Species-dependent antigenicity of the 34-kDa glycoprotein found on the membrane of various primate lymphocytes transformed by human T-cell leukemia virus type-I (HTLV-I) and simian T-cell leukemia virus (STLV-I)

Association of high levels of plasma OX40 with acute adult T-cell leukemia

OX40, a member of the tumor necrosis factor receptor (TNFR) superfamily, co-stimulates activated T cells following interaction with its own ligand OX40L. Human T-cell leukemia virus type-1 (HTLV-1) is an etiological agent of adult T-cell leukemia (ATL). ATL cells are known to express cell surface OX40; however, the level of soluble OX40 (sOX40) in blood samples from ATL patients is unknown. Quantitative enzyme-linked immune-sorbent assay (ELISA) showed that sOX40 levels were significantly higher in plasma from acute ATL patients than those from asymptomatic HTLV-1 carriers and healthy donors, and correlated with sCD25 levels and HTLV-1 proviral loads in peripheral blood mononuclear cells (PBMCs). Fresh PBMCs from acute ATL patients showed a higher percentage of OX40-positive cells compared with those from carriers, and shed sOX40 into culture supernatants. Shedding of sOX40 was partially inhibited by a matrix metalloproteinase (MMP) inhibitor, GM6001. A fraction of sOX40 was capable of binding to OX40L. These results suggest that high levels of sOX40 are shed into blood from a large number of ATL cells in acute ATL patients. Thus, abnormally elevated plasma sOX40 levels may be useful as an additional diagnostic marker of acute ATL.

Cross-Linking Cell Surface Chemokine Receptors Leads to Isolation, Activation, and Differentiation of Monocytes into Potent Dendritic Cells

Monocytes express on the cell surface several kinds of chemokine receptors that facilitate chemotaxis followed by differentiation in target tissues. In the present study, we found that a large number of monocytes from peripheral blood mononuclear cells (PBMCs) tightly adhered to plastic cell culture plates precoated with a monoclonal antibody (mAb, clone T312) specific for human CCR5 but not an isotype control after overnight incubation. Soluble T312 did not induce such adhesion, indicating that cross-linking of CCR5 is required for the enhanced adhesion of monocytes. The adhesion was blocked by a PI3-K inhibitor and an anti-CD18 blocking mAb. Following the cross-linking of CCR5, monocytes synthesized high levels of M-CSF, RANTES, MIP-1α, and MIP-1β associated with a readily detectable downmodulation of CD14, CD4, CCR5, and CXCR4 expression. The T312-enriched monocytes differentiated into dendritic cells (DCs) in the presence of interleukin-4 alone. After maturation with β-interferon, the T312-induced DCs stimulated proliferation of allogeneic naïve CD4+ T cells accompanied by the synthesis of high levels of γ-interferon in vitro. Furthermore, the T312-induced DCs were capable of stimulating antigen-specific human T- and B-cell immune responses in our hu-PBL-SCID mouse system. Finally, screening of other anti-chemokine receptor mAbs showed that select clones of mAbs against CXCR4 and CCR3 were also capable of facilitating enrichment of monocytes similar to T312. These results show that cross-linking of chemokine receptors on monocytes by appropriate mAbs leads to activation and differentiation of monocytes and that the method described herein provides an alternate simple strategy for adherence-based isolation of monocytes and generation of functional DCs.

Human T-cell leukemia virus type 1 (HTLV-1) Tax1 oncoprotein but not HTLV-2 Tax2 induces the expression of OX40 ligand by interacting with p52/p100 and RelB

Human T-cell leukemia virus type 1 (HTLV-1) is a causative retrovirus of adult T-cell leukemia and HTLV-1-associated myelopathy. Unlike HTLV-1, the same group of retrovirus HTLV-2 has not been found to be associated with these diseases. HTLV-1 and HTLV-2 encode transforming proteins Tax1 and Tax2, and a few distinct activities of Tax1 from those of Tax2 have been proposed to contribute to the HTLV-1-specific pathogenesis of disease. One significant difference of Tax1 from Tax2 is the activation of transcription factor NF-κB2/p100/p52. We found that Tax1 but not Tax2 induces the expression of OX40 ligand (OX40L) in a human T-cell line. To induce the OX40L expression, Tax1 but not Tax2 was observed to interact with NF-κB2/p100/p52 and RelB and the distinct interaction activity was mediated by the Tax1 amino acid region of 225-232. In addition, Tax1 but not Tax2 or Tax1/225-232 interacted with p65, p50, and c-Rel; however, the interactions were much less than those noted with NF-κB2/p100/p52 and RelB. OX40L is a T-cell costimulatory molecule of the tumor necrosis factor family, and its signal plays a critical role in establishing adaptive immunity by inducing the polarized differentiation of T-cells to cells such as T helper type 2 and T follicular helper cells. Therefore, the present findings suggest that Tax1 might alter the immune response to HTLV-1 and/or differentiation of HTLV-1-infected T-cells via OX40L induction, thereby acting as a factor mediating the distinct phenotypes and pathogenesis of HTLV-1 from that of HTLV-2.

Natural OX40L expressed on human T cell leukemia virus type-I-immortalized T cell lines interferes with infection of activated peripheral blood mononuclear cells by CCR5-utilizing human immunodeficiency virus

BACKGROUND

OX40 ligand (OX40L) co-stimulates and differentiates T cells via ligation of OX40 that is transiently induced on T cells upon activation, resulting in prolonged T cell survival and enhanced cytokine production by T cells. This view has led to the targeting of OX40 as a strategy to boost antigen specific T cells in the context of vaccination. In addition, the ligation of OX40 has also been shown to inhibit infection by CCR5-utilizing (R5) but not CXCR4-utilizing (X4) human immunodeficiency virus type-1 (HIV-1) via enhancement of production of CCR5-binding β-chemokines. It was reasoned that human T cell leukemia virus type-I (HTLV-1) immortalized T cell lines that express high levels of OX40L could serve as an unique source of physiologically functional OX40L. The fact that HTLV-1+ T cell lines simultaneously also express high levels of OX40 suggested a potential limitation.

RESULTS

Results of our studies showed that HTLV-1+ T cell lines bound exogenous OX40 but not OX40L, indicating that HTLV-1+ T cell lines express an active form of OX40L but an inactive form of OX40. Anti-OX40 non-blocking monoclonal antibody (mAb), but not blocking mAb, stained HTLV-1+ T cell lines, suggesting that the OX40 might be saturated with endogenous OX40L. Functionality of the OX40L was confirmed by the fact that a paraformaldehyde (PFA)-fixed HTLV-1+ T cell lines inhibited the infection of autologous activated peripheral blood mononuclear cells (PBMCs) with R5 HIV-1 which was reversed by either anti-OX40L blocking mAb or a mixture of neutralizing mAbs against CCR5-binding β-chemokines.

CONCLUSIONS

Altogether, these results demonstrated that autologous T cell lines immortalized by HTLV-1 can be utilized as a conventional source of physiologically functional OX40L.

Suppression of CCR5-tropic HIV type 1 infection by OX40 stimulation via enhanced production of β-chemokines

To elucidate the immunological role for the costimulatory molecule OX40 against the early stage of HIV-1 infection, fresh peripheral blood mononuclear cells (PBMCs) from normal donors were stimulated with immobilized anti-CD3 monoclonal antibody (mAb) together with soluble anti-CD28 mAb for 24 h, infected with CCR5-tropic (R5) HIV-1, and then cocultured in the presence or absence of OX40 ligand (OX40L). Results of these studied showed that OX40 stimulation led to a marked reduction in levels of p24, the frequency of intracellular p24(+) cells, as well as HIV-1-mediated syncytium formation. The suppression was reversed by anti-OX40L mAb. The mechanism underlying the R5 HIV-1 suppression was shown to be mediated in part by the CCR5-binding β-chemokines RANTES, MIP-1α, and MIP-1β, since the effect of the OX40 stimulation was reversed by a neutralizing antibody mixture against these three β-chemokines. Thus, OX40 stimulation enhanced the production of these CCR5-binding β-chemokines by the activated PBMCs and subsequently down-modulated CCR5 expression on the activated CD4(+) T cells. Taken together, the present data revealed a new role for OX40 in HIV-1 infection and documents the fact that OX40 stimulation suppresses the infection of primary activated PBMCs with R5 HIV-1 via enhanced production of R5 HIV-1 suppressing β-chemokines.

Rapid induction of OX40 ligand on primary T cells activated under DNA-damaging conditions

We have previously demonstrated that normal human T cells either long-term repeatedly stimulated or freshly activated in vitro in the presence of TGF-beta express the cell surface T-cell costimulating molecule OX40 ligand (OX40L). To further elucidate the kinetics of OX40L expression by human T cells, we have examined whether cell proliferation was required for the expression of OX40L. Thus, normal fresh peripheral blood mononuclear cells were stimulated with immobilized anti-CD3 antibody in the presence of the DNA synthesis-blocking agents such as mitomycin C, 5-fluorouracil, or X-ray irradiation. Flow cytometric analyses demonstrated that a significant frequency of these DNA-damaged activated primary CD4+ and CD8+ T cells became OX40L+ as early as 1 hour after treatment. The OX40L induction on the DNA-damaged activated T cells was inhibited by treatment with either RNA or protein synthesis inhibitors, actinomycin D, or cycloheximide, respectively. Induced OX40L on T cells was functional because it bound recombinant OX40. These data indicate that human primary T cells are programmed to rapidly express functional OX40L molecules after stimulation under DNA-damaging conditions, demonstrating that the induction of OX40L by T cells is independent of cell proliferation. The clinical implications of these new findings are discussed.

Enhancement of OX40-induced apoptosis by TNF coactivation in OX40-expressing T cell lines in vitro leading to decreased targets for HIV type 1 production

OX40, a member of the tumor necrosis factor receptor (TNF-R) superfamily, has been shown to play an important role in the survival of antigen-specific CD4(+) T cells. We have previously reported that stimulation of the OX40-expressing and HIV-1 chronically infected T cell line, ACH-2/OX40, with either OX40 ligand (OX40L)-expressing cells or with TNF resulted in the activation of HIV-1 followed by apoptotic cell death. In the present study we found that costimulation via OX40 and TNF-R in OX40-expressing HIV-1-infected T cell lines leads to a marked reduction of HIV-1 production associated with rapid cell death. Since HIV-1-negative OX40(+) T cell lines underwent rapid apoptotic cell death after OX40L and TNF stimulation, it was reasoned that the ACH-2/OX40 cell death was unlikely to be due to HIV-1 infection. Furthermore, we found that the OX40-mediated apoptosis of the CD4(+) T cell line, Molt-4/CCR5-OX40 (M/R5-OX40), required (1) signals mediated via the cytoplasmic tail of OX40, (2) activation of the caspase cascade, including caspase-8 and caspase-3, and (3) induction of endogenous TNF-alpha, but not of TNF-beta, FasL, or TNF-related apoptosis-inducing ligand (TRAIL), suggesting that this apoptosis occurred indirectly via the TNF/TNF-R system. Finally, a fraction of primary activated CD4(+) T cells, expressing high levels of OX40, underwent apoptosis, as revealed by annexin V staining, after cocultivation with OX40L(+) cells. These results suggest a new biological role of the OX40L/OX40 system in controlling the fate of activated CD4(+) T cells and of controlling HIV-1 infection in inflammatory environments.

Requirements for the functional expression of OX40 ligand on human activated CD4+ and CD8+ T cells

Interaction between OX40 expressed on activated T cells and its ligand (OX40L) on antigen presenting cells (APC) provides a co-stimulatory signal for T cells to promote acquired immunity. In the present study, we have examined various culture conditions for optimum OX40L expression on T cells stimulated with immobilized anti-CD3/CD28 monoclonal antibodies (mAbs). Although the day 3 primed T cells expressed minimal OX40L, after repeated stimulations both the CD4+ and CD8+ T cells became OX40L positive as determined by flow cytometry. Interleukin (IL)-12 interfered with the OX40L expression. Among activated T cells, a higher frequency of CD8+ T cells expressed OX40L than CD4+ T cells. By blocking OX40L-OX40 interaction by an anti-OX40 mAb, the number of OX40L+ T cells significantly increased. Screening of various cytokines showed that transforming growth factor (TGF)-beta1 was capable of induction of OX40L on the activated T cells within 3 days. The OX40L expressed on T cells was functional, as they bound soluble OX40 and stimulated human immunodeficiency virus-1 (HIV-1) production from cell lines chronically infected with HIV-1 and expressing OX40. Altogether the present study findings indicate that functional OX40L is inducible on human activated CD4+ and CD8+ T cells, and that the expression is enhanced by TGF-beta1.

OX40 signaling renders adult T-cell leukemia cells resistant to Fas-induced apoptosis

We reported previously that OX40, a member of the tumor necrosis factor receptor family, is expressed constitutively on fresh leukemia/lymphoma cells isolated from patients with adult T-cell leukemia (ATL). In this study, we tested whether OX40 signaling affects the Fas-mediated apoptosis of fresh ATL cells isolated from 7 patients (3 acute type, 3 chronic type, and 1 smoldering type). In all these patients, the coculture of ATL cells with MMCE/OX40 ligand gp34, a stable human gp34 transfectant of a mouse epithelial cell line, resulted in a decrease in the percentage of apoptotic cells after treatment with anti-Fas monoclonal antibody, compared to coculture with MMCE/mock controls. Similar findings were obtained in OX40(+)- human T-cell leukemia virus type I-transformed T-cell lines. To elucidate the molecular mechanism of this phenomenon, we used Kit225/OX40, a stable OX40 transfectant of an IL-2-dependent T-cell line, and its deletion mutant, Kit225/del-OX40, in which the intracytoplasmic domain of OX40 had been deleted. Coculture with MMCE/gp34 inhibited the apoptosis of Kit225/OX40, but Kit225/del-OX40 apoptosis was hardly affected. These results suggest that ATL cells may escape Fas-mediated destruction of the immune system through OX40 signaling.

Expression of tumor necrosis factor ligand superfamily costimulatory molecules CD27L, CD30L, OX40L and 4-1BBL in the heart of patients with acute myocarditis and dilated cardiomyopathy

BACKGROUND

T-cell-mediated myocardial damage is known to be involved in acute myocarditis and dilated cardiomyopathy. Recently, we found that tumor necrosis factor (TNF) ligand superfamily costimulatory molecules, especially 4-1BBL, played an important role in the myocardial damage of murine acute viral myocarditis.

METHODS AND RESULTS

To investigate the roles for CD27L, CD30L, OX40L and 4-1BBL, which belong to TNF ligand superfamily, in the development of acute myocarditis and dilated cardiomyopathy, we analyzed the expression of these antigens in the myocardial tissues of patients with acute myocarditis and dilated cardiomyopathy. We also examined expression of the receptors for these molecules, CD27, CD30, OX40 and 4-1BB, which belong to TNF receptor superfamily, on the infiltrating cells. Strong expression of CD27L, CD30L and 4-1BBL and weak to moderate expression of OX40L was found in the cardiac myocytes of patients with acute myocarditis. Moderate expression of CD27L, CD30L and 4-1BBL and weak expression of OX40L was found on the cardiac myocytes of patients with dilated cardiomyopathy. Most of the infiltrating cells expressed CD27, CD30 and 4-1BB and a part of the infiltrating cells expressed OX40.

CONCLUSIONS

Our findings suggest that expression of TNF ligand superfamily costimulatory molecules on cardiac myocytes may play a role in the cell-mediated myocardial damage in patients with acute myocarditis and dilated cardiomyopathy as in murine viral myocarditis.

OX40 stimulation by gp34/OX40 ligand enhances productive human immunodeficiency virus type 1 infection

OX40 is a member of the tumor necrosis factor (TNF) receptor superfamily and known to be an important costimulatory molecule expressed on activated T cells. To investigate the role of costimulation of OX40 in human immunodeficiency virus type 1 (HIV-1) infection by its natural ligand, gp34, the OX40-transfected ACH-2 cell line, ACH-2/OX40, chronically infected with HIV-1, was cocultured with paraformaldehyde (PFA)-fixed gp34-transfected mouse cell line, SV-T2/gp34. The results showed that HIV-1 production was strongly induced. This was followed by apparent apoptosis, and both processes were specifically inhibited by the gp34-specific neutralizing monoclonal antibody 5A8. Endogenous TNF alpha (TNF-alpha) and TNF-beta production were not involved in the enhanced HIV-1 production. Furthermore, enhanced HIV-1 transcription in gp34-stimulated ACH-2/OX40 cells was dependent on the kappa B site of the HIV-1 long terminal repeat, and the OX40-gp34 interaction activated NF-kappa B consisting of p50 and p65 subunits. When primary activated CD4(+) T cells acutely infected with HIV-1(NL4-3) (CXCR4-using T-cell-line-tropic) were cocultured with PFA-fixed gp34(+) human T-cell leukemia virus type 1-bearing MT-2 cells or SV-T2/gp34 cells, HIV-1 production was also markedly enhanced. The enhancement was again significantly inhibited by 5A8. The present study first shows that OX40-gp34 interaction stimulates HIV-1 expression and suggests that OX40 triggering by gp34 may play an important role in enhancing HIV-1 production in both acutely and latently infected CD4(+) T cells in vivo.

Restricted usage of T-cell receptor Vgamma-Vdelta genes and expression of costimulatory molecules in Takayasu's arteritis

To further investigate the immunological mechanisms involved in Takayasu's arteritis, we analyzed the T-cell receptor (TCR) Vgamma and Vdelta gene usage by infiltrating gammadelta T-cells and the expression of costimulatory molecules B7-1, B7-2, CD40, CD27 ligand (CD27L), CD30L, OX40L in the arterial tissue of a patient with Takayasu's arteritis. We found that the repertoires of TCR Vgamma as well as Vdelta gene transcripts of the infiltrating cells were restricted as compared with those of peripheral blood lymphocytes from a patient with Takayasu's arteritis. This strongly suggests that gammadelta T-cells as well as alphabeta T-cells, as we previously reported, were specifically involved in the pathogenesis of Takayasu's arteritis. We also found that B7-1, B7-2, CD40, CD27L, CD30L, and OX40L were expressed in the arterial tissue, suggesting the roles for these costimulatory molecules in T-cell-mediated vascular injury in Takayasu's arteritis. Our findings strongly support the involvement of T-cell-mediated immunological mechanisms in the pathogenesis of Takayasu's arteritis.

Characterization of rat OX40 ligand by monoclonal antibody

OX40 (CD134) is a member of the tumor necrosis factor (TNF) receptor superfamily first identified as a rat T cell activation marker. We previously identified the rat ligand for OX40 (OX40L) by molecular cloning. In the present study, we newly generated an anti-rat OX40L mAb (ATM-2) that can inhibit the binding of OX40 to rat OX40L and thus efficiently inhibits the T cell costimulatory activity of rat OX40L. Flow cytometric analyses using ATM-2 and an anti-rat OX40 mAb (MRC OX40) indicated that OX40 was inducible on splenic CD4(+) T cells by stimulation with immobilized anti-CD3 mAb, while OX40L was not expressed on resting or activated T cells. OX40L was expressed on splenic B cells after stimulation with lipopolysaccharide (LPS), but not on peritoneal macrophages. Interestingly, splenic dendritic cells (DC) expressed OX40L constitutively, which was further upregulated by LPS stimulation. The potent costimulatory activities of splenic DC for anti-CD3-stimulated rat CD4(+) T cell proliferation and cytokine (IL-2, IFN-gamma, IL-10, and IL-13) production were substantially inhibited by ATM-2. These results indicated that OX40L is expressed on professional antigen-presenting cells (APC), and may be involved in humoral immune responses via T-B interaction and in cellular immune responses via T-DC interaction in the rat system.

Mechanisms of T-cell activation by human T-cell lymphotropic virus type I

The interactions between human T-cell lymphotropic virus type I (HTLV-I) and the cellular immune system can be divided into viral interference with functions of the infected host T cell and the subsequent interactions between the infected T cell and the cellular immune system. HTLV-I-mediated activation of the infected host T cell is induced primarily by the viral protein Tax, which influences transcriptional activation, signal transduction pathways, cell cycle control, and apoptosis. These properties of Tax may well explain the ability of HTLV-I to immortalize T cells. It is not clear, though, how HTLV-I induces T-cell transformation (interleukin-2 [IL-2] independence). Recent evidence suggests that Tax may promote the G1- to S-phase transition, although this may involve additional proteins. A role for other viral proteins that may constitutively activate the IL-2 receptor pathway has also been suggested. By virtue of their activated state, HTLV-I-infected T cells can nonspecifically activate resting, uninfected T cells via virus-mediated upregulation of adhesion molecules. This may favor viral dissemination. Moreover, the induction of a remarkably high frequency of antiviral CD8(+) T cells does not appear to eliminate the infection. Indeed, individuals with a high frequency of virus-specific CD8(+) T cells have a high viral load, indicating a state of chronic immune system stimulation. Thus, while an activated immune system is needed to eradicate the infection, the spread of the HTLV-I is also accelerated under these conditions. A detailed knowledge of the molecular interactions between virus-specific CD8(+) T cells and immunodominant viral epitopes holds promise for the development of specific antiviral therapy.

OX40 Costimulation Enhances Interleukin-4 (IL-4) Expression at Priming and Promotes the Differentiation of Naive Human CD4+ T Cells Into High IL-4–Producing Effectors

Th2 cell development is critically dependent on the presence of interleukin-4 (IL-4) at priming. The cellular origin and the mechanisms regulating this early production of IL-4 at the site of naive T-cell priming are extensively investigated. We previously reported that anti-CD3–activated and CD28-costimulated naive human CD4+ T cells themselves release very low but sufficient levels of IL-4 to support their development into high IL-4–producing cells. We show here that ligation of OX40 Ag, a member of the tumor necrosis factor receptor (TNF-R) family, on activated umbilical cord blood CD4+ T cells upregulates IL-4 production at priming and thereby promotes their development into effector cells producing high levels of the type 2 cytokines IL-4, IL-5, and IL-13. OX40 ligation increases four times the expression of IL-4 mRNA after 48 hours of anti-CD3/B7.1 activation and significantly augments the release of IL-4 and IL-13 in primary cultures. The effects of OX40 costimulation on Th cell differentiation are observed in the presence of optimal and suboptimal CD28 stimulation. Because OX40 ligand is expressed on dendritic cells, the OX40 costimulation pathway may be involved in the physiological regulation of Th cell development by augmenting the differentiation of IL-4–producing cells.

© 1998 by The American Society of Hematology.

OX40 Costimulation Enhances Interleukin-4 (IL-4) Expression at Priming and Promotes the Differentiation of Naive Human CD4+ T Cells Into High IL-4–Producing Effectors

Th2 cell development is critically dependent on the presence of interleukin-4 (IL-4) at priming. The cellular origin and the mechanisms regulating this early production of IL-4 at the site of naive T-cell priming are extensively investigated. We previously reported that anti-CD3–activated and CD28-costimulated naive human CD4+ T cells themselves release very low but sufficient levels of IL-4 to support their development into high IL-4–producing cells. We show here that ligation of OX40 Ag, a member of the tumor necrosis factor receptor (TNF-R) family, on activated umbilical cord blood CD4+ T cells upregulates IL-4 production at priming and thereby promotes their development into effector cells producing high levels of the type 2 cytokines IL-4, IL-5, and IL-13. OX40 ligation increases four times the expression of IL-4 mRNA after 48 hours of anti-CD3/B7.1 activation and significantly augments the release of IL-4 and IL-13 in primary cultures. The effects of OX40 costimulation on Th cell differentiation are observed in the presence of optimal and suboptimal CD28 stimulation. Because OX40 ligand is expressed on dendritic cells, the OX40 costimulation pathway may be involved in the physiological regulation of Th cell development by augmenting the differentiation of IL-4–producing cells.

© 1998 by The American Society of Hematology.

Identification of rat OX40 ligand by molecular cloning

OX40 (CD134) is a member of the tumor necrosis factor (TNF) receptor superfamily first identified as a rat T cell activation marker. In the present study, we identified the rat ligand for OX40 (OX40L) by molecular cloning. Rat OX40L cDNA was cloned from a HTLV-1-transformed rat T cell line by cross-hybridization with mouse OX40L cDNA. The predicted rat OX40L polypeptide is composed of 199 amino acids, showing 80.9 and 43.3% homology to mouse and human OX40L, respectively. Expression of rat OX40L mRNA was found in HTLV-1-transformed rat T cell lines. Expression of OX40L on the cell surface of these HTLV-1-transformed rat T cell lines was also demonstrated by flow cytometric analysis with a soluble fusion protein composed of the extracellular region of the Fc portion of human IgG (OX40-Ig). To explore the function of rat OX40L, we generated cDNA transfectants stably expressing rat OX40L. The rat OX40L transfectants exhibited a potent costimulatory activity for proliferation and IL-2 production of anti-CD3-stimulated rat T cells. These results indicated that rat OX40L can provide an efficient costimulation for rat T cells and that it may be involved in HTLV-1-associated pathologies in the rat system as has been suggested in the human system.

OX40 Expressed on Fresh Leukemic Cells From Adult T-Cell Leukemia Patients Mediates Cell Adhesion to Vascular Endothelial Cells: Implication for the Possible Involvement of OX40 in Leukemic Cell Infiltration

We demonstrated previously that OX40 and its ligand, gp34, directly mediate adhesion of activated normal CD4+ T cells, as well as human T-cell leukemia virus type I (HTLV-I)–transformed T cells to vascular endothelial cells. In the present study, we examined expression of OX40 on fresh leukemic cells from patients with adult T-cell leukemia (ATL) and its possible involvement in cell adhesion. Flow cytometric analysis showed that peripheral blood mononuclear cells (PBMC) or lymph node tumor cells from 15 of 17 cases expressed significant levels of OX40 without stimulation. On the other hand, gp34 was not expressed on these cells, although its expression is also known to be associated with HTLV-I-infection. In Western blot analysis, a 50-kD protein band was detected by anti-OX40 monoclonal antibody (MoAb) in two ATL cases examined, as well as phytohemagglutinin (PHA) blasts and Hut102, an HTLV-I–infected T-cell line, but not in resting PBMC or Jurkat. Expression of OX40 mRNA was shown by reverse transcriptase-polymerase chain reaction in all ATL cases tested, PHA-blasts, and Hut102, but not in resting PBMC or Jurkat. We could not detect expression of HTLV-I viral mRNA in any of the cases tested. Cell adhesion assay was performed and in at least three cases, fresh ATL cells exhibited adhesion to human umbilical vein endothelial cells that could be considerably inhibited by either anti-OX40 MoAb or anti-gp34 MoAb. Immunohistochemical staining of skin biopsy specimens indicated that infiltrating mononuclear cells express OX40 in vivo. Taken together, these data indicate that leukemic cells from most, but not all, ATL patients constitutively express OX40, which may play a role in leukemic cell infiltration in addition to cell adhesion in vivo.

ATL and HTLV-I: in vivo cell growth of ATL cells

The mechanism of leukemogenesis or neoplastic cell growth in adult T cell leukemia (ATL) still remains unclear, although Tax of human T cell leukemia/lymphoma virus type I (HTLV-I), the etiologic virus, has been reported to affect the expression of various cellular genes which encode molecules involved in cell growth or cell death. We have studied the cell growth of HTLV-I-infected human T cells in severe combined immunodeficiency (SCID) mice and found that fresh leukemic cells or cell lines derived from leukemic cell clones but not HTLV-I-infected cell lines of nonleukemic cell origin showed tumorigenicity, and neither HTLV-I nor IL-2 expression was needed for cell growth in vivo, indicating that accumulating changes in addition to the initial events induced by HTLV-I infection were required for the development of ATL. The interaction between ATL cells and vascular endothelial cells appears to be one of the important factors which determine the pattern of organ infiltration by leukemic cells. E-selectin and its ligand are one of the major cell adhesion pathways between ATL cells and human umbilical vein endothelial cells (HUVEC). Another pathway that had not been identified was studied using newly developed monoclonal antibodies capable of blocking cell adhesion. The molecules which directly mediate adhesion between ATL cells and HUVEC were determined to be OX40 and gp34, a member of the tumor necrosis factor receptor (TNF-R) family and TNF family, respectively. The OX40/gp34 system may play a key role in the trafficking and homing of not only ATL cells but also activated normal T cells.

Molecular, structural, and biological characteristics of the tumor necrosis factor ligand superfamily

The tumor necrosis factor receptor superfamily at present consists of ten different transmembrane (type I) glycoproteins with characteristic limited sequence homology for the cysteine-rich repeats in the extracellular domain. In parallel the tumor necrosis factor ligand super-family has been recognized by discovery of ligands for all members of the receptor superfamily. These molecules are also transmembrane (type II) glycoproteins, with the exception of lymphotoxin-alpha which is the only entirely secreted protein of the tumor necrosis factor-like proteins. Several members of the ligand superfamily, including tumor necrosis factor and CD95L also exist in a biologically active soluble form. The tumor necrosis factor ligand superfamily contains at present ten different proteins. In addition, NGFR p75 binds to a second family of proteins (neurotrophins). These nerve growth factor-like dimeric soluble molecules are basic neurotrophic factors and the five members (NGF, BDNF, NT-3, NT-4, NT-5) are not related to the tumor necrosis factor superfamily ligands. The members of the tumor necrosis factor ligand superfamily (TNF, LT-alpha, LT-beta, CD27L, CD30L, CD40L, CD95L, 4-IBB, OX40L, TRAIL) share common biological activities, but some properties are shared by only some ligands, while others are unique. The diverse biological activities triggered through tumor necrosis factor receptors have been linked to the regulation of cellular activation, including immune responses and inflammatory reactions, but also with the pathology of a series of human diseases.

The human OX40/gp34 system directly mediates adhesion of activated T cells to vascular endothelial cells

Fresh leukemic cells from patients with adult T cell leukemia (ATL) and some ATL-derived T cell lines show adhesion to human umbilical vein endothelial cells (HUVECs) mainly through E-selectin, but a proportion of this binding remains unaffected by the addition of combinations of antibodies against known adhesion molecules. By immunizing mice with one of such cell lines, we established monoclonal antibodies (mAbs), termed 131 and 315, that recognize a single cell surface antigen (Ag) and inhibit the remaining pathway of the adhesion. These mAbs did not react with normal resting peripheral blood mononuclear cells (PBMC) or most of the cell lines tested except for two other human T cell leukemia virus type I (HTLV-I)-infected T cell lines. After stimulation with phytohemagglutinin (PHA), PBMC expressed Ag 131/315 transiently, indicating that these mAbs define a T cell activation Ag. Western blotting and immunoprecipitation revealed that Ag 131/315 has an apparent molecular mass of 50 kD. Expression cloning was done by transient expression in COS-7 cells and immunological selection to isolate a cDNA clone encoding Ag 131/315. Sequence analysis of the cDNA indicated that it is identical to human OX40, a member of the tumor necrosis factor/nerve growth factor receptor family. We then found that gp34, the ligand of OX40, was expressed on HUVECs and other types of vascular endothelial cells. Furthermore, it was shown that the adhesion of CD4+ cells of PHA-stimulated PBMC to unstimulated HUVECs was considerably inhibited by either 131 or 315. Finally, OX40 transfectants of Kit 225, a human interleukin 2-dependent T cell line, were bound specifically to gp34 transfectants of MMCE, a mouse epithelial cell line, and this binding was blocked by either 315 or 5A8, an anti-gp34 mAb. These results indicate that the OX40/gp34 system directly mediates adhesion of activated T cells or OX40+-transformed T cells to vascular endothelial cells.

Identification of a human OX-40 ligand, a costimulator of CD4+ T cells with homology to tumor necrosis factor

The human OX-40 cell surface antigen is a CD4+ T cell activation marker that acts as a costimulatory receptor and is a member of the nerve growth factor receptor/tumor necrosis factor (TNF) receptor family. Using a soluble form of the receptor, the extracellular region fused with human immunoglobulin Fc, we expression cloned the human OX-40 ligand cDNA from a library derived from an activated B lymphoblastoid cell line MSAB. The encoded protein is identified as gp34, a type II transmembrane antigen previously known to be expressed only by human T cell lymphotropic virus 1-infected cells. We describe gp34 as a new member of the TNF family, and find that the recombinant ligand expressed in COS cells costimulates phorbol myristate acetate, phytohemagglutinin, and anti-CD3-induced CD4+ T cell proliferation.

Characterization, isolation and amino terminal sequencing of a rat colon carcinoma-associated antigen

Monoclonal antibodies have been raised against a cell line derived from a dimethylhydrazine-induced rat colon carcinoma. One of these antibodies (MAb E4) has previously been shown to react slightly with normal small intestine and colon, and not with other normal tissues as determined by immunohistochemistry. Using Western immunoblotting we confirmed this tumor specificity. Therefore, the Mr of approx. 66,000 glycosylated antigen (pE4) recognized by MAb E4 appeared to be a potential marker of colon carcinoma. Fifteen human tumor cell lines were tested by flow cytometry for the expression of pE4. This antigen was not detected on these cells. In the rat colon carcinoma cell, pE4 was exclusively found on the cell membrane. pE4 was purified to near homogeneity by immunoaffinity chromatography. The first 20 N-terminal amino acids were identified. Comparison with the NBRF data bank did not reveal a complete homology with known sequenced proteins but similarities were found with the mouse L3T4 precursor, the env polyprotein of human immunodeficiency virus type I, flagellin from Halobacterium halobium and the gp30 from hepatitis B surface antigen. Homology was always found in transmembranous or hydrophobic domains of these proteins. By indirect immunofluorescence analysis of adherent cells and size exclusion chromatography under native conditions, pE4 was found to interact with other molecules and perhaps to be involved in intercellular contact.

Molecular cloning and characterization of a novel glycoprotein, gp34, that is specifically induced by the human T-cell leukemia virus type I transactivator p40tax

We have cloned and sequenced a cDNA encoding gp34, a novel glycoprotein expressed in cells bearing human T-cell leukemia virus type I (HTLV-I). HTLV-I has a trans-acting transcriptional activator, p40tax, that is thought to be implicated in leukemogenesis through the activation of cellular enhancers. With a subline (JPX-9) of the human T-cell line Jurkat, in which p40tax is inducible, gp34 was shown to be of cellular origin and to be transcriptionally activated by p40tax. It was also demonstrated that two species of mRNA are generated from one copy of the gp34 gene and that these mRNAs encode the identical gp34 product and differ in the 3' untranslated region. Analysis of the deduced amino acid sequence of gp34 showed that it lacks typical signal peptides; however, it has a hydrophobic stretch for membrane anchoring and four possible N-linked glycosylation sites at the carboxy-terminal portion, indicating that it belongs to the family of membrane proteins whose carboxy-terminal portion protrudes out of the cell. The gp34 gene displayed relatively delayed induction compared with other genes activated by p40tax. Taken together with the observation of the dependence of gp34 expression on HTLV-I p40tax, unlike other p40tax-dependent genes such as those for the interleukin-2 receptor alpha chain and c-fos, which are expressed or induced under physiological conditions, we predict that the mechanism involved in the induction of gp34 expression by p40tax is distinct from and more intricate than those for the previously characterized genes.

Molecular cloning and characterization of a novel glycoprotein, gp34, that is specifically induced by the human T-cell leukemia virus type I transactivator p40tax

We have cloned and sequenced a cDNA encoding gp34, a novel glycoprotein expressed in cells bearing human T-cell leukemia virus type I (HTLV-I). HTLV-I has a trans-acting transcriptional activator, p40tax, that is thought to be implicated in leukemogenesis through the activation of cellular enhancers. With a subline (JPX-9) of the human T-cell line Jurkat, in which p40tax is inducible, gp34 was shown to be of cellular origin and to be transcriptionally activated by p40tax. It was also demonstrated that two species of mRNA are generated from one copy of the gp34 gene and that these mRNAs encode the identical gp34 product and differ in the 3' untranslated region. Analysis of the deduced amino acid sequence of gp34 showed that it lacks typical signal peptides; however, it has a hydrophobic stretch for membrane anchoring and four possible N-linked glycosylation sites at the carboxy-terminal portion, indicating that it belongs to the family of membrane proteins whose carboxy-terminal portion protrudes out of the cell. The gp34 gene displayed relatively delayed induction compared with other genes activated by p40tax. Taken together with the observation of the dependence of gp34 expression on HTLV-I p40tax, unlike other p40tax-dependent genes such as those for the interleukin-2 receptor alpha chain and c-fos, which are expressed or induced under physiological conditions, we predict that the mechanism involved in the induction of gp34 expression by p40tax is distinct from and more intricate than those for the previously characterized genes.