-transplanted patients. Anti-B-cell Murine monoclonal antibodies (MoAbs) have proven effective but are no longer available for human use. We report the activity of a humanized anti CD 20 Mo Ab (Rituximab-MABTHERA Roche) in 32 episodes of BLPD treated in 14 French centers. Between November 1997 and September 1998, 32 patients were diagnosed with BLPD. Twenty-six patients had undergone solid organ transplants (liver 8, kidney 8, heart 4, lung 3, heart lung 1, kidney-pancreas 1, liver-kidney 1) and six patients had received bone marrow transplantations. The median age of the patients was 34 years (3-67 years) and the median delay between graft and tumor 5 months (1-156 months). In organ recipients, tumors were classified as polymorphic and monomorphic in 10 and 15 cases, respectively; 4 of 6 bone marrow transplant recipients were treated without pathology documentation because of a rise in EBV load, fever and lymph node enlargement. Tumors were associated with EBV in 22 of 26 tested cases. Rituximab was used as first-line therapy in 30 patients (after reduction of immunosuppressive treatment in 27 patients) and as salvage therapy in 2 patients (after failure of chemotherapy). The median time from diagnosis of BLPD to treatment with Rituximab was 14 days (1-110 days). Two patients received eight infusions, twenty-six patients four infusions, one patient three infusions and three patients two infusions of 375 mg/m2. The tolerance of rituximab was good. The overall response rate was 69%, with 20 complete responses and 2 partial responses. In solid organ transplant the response rate was 65% (15 CR and 2 PR) while it was 83% in bone marrow-transplanted patients (5 CR). With a median follow-up of 8 months (1-16 months) 24 patients are still alive. The one-year projected survival is 73%. Of the 22 patients who achieved response, 15 patients (11 solid organ transplant and 4 bone marrow transplant) are alive with no evidence of disease, 4 patients relapsed a median of 7 months (3-10 months) after treatment and 3 died while in CR of concurrent diseases. Of the 10 patients who did not respond to Rituximab 5 are alive with no evidence of disease after salvage therapy. The use of rituximab appears to be a safe and relatively efficient therapy in BLPDs. The results need to be confirmed in a prospective multicentric trial.

Anti–B-Cell Monoclonal Antibody Treatment of Severe Posttransplant B-Lymphoproliferative Disorder: Prognostic Factors and Long-Term Outcome

B-lymphoproliferative disorder (BLPD) is a rare but severe complication of organ and bone marrow transplantation (BMT). Profound cytotoxic T-cell deficiency is thought to allow the outgrowth of Epstein-Barr virus–transformed B cells. When possible, reduction of immunosuppressive treatment or surgery for localized disease may cure BLPD. Therapeutic approaches using chemotherapy or antiviral drugs have limited effects on survival. Adoptive immunotherapy with donor T-cell infusions has given promising results in BMT recipients. We previously reported that administration of two monoclonal anti–B-cell antibodies (anti-CD21 and anti-CD24) could contribute to the control of oligoclonal BLPD. Here we report the long-term results of treatment with these monoclonal anti–B-cell antibodies for cases of severe BLPD. In an open multicenter trial, 58 patients in whom aggressive B-cell lymphoproliferative disorder developed after BMT (n = 27) or organ (n = 31) transplantation received 0.2 mg/kg/d of specific anti-CD21 and anti-CD24 murine monoclonal antibodies (MoAbs) for 10 days. The treatment was well tolerated. Thirty-six of the 59 episodes of BLPD in the 58 patients presented complete remission (61%). The relapse rate was low (3 of 36, 8%). Multivariate analysis identified the following risk factors for partial or no response to anti–B-cell MoAb therapy: multivisceral disease (P ≤ .005), central nervous system involvement (P ≤ .05), and late onset of BLPD (P ≤ .005). The overall long-term survival was 46% (median follow-up, 61 months); it was lower among BMT patients (35%) than organ transplant patients (55%). None of the patients who had received BMT for hematological malignancy survived for 1 year. Eight of these 11 patients presented monoclonal BLPD. Tumor burden was the only other variable that contributed significantly to poor survival. Thus, as assessed from this long-term study, the use of anti–B-cell MoAbs therefore appears to be a safe and relatively effective therapy for severe posttransplant BLPD.© 1998 by The American Society of Hematology.

Splenic lymphoma with villous lymphocytes in tropical West Africa

Splenic lymphoma with villous lymphocytes (SLVL) is a monoclonal B-lymphoproliferative disorder characterised by splenomegaly and distinctive villous lymphocytes in the peripheral blood. It has not previously been reported from Africa, but we describe ten Ghanaian patients with SLVL seen at one hospital during a 4-year period. The clinical presentation is similar in Africa and in temperate regions, though the lymphocyte count is higher in African patients and the disorder predominantly affects middle-aged women rather than elderly men. It is likely that SLVL has previously been classified as splenic chronic lymphocytic leukaemia or hyper-reactive malarial splenomegaly.

Clonal origins of lymphoproliferative disease induced by Epstein-Barr virus.

Analysis of immunoglobulin gene rearrangements in 16 B-cell lineages clonally propagated from two mononucleosis patients supported the notion that mononucleosis is a polyclonal B-lymphoproliferative disorder. Three of seven cell clones from a patient with a fatal B lymphoma revealed the same pattern of immunoglobulin gene rearrangement, indicating that this patient's disease was oligoclonal. The three similar clones were propagated from two sites (blood and spleen), indicating that they represent a metastatic cell lineage which arose during the patient's fatal B lymphoproliferation.