Survival signals in leukemic large granular lymphocytes

The central hypothesis of our laboratory research program in large granular lymphocyte (LGL) leukemia is that leukemic LGL represent antigen-driven cytotoxic T lymphocytes (CTL) with characteristics of dysregulated apoptosis. The clinical features of LGL leukemia highlight the association of autoimmune diseases such as rheumatoid arthritis with the T-cell form of LGL leukemia. We therefore used LGL leukemia as a model disease of dysregulated apoptosis leading to both malignant and autoimmune diseases. Here, we review our understanding of survival signals activated in leukemic LGL in the context of knowledge concerning apoptotic pathways in activated normal lymphocytes.     

CD3+ leukemic large granular lymphocytes utilize diverse T-cell receptor V beta genes

CD3+ large granular lymphocyte (LGL) leukemia is a disease of unknown etiology characterized by clonal proliferation of T cells that usually express T-cell receptor (TCR) alpha beta heterodimers. The purpose of this study was to identify the variable (V), joining (J), and diversity (D) region TCR beta-chain genes expressed by CD3+ LGL leukemic cells in an attempt to gain insights into the etiology of this disorder. Twelve patients with LGL leukemia were studied, including seven with both LGL leukemia and rheumatoid arthritis (RA). RA is also a disease of unknown etiology that occurs frequently in patients with LGL leukemia. Clonally expanded T cells that express specific TCR V beta genes have been identified in fluid and tissue specimens from the joints of patients with RA. In this study, V beta expression was determined by PCR using a panel of 22 unique V beta primers to amplify cDNA prepared from peripheral blood mononuclear cells (PBMC). A dominant V beta gene product was readily apparent in all patients. To confirm that the dominant V beta gene originated from a clonal expansion, DNA fragments corresponding to the dominant V beta genes were subcloned into plasmids and independently isolated recombinants were sequenced. V-D-J region sequences that occurred repeatedly indicated clonality. The V beta and J beta genes expressed by the leukemic cells showed a pattern of distribution that followed the frequency with which these genes are represented in the peripheral blood. The residues corresponding to the third complementarity-determining region of the TCR beta chain were different in all cases. A specific pattern of VDJ usage was not identified for those patients with both LGL leukemia and RA; however, utilization of V beta-6 by LGL clones (N = 3) was observed only in the setting of RA. These data suggest that leukemic CD3+ LGL cells have been clonally transformed in a random fashion with respect to the TCR beta chain.     

CD100/Plexin-B1 interactions sustain proliferation and survival of normal and leukemic CD5+ B lymphocytes

Growth and survival of chronic B-cell tumors are favored by the malignant cell's capacity to respond to selected microenvironmental stimuli provided by nontumoral bystander cells. To investigate which mechanisms operate in these crosstalks and whether they are malignancy-related or reproduce the mechanisms used by normal B cells we have studied the expression and functional role of semaphorin CD100 (now called Sema4D) in chronic lymphocytic leukemia (CLL) cells and normal CD5+ B cells. We demonstrate here that (1) leukemic and normal CD5+ B lymphocytes uniformly express CD100; (2) the CD100 high-affinity receptor Plexin-B1 is expressed by bone marrow stromal cells, follicular dendritic cells, and activated T lymphocytes, and is thus available to CD100+ lymphocytes in different specific microenvironments; and (3) upon interaction between CD100 and Plexin-B1 both CLL and normal CD5+ B cells increase their proliferative activity and extend their life span. These findings establish that Plexin-B1 is an easily accessible receptor for CD100 within the immune system. The encounter of CD100+ leukemic cells with Plexin-B1 may promote the proliferation and survival of malignant cells. The crosstalk operated by the CD100/Plexin-B1 interaction is not malignancy related but reproduces a mechanism used by normal CD5+ B cells.     

Activation via the CD3 and CD16 pathway mediates interleukin-2-dependent autocrine proliferation of granular lymphocytes in patients with granular lymphocyte proliferative disorders.

Granular lymphocytes (GLs) in patients with GL-proliferative disorders (GLPDs) are known to express the interleukin-2 receptor (IL-2R) beta chain (p70-75) constitutively and to proliferate in response to stimulation with IL-2 via the beta chain. In this report, we found that the anti-CD3 monoclonal antibody (MoAb) OKT3 could induce the proliferation of GLs from patients with T-cell lineage GLPDs (T-cell receptor-alpha beta+/CD3+16+), but not that of natural killer (NK) cell lineage GLs (T-cell receptor-alpha beta-/CD3-16+). In contrast, the anti-CD16 MoAb 3G8 that reacts with NK-lineage GLs could induce the proliferation of these GLs but not that of GLs with a T-cell phenotype. Furthermore, the anti-CD16 MoAbs CLB FcR gran1 (VD2) and OK-NK, which react with both T- and NK-lineage GLs, induced the proliferation of GLs with both T- and and NK-cell phenotypes. The proliferative response induced via the CD3 or IgG Fc receptor III (Fc gamma RIII: CD16) pathway was shown to be associated with the IL-2-dependent autocrine pathway by various findings, including the induction of endogenous IL-2 production, the coexpression of the IL-2R alpha chain (p55) and the IL-2R beta chain, and the inhibition of GL proliferation by anti-IL-2 or anti-IL-2R MoAb. These results suggest that GL proliferation is mediated at least partly through the IL-2-dependent autocrine pathway, and that the TCR/CD3 complex in T-cell phenotype GLs and the Fc gamma RIII in both T- and NK-cell phenotype GLs play a role in their activation in GLPDs.     

Monoclonal proliferation of CD4+ large granular lymphocytes with cytolytic activity

Summary. A rare case of monoclonal proliferation of CD3⁺4⁺8∼ T-cell receptor-αβ⁺ large granular lymphocytes (LGL) is presented. CD4⁺ LGL in the present case showed spontaneous cytotoxicity against herpes simplex virus-infected cells and antibody- and lectin-dependent cytotoxicity. Perforin, which is one of the important cytolytic mediators of cytotoxic T cells (CTL) and natural killer cells, was abundantly expressed in CD4⁺ LGL of this case. The present case suggests that perforin-positive CD4⁺ CTL, which have recently been shown in the in vitro studies, certainly exist in vivo.     

Activation of human T lymphocytes: differential effects of CD3- and CD8-mediated signals.

T cells are activated physiologically by triggering the T-cell receptor-CD3 complex. There is evidence that invariant accessory molecules on the T-cell membrane (CD8 and CD4) are involved in the major histocompatibility complex-restricted recognition process. Moreover, binding and crosslinking of these accessory molecules to the T-cell receptor-CD3 complex exerts a positive synergistic signal, as has been shown by stimulation with crosslinked antibodies. Here we demonstrate that stimulation mediated by immobilized anti-CD3/CD8 antibodies differs from stimulation mediated solely by anti-CD3. Whereas interleukin 2 receptor expression and interferon gamma production are seen to a similar extent in both cases, a second signal provided by the additional involvement of CD8 seems to be essential for interleukin 2 production and full interleukin 2 responsiveness in CD8+ T cells. This second signal is much more sensitive to inhibition by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C and cGMP/cAMP-dependent kinases. Our results also show that substantial modulation of the T-cell receptor complex and most likely CD3 phosphorylation are not essential for initiating the activation of resting T cells. Instead, we found a 22- to 24-kDa phosphoprotein whose strong phosphorylation correlated reliably with T-cell activation.     

Clonal proliferation of large granular lymphocytes in rheumatoid arthritis

Some patients with chronically elevated large granular lymphocyte (LGL) numbers have rheumatoid arthritis (RA). Since these patients also may have neutropenia and splenomegaly, their symptoms resemble those of patients diagnosed as having Felty's syndrome (FS). We studied the immunophenotypic and genotypic characteristics of mononuclear cells from patients with RA and neutropenia to better determine the extent of heterogeneity in this condition. Four patients had markedly increased numbers of LGLs, which expressed HNK-1 antigen and IgG Fc receptors. In contrast, the remaining 8 patients, who had FS, had normal LGL counts, and surface marker studies showed normal numbers of HNK-1 and IgG Fc receptor positive cells. Clonal rearrangement of the T cell receptor beta chain gene was demonstrated in all 4 patients with excess LGLs, whereas a germline configuration of this gene was present in all 6 FS patients in whom this was studied. These results suggest that there are diverse groups among patients with RA and neutropenia. Since prognosis may differ, it is important to recognize that some patients who are considered to have Felty's syndrome may have a clonal proliferation of LGLs.     

Phosphatidylinositol-3-phosphate kinase pathway activation protects leukemic large granular lymphocytes from undergoing homeostatic apoptosis

T-cell large granular lymphocytic leukemia (T-LGL) is characterized by chronic clonal lymphoproliferation of cytotoxic T lymphocytes (CTLs). Despite exhibiting phenotypic properties of antigen-activated cells, including expression of Fas and FasL, T-LGL cells accumulate and demonstrate resistance to apoptosis. We propose that increased activity of a prosurvival signaling pathway in T-LGL is responsible for attenuated apoptosis in T-LGL. Given the importance of the phosphatidylinositol-3 kinase (PI3K)-AKT pathway in regulating the balance between survival and apoptosis, we analyzed AKT activity in T-LGL cells. Compared with resting CTLs from healthy donors, patients' T-LGL cells showed higher levels of phosphorylated AKT. We demonstrate that phospho-AKT induction is dependent on the upstream activity of a Src family kinase. Since the PI3K-AKT pathway can antagonize the ability of Fas to initiate apoptosis, we hypothesized that inhibition of PI3K would lead to reacquisition of Fas sensitivity in T-LGL. Inhibition of the PI3K-AKT pathway alone led to brisk spontaneous apoptosis of T-LGL. These results suggest that T-LGL pathogenesis is dependent on activity of the PI3K-AKT pathway, without which the leukemic cells will begin to undergo spontaneous apoptosis. We propose that novel therapeutics inhibiting the PI3K-AKT axis may provide effective treatment for T-LGL.     

A CD4+ proliferation of large granular lymphocytes expresses the protease activated receptor-1

The platelet-type thrombin receptor was the first member to be identified in a family of protease activated receptors (PARs) and has been designated PAR-1. We recently reported that the large granular lymphocytes (LGLs) in patients with proliferations of CD8⁺ cells co-expressed PAR-1 and the expression of PAR-1 correlated with the expression of CD57. Here we show, by three-colour immunofluorescence, that the LGLs from a patient with a rare CD4⁺ CD57⁺ monoclonal expansion also expressed PAR-1. Northern blot analysis confirmed the presence of high levels of mRNA for PAR-1 in these LGLs.     

Transient monoclonal expansion of CD8+/CD57+ T-cell large granular lymphocytes after primary cytomegalovirus infection

Lymphocytosis associated with viral infection is generally polyclonal or oligoclonal. In this article, we describe a case of transient monoclonal CD8+/CD57+ T-cell lymphocytosis with large granular lymphocyte (LGL) morphology occurring after primary CMV infection and review cases of virus-associated monoclonal CD8+ T-cell expansions reported in the literature. Several clinical features shared by virus-associated monoclonal CD8+ T-cell expansions suggest the reactive nature of the lymphocytosis. Based on this, our case report and those reported in the literature support the notion that T-cell receptor clonality per se is not necessarily indicative of malignancy. These observations further corroborate the need for a close follow-up before assigning the diagnosis of LGL leukemia to individuals developing monoclonal CD8+ T-cell expansions.     

Chromosomal abnormalities define clonal proliferation in CD3- large granular lymphocyte leukemia

Six patients with lymphoproliferative disorder of large granular lymphocytes (LDGL) were studied for chromosomal abnormalities. When the patients were divided into two groups depending on the expression of a mature antigen of T cell lineage, CD3, two with CD3+ phenotype had a stable disease, whereas three of the four patients with CD3- phenotype had marked hepatosplenomegaly and a highly aggressive disease. Chromosomal abnormalities were detected in four of six patients, indicating a clonal proliferation of large granular lymphocytes in individual patients. In particular, chromosomal abnormalities were found in three of the four patients with CD3- LDGL, all of which had a germ-line configuration of the T cell receptor beta-chain gene. Thus, the chromosomal abnormalities provide definitive evidence for the clonal origin of the expanded cells in the CD3- LDGL.     

Multiple autoimmune haemopoietic disorders and insidious clonal proliferation of large granular lymphocytes

We report a patient with clonal proliferation of CD3+8+TCRalphabeta+ large granular lymphocytes (LGL) presenting multiple episodes of autoimmune cytopenia, including autoimmune neutropenia, idiopathic thrombocytopenic purpura, autoimmune haemolytic anaemia, and pure red cell aplasia. Each disorder appeared separately or as a combination during an 11-year clinical course. The increase of blood CD3+8+TCRalphabeta+ LGL was detected 6 years after the initial diagnosis of cytopenia, but the absolute number of LGL cells was always < 1.0 x 109/l. LGL cells were of monoclonal origin and had a chromosomal abnormality. LGL cells transiently responded to cyclosporine A therapy, which was also effective on all of these autoimmune cytopenias. Accordingly, an undetectable level of proliferation of a clonal LGL population could cause various autoimmune haemopoietic disorders.     

Pure red cell aplasia associated with expansion of CD3+ CD8+ granular lymphocytes expressing cytotoxicity against HLA-E+ cells

T-cell granular lymphocyte-proliferative disorder (T-GLPD) is characterized by the proliferation of cytotoxic T lymphocytes, and is often associated with pure red cell aplasia (PRCA). The mechanism involved in the development of PRCA in T-GLPD is unknown. Peripheral blood mononuclear cells were isolated from 20 patients with T-GLPD. Ten patients had associated PRCA. Granular lymphocytes (GLs) of T-GLPD are positive for CD94, but not NKG2A. To clarify the functional role of CD94 in T-GLPD, we performed a cytotoxicity assay against the trophoblast cell line, BeWo, which is known to express human leucocyte antigen (HLA)-E, a natural ligand of CD94, and is deficient in other HLA class I and class II antigens. GLs isolated from T-GLPD with PRCA patients killed BeWo cells more significantly than GLs from T-GLPD without PRCA patients. Furthermore, GLs from T-GLPD with PRCA were significantly stimulated by a monoclonal antibody against CD94, whereas those of T-GLPD without PRCA were not. Taken together, HLA-E, a ligand of CD94, was suggested to stimulate CD94+ cells to kill HLA-E+ cells in T-GLPD with PRCA. GLs of T-GLPD with PRCA have a potential positive activity against HLA-E+ cells, whereas GLs from T-GLPD without PRCA do not. CD94 may play a key role in the pathogenesis of PRCA in T-GLPD.     

Differential dependence of CD4+CD25+ regulatory and natural killer-like T cells on signals leading to NF-kappaB activation

Natural killer-like (NK) T, regulatory T (TR), and memory type T cells display surface phenotypes reminiscent of activated T cells. Previously, we reported that the generation of TR cells and, to a lesser extent, of memory type T cells, depends on IkappaB kinase 2. Here, we show that T cell-specific ablation of IkappaB kinase 2, in addition, completely precludes NKT cell development. T cell antigen receptor (TCR)-induced signals to activate NF-kappaB are essential for mature T cell activation, leading us to hypothesize that this pathway could play an important role in the generation of the antigen-driven T cell subsets comprising TR, memory type T, and NKT cells. TCR-mediated NF-kappaB activation critically depends on Bcl10 and PKCtheta. By using mice deficient for these proteins, we demonstrate that the generation of TR and, to a lesser extent, of memory type T cells, depends on Bcl10 and PKCtheta, and therefore, most likely on NF-kappaB activation initiated by TCR engagement. NKT cells, on the other hand, require PKCtheta for thymic development, whereas absence of Bcl10 leads primarily to the reduction of peripheral NKT cell numbers.     

TCR1+ large granular lymphocyte proliferation in rheumatoid arthritis

The T-lymphoproliferative syndrome is characterized by a proliferation of large granular lymphocytes (LGL). It is often associated with neutropenia, and in 30% of cases with rheumatoid arthritis (RA). Phenotypic analysis has demonstrated that in most cases of RA with T-proliferative disease, the LGL represent T cells with a clonal rearrangement of the / T cell receptor (TCR2). Here, three patients with / TCR1⁺ LGL proliferation suffering from long-standing arthritis and neutropenia are described. The first patient with RA showed an expansion of a heterogeneous CD2⁺ CD16⁺ CD56^- LGL population, of which 30% coexpressed TCR1 with V1 rearrangement. The second patient with ankylosing spondylitis and RA was suffering from proliferation of TCR1⁺ (V9^-, V1^-), CD2⁺ CD16^- CD56^- LGL with low coexpression of CD8. The third patient with RA was suffering from a proliferation of TCR1⁺ (V1⁺, V9^-) CD4^- CE8^- CD16^- CD56^- lymphocytes. On the basis of these unusual findings, the pathogenetic role of TCR1⁺ T cells in RA is discussed.     

Osmotic behavior of normal and leukemic lymphocytes

The response of normal human peripheral blood lymphocytes to a hypotonic environment may be divided into two phases: the cells first exhibit rapid osmotic swelling, followed by a slower shrinking phase, during which they regain their initial physiologic volume. This osmotic behavior is characteristic of most mammalian and avian nucleated cells so far examined. The normal human blood lymphocyte, however, shows the most rapid recovery phase (5 min). Lymphocytes from chronic lymphatic leukemia patients, in comparison, show a strikingly slower rate of return to their initial isotonic volumes. The mechanism underlying osmotic cell volume regulation and its significance are discussed.