Aliakbar Shahsafaei

Programmed Death-1 (PD-1) is a Marker of Germinal Center-associated T Cells and Angioimmunoblastic T-Cell Lymphoma

Programmed death-1 (PD-1), a member of the CD28 costimulatory receptor family, is expressed by germinal center-associated T cells in reactive lymphoid tissue. In a study of a wide range of lymphoproliferative disorders, neoplastic T cells in 23 cases of angioimmunoblastic lymphoma were immunoreactive for PD-1, but other subtypes of T cell and B cell non-Hodgkin lymphoma, as well as classic Hodgkin lymphoma, did not express PD-1. The pattern of PD-1 immunostaining of neoplastic cells in angioimmunoblastic lymphoma was similar to that reported for CD10, a recently described marker of neoplastic T cells in angioimmunoblastic lymphoma. Tumor-associated follicular dendritic cells in cases of angioimmunoblastic lymphoma were found to express PD-L1, the PD-1 ligand. In addition, PD-1-positive reactive T cells formed rosettes around neoplastic L&H cells in 14 cases of nodular lymphocyte predominant Hodgkin lymphoma studied. These findings, along with data from previous studies, suggest that angioimmunoblastic lymphoma is a neoplasm of germinal center-associated T cells and that there is an association of germinal center-associated T cells and neoplastic cells in nodular lymphocyte predominant Hodgkin lymphoma. PD-1 is a useful new marker for angioimmunoblastic lymphoma and lends further support to a model of T-cell lymphomagenesis in which specific subtypes of T cells may undergo neoplastic transformation and result in specific, distinct histologic, immunophenotypic, and clinical subtypes of T-cell neoplasia.

Complement Regulator CD59 Protects Against Atherosclerosis by Restricting the Formation of Complement Membrane Attack Complex

Complement is a central effector system within the immune system and is implicated in a range of inflammatory disorders. CD59 is a key regulator of complement membrane attack complex (MAC) assembly. The atherogenic role of terminal complement has long been suspected but is still unclear. Here, we demonstrate that among mice deficient in apolipoprotein (Apo)E, the additional loss of murine CD59 (mCd59ab−/−/ApoE−/−) accelerated advanced atherosclerosis featuring occlusive coronary atherosclerosis, vulnerable plaque, and premature death and that these effect could be attenuated by overexpression of human CD59 in the endothelium. Complement inhibition using a neutralizing anti-mouse C5 antibody attenuated atherosclerosis in mCd59ab−/−/ApoE−/− mice. Furthermore, MAC mediated endothelial damage and promoted foam cell formation. These combined results highlight the atherogenic role of MAC and the atheroprotective role of CD59 and suggest that inhibition of MAC formation may provide a therapeutic approach for the treatment of atherosclerosis.

Germinal-Center T-Helper-Cell Markers PD-1 and CXCL13 Are Both Expressed by Neoplastic Cells in Angioimmunoblastic T-Cell Lymphoma

Gene expression profiling identified genes uniquely expressed by human germinal-center T-helper (GCTh) cells, including programmed death-1 (PD-1) and CXCL13. Recently, we demonstrated that PD-1 is an immunophenotypic marker of GCTh cells and angioimmunoblastic T-cell lymphoma (AITL). The goal of this study was to investigate the expression pattern of CXCL13 in comparison with PD-1. We studied 63 cases of T-cell lymphoproliferative disorders, including 22 cases of AITL. In cases of AITL, PD-1+ and CXCL13+ neoplastic cells were seen at foci of expanded CD21+ follicular dendritic cell networks. CXCL13 expression was limited in other peripheral T-cell lymphomas. PD-1 and CXCL13 identified germinal-center T-helper cells, showed a similar pattern of expression in AITL, and should serve as useful new markers for AITL. The similar pattern of expression of CXCL13 and PD-1 in AITL provides further evidence that AITL is a neoplasm derived from germinal-center T-helper cells.

Characteristic proliferations of reticular and dendritic cells in angioimmunoblastic lymphoma.

Angioimmunoblastic lymphoma (AIL) is a T-cell proliferation with a distinct clinical presentation that often poses a difficult diagnostic challenge. Angioimmunoblastic lymphoma is characterized by prominent vascular and stromal proliferations. Using a panel of antibodies, we investigated the nature of the stromal component in 15 cases of AIL as compared with 40 cases of nodal-based peripheral T-cell lymphoma (PTCL) of other types. As has been previously noted, extrafollicular proliferations of follicular dendritic cells (detected by CD21 and low molecular-weight nerve growth factor receptor staining) were highly associated with AIL and were only rarely seen in other lesions. Unexpectedly, large networks of desmin-positive reticulum cells also were noted in all cases of AIL evaluated. These cells with characteristic long cytoplasmic processes were present in much smaller numbers or only rarely in other types of peripheral T-cell lymphoma. This population of nodal stromal cells, a subset of the fibroblastic reticulum cells detected by vimentin immunostaining, may be responsible for the prominent reticulum deposition seen in AIL. No association of AIL with proliferations of other types of reticulum cells (e.g., interdigitating dendritic cells or histiocytes) was noted. These findings suggest that networks of follicular dendritic and desmin-positive reticulum cells are useful diagnostic features in angioimmunoblastic lymphoma and probably are related to the pathogenesis of this entity.

T-bet, a T-Cell–Associated Transcription Factor, Is Expressed in a Subset of B-Cell Lymphoproliferative Disorders

T-bet, a T-box transcription factor, is expressed in CD4+ T lymphocytes committed to Th1 T-cell development and in a subset of T-cell non-Hodgkin lymphomas. Recent evidence indicates that T-bet also is expressed in B lymphocytes and might participate in immunoglobulin class switching. We examined T-bet expression in 116 cases of B-cell lymphoproliferative disorders by immunostaining and found that T-bet was expressed consistently in precursor B-cell lymphoblastic leukemia/lymphoblastic lymphoma (14/14 cases) in contrast with precursor T-cell lymphoblastic leukemia/lymphoblastic lymphoma, which is consistently T-bet- (13 cases), as previously reported. T-bet is expressed in memory B cell-derived neoplasms (chronic lymphocytic leukemia, marginal zone lymphoma, hairy cell leukemia; 35/42 cases) but not in cases of mantle cell, follicular, and large cell lymphoma (43 cases). Expression of T-bet in precursor B-cell lymphoblastic leukemia/lymphoblastic lymphoma was confirmed by Western blot analysis. The expression of T-bet in a significant subset of B-cell lymphoproliferative disorders but not in the vast majority of reactive B cells suggests it might have a role in the oncogenesis of T-bet+ B-cell neoplasms. In addition, T-bet should serve as a useful new marker for the diagnosis and subtyping of B-cell lymphoproliferative disorders.

CD200 (OX-2 membrane glycoprotein) expression in b cell-derived neoplasms.

We studied the expression of CD200, an immunoglobulin superfamily membrane glycoprotein, in a wide range of B cell-derived neoplasms by immunohistochemical staining of paraffin-embedded tissue sections. In addition to chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL), CD200 is expressed in other B-cell lymphoproliferative disorders, including hairy cell leukemia. In addition, neoplastic cells in classical Hodgkin lymphoma are immunoreactive for CD200. CD200 was previously reported to be expressed in acute myeloid leukemia, and we find that it is also expressed in B-lymphoblastic leukemia/lymphoma. We conclude that CD200 may be a useful immunophenotypic marker in the evaluation of B cell-derived neoplasms. Furthermore, since an anti-CD200 immunotherapeutic agent is in clinical trials, a number of B cell-derived neoplasms in addition to CLL/SLL may be suitable therapeutic targets.

Genomic structure, functional comparison, and tissue distribution of mouse Cd59a and Cd59b.

CD59 is a crucial complement regulatory protein that inhibits the terminal step of the complement activation cascade by interfering with the binding of C9 to C5b-8, thus preventing the formation of the membrane attack complex (MAC). We recently reported that the mouse genome contains two Cd59 genes, while the human and rat genomes each contain only one Cd59 gene (Qian et al. 2000). Here, we describe the genomic structure, comparative activity, and tissue distribution of these two mouse genes, designated Cd59a and Cd59b. The mouse Cd59 genes encompass a total of 45.6 kb with each gene having four exons. Cd59a spans 19 kb, and Cd59b spans 15 kb, with approximately 11.6 kb of genomic DNA separating the two genes. The overall sequence similarity between Cd59a and Cd59b is approximately 60%. The sequence similarity between exon 2, exon 3, and exon 4 and the respective flanking regions between the two genes is over 85%, but exon 1 and its flanking regions are totally different. Comparative studies of the activity of both genes as inhibitors of MAC formation revealed that Cd59b has a specific activity that is six times higher than that of Cd59a. Using polyclonal antibodies specific to either Cd59a or Cd59b, we showed that Cd59a and Cd59b are both widely expressed in the kidneys, brain, lungs, spleen, and testis, as well as in the blood vessels of most mouse tissues. Interestingly, testicular Cd59a appeared to be expressed exclusively in spermatids, whereas Cd59b was expressed in more mature sperm cells. These results suggest that even though Cd59a and Cd59b are expressed in multiple tissues, they may play some different roles, particularly in reproduction.

Subsets of Human Origin Recognition Complex (ORC) Subunits Are Expressed in Non-proliferating Cells and Associate with Non-ORC Proteins

The origin recognition complex (ORC) in yeast is a complex of six tightly associated subunits essential for the initiation of DNA replication. Human ORC subunits are nuclear in proliferating cells and in proliferative tissues like the testis, consistent with a role of human ORC in DNA replication. Orc2, Orc3, and Orc5 also are detected in non-proliferating cells like cardiac myocytes, adrenal cortical cells, and neurons, suggesting an additional role of these proteins in non-proliferating cells. Although Orc2–5 co-immunoprecipitate with each other under mild extraction conditions, a holo complex of the subunits is difficult to detect. When extracted under more stringent extraction conditions, several of the subunits co-immunoprecipitate with stoichiometric amounts of other unidentified proteins but not with any of the known ORC subunits. The variation in abundance of individual ORC subunits (relative to each other) in several tissues, expression of some subunits in non-proliferating tissues, and the absence of a stoichiometric complex of all the subunits in cell extracts indicate that subunits of human ORC in somatic cells might have activities independent of their role as a six subunit complex involved in replication initiation. Finally, all ORC subunits remain consistently nuclear, and Orc2 is consistently phosphorylated through all stages of the cell cycle, whereas Orc1 is selectively phosphorylated in mitosis.

Loss of Expression of the WNT/β-Catenin-Signaling Pathway Transcription Factors Lymphoid Enhancer Factor-1 (LEF-1) and T Cell Factor-1 (TCF-1) in a Subset of Peripheral T Cell Lymphomas

T cell factor-1 (TCF-1) and lymphoid enhancer factor-1 (LEF-1), members of the TCF/LEF family of transcription factors, play a significant role in T cell development and are expressed in thymocytes and peripheral CD3+ T cells. Previously, precursor T lymphoblastic leukemia/lymphoblastic lymphoma (T-ALL/LyL) was found to express TCF-1, and we find that 9 of 10 cases of T-ALL/LyL express LEF-1 as well as TCF-1, exhibiting uniform nuclear immunostaining for both transcription factors. In addition, a significant subset of cases of peripheral T cell lymphoma (PTCL), 39 of 81 cases (48%), are immunoreactive for LEF-1 and/or TCF-1, with 36 of 38 cases immunoreactive for both, indicating that these transcription factors are coordinately expressed in PTCL. The vast majority of LEF-1+ and/or TCF-1+ PTCL (34 of 39 or 87%) exhibit a composite Th1 T-cell-like immunophenotype, based on expression of Th1 T cell-associated, but not Th2 T cell-associated, chemokine receptors and activation markers. Of the Th1-like PTCL studied, 33 of 42 (79%) were immunoreactive for LEF-1 and 32 of 42 (76%) were immunoreactive for TCF-1, including most cases of angioimmunoblastic lymphoma and all cases of lymphoepithelioid lymphoma. Surprisingly, none of the 21 cases of Th2-like PTCL studied, all cases of anaplastic large cell lymphoma, were immunoreactive for LEF-1 or TCF-1 (P < 0.0001), suggesting that LEF-1 and TCF-1 transcription factor expression may be lost in Th2 T cells or Th2-like PTCL. LEF-1 and TCF-1 immunostaining can serve to identify specific subtypes of PTCL, and lends support to a bipartite model of PTCL development, based on expression of activation markers.

Characteristic expression patterns of TCL1, CD38, and CD44 identify aggressive lymphomas harboring a MYC translocation.

The distinction between Burkitt (BL) or atypical Burkitt/Burkitt-like lymphomas harboring a MYC translocation (MYC+) and diffuse large B-cell lymphomas (DLBCLs) with high proliferation fractions but without a MYC translocation (MYC−) can be difficult using standard morphologic and immunohistochemical criteria. Recently, unique gene expression profiles differentiating BL and DLBCL were reported and include higher transcript levels of T-cell leukemia-1 (TCL1) and CD38 and lower transcript levels of CD44 in MYC+ BL relative to MYC− DLBCL. We examined a cohort of 67 cytogenetically defined aggressive lymphomas using immunohistochemical techniques for expression of TCL1, CD38, and CD44 and found distinct expression patterns between MYC+ and MYC− tumors. Furthermore, these markers are better predictors of MYC status than combined staining for CD10 and BCL2. Thus staining for TCL1, CD38, and CD44 are useful ancillary tests to identify B-cell tumors for which confirmatory cytogenetic and/or fluorescent in situ hybridization studies assessing the status of the MYC locus should be pursued.