IL-2-dependent ATL cell lines with phenotypes differing from the original leukemia cells

A frequent PLCγ1 mutation in adult T-cell leukemia/lymphoma determines functional properties of the malignant cells

BACKGROUND

Development of adult T-cell leukemia/lymphoma (ATL) involves human T-cell leukemia virus type 1 (HTLV-1) infection and accumulation of somatic mutations. The most frequently mutated gene in ATL (36 % of cases) is phospholipase C gamma1 (PLCG1). PLCG1 is also frequently mutated in other T-cell lymphomas. However, the functional consequences of the PLCG1 mutations in cancer cells have not been characterized.

METHODS

We compared the activity of the wild-type PLCγ1 with that of a mutant carrying a hot-spot mutation of PLCγ1 (S345F) observed in ATL, both in cells and in cell-free assays. To analyse the impact of the mutation on cellular properties, we quantified cellular proliferation, aggregation, chemotaxis and apoptosis by live cell-imaging in an S345F+ ATL-derived cell line (KK1) and a KK1 cell line in which we reverted the mutation to the wild-type sequence using CRISPR/Cas9 and homology-directed repair.

FINDINGS

The PLCγ1 S345F mutation results in an increase of basal PLC activity in vitro and in different cell types. This higher basal activity is further enhanced by upstream signalling. Reversion of the S345F mutation in the KK1 cell line resulted in reduction of the PLC activity, lower rates of proliferation and aggregation, and a marked reduction in chemotaxis towards CCL22. The PLCγ1-pathway inhibitors ibrutinib and ritonavir reduced both the PLC activity and the tested functions of KK1 cells.

INTERPRETATION

Consistent with observations from clinical studies, our data provide direct evidence that activated variants of the PLCγ1 enzyme contribute to the properties of the malignant T-cell clone in ATL.

FUNDING

MRC (UK) Project Grant (P028160).

Acute type adult T-cell leukemia cells proliferate in the lymph nodes rather than in peripheral blood

A massive increase in the number of mature CD4⁺ T-cells in peripheral blood (PB) is a defining characteristic of acute type of adult T-cell leukemia (ATL). To date, the site of proliferation of ATL cells in the body has been unclear. In an attempt to address this question, we examined the expression of the proliferation marker, Ki-67, in freshly isolated ATL cells from PB and lymph nodes (LNs) of patients with various types of ATL. Our findings reveal that LN-ATL cells display higher expression of the Ki-67 antigen than PB-ATL cells in acute type patients. The gene expression of T-cell quiescence regulators such as Krüppel-like factor 2/6 and forkhead box protein 1 was substantially high in acute type PB-ATL cells. The expression of human telomerase reverse transcriptase, which is involved in T-cell expansion, was significantly low in PB-ATL cells from acute type patients, similar to that in normal resting T-cells. These findings suggest that ATL cells proliferate in the LNs rather than in PB.

WRN-targeted therapy using inhibitors NSC 19630 and NSC 617145 induce apoptosis in HTLV-1-transformed adult T-cell leukemia cells

Background

Human T-cell leukemia virus type 1 (HTLV-1) infection is associated with adult T-cell leukemia/lymphoma (ATLL), a lymphoproliferative malignancy with a dismal prognosis and limited therapeutic options. Recent evidence shows that HTLV-1-transformed cells present defects in both DNA replication and DNA repair, suggesting that these cells might be particularly sensitive to treatment with a small helicase inhibitor. Because the “Werner syndrome ATP-dependent helicase” encoded by the WRN gene plays important roles in both cellular proliferation and DNA repair, we hypothesized that inhibition of WRN activity could be used as a new strategy to target ATLL cells.

Methods

Our analysis demonstrates an apoptotic effect induced by the WRN helicase inhibitor in HTLV-1-transformed cells in vitro and ATL-derived cell lines. Inhibition of cellular proliferation and induction of apoptosis were demonstrated with cell cycle analysis, XTT proliferation assay, clonogenic assay, annexin V staining, and measurement of mitochondrial transmembrane potential.

Results

Targeted inhibition of the WRN helicase induced cell cycle arrest and apoptosis in HTLV-1-transformed leukemia cells. Treatment with NSC 19630 (WRN inhibitor) induces S-phase cell cycle arrest, disruption of the mitochondrial membrane potential, and decreased expression of anti-apoptotic factor Bcl-2. These events were associated with activation of caspase-3-dependent apoptosis in ATL cells. We identified some ATL cells, ATL-55T and LMY1, less sensitive to NSC 19630 but sensitive to another WRN inhibitor, NSC 617145.

Conclusions

WRN is essential for survival of ATL cells. Our studies suggest that targeting the WRN helicase with small inhibitors is a novel promising strategy to target HTLV-1-transformed ATL cells.

Downregulation of proapoptotic Bim augments IL-2-independent T-cell transformation by human T-cell leukemia virus type-1 Tax

Human T-cell leukemia virus type 1 (HTLV-1), an etiological agent of adult T-cell leukemia, immortalizes and transforms primary human T cells in vitro in both an interleukin (IL)-2-dependent and IL-2-independent manner. Expression of the HTLV-1 oncoprotein Tax transforms the growth of the mouse T-cell line CTLL-2 from being IL-2-dependent to IL-2-independent. Withdrawal of IL-2 from normal activated T cells induces apoptosis, which is mediated through the inducible expression of several proapoptotic proteins, including Bim. In this study, we found that Tax protects IL-2-depleted T cells against Bim-induced apoptosis. Withdrawal of IL-2 from CTLL-2 cells induced a prominent increase in the level of Bim protein in CTLL-2 cells, but not in Tax-transformed CTLL-2 cells. This inhibition of Bim in Tax-transformed CTLL-2 cells was mediated by two mechanisms: downregulation of Bim mRNA and posttranscriptional reduction of Bim protein. Transient expression of Tax in CTLL-2 cells also inhibited IL-2 depletion–induced expression of Bim, however, this decrease in Bim protein expression was not due to downregulation of Bim mRNA, thus indicating that Bim mRNA downregulation in Tax-transformed CTLL-2 occurs only after long-term expression of Tax. Transient expression of Tax in CTLL-2 cells also induced Erk activation, however, this was not involved in the reduction of Bim protein. Knockdown of Bim expression in CTLL-2 cells augmented Tax-induced IL-2-independent transformation. HTLV-1 infection of human T cells also reduced their levels of Bim protein, and restoring Bim expression in HTLV-1-infected cells reduced their proliferation by inducing apoptosis. Taken together, these results indicate that Tax-induced downregulation of Bim in HTLV-1-infected T cells promotes their IL-2-independent growth, thereby supporting the persistence of HTLV-1 infection in vivo.

Long-term stimulation of trout head kidney cells with the cytokines MCSF, IL-2 and IL-6: gene expression dynamics

The production of salmonid leukocyte cell lines from primary cell cultures has been attempted on several occasions, however, to date only monocyte/macrophage like cell lines exist (e.g. RTS-11 and SHK-1 cells). With the increasing number of cytokines discovered in fish in recent years, many of which are growth factors for leukocytes, we now have the possibility of using these molecules to promote leukocyte development and differentiation in culture. We have generated stable cell lines transfected with a variety of plasmids expressing cytokines (Interleukin (IL)-2, IL-6 and Macrophage Colony Stimulating Factor (MCSF)), in order to produce conditioned media rich in these cytokines. The cytokine-conditioned media were used to assess their activity and ability to support the growth of primary head kidney (HK) leukocyte cultures. Here, we describe a series of experiments aimed to determine which cell population(s) of primary HK cultures is supported and will grow in conditioned media containing MCSF, IL-2 or IL-6. For a period of 5 weeks, cells were incubated at 22°C and media were changed every 3-4 days. Samples were taken at different time points, from freshly isolated HK cells (T0), one week post-stimulation (1-WPS), 3-WPS and 5-WPS for RNA extraction. A variety of cell lineage markers (MCSF Receptor 2 (MCSFR2) for macrophages, CD4 and CD8a for T cells and IgM heavy chain for B cells) were then analysed by real-time qPCR to study the cell population dynamics as influenced by the different recombinant cytokines in the cultures. We show here that whilst MCSF appears to drive macrophage differentiation and maintenance, IL-2 and IL-6 seem to preferentially drive lymphocyte differentiation.

Dual-Positive (CD4+/CD8+) Acute Adult T-Cell Leukemia/Lymphoma Associated with Complex Karyotype and Refractory Hypercalcemia: Case Report and Literature Review

We describe a rare case of adult T-cell leukemia characterized by an expansion of CD4+ CD8+ double-positive lymphocytes associated with human T-lymphotropic virus type 1 (HTLV-1) and a complex karyotype in a 43-year-old Caribbean male who was initially admitted to our hospital with significant lethargy, visual disturbances, dysphagia, right facial palsy and numbness in both feet for 3 days. He was found to have severe hypercalcemia (15.6 mg/dl). Peripheral blood smear showed multilobulated clover-shaped nuclei. Bone marrow and CSF flow cytometries revealed abnormal monoclonal expansion of T cells positive for CD4, CD5, CD8 and CD25 but negative for CD7, CD20, CD56, CD68 and terminal deoxynucleotidyl transferase. The polymerase chain reaction analysis showed a distinct band of the T-cell receptor γ gene, revealing T-cell clonal integration of the proviral DNA of HTLV-1, thus confirming the diagnosis of acute adult T-cell leukemia/lymphoma. Cytogenetic study revealed a male karyotype with monosomy 12, unbalanced translocation 5q and 13q and additional material on 5q, 7q, 14q and 17q. The patient underwent prednisone (EPOCH) chemotherapy followed by autologous transplantation with BEAM regimen. Although patients with a rare mixed CD4+ CD8+ immunophenotype usually present with an aggressive clinical course and have a poor prognosis, our patient was able to survive for 2.5 years.

Comprehensive analysis of FOXP3 mRNA expression in leukemia and transformed cell lines

Studies of FOXP3 expression have thus far focused on T cells, including both normal and malignant T cells. In particular, adult T cell leukemia/lymphoma (ATLL) cells have been studied intensively because their phenotype resembles that of normal CD4(+)CD25(+) regulatory T (Treg) cells. However, a comprehensive study of FOXP3 expression covering all hematopoietic cell lineages has not yet been performed. In this study, FOXP3 mRNA expression was examined by quantitative PCR using a large collection of human hematopoietic cell lines derived from leukemia/lymphoma or virus-transformation, including cells lines with T, B, plasmacytoid, myeloid, monocytic, megakaryocytic, erythroid, and NK lineages. Unexpectedly, we found FOXP3 mRNA expression in a number of cell lines belonging to all of the cell lineages investigated. In sharp contrast, FOXP3 protein expression was found in only three cell lines, all of which were HTLV-I-infected. Several non-T cell lines expressed higher levels of mRNA but were still negative for protein expression. The broad mRNA expression contrasts with the restricted protein expression of FOXP3 in human hematopoietic cell lines, suggesting that post-transcriptional control mechanisms may control FOXP3 protein expression.

Multidrug resistance protein expression of adult T-cell leukemia/lymphoma

In adult T-cell leukemia/lymphoma (ATL), it is difficult to achieve remission and the reason for the resistance to chemotherapeutic agents may be linked to the presence of multidrug resistance (MDR) proteins. Lung resistance-related protein (LRP), multidrug resistance-associated protein and P-glycoprotein are three MDR proteins which we examined in ATL cells using multiparametric flow cytometry and real-time RT-PCR. LRP was highly expressed and suppressing LRP function increased doxorubicin accumulation in nuclei. This indicates LRP may be contributing to drug resistance in ATL patients, and the suppression of LRP function could be a new strategy for ATL treatment.

Elevated expression of CD30 in adult T-cell leukemia cell lines: possible role in constitutive NF-kappaB activation

Background

Human T-cell leukemia virus type 1 (HTLV-1) is associated with the development of adult T-cell leukemia (ATL). HTLV-1 encoded Tax1 oncoprotein activates the transcription of genes involved in cell growth and anti-apoptosis through the NF-κB pathway, and is thought to play a critical role in the pathogenesis of ATL. While Tax1 expression is usually lost or minimal in ATL cells, these cells still show high constitutive NF-κB activity, indicating that genetic or epigenetic changes in ATL cells induce activation independent of Tax1. The aim of this study was to identify the molecules responsible for the constitutive activation of NF-κB in ATL cells using a retroviral functional cloning strategy.

Results

Using enhanced green fluorescent protein (EGFP) expression and blasticidin-resistance as selection markers, several retroviral cDNA clones exhibiting constitutive NF-κB activity in Rat-1 cells, including full-length CD30, were obtained from an ATL cell line. Exogenous stable expression of CD30 in Rat-1 cells constitutively activated NF-κB. Elevated expression of CD30 was identified in all ATL lines examined, and primary ATL cells from a small number of patients (8 out of 66 cases).

Conclusion

Elevated CD30 expression is considered one of the causes of constitutive NF-κB activation in ATL cells, and may be involved in ATL development.

Rapid isolation of viral integration site reveals frequent integration of HTLV-1 into expressed loci

Although there is tight association of the human T-cell leukemia virus type-1 (HTLV-1) with adult T-cell leukemia/lymphoma (ATLL), it has remained unresolved whether the HTLV-1 integration into the host genome has any role in the development of this disease. We isolated a total of 58 HTLV-1 integration sites using newly developed, adaptor-ligated PCR from 33 ATLL patients and five ATLL cell lines. We compared our data as well as the previously reported ones with the complete human genomic sequence for the location of its placement, structure, and expression of genes nearby the integration site. The chromosomal target for integration was selected at random, but the integration favorably occurred within the transcription units; more than 59.5% of total integration was observed within the transcriptional unit. All inserted genes by HTLV-1 integration were expressed in normal T cells. Upregulation of genes due to viral integration was found in two out of nine ATLL cases; about 4.4- and 102-fold elevated ankyrin-1 ( ANK-1) and gephyrin ( GPHN) gene expressions were observed, respectively. These data suggest that the preferential integration of HTLV-1 into an expressed locus occasionally causes deregulation of corresponding gene, which may lead to leukemogenesis of a fraction of ATLL.

Chemotherapy targeting methylthioadenosine phosphorylase (MTAP) deficiency in adult T cell leukemia (ATL)

Methylthioadenosine phosphorylase (MTAP) is an important enzyme used for the salvage of adenine and methionine. Cells lacking this enzyme are expected to be sensitive to purine synthesis inhibitors and/or methionine starvation. We reported previously that the MTAP gene is deleted in adult T cell leukemia (ATL) cells. In the present study, we expanded our series and used a real-time quantitative PCR assay for accurate diagnosis of the deletion and nine of 65 primary ATL samples (13.8%) were MTAP negative. In spite of this low incidence, ATL cells showed significantly higher sensitivity to L-alanosine, an inhibitor of de novo adenosine monophosphate (AMP) synthesis, than normal lymphocytes, suggesting that the MTAP gene is inactivated not only by deletion but also by other mechanisms. Indeed, a real-time quantitative RT-PCR assay disclosed that primary ATL cells had significantly lower MTAP mRNA expression than normal lymphocytes. Since MTAP-negative ATL cell lines also showed much higher sensitivity to L-alanosine than MTAP-positive ATL cell lines, we used these cell lines to investigate whether it is possible to develop selective therapy targeting MTAP deficiency. A substrate of MTAP, methylthioadenosine (MTA) or its substitutes rescued concanavalin A (Con A)-activated normal lymphocyte proliferation from L-alanosine toxicity. All the compounds except 5'-deoxyadenosine, however, also caused the undesirable rescue of MTAP-negative ATL cell lines. 5'-Deoxyadenosine had the desired ability to rescue hematopoietic progenitor cells without rescuing ATL cell lines. These results support the rationale for a chemotherapy regimen of L-alanosine combined with 5'-deoxyadenosine rescue in MTAP-deficient ATL.

Multiple gammac-receptor expression in adult T-cell leukemia

Constitutive expression of the IL-2 receptor (IL-2R) on adult T-cell leukemia (ATL) cells and the presence of permanent IL-2-dependent ATL cell lines indicate that the signal transduction system via IL-2R is a key element for the development of this disease. IL-2R is a member of the common gamma-chain (gammac)-receptor family and shares gamma with IL-4R, IL-7R, IL-9R, and IL-15R. In addition to IL-2R, ATL cells express IL-15R and respond to IL-15. In the present study, we examined other members of this receptor family. ATL cells showed various levels of IL-4Ralpha (CD124) and IL-7Ralpha (CD127) expression, and responded to these cytokines. In contrast, ATL cells hardly responded to IL-9. As primary samples were a mixed population and the results may have been modified by contaminating normal cells, we used ATL cell lines as pure ATL cell populations. Here, we report that IL-2-dependent ATL cell lines also express IL-4Ralpha and respond to IL-4, which was verified by the activation of cytoplasmic transcriptional activator Stat6 protein. Moreover, a novel ATL cell line that grows stably in an IL-7-dependent manner was established from one of the cell lines, and IL-7 induced Stat5 activation in this cell line. These results indicated that ATL cells have the potential to express all gammac-receptors except IL-9R. Overlapping and switching of cytokine receptors supported the idea that ATL cells can rapidly select the appropriate gammac-receptor according to conditions.

Pleiotropic effects of HTLV type 1 Tax protein on cellular metabolism: mitotic checkpoint abrogation and NF-kappaB activation

Tax protein expressed by human T cell leukemia virus type 1 (HTLV-1) is a strong trans-activator of its own LTR promoter; it also affects the function of multiple cellular genes involved in cell cycle control and transcription. One way in which Tax exerts its pleiotropic effects is through protein-protein interaction with cellular cofactors. By using yeast two-hybrid technology, we have isolated several cellular proteins that bind to Tax. Two of these are MAD1, a mitotic checkpoint control protein, and TXBP151, a suppressor of tumor necrosis factor alpha-induced apoptosis. Here we discuss findings describing the role of MAD1 in exit of cells from mitosis and TXBP151 in NF-kappaB activation.

Expression and phosphorylation status of retinoblastoma protein in adult T-cell leukemia/lymphoma

The deletion or hyperphosphorylation of the retinoblastoma protein (pRB), is reported to progress various tumors. But its relevance to adult T-cell leukemia/lymphoma (ATL) remains to be elucidated. To better understand the role of pRB in ATL, we examined the expression and phosphorylation status of pRB in three ATL cell lines and 43 clinical samples, eight peripheral blood samples and 35 lymph node samples, from patients with ATL by Western blotting. In addition, 30 lymph node sections were also evaluated immunohistochemically. As a result, Western blotting analysis revealed that the pRB in the ATL cell lines was in the hyperphosphorylated, but that in 39 of 43 clinical samples, pRB was exclusively in the hypophosphorylated form. Four peripheral blood samples were negative for pRB. Immunohistochemistry revealed that the lymph nodes of all of 30 patients tested were positive for pRB at various staining levels, weak, mild, and strong. But weak expression may be essentially negative for pRB function. Patients with weak pRB expression in their lymph nodes lived significantly shorter lives than those with mild expression. Surprisingly, patients with strong expression also showed a significantly worse prognosis than those with mild expression. Although only the absence of pRB expression was considered previously to be indicative of RB functional loss, it has been reported recently that overexpression of pRB is correlated with progression of disease in patients with advanced bladder carcinoma or follicular lymphoma. These findings indicate that pRB controls tumor proliferation not only as a cell cycle regulator but also by other mechanisms, possibly through the inhibition of apoptosis, as suggested by recent findings in an osteosarcoma cell line, Saos-2. In conclusion, pRB may play an essential role in its hypophosphorylated form for progression of ATL, as well as a cell cycle promoter in hyperphosphorylated or negative/excessive reduced form.

Fas-resistance in ATL cell lines not associated with HTLV-I or FAP-1 production

A preventive role for human T-cell leukemia virus type-I (HTLV-I) and Fas-associated phosphatase-1 (FAP-1) in Fas-mediated apoptosis has been reported in HTLV-I-infected cells. In the present study, we examined whether these molecules increased during the acquisition of Fas-resistance in adult T-cell leukemia (ATL) cell lines. SO4, ST1 and KK1 are Fas-sensitive ATL cell lines, and produce small amounts of HTLV-I in vitro. Although their subclones RSO4 and RST1 are completely Fas-resistant, they produced an equivalent amount of HTLV-I to SO4 and ST1. Moreover, FAP-1 mRNA was not detected in these cell lines irrespective of Fas sensitivity. Thus, Fas resistance in ATL cells was not directly associated with the increased production of HTLV-I or FAP-1.

Retinoic acids induce growth inhibition and apoptosis in adult T-cell leukemia (ATL) cell lines

Adult T-cell leukemia (ATL) is a peripheral T-cell neoplasm caused by human T-cell leukemia virus type I (HTLV-I). Despite the administration of combined intensive chemotherapy, the reported survival time of patients with acute and lymphoma types of ATL is less than 10 months. We therefore examine the effects of all-trans-retinoic acid (ATRA), 9-cis-RA and 13-cis-RA and tried to elucidate the mechanisms of inducing growth inhibition and apoptosis by these RAs using four ATL cell lines established in our laboratory. All the investigated RAs inhibited cell growth and the cells were arrested at the G1 phase. Apoptosis was induced in three out of four cell lines. Among the growth regulatory proteins examined, the level of p21Waf1/Cip1 protein was found to increase after RA treatment, thus resulting in pRb hypophosphorylation which also induced the arrest of the cells at the G1 phase. In addition, the p53 level decreased at the same time. Fas-FasL system and the downregulation of CD25 (IL-2R/alpha) expression did not seem to be involved. Based on these findings, the ability of RAs to induce a remission of ATL is thus strongly suggested.

Interleukin-15 (IL-15) Can Replace the IL-2 Signal in IL-2–Dependent Adult T-Cell Leukemia (ATL) Cell Lines: Expression of IL-15 Receptor α on ATL Cells

Interleukin-15 receptor (IL-15R) and IL-2R have the same β and γ chains, but IL-15R has a specific α chain distinct from that of IL-2Rα, which is indispensable for the high affinity binding of IL-15. In the present study, we examined four IL-2-dependent adult T-cell leukemia (ATL) cell lines for their IL-15R expression. All cell lines bound IL-15, which was not inhibited by a 100-fold excess amount of IL-2, proliferated in response to IL-15 to the same degree as to the stimulation with IL-2, and were maintained without IL-2. The responses to 1L-15 were inhibited by the antibodies against IL-2R β or γ chains but was not by the IL-2R α chain antibody. [125I]–IL-15 exhibited a single high-affinity binding with an apparent kd of 0.17 nmol/L. Reverse transcription–coupled polymerase chain reaction (RT-PCR) showed that the cell lines had the mRNA of IL-15R α. The cell lines also had IL-15 mRNA. Despite the presence of IL-15 mRNA, the cell lines did not secrete IL-15, and the culture supernatants of fresh ATL cells and plasma from the patients did not contain a detectable amount of IL-15 with a few exceptional cases, although fresh ATL cells also responded to IL-15. These results suggest that ATL cells have the complete form of IL-15R and respond to IL-15. Such an IL-15–dependent cell proliferation mechanism might be used in the development of ATL and for the invasion and proliferation of ATL cells in the visceral organs.

Interleukin-15 (IL-15) Can Replace the IL-2 Signal in IL-2–Dependent Adult T-Cell Leukemia (ATL) Cell Lines: Expression of IL-15 Receptor α on ATL Cells

Interleukin-15 receptor (IL-15R) and IL-2R have the same β and γ chains, but IL-15R has a specific α chain distinct from that of IL-2Rα, which is indispensable for the high affinity binding of IL-15. In the present study, we examined four IL-2-dependent adult T-cell leukemia (ATL) cell lines for their IL-15R expression. All cell lines bound IL-15, which was not inhibited by a 100-fold excess amount of IL-2, proliferated in response to IL-15 to the same degree as to the stimulation with IL-2, and were maintained without IL-2. The responses to 1L-15 were inhibited by the antibodies against IL-2R β or γ chains but was not by the IL-2R α chain antibody. [125I]–IL-15 exhibited a single high-affinity binding with an apparent kd of 0.17 nmol/L. Reverse transcription–coupled polymerase chain reaction (RT-PCR) showed that the cell lines had the mRNA of IL-15R α. The cell lines also had IL-15 mRNA. Despite the presence of IL-15 mRNA, the cell lines did not secrete IL-15, and the culture supernatants of fresh ATL cells and plasma from the patients did not contain a detectable amount of IL-15 with a few exceptional cases, although fresh ATL cells also responded to IL-15. These results suggest that ATL cells have the complete form of IL-15R and respond to IL-15. Such an IL-15–dependent cell proliferation mechanism might be used in the development of ATL and for the invasion and proliferation of ATL cells in the visceral organs.

The methylthioadenosine phosphorylase gene is frequently co-deleted with the p16INK4a gene in acute type adult T-cell leukemia

Adult T-cell leukemia (ATL) is a retrovirus-associated leukemia with poor prognosis and often has deletions of the p16INK4a and p15INK4b genes on chromosome 9p21. The gene for methylthioadenosine phosphorylase (MTAP), a purine and methionine metabolic enzyme, resides approximately 100 Kb telomeric to the p16INK4a gene and is frequently co-deleted with the tumor suppressor gene in a variety of cancers. This enzyme deficiency can be exploited for selective chemotherapy with de novo purine synthesis inhibitors and/or methionine depletion. To determine whether ATL can be a candidate for selective chemotherapy based on genetic alterations on chromosome 9p21, we analyzed the MTAP gene in 41 samples from ATL patients (27 acute type and 14 chronic type ATL) and 3 cell lines established from ATL patients. Five samples from the acute type had deletions of the MTAP gene (4 total deletions and 1 partial deletion of exons 6-8). The MTAP gene was always co-deleted with p16INK4a. No deletion of the MTAP gene was detected in samples from the chronic type. Of 3 cell lines, 2 showed partial deletions of exons 5-8 of the MTAP gene, and 1 lost all exons. The p16INK4a gene was deleted in all cell lines. In conclusion, deletions of the MTAP gene were found in 5 of 27 acute type ATL samples. Acute type ATL with MTAP deficiency can be a good candidate for selective chemotherapy by depleting purines and/or methionine.

Plasma M-CSF as an indicator of response to chemotherapy in adult T cell leukemia patients

The plasma concentration of macrophage colony-stimulating factor (M-CSF) was measured in 10 patients with acute type adult T cell leukemia (ATL) during the clinical course before and after chemotherapy. M-CSF concentration decreased significantly when the patients achieved complete remission (CR) or partial remission (PR) (t-test: p = 0.0001). Five of the patients showed disease progression after several months of PR, and plasma M-CSF increased at that time (t-test: p = 0.0456). Thus, plasma M-CSF concentration appeared to accurately reflect the disease activity in ATL. In support of these results, all three ATL cell lines established from these patients secreted M-CSF in vitro after stimulation with phorbol myristate acetate (PMA) or concanavalin A (Con A). Plasma M-CSF concentration, however, increased transiently when the patients were febrile (t-test: p = 0.0001), even though their ATL condition was unchanged. Taken together, these results indicate that there are two sources of increased plasma M-CSF concentration in ATL; ATL cells themselves and normal parenchymal cells that cause this increase as the result of elevated body temperature due to inflammation.

Features of the cytokines secreted by adult T cell leukemia (ATL) cells

Adult T cell leukemia (ATL) cells show a mature helper-inducer T cell phenotype and are thought to secrete many kinds of cytokines in vivo, complicating the clinical features in these patients. In an attempt to specify the cytokines produced by ATL cells, we measured the cytokine concentration in the culture supernatants of three ATL cell lines, all of which were confirmed to be true peripheral blood ATL cell in origin. All these cell lines showed the same cytokine production profile, secreting IL1-alpha, IL1-beta, LD78(MIP-l alpha), TNF-alpha, IFN-gamma, and GM-CSF, but not secreting IL-1 alpha, IL-1 beta, IL-1 receptor antagonist (IL-1 Ra), IL-4, IFN-alpha, and G-CSF irrespective of the stimulatory agents used. Such limited cytokine production may indicate the specific origin of ATL cells within the helper-inducer T cell subtypes. Moreover, these results explain some of the unusual clinical features of ATL patients.

Characterization of a HTLV-I-infected cell line derived from a patient with adult T-cell leukemia with stable co-expression of CD4 and CD8

A long-term T-cell line, termed SP+, was developed from a human T-cell leukemia virus type I (HTLV-I)-infected patient with adult T-cell leukemia that is dependent on exogenous IL-2 for growth. The SP+ expresses a full complimentation of HTLV-I-specific viral proteins, and contains replication competent viral particles. Restriction enzyme digestion followed by Southern blot analysis demonstrated the presence of a single integrated proviral copy and limiting dilution analysis confirmed the clonality of the cell line. Interestingly, phenotypically, the SP+ cell line is CD2+, CD3+ and coexpresses CD4 and CD8, yet lacks TCR alpha beta and TCR tau delta expression. Further ontogenetic characterization of the SP+ cell line demonstrated the lack of thymic T-cell precursor markers, including absence of cell surface expression of CD1, intracellular thymic terminal deoxynucleotidyl transferase (TdT) enzyme, as well as message expression for V(D)J recombinase activating gene-1 (RAG-1). Furthermore, the SP+ cell did express the message for the CD3 delta chain. Taken together, these data suggest that the SP+ cell line resulted from HTLV-I infection of a mature CD4+/CDB+ lymphocyte. This cell line can be potentially useful as a model, both for regulation of cellular functions by HTLV-I and for immunologic functions of mature dual CD4/CD8 positive T-cells.

Established IL-2-dependent double-negative (CD4- CD8-) TCR alpha beta/CD3+ ATL cells: induction of CD4 expression

We established IL-2-dependent T cells from an adult T-cell leukaemia (ATL) patient whose leukaemic cells changed from CD4 single-positive in the initial phase to double-negative (CD4- CD8-) at the time of exacerbation. The cells termed SO-4 were of ATL cell origin and showed the double-negative TCR alpha beta/CD3+ T-cell phenotype. SO-4 cells acquired CD4 antigen expression following stimulation with concanavalin A (ConA) or immobilized anti-CD3 antibody. The induction was inhibited by herbimycin A, an inhibitor of protein tyrosine kinase (PTK) activity. No CD4 mRNA was detectable in unstimulated SO-4 cells but a 3.0 kb signal specific for CD4 mRNA was detected after stimulation. These findings indicate that SO-4 cells return to their original phenotype (CD4 single-positive) by stimulation involving PTK. The results indicate that there is a pathway of phenotypic cycling between CD4 single-positive and double-negative T cells.

Co-expression of CD4 and CD8 associated with elevated interleukin-4 in a cord T cell line derived by co-cultivating normal cord leukocytes and an HTLV-II-producing simian leukocyte cell line (Si-IIA)

A new interleukin-2(IL-2)-dependent T cell line, designated CS-IIA, was established by co-cultivating normal human cord leukocytes and a lethally X-irradiated HTLV-II-producing simian leukocyte cell line (Si-IIA). CS-IIA showed CD4 dominance during the early culture. However, after addition of IL-2, CS-IIA predominantly co-expressed CD4 and CD8 (69.5%) and also expressed the surface markers CD1-, CD3+, CD19-, CD25+ and HLA-DR+. A significantly elevated level of IL-4 (1697 pg/ml) was observed in the culture supernatant from CS-IIA. In addition, the conversion of phenotype from some CD4+CD8+ cells to CD4+CD8- was demonstrated by the neutralization assay using anti-IL-4 antibody. CS-IIA had a normal human karyotype and was free from Epstein-Barr virus nuclear antigen and immunoreactive with sera of HTLV-I- or HTLV-II-infected patients and anti-HTLV-1, p19 or p24 mAb. The provirus genome of HTLV-II was detected in this cell line by the polymerase chain reaction combined with a digoxigenin-enzyme-linked immunosorbent assay. However, electron microscopy of CS-IIA cells revealed no C-type virus particles in the extracellular space. These results indicate that HTLV-II can be transmitted from an HTLV-II-infected simian leukocyte cell line to human cord T lymphocytes and suggest that co-expression of CD4 and CD8 on T cells may be induced by the high level of IL-4, which can mediate CD8 induction on CD4+ T cell clones.