Intratumoral Heterogeneity of HER-2/neu in Invasive Mammary Carcinomas Using Fluorescence In-Situ Hybridization and Tissue Microarray

Fluorescence in-situ hybridization is increasingly being used to determine HER-2/neu status in patients with breast carcinoma. The possibility that intratumoral heterogeneity of HER-2/neu gene amplification may potentially contribute to inaccurate assessment of HER-2/neu status was investigated in routine cases of invasive mammary carcinomas. From 169 representative formalin-fixed, paraffin-embedded blocks of invasive duct mammary carcinomas with grade 3 architecture, 48 cases were analyzed by fluorescence in-situ hybridization and 59 analyses were performed. Intratumoral heterogeneity for HER-2/neu gene amplification was demonstrated in only 5 (16%) of 31 cases where morphologically similar areas of a single tumor were analyzed. We conclude from this study that intratumoral heterogeneity of HER-2/neu gene amplification is a demonstrable but relatively uncommon occurrence. For invasive mammary carcinomas, the accurate assessment of HER-2/neu status by fluorescence in-situ hybridization analysis is not significantly confounded by intratumoral heterogeneity of HER-2/neu gene amplification in individual tumors.

Neutrophilic leukocytosis in advanced stage polycythemia vera: hematopathologic features and prognostic implications

Polycythemia vera in 20-30% of cases progresses towards post-polycythemic myelofibrosis, an advanced phase characterized by decreased red blood cells counts and increasing splenomegaly with extramedullary hematopoiesis. There is evidence that the presence of neutrophilic leukocytosis at polycythemia vera disease outset is associated with an increased risk of recurrent thrombosis. However, its clinical significance when developing later in the course of the disease is not well defined. Over a period of 8 years we identified from the files of two reference centers 10 patients (7M/3F, median age: 68 years) who developed persistent absolute leukocytosis ≥ 13 × 10⁹/l (median: 25.1 × 10⁹/l; range: 16.1-89.7 × 10⁹/l) at or around the time of diagnosis of post-polycythemic myelofibrosis (median interval from diagnosis:0 months; range: -6/31) and persisted for a median period of 13 months. Peripheral blood smears showed numerous neutrophils without dysplastic features and, in four, ≥ 10% immature myeloid precursors. In five cases, corresponding marrow specimens obtained at or immediately after the onset of leukocytosis showed a markedly increased myeloid:erythroid ratio due to granulocytic proliferation. No change in JAK2 and BCR-ABL1 status or cytogenetic evolution was associated with the development of leukocytosis. The mutational status of CSF3R, SETBP1, and SRSF2, genes associated with other chronic myeloid neoplasms where neutrophilic leukocytosis occurs, was investigated but all cases showed wild-type only alleles. Four patients died after developing leukocytosis and one experienced worsening disease. Compared with a control group of post-polycythemic myelofibrosis patients (n=23) who never developed persistent leukocytosis, patients with leukocytosis showed higher white blood cells counts and a shorter overall survival. This is the first study describing the development of significant neutrophilic leukocytosis during advanced stages of polycythemia vera; it includes comprehensive hematologic, marrow morphological, molecular, and clinical data. Our findings suggest that persistent leukocytosis occurring at or around the time of progression to post-polycythemic myelofibrosis is associated with an overall more aggressive course of the disease.

Cyclin D1-positive diffuse large B-cell lymphoma with IGH-CCND1 translocation and BCL6 rearrangement: a report of two cases

OBJECTIVES

To demonstrate and confirm the existence of cyclin D1-positive diffuse large B-cell lymphoma (DLBCL) with IGH-CCND1 rearrangement and discuss the rationale of differentiating this entity from blastoid and pleomorphic variants of mantle cell lymphoma (MCL).

METHODS

Two cyclin D1-positive lymphomas with morphologic features of DLBCL and IGH-CCND1 translocations were characterized with respect to clinical features, as well as morphologic, immunophenotypic, cytogenetic, and molecular findings.

RESULTS

The large tumor cells were CD20+, CD5-, CD10-, BCL6+, MUM1+, and cyclin D1+ in both cases. SOX11 was negative. Epstein-Barr virus-encoded RNA in situ hybridization demonstrated diffuse positivity in case 1. BCL6 and IGH-CCND1 rearrangements were identified by fluorescence in situ hybridization in both cases. Specifically, the diagnosis of a relapsed DLBCL with acquisition of IGH-CCND1 was rendered for case 1, molecularly confirmed by the detection of identical monoclonal IGH rearrangements between the initial diagnostic DLBCL and relapse lymphoma.

CONCLUSIONS

Our study demonstrates convincingly that IGH-CCND1 rearrangement leading to cyclin D1 overexpression can occur in DLBCL and pose a potential diagnostic pitfall, requiring thorough knowledge of the clinicopathologic findings to allow accurate discrimination from a blastoid or pleomorphic MCL. The coexistence of IGH-CCND1 and IGH-BCL6 rearrangements suggest that BCL6 and cyclin D1 may cooperate in the pathogenesis of DLBCL.

Development of monocytosis in patients with primary myelofibrosis indicates an accelerated phase of the disease

Primary myelofibrosis is a type of chronic myeloproliferative neoplasm characterized by progressive bone marrow failure with worsening cytopenia and in a subset of patients, progression to acute leukemia. Published data in patients with myelodysplastic syndromes have shown that the development of monocytosis in the course of myelodysplastic syndromes is associated with a poor prognosis. A similar occurrence has been only sporadically reported in patients with primary myelofibrosis. Over a period of four years we identified 10 out of 237 cases of primary myelofibrosis who developed persistent absolute monocytosis (>1 × 10(9)/l) during the course of disease (5 men and 5 women; median age/range: 68 years/52-82). Monocytosis developed at a median interval of 42 months from diagnosis (range: 1-180) and persisted for a median period of 23 months (range: 2-57). Five patients died after developing monocytosis (range: 20-188 months) and two experienced worsening disease and became transfusion dependent. Monocytosis was associated with increased white blood cells, decreased hemoglobin, decreased platelet count, and the presence of circulating blasts. In three cases, bone marrow biopsies after the onset of monocytosis showed marked myelomonocytic proliferation with morphological shifting from a typical primary myelofibrosis marrow appearance to aspects compatible with an overt 'secondary' chronic myelomonocytic leukemia. Before the development of monocytosis, 5 of 10 patients carried the JAK2V617F mutation; five patients showed karyotypic alterations. No change in JAK2 mutational status or cytogenetic evolution were associated with the development of monocytosis. Four of nine patients analyzed showed KRAS mutation in codon 12 or 13 with low allele burden. This is the first study correlating monocytosis developing in primary myelofibrosis patients with bone marrow morphology, laboratory data, molecular analysis and clinical follow-up. Development of monocytosis in patients with established primary myelofibrosis is associated with rapid disease progression and these patients should be considered as a high-risk group associated with short survival.

Bone marrow morphology predicts additional chromosomal abnormalities in patients with myelodysplastic syndrome with del(5q)

The current World Health Organization classification considers myelodysplastic syndrome with isolated del(5q) a distinct entity owing to its characteristic clinical and pathologic features. Recently, several studies have examined survival, leukemic transformation, and various prognostic factors in these patients. However, there is a lack of detailed comparative pathologic analysis of myelodysplastic syndrome cases in which del(5q) is present in association with additional cytogenetic abnormalities. We studied 26 cases of myelodysplastic syndrome at initial diagnosis with 5q- alone, 5q- plus 1 additional abnormality, and 5q- as part of a complex karyotype. Four of 17 patients had evidence of JAK2 V617F mutation. In contrast to cases of myelodysplastic syndrome with isolated 5q-, patients with additional abnormalities had normal mean corpuscular volume and decreased platelet counts (P < .001). Based on bone marrow examination, they were significantly more likely to have increased cellularity, trilineage dysplasia, lower proportion of small hypolobated megakaryocytes, higher number of blasts, and fibrosis. The presence of these morphologic features can be used to distinguish these more aggressive cases from those with myelodysplastic syndrome with isolated 5q- and a more benign clinical course.

Splenic extramedullary hematopoietic proliferation in Philadelphia chromosome-negative myeloproliferative neoplasms: heterogeneous morphology and cytological composition

We studied 24 spleens with extramedullary hematopoietic proliferation (EMHP), a key feature of advanced-stage Philadelphia chromosome-negative myeloproliferative neoplasms, obtained from 24 patients (14 primary myelofibrosis, 7 polycythemia vera and 3 unclassifiable). Hematoxylin and eosin, reticulin and trichrome stains, and immunohistochemical stains for myeloperoxidase, glycophorin-C, CD42b, CD34, CD117, CD8, nerve growth factor receptor and smooth muscle actin were evaluated. Clinical information was correlated with the morphological findings. Three distinct histological patterns of EMHP were recognized: diffuse (12), nodular (5), and mixed-nodular and diffuse (7). The preponderant lineage was granulocytic in diffuse, trilineage in nodular and erythroid in mixed EMHP. Erythropoiesis was largely intravascular, granulopoiesis was within the splenic cords and megakaryopoiesis was observed in both locations. The stromal changes paralleled the histological pattern with preservation of the splenic stromal and vascular architecture in the diffuse areas as opposed to areas of nodular EMHP. The morphological features of the splenic EMHP did not correlate with specific subtypes of myeloproliferative neoplasms. The mean duration of follow-up from initial diagnosis was 80 months. A total of 15 of the 24 patients died of disease: 8 of 12 (67%) with diffuse, 2 of 5 (40%) with nodular and 5 of 7 (71%) with mixed growth patterns. The mean duration from diagnosis to splenectomy was shorter in patients with diffuse (83 months) as compared with those with nodular EMHP (127 months). Our study demonstrates that splenic extramedullary hematopoietic proliferation in Philadelphia chromosome-negative myeloproliferative neoplasms shows distinct histological patterns that do not correlate with disease subtypes, but appear to suggest a trend between the histological patterns and clinical behavior. These results suggest a different biology of the disease in the nodular and diffuse extramedullary hematopoietic proliferation groups.

Stromal endothelial cells establish a bidirectional crosstalk with chronic lymphocytic leukemia cells through the TNF-related factors BAFF, APRIL, and CD40L

Chronic lymphocytic leukemia (CLL) is a clonal B cell disorder of unknown origin. Accessory signals from the microenvironment are critical for the survival, expansion, and progression of malignant B cells. We found that the CLL stroma included microvascular endothelial cells (MVECs) expressing BAFF and APRIL, two TNF family members related to the T cell-associated B cell-stimulating molecule CD40L. Constitutive release of soluble BAFF and APRIL increased upon engagement of CD40 on MVECs by CD40L aberrantly expressed on CLL cells. In addition to enhancing MVEC expression of CD40, leukemic CD40L induced cleavases that elicited intracellular processing of pro-BAFF and pro-APRIL proteins in MVECs. The resulting soluble BAFF and APRIL proteins delivered survival, activation, Ig gene remodeling, and differentiation signals by stimulating CLL cells through TACI, BAFF-R, and BCMA receptors. BAFF and APRIL further amplified CLL cell survival by upregulating the expression of leukemic CD40L. Inhibition of TACI, BCMA, and BAFF-R expression on CLL cells; abrogation of CD40 expression in MVECs; or suppression of BAFF and APRIL cleavases in MVECs reduced the survival and diversification of malignant B cells. These data indicate that BAFF, APRIL, and CD40L form a CLL-enhancing bidirectional signaling network linking neoplastic B cells with the microvascular stroma.

Composite chronic lymphocytic leukemia/small lymphocytic lymphoma and follicular lymphoma are biclonal lymphomas: a report of two cases

Composite lymphomas (CLs) consisting of 2 indolent B-cell lymphomas are rare. We present 2 CL cases composed of chronic lymphocytic leukemia (CLL) and follicular lymphoma (FL), each with unique clinicopathologic features. In the first case, the FL was negative for IGH-BCL2 and harbored a novel IGH-associated translocation; in the second case, the CL manifested in the skin. The individual components in both CLs were derived from different B-cell clones. This is the first complete characterization, including molecular analysis, of CLs composed of leukemic CLL and FL and the first report of a cutaneous CL derived from 2 low-grade B cell lymphomas. Our results provide additional supporting evidence that CLs of indolent B-cell lymphomas are biclonal and suggest that they are pathogenetically different from CLs composed of a low-grade B-cell lymphoma and an aggressive B-cell lymphoma or Hodgkin lymphoma, which are usually clonally related.

Clonal X-chromosome inactivation suggests that splenic cord capillary hemangioma is a true neoplasm and not a subtype of splenic hamartoma

Splenic hamartoma is a rare tumor-like lesion composed of structurally disorganized red pulp elements. It has been hypothesized that two other splenic lesions, cord capillary hemangioma and myoid angioendothelioma, may fall within the spectrum of splenic hamartoma, simply representing morphological variants. In this study, we compared the vascular and stromal composition of cord capillary hemangioma and myoid angioendothelioma with those of classical hamartoma. In addition, we assessed the clonal vs polyclonal nature of the lesions in nine female cases by performing clonality analysis for X-chromosome inactivation at the human androgen receptor locus (HUMARA) on laser-assisted microdissected samples. In 15 of 17 cases, increased reticulin and/or collagen content was observed. The classical hamartoma cases showed a vasculature predominantly composed of CD8+ CD31+ CD34- splenic sinuses, whereas cases of cord capillary hemangioma and myoid angioendothelioma contained many CD8- CD31+ CD34+ cord capillaries, but very little CD8+ vasculature. All cases lacked expression of D2-40 and Epstein Barr virus-encoded RNA. All cases showed a proliferation index of ≤5% by Ki-67. Cases of classical hamartoma lacked significant perisinusoidal expression of collagen IV and low-affinity nerve growth factor receptor. Both markers were variably expressed in the other lesions. Increased CD163-positive histiocytes were found in four cases (three cord capillary hemangiomas and one myoid angioendothelioma). HUMARA analysis was informative in all nine tested cases, of which three cases showed a non-random X-chromosome inactivation pattern, indicating clonality. All three clonal cases were cord capillary hemangiomas. Our study has shown that in spite of considerable morphologic heterogeneity and overlapping features, classical hamartoma and cord capillary hemangioma and myoid angioendothelioma are different in terms of their vascular and stromal composition. Clonality analysis supports a true neoplastic origin for the cord capillary hemangioma. A larger study using additional immunohistochemical and molecular studies is necessary to further evaluate the biological significance of the current findings.

Epigenetic down-regulation of the tumor suppressor gene PRDM1/Blimp-1 in diffuse large B cell lymphomas: a potential role of the microRNA let-7

PRDM1/Blimp-1, a master regulator for B cell terminal differentiation, is a putative tumor suppressor in diffuse large B cell lymphomas (DLBCL). Inactivating mutations of PRDM1 have been previously identified in a subset of nongerminal center B cell-like (GCB) DLBCL. We investigated the presence of alternative mechanisms of down-regulating PRDM1 in a cohort of 25 primary DLBCL and six DLBCL cell lines. While some DLBCL, predominantly the GCB-type, showed low levels of both PRDM1alpha mRNA and protein, presumably as a result of direct transcription repression, discordant expressions between the two were identified in a subset of DLBCL without PRDM1 mutations, the primarily non-GCB type, consistent with translational down-regulation. This subset of DLBCL exhibits relatively high PRDM1alpha mRNA levels but low levels of PRDM1. Data obtained from expression analysis, luciferase reporter assays, and transfection experiments support a role of targeting of PRDM1 by microRNA let-7 family in mediating this down-regulation. Let-7, in particular let-7b, is overexpressed in DLBCL relative to normal GCB cells, suggesting that it is deregulated. Thus, abnormal epigenetic down-regulation of PRDM1 by let-7 and other microRNAs may represent an alternative mechanism of reducing normal PRDM1 function in a subset of DLBCL with relatively high PRDM1alpha mRNA expression and unmutated PRDM1. These findings provide further evidence for an important role of impairment of terminal B cell differentiation in DLBCL pathogenesis.

Activities of SYK and PLCgamma2 predict apoptotic response of CLL cells to SRC tyrosine kinase inhibitor dasatinib

PURPOSE

B-cell receptor signaling plays an important role in the pathogenesis of chronic lymphocytic leukemia (CLL). However, blocking B-cell receptor signaling with dasatinib, an inhibitor of SRC kinase, produced variable results in preclinical and clinical studies. We aim to define the molecular mechanisms underlying the differential dasatinib sensitivity and to uncover more effective therapeutic targets in CLL.

EXPERIMENTAL DESIGN

Fresh CLL B cells were treated with dasatinib, and cell viability was followed. The CLL cases were then divided into good and poor responders. The cellular response was correlated with the activities of B-cell receptor signaling molecules, as well as with molecular and cytogenetic prognostic factors.

RESULTS

Among 50 CLL cases, dasatinib treatment reduced cell viability by 2% to 90%, with an average reduction of 47% on day 4 of culture. The drug induced CLL cell death through the intrinsic apoptotic pathway mediated by reactive oxygen species. Unexpectedly, phosphorylation of SRC family kinases was inhibited by dasatinib in good, as well as poor, responders. As opposed to SRC family kinases, activities of two downstream molecules, SYK and phospholipase Cgamma2, correlate well with the apoptotic response of CLL cells to dasatinib.

CONCLUSIONS

Thus, SYK inhibition predicts cellular response to dasatinib. SYK, together with phospholipase Cgamma2, may serve as potential biomarkers to predict dasatinib therapeutic response in patients. From the pathogenic perspective, our study suggests the existence of alternative mechanisms or pathways that activate SYK, independent of SRC kinase activities. The study further implicates that SYK might serve as a more effective therapeutic target in CLL treatment.

Transformation of chronic lymphocytic leukemia/small lymphocytic lymphoma to interdigitating dendritic cell sarcoma: evidence for transdifferentiation of the lymphoma clone

Interdigitating dendritic cell sarcoma (IDCS) is a rare tumor derived from interdigitating dendritic cells. Three cases of IDCS associated with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) have been described, but no clonal relationship between the 2 neoplasms was demonstrated. We present a detailed case analysis of a CLL/SLL with metachronous IDCS and demonstrate that these 2 neoplasms are clonally related. The IDCS and CLL cells had trisomy 12 and identical monoclonal immunoglobulin heavy chain gene rearrangements. Analysis of transcription factors with a role in myeloid differentiation demonstrated PU.1 up-regulation and C/EBPalpha down-regulation in IDCS compared with CLL. High-density array comparative genomic hybridization also identified gains in part of chromosome 16q in IDCS. Our study demonstrates for the first time clonal transformation of CLL/SLL into IDCS. This phenomenon may be triggered by alterations in lineage-determining transcription programs, which result in transdifferentiation, coupled with additional oncogenic stimuli caused by chromosomal imbalances.

Diffuse blastoid B-cell lymphoma: a histologically aggressive variant of t(14;18)-negative follicular lymphoma

Among the diffuse lymphomas of B-cell origin, we have encountered one variant displaying blastoid features that morphologically mimic lymphoblastic lymphoma, the blastoid variant of mantle cell lymphoma, and the so-called blastoid transformation of follicular lymphoma. To better characterize this entity, we studied eight cases morphologically, immunohistochemically, and by fluorescence in situ hybridization (FISH) for cytogenetic abnormalities commonly associated with follicular lymphoma and B-cell lymphomas exhibiting high-grade histological features. All eight cases were presented as de novo neoplasms, and displayed an entirely diffuse (five cases) or only minimal follicular (three cases) growth pattern. The neoplastic lymphoid cells were of medium size with round nuclei, fine chromatin, inconspicuous nucleoli, and high mitotic rate; they expressed CD10, BCL6, and BCL2-a phenotype consistent with follicle center cell origin. A proportion of cases expressed MUM1. Their lack of TdT and CYCLIN D1 distinguished them from lymphoblastic lymphoma and the blastoid mantle cell lymphoma, respectively. The neoplastic lymphoid cells consistently expressed CD43 (seven of eight cases) and occasionally other T-cell-associated antigens, including CD5, CD7, CD8, and CD57. Although all cases overexpressed BCL2, t(14;18) was not detected in any of the five cases examined by FISH; instead, extra copies of chromosome 18 were found in four of five cases. Finally, other cytogenetic abnormalities, including structural abnormalities of BCL6 (allelic loss/gain, rearrangement), monosomy 7, del(13)(q14), and MYC allelic loss, were frequently detected. The combination of a B-cell CD10+ BCL6+ BCL2+ phenotype in the presence of structural abnormalities of BCL6 is consistent with a follicular center cell derivation for our cases. The lack of t(14;18) seen in our cases, although rare in most cases of follicular lymphoma, has been nevertheless reported in cases of follicular lymphoma with a predominantly diffuse growth pattern. The molecular pathogenesis, clinical manifestations, and prognostic significance of these lesions remain to be elucidated.

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.

Outcome of deferred initial therapy in mantle-cell lymphoma

PURPOSE

Treatment of mantle-cell lymphoma (MCL) is nonstandardized, though patients are commonly treated immediately at diagnosis. Because data on observation, or "watch and wait," have not been previously reported, we analyzed the outcome of deferred initial therapy.

PATIENTS AND METHODS

Inclusion criteria in this retrospective analysis were a diagnosis of MCL between 1997 and 2007 and known date of first treatment. Hospital and research charts were reviewed for prognostic and treatment-related information. Date of death was derived from hospital records and confirmed using an online Social Security death index.

RESULTS

Of 97 patients with MCL evaluated at Weill Cornell Medical Center, 31 patients (32%) were observed for more than 3 months before initial systemic therapy, with median time to treatment for the observation group of 12 months (range, 4 to 128 months). The observation group (median follow-up, 55 months) had a median age of 58 years (range, 40 to 81 years). Prognostic factors in assessable patients included advanced stage (III/IV) in 75%, elevated lactate dehydrogenase in 25%, and intermediate- or high-risk Mantle Cell International Prognostic Index in 54%. Better performance status and lower-risk standard International Prognostic Index scores were more commonly present in those undergoing observation. Although time to treatment did not predict overall survival in a multivariate analysis, the survival profile of the observation group was statistically superior to that of the early treatment group (not reached v 64 months, P = .004).

CONCLUSION

In selected asymptomatic patients with MCL, deferred initial treatment ("watch and wait") is an acceptable management approach.

Immunophenotypic analysis of the Kaposi sarcoma herpesvirus (KSHV; HHV-8)-infected B cells in HIV+ multicentric Castleman disease (MCD)

AIMS

Kaposi sarcoma herpesvirus (KSHV) is aetiologically related to Kaposi sarcoma, classical and extracavitary primary effusion lymphoma (PEL; EC-PEL) and multicentric Castleman disease (MCD), entities preferentially occurring in HIV-infected individuals. Characterization of HIV-associated PELs/EC-PELs suggests that the KSHV-infected malignant cells originate from a pre-terminal stage of B-cell differentiation. However, only limited phenotypic studies have been performed on HIV+ MCD, including for PR domain containing 1 with zinc finger domain/B lymphocyte-induced maturation protein 1 (PRDM1/BLIMP1), a key regulator of terminal B-cell differentiation. The aim was to characterize KSHV-infected cells in 17 cases of HIV+ MCD.

METHODS AND RESULTS

Double immunohistochemistry and immunohistochemistry-in situ hybridization were used to characterize the KSHV-infected cells in MCD; the results were compared with the phenotypic profiles of 39 PELs/EC-PELs and seven PEL cell lines. Whereas the immunophenotype of KSHV-infected cells in MCD and malignant KSHV+ PEL cells was similar (PAX5, Bcl-6-; PRDM1/BLIMP1, IRF4/MUM1+; Ki67+), the MCD KSHV-infected cells differed, as they expressed OCT2, cytoplasmic lambda immunoglobulin; variably expressed CD27; lacked CD138; and were Epstein-Barr virus negative.

CONCLUSIONS

Although both PEL and MCD originate from KSHV-infected pre-terminally differentiated B cells, these findings, with previously reported genetic studies, indicate HIV+ MCD may arise from extrafollicular B cells, whereas PELs may originate from cells that have traversed the germinal centre.

Expression of the follicular lymphoma variant translocation 1 gene in diffuse large B-cell lymphoma correlates with subtype and clinical outcome

Sphingolipids serve an important role as effector molecules in signaling pathways bearing on apoptosis and cell survival. The balance between proapoptotic ceramide and prosurvival sphingosine-1-phosphate, sometimes termed the "sphingolipid rheostat," has received particular attention. Less well studied is the role of the follicular lymphoma variant translocation 1 (FVT1) gene, which was identified through its involvement in an atypical follicular lymphoma translocation and which encodes an enzyme in the synthetic pathway of ceramide. We investigated the expression of FVT1 in a variety of B-cell non-Hodgkin lymphomas and found that FVT1 is significantly underexpressed by germinal center-type diffuse large B-cell lymphoma (DLBCL) when compared with non-germinal center-type DLBCL, follicular lymphoma, and normal tonsil control samples. Increased expression of FVT1 correlated with decreased survival, suggesting that changes in the expression of FVT1 and in the concentrations of bioactive sphingolipids may be important in the pathogenesis and treatment of some types of DLBCL.

MicroRNA-mediated down-regulation of PRDM1/Blimp-1 in Hodgkin/Reed-Sternberg cells: a potential pathogenetic lesion in Hodgkin lymphomas

PRDM1/Blimp-1, a master regulator in terminal B-cell differentiation, has been recently identified as a tumor suppressor target for mutational inactivation in diffuse large B-cell lymphomas of the activated B-cell type. Our studies here demonstrate that PRDM1/blimp-1 is also a target for microRNA (miRNA)-mediated down-regulation by miR-9 and let-7a in Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma (HL). MiRNA expression profiling by direct miRNA cloning demonstrated that both of these miRNAs are among the most highly expressed in cultured HRS cells. These miRNAs functionally targeted specific binding sites in the 3' untranslated region of PRDM1/blimp-1 mRNA and repressed luciferase reporter activities through repression of translation. In addition, high levels of miR-9 and let-7a in HL cell lines correlated with low levels of PRDM1/Blimp-1. Similar to their in vitro counterparts, the majority of HRS cells in primary HL cases showed weak or no PRDM1/Blimp-1 expression. Over-expression of miR-9 or let-7a reduced PRDM1/Blimp-1 levels in U266 cells by 30% to 50%, whereas simultaneous inhibition of their activities in L428 cells resulted in an approximately 2.6-fold induction in PRDM1/Blimp-1. MiRNA-mediated down-regulation of PRDM1/Blimp-1 may contribute to the phenotype maintenance and pathogenesis of HRS cells by interfering with normal B-cell terminal differentiation, thus representing a novel molecular lesion, as well as a potential therapeutic target in HL.

Tyrosine kinase inhibition in diffuse large B-cell lymphoma: molecular basis for antitumor activity and drug resistance of dasatinib

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. Although some patients can be cured by current therapies, novel agents are needed to further improve outcomes. We hypothesized that Src tyrosine kinase inhibition by dasatinib may have antilymphoma effects. Here, we demonstrate that dasatinib inhibits cell growth through G(1)-S blockage in five of seven DLBCL cell lines at clinically achievable concentrations. Compared to resting B cells, DLBCL has increased tyrosine phosphorylation activities. As expected, dasatinib inhibits phosphorylation of several Src family kinase members. However, this inhibition occurs in all cell lines regardless of their proliferative response to the drug. In contrast, the activity of two downstream signaling molecules, Syk and phospholipase Cgamma2 (PLCgamma2), are well correlated with cell line sensitivity to dasatinib, suggesting that these molecules are crucial in mediating the proliferation of activated lymphoma cells. Furthermore, dasatinib inhibits B-cell receptor signaling in primary lymphoma cells. Together, our findings not only show dasatinib as a potentially useful therapy for DLBCL but also provide insights into the pathogenesis of the lymphoma. The results further suggest the possibility of using Syk and PLCgamma2 as biomarkers to predict dasatinib therapeutic response in prospective clinical trials.

Evaluation of JAK2 in B and T cell neoplasms: identification of JAK2(V617F) mutation of undetermined significance (JMUS) in the bone marrow of three individuals

BACKGROUND/AIMS

The JAK2(V617F) mutation, which has been found in patients with myeloproliferative disorders (MPD), has not yet been evaluated in lymphoproliferative disorders by any adequately sensitive techniques.

METHODS

We investigated whether low levels of JAK2(V617F) are present in lymphoid neoplasms using a highly sensitive and highly specific amplification refractory mutation system PCR (ARMS-PCR) assay.

RESULTS

While 234 of 237 cases did not carry the JAK2(V617F) allele, it was identified in the bone marrow of 3 B cell lymphoma patients. The mutation was found to be neither associated with the lymphomas per se, nor with any signs, symptoms or laboratory findings of MPD. Moreover, JAK2(V617F) appeared subsequently in the peripheral blood of 2 of the 3 patients.

CONCLUSION

These findings suggest that JAK2(V617F) arises in the bone marrow of individuals before clinical manifestation of any myeloid disorders. Presence of JAK2(V617F) in bone marrow might therefore increase the risk of future MPD development, just as monoclonal gammopathy of undetermined significance (MGUS) increases the risk of multiple myeloma. We term this phenomenon 'JAK2(V617F) of undetermined significance' (JMUS). Its clinical significance remains to be determined. To our knowledge, these findings represent the first identification of JAK2(V617F) in the bone marrow of patients without myeloid malignancies.

Intestinal bacteria trigger T cell-independent immunoglobulin A(2) class switching by inducing epithelial-cell secretion of the cytokine APRIL

Bacteria colonize the intestine shortly after birth and thereafter exert several beneficial functions, including induction of protective immunoglobulin A (IgA) antibodies. The distal intestine contains IgA(2), which is more resistant to bacterial proteases than is IgA(1). The mechanism by which B cells switch from IgM to IgA(2) remains unknown. We found that human intestinal epithelial cells (IECs) triggered IgA(2) class switching in B cells, including IgA(1)-expressing B cells arriving from mucosal follicles, through a CD4(+) T cell-independent pathway involving a proliferation-inducing ligand (APRIL). IECs released APRIL after sensing bacteria through Toll-like receptors (TLRs) and further increased APRIL production by activating dendritic cells via thymic stromal lymphopoietin. Our data indicate that bacteria elicit IgA(2) class switching by linking lamina propria B cells with IECs through a TLR-inducible signaling program requiring APRIL. Thus, mucosal vaccines should activate IECs to induce more effective IgA(2) responses.

Intestinal Bacteria Induce T Cell-Independent IgA2 Class Switching by Linking Epithelial Cells with Lamina Propria B Cells through APRIL (40.3)

Bacteria colonize the intestine shortly after birth and thereafter exert several beneficial functions, including induction of protective IgA antibodies. The distal intestine contains IgA2, which is more resistant to bacterial proteases than IgA1. The mechanism by which B cells undergo IgA2 class switching remains unknown. We found that human intestinal epithelial cells (IECs) triggered IgA2 class switching by activating B cells, including IgA1-expressing effector B cells, through a T cell-independent pathway involving a proliferation-inducing ligand (APRIL). IECs released APRIL after sensing whole bacteria or bacterial products, such as lipopolysaccharide or flagellin, through a Toll-like receptor (TLR)-mediated MyD88-dependent pathway. Bacteria-activated IECs further increased APRIL production by cross talking with dendritic cells via thymic stromal lymphopoietin (TSLP), an IL-7-like cytokine. Our findings indicate that bacteria and their products elicit IgA1-to-IgA2 diversification by linking lamina propria effector B cells arriving from mucosal lymphoid follicles with IECs through a TLR-inducible APRIL-dependent signaling program. Our data also suggest that vaccines should activate IECs to effectively induce protective IgA2 responses in the intestinal mucosa.

This work was supported by NIH grant AI057653 (to A.C.) and NIH T32 training grant AI07621.

HIV-1 induces targeted down-regulation of the Ig gene-diversifying enzyme AID in the germinal center of infected lymphoid follicles (45.1)

Class switching from IgM to IgG and IgA is essential for antiviral immunity and requires activation-induced cytidine deaminase (AID), an APOBEC family member with DNA-editing activity. Germinal center (GC) B cells express AID upon activation by CD4+ T cells through CD40 ligand (CD40L) and IL-4. HIV-1 is thought to impair IgG and IgA responses to viral antigens, opportunistic pathogens and vaccines by causing progressive loss of CD4+ T cells and by rendering B cells poorly responsive to CD4+ T cell help. It remains unknown whether HIV-1 targets AID to hamper protective IgG and IgA responses. We found that infected GCs contained less AID, but normal APOBEC3G, an AID-related RNA-editing protein. AID down-regulation was not associated with local loss of CD4+ T cells and CD40L, but rather correlated with decreased activation of AID-inducing transcription factors, such as NF-κB and STAT6, and with increased expression of feedback inhibitors of NF-κB and STAT6, including IκBα, SOCS1 and SOCS3. AID down-regulation also correlated with accumulation of the viral protein Nef in the GC and with trafficking of Nef within membrane channels connecting infected myeloid cells to B cells. Together with our recent in vitro studies showing that Nef penetrates B cells and inhibits class, the present in vivo data suggest that HIV-1 evades protective IgG and IgA responses by targeting the class switch recombinase machinery.