HTLV-I--associated B-cell CLL: indirect role for retrovirus in leukemogenesis

Lymphoma-associated dysimmune polyneuropathies

Lymphoma consists of a variety of malignancies of lymphocyte origin. A spectrum of clinical peripheral neuropathy syndromes with different disease mechanisms occurs in about 5% of lymphoma patients. There exists a complex inter-relationship between lymphoproliferative malignancies and autoimmunity. An imbalance in the regulation of the immune system presumably underlies various immune-mediated neuropathies in patients with lymphoma. This article reviews lymphoma and more-or-less well-defined dysimmune neuropathy subgroups that are caused by humoral and/or cell-mediated immune disease mechanisms directed against known or undetermined peripheral nerve antigens.

Simian T-cell lymphotropic virus type I alters the proviral load and biodistribution of simian retrovirus type 2 in co-infected macaques, supporting advancement of immunosuppressive pathology

The infection dynamics and pathology of a retrovirus may be altered by one or more additional viruses. To investigate this further, this study characterized proviral load, biodistribution and the immune response in Macaca fascicularis naturally infected with combinations of simian retrovirus type 2 (SRV-2) and simian T-cell lymphotropic virus type I (STLV-I). As the mesenteric lymph node (MLN) and the spleen have been implicated previously in response to retroviral infection, the morphology and immunopathology of these tissues were assessed. The data revealed a significant change in SRV-2 biodistribution in macaques infected with STLV-I. Pathological changes were greater in the MLN and spleen of STLV-I-infected and co-infected macaques compared with the other groups. Immune-cell populations in co-infected macaque spleens were increased and there was an atypical distribution of B-cells. These findings suggest that the infection dynamics of each virus in a co-infected individual may be affected to a different extent and that STLV-I appears to be responsible for enhancing the biodistribution and associated pathological changes in SRV-2 in macaques.

Torque teno virus 10 isolated by genome amplification techniques from a patient with concomitant chronic lymphocytic leukemia and polycythemia vera

An infectious etiology has been proposed for many human cancers, but rarely have specific agents been identified. One difficulty has been the need to propagate cancer cells in vitro to produce the infectious agent in detectable quantity. We hypothesized that genome amplification from small numbers of cells could be adapted to circumvent this difficulty. A patient with concomitant chronic lymphocytic leukemia (CLL) and polycythemia vera (PV) requiring therapeutic phlebotomy donated a large amount of phlebotomized blood to test this possibility. Using genome amplification methods, we identified a new isolate (BIS8-17) of torque teno virus (TTV) 10. The presence of blood isolate sequence 8-17 (BIS8-17) in the original plasma was confirmed by polymerase chain reaction (PCR), validating the approach, since TTV is a known plasma virus. Subsequent PCR testing of plasmas from additional patients showed that BIS8-17 had a similar incidence (~20%) in CLL (n = 48) or PV (n = 10) compared with healthy controls (n = 52). CLL cells do not harbor BIS8-17; PCR did not detect it in CLL peripheral blood genomic deoxyribonucleic acid (DNA) (n = 20). CLL patient clinical outcome or prognostic markers (immunoglobulin heavy chain variable region [IGHV ] mutation, CD38 or zeta-chain associated protein kinase 70 kDa [ZAP-70]) did not correlate with BIS8-17 infection. Although not causative to our knowledge, this is the first reported isolation and detection of TTV in either CLL or PV. TTV could serve as a covirus with another infectious agent or TTV variant with rearranged genetic components that contribute to disease pathogenesis. These results prove that this method identifies infectious agents and provides an experimental methodology to test correlation with disease.

Activation and detection of HTLV-I Tax-specific CTLs by epitope expressing single-chain trimers of MHC class I in a rat model

Background

Human T cell leukemia virus type I (HTLV-I) causes adult T-cell leukemia (ATL) in infected individuals after a long incubation period. Immunological studies have suggested that insufficient host T cell response to HTLV-I is a potential risk factor for ATL. To understand the relationship between host T cell response and HTLV-I pathogenesis in a rat model system, we have developed an activation and detection system of HTLV-I Tax-specific cytotoxic T lymphocytes (CTLs) by Epitope expressing Single-Chain Trimers (SCTs) of MHC Class I.

Results

We have established expression vectors which encode SCTs of rat MHC-I (RT1.A^l) with Tax180-188 peptide. Human cell lines transfected with the established expression vectors were able to induce IFN-γ and TNF-α production by a Tax180-188-specific CTL line, 4O1/C8. We have further fused the C-terminus of SCTs to EGFP and established cells expressing SCT-EGFP fusion protein on the surface. By co-cultivating the cells with 4O1/C8, we have confirmed that the epitope-specific CTLs acquired SCT-EGFP fusion proteins and that these EGFP-possessed CTLs were detectable by flow cytometric analysis.

Conclusion

We have generated a SCT of rat MHC-I linked to Tax epitope peptide, which can be applicable for the induction of Tax-specific CTLs in rat model systems of HTLV-I infection. We have also established a detection system of Tax-specific CTLs by using cells expressing SCTs fused with EGFP. These systems will be useful tools in understanding the role of HTLV-I specific CTLs in HTLV-I pathogenesis.

Enhanced replication of human T-cell leukemia virus type 1 in T cells from transgenic rats expressing human CRM1 that is regulated in a natural manner

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). To develop a better animal model for the investigation of HTLV-1 infection, we established a transgenic (Tg) rat carrying the human CRM1 (hCRM1) gene, which encodes a viral RNA transporter that is a species-specific restriction factor. At first we found that CRM1 expression is elaborately regulated through a pathway involving protein kinase C during lymphocyte activation, initially by posttranscriptional and subsequently by transcriptional mechanisms. This fact led us to use an hCRM1-containing bacterial artificial chromosome clone, which would harbor the entire regulatory and coding regions of the CRM1 gene. The Tg rats expressed hCRM1 protein in a manner similar to expression of intrinsic rat CRM1 in various organs. HTLV-1-infected T-cell lines derived from these Tg rats produced 100- to 10,000-fold more HTLV-1 than did T cells from wild-type rats, and the absolute levels of HTLV-1 were similar to those produced by human T cells. We also observed enhancement of the dissemination of HTLV-1 to the thymus in the Tg rats after intraperitoneal inoculation, although the proviral loads were low in both wild-type and Tg rats. These results support the essential role of hCRM1 in proper HTLV-1 replication and suggest the importance of this Tg rat as an animal model for HTLV-1.

Among B cell non-Hodgkin's lymphomas, MALT lymphomas express a unique antibody repertoire with frequent rheumatoid factor reactivity

We analyzed the structure of antigen receptors of a comprehensive panel of mature B non-Hodgkin's lymphomas (B-NHLs) by comparing, at the amino acid level, their immunoglobulin (Ig)V_H-CDR3s with CDR3 sequences present in GenBank. Follicular lymphomas, diffuse large B cell lymphomas, Burkitt's lymphomas, and myelomas expressed a CDR3 repertoire comparable to that of normal B cells. Mantle cell lymphomas and B cell chronic lymphocytic leukemias (B-CLLs) expressed clearly restricted albeit different CDR3 repertoires. Lymphomas of mucosa-associated lymphoid tissues (MALTs) were unique as 8 out of 45 (18%) of gastric- and 13 out of 32 (41%) of salivary gland-MALT lymphomas expressed B cell antigen receptors with strong CDR3 homology to rheumatoid factors (RFs). Of note, the RF-CDR3 homology without exception included N-region–encoded residues in the hypermutated IgV_H genes, indicating that they were stringently selected for reactivity with auto-IgG. By in vitro binding studies with 10 MALT lymphoma–derived antibodies, we showed that seven of these cases, of which four with RF-CDR3 homology, indeed possessed strong RF reactivity. Of one MALT lymphoma, functional proof for selection of subclones with high RF affinity was obtained. Interestingly, RF-CDR3 homology and t(11;18) appeared to be mutually exclusive features and RF-CDR3 homology was not encountered in any of the 19 pulmonary MALT lymphomas studied.

Mechanisms of B-cell lymphoma pathogenesis

Chromosomal translocations involving the immunoglobulin loci are a hallmark of many types of B-cell lymphoma. Other factors, however, also have important roles in the pathogenesis of B-cell malignancies. Most B-cell lymphomas depend on the expression of a B-cell receptor (BCR) for survival, and in several B-cell malignancies antigen activation of lymphoma cells through BCR signalling seems to be an important factor for lymphoma pathogenesis. Recent insights into the lymphomagenic role of factors supplied by the microenvironment also offer new therapeutic strategies.

Human T-cell lymphotropic virus type 1 (HTLV-1) and lymphoid malignancies in Dominica: a seroprevalence study

Human T-cell lymphotropic virus type 1 (HTLV-1) is endemic in certain regions of the world where it is associated with lymphoid malignancies. Herein we aim to describe the seroprevalence of HTLV-1 in lymphoid malignancies in Dominica. We carried out a 10-year retrospective study of histologically proven hematologic malignancies and HTLV-1 seropositivity at the Princess Margaret Hospital, Dominica. Ninety-eight cases were reviewed (59% males, 41% females), ranging in age from 3 to 91 years. HTLV-1 was seropositive in 38.6% (31/80) of all hematologic malignancies. Three of 6 cases of Hodgkin disease (50%), 16 of 36 (44.4%) of non-Hodgkin lymphoma, and 3 out of 8 unclassified lymphomas (37.5%) were seropositive; all 6 cases (100%) of acute adult T-cell leukemia/lymphoma (ATLL) were seropositive. One case each of chronic lymphocytic leukemia and myeloproliferative disorder was seropositive. HTLV-1-seropositive lymphomas presented at a younger age than did seronegative cases. Thus, HTLV-1 is significantly associated with lymphoid malignancies in Dominica, and further studies are needed before a causal relationship with Hodgkin disease can be established.

Multiple distinct sets of stereotyped antigen receptors indicate a role for antigen in promoting chronic lymphocytic leukemia

Previous studies suggest that the diversity of the expressed variable (V) region repertoire of the immunoglobulin (Ig)H chain of B-CLL cells is restricted. Although limited examples of marked constraint in the primary structure of the H and L chain V regions exist, the possibility that this level of restriction is a general principle in this disease has not been accepted. This report describes five sets of patients, mostly with unmutated or minimally mutated IgV genes, with strikingly similar B cell antigen receptors (BCRs) arising from the use of common H and L chain V region gene segments that share CDR3 structural features such as length, amino acid composition, and unique amino acid residues at recombination junctions. Thus, a much more striking degree of structural restriction of the entire BCR and a much higher frequency of receptor sharing exists among patients than appreciated previously. The data imply that either a significant fraction of B-CLL cells was selected by a limited set of antigenic epitopes at some point in their development and/or that they derive from a distinct B cell subpopulation with limited Ig V region diversity. These shared, stereotyped Ig molecules may be valuable probes for antigen identification and important targets for cross-reactive idiotypic therapy.

Recent advances in the molecular biology and immunobiology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) has long been viewed as a relatively homogeneous disease caused by the accumulation of monoclonal immature, immunoincompetent B cells with faulty apoptotic capacities. However, recent evidence, reviewed here, demonstrates that at least two different B-CLL subgroups exist with different clinical courses and outcomes. The malignant cells from both B-CLL subgroups are antigen-experienced cells that have a normal apoptotic apparatus and turnover continually. The leukemic cells of the two B-CLL subgroups have engaged antigen before transformation, although primarily the cells of patients in the poor outcome subgroup can respond to antigens following transformation. The difference in the ability to respond to antigen as a full-fledged B-CLL probably accounts for the different biological features and clinical outcomes of the patients in these subgroups.

HTLV-1 carriers with B-cell lymphoma of localized stage head and neck: prognosis, clinical and immunopathological features

Human T-lymphotropic virus type I (HTLV-I) is closely associated with T-cell lymphoma/leukaemia, which always shows monoclonal HTLV-1 provirus DNA integration. HTLV-1 is not associated with B-cell lymphoma. The relationship between B-cell lymphoma and HTLV-1 was analysed retrospectively in early stage B-cell non-Hodgkin's lymphoma (NHL) according to HTLV-1 infection and pathological features. We analysed 198 cases of head and neck B-cell NHL treated with radiotherapy and/or chemotherapy; 21 were seropositive and 177 were seronegative for HTLV-1. We also immunostained 26 cases of diffuse large B-cell lymphoma (DLBL), including 12 seropositive and 14 seronegative for HTLV-1 respectively, for CD20, CD3, CD4, CD8, CD56, MIB-1 and T-cell-restricted intracellular antigen (TIA-1) to examine the phenotype, immunity and proliferation activity. The 5-year overall survival rates were 78% and 49% (P = 0.007, log rank test) for HTLV-1 seronegative and seropositive cases respectively. Infection with HTLV-1 was significantly associated with poor survival in patients with B-cell lymphoma by multivariate analysis. For DLBL, HTLV-1 infection was not a significant factor, but the overall survival curve was similar to that of the 21 seropositive B-cell lymphoma cases. Lymphoma cells were negative for TIA-1, but the background lymphocytes were positive for this marker. The number of TIA-1-positive cells was higher in HTLV-1-negative cases than in-positive cases. In conclusion, patients with B-cell-NHL (B-NHL) who are also HTLV-1 carriers have a poorer prognosis than non-carriers. HTLV-1 does not seem to be associated with lymphomagenesis of the B phenotype itself, but correlates with host immunity by reducing the number of cytotoxic T-cells.

Human T lymphotropic virus type 1 in a seronegative B chronic lymphocytic leukemia patient

Human T lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis. HTLV-1 infection in patients with B cell-type chronic lymphocytic leukemia (B-CLL) is rare and has been reported only in areas in which HTLV-1 is endemic. In the present study, we detected HTLV-1 proviral DNA by polymerase chain reaction, using tax primers, in peripheral blood lymphocytes from a B-CLL patient, an immigrant to Israel, where HTLV-1 infection is not endemic. F344 rats injected intravenously with peripheral blood lymphocytes obtained from the patient developed HTLV-1 antibodies. Titers of antibody to HTLV-1 in the rat blood were 1:512 by particle agglutination; enzyme-linked immunosorbent assay and Western blotting were also positive. No antibody against HTLV-1 was demonstrated in the animal model after inoculation of either purified B lymphocytes from the B-CLL patient or peripheral blood mononuclear cells from healthy donors. This is one of the few studies showing the presence of HTLV-1 provirus in T lymphocytes of a B-CLL patient who had multiple infections, and died of salmonella sepsis, and the first report of HTLV-1 antibody induction in an animal model by inoculation of lymphocytes obtained from an HTLV-1-infected B-CLL patient.

B cell chronic lymphocytic leukemia: lessons learned from studies of the B cell antigen receptor

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

Correlation of major histocompatibility complex class I downregulation with resistance of human T-cell leukemia virus type 1-infected T cells to cytotoxic T-lymphocyte killing in a rat model

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATL) in infected individuals after a long incubation period. Despite the apparent transforming ability of HTLV-1 under experimental conditions, most HTLV-1 carriers are asymptomatic. These facts suggest that HTLV-1 is controlled by host immunity in most carriers. To understand the interplay between host immunity and HTLV-1-infected cells, in this study, we isolated several HTLV-1 Tax-specific cytotoxic T-lymphocyte (CTL) lines from rats inoculated with Tax-coding DNA and investigated the long-term effects of the CTL on syngeneic HTLV-1-infected T cells. Our results demonstrated that long-term mixed culture of these CTL and the virus-infected T cells led to the emergence of CTL-resistant HTLV-1-infected cells. Although the Tax expression level in these resistant cells was equivalent to that in the parental cells, expression of surface major histocompatibility complex class I (MHC-I) was significantly downregulated in the resistant cells. Downregulation of MHC-I was more apparent in RT1.A(l), which presents a Tax epitope recognized by the CTL established in this study. Moreover, peptide pulsing resulted in killing of the resistant cells by CTL, indicating that resistance was caused by a decreased epitope density on the infected cell surface. This may be one of the mechanisms for persistence of HTLV-1-infected cells that evade CTL lysis and potentially develop ATL.

Malignant B cells and antigenic receptor: necessity or habit?

B-cell malignancies account for the majority of lymphoid tissue neoplasia. Similar to normal B cells, malignant B cells in most Hodgkin's and non-Hodgkin's types of lymphomas express B-cell receptor (BCR) on their membrane. Since neoplastic B cells retain the capacity to respond to microenvironmental signals, and in many respects still behave as normal B cells, it does not seem bizarre that the BCR, which dominates the biology of normal B cells, can remain equally important for some malignant B cells. Indirect evidence suggests that retained BCR expression, and in certain cases coupled with stimulation by antigen (Ag), may be necessary for the viability of some B-cell tumors. The aim of this review is to consider the evidence regarding the role of the BCR in tumorigenesis of B-cell lymphomas, and discuss different approaches used in evaluating this role in the persistence and progression of these malignancies. The diversity in B-cell lymphomas prevents easy classification of these cancers based on their dependence on BCR expression. It seems likely that some malignant B cells need BCR expression, or additionally, stimulation by Ag in order to survive. However, through accumulation of additional genetic changes, the original tumor can give rise to a clone that no longer requires signals from the BCR to survive. Thus, most B-cell lymphomas may initially retain dependence on BCR expression that governs normal B-cell physiology and may lose it only at later stages of tumor progression, through the accumulation of additional transforming events.

Malignancy: Human T-Cell Lymphotropic Virus Type I and Adult T-Cell Leukaemia/Lymphoma

Adult T-cell leukaemia/lymphoma (ATLL) was first identified in Japan in 1977 [1,2]. The causative agent, the human T-lymphotropic virus type I (HTLV-I), was isolated 3 years later by Gallo's group from a patient initially diagnosed as having mycosis fungoides but subsequently reclassified as a case of ATLL [3]. Since this time, much has been discovered about the molecular pathogenesis of the disease. Despite this, treatment of ATLL remains disappointing and the prognosis of acute and lymphoma types poor. In the United Kingdom, cases of ATLL are mainly restricted to people of Afro-Caribbean descent but the disease is of general importance because ATLL has also been reported in non-endemic areas and may possibly spread into other populations via blood transfusion as blood donors in the UK are currently not screened for HTLV-I.

Clonal evolution in Waldenstrom macroglobulinemia highlights functional role of B-cell receptor

The course of clonal evolution of 2 related clones in the blood of a patient with Waldenstrom macroglobulinemia (WM) indicates the functional importance for the expression of the B-cell receptor for the survival of these malignant cells. Protein and nucleotide sequencing of the paraproteins' variable regions revealed 2 predominant Vlambda and 2 VH sequences, each set comprised in the ratio 1:1.5. The 2 VH sequences and 2 Vlambda sequences shared the same VDJ and VJ junctional sequences, respectively, indicating that 2 malignant clones had evolved from a common ancestor. This is the first report on intraclonal heterogeneity in WM. Comparison of the Vlambda and VH sequences with the closest matching known germline genes showed that they contained approximately 10 somatic mutations each. The distribution and type of mutations demonstrate that mutations have continued to accumulate in the malignant clones and that selection has been operating to preserve immunoglobulin structure.

Human retroviruses: their role in cancer

Viruses are etiologically linked to approximately 20% of all malignancies worldwide. Retroviruses account for approximately 8%-10% of the total. For human T-cell leukemia virus 1 (HTLV-I), the viral regulatory tax gene product is responsible for enhanced transcription of viral and cellular genes that promote cell growth by stimulating various growth factors and through dysregulation of cellular regulatory suppressor genes, such as p53. After a long latent period, adult T-cell leukemia/lymphoma (ATL) occurs in 1 per 1000 carriers per year, resulting in 2500-3000 cases per year worldwide and over half of the adult lymphoid malignancies in endemic areas. Human immunodeficiency virus 1 (HIV-1) accounts for a significant cancer burden, and its transactivating regulatory protein Tat enhances direct and indirect cytokine and immunological dysregulation to cause diverse cancers. Kaposi's sarcoma (KS) is a very rare tumor except after HIV-1 infection, when its incidence is greatly amplified reaching seventy thousand-fold in HIV-infected homosexual men. Human herpesvirus 8 (HHV-8), which is also known as Kaposi's sarcoma-associated virus (KSHV), is a necessary but not sufficient etiological factor in KS. The dramatic decline of KS since the introduction of highly active antiretroviral therapy (HAART) could be due to suppression of HIV-1 tat. B-cell non-Hodgkin's lymphoma occurs as their first acquired immunodeficiency syndrome-defining diagnosis in 3%-4% of HIV-infected patients. Hodgkin's lymphoma is also associated with HIV infection but at a lower risk. Human papillomaviruses are linked to invasive cervical cancer and anogenital cancers among HIV-infected patients. Human retroviruses cause malignancy via direct effects as well as through interactions with other oncogenic herpesviruses and other viruses.

Sensorimotor polyneuropathy associated with chronic lymphocytic leukemia, IgM antigangliosides antibody and human T-cell leukemia virus I infection

A 65-year-old man presented with a sensorimotor polyneuropathy associated with B-cell chronic lymphocytic leukemia (CLL) and immunoglobulin M (IgM) antibody to various gangliosides. Electrophysiological studies denoted significant abnormalities of motor and sensory nerve conduction. Although the pathology of sural nerve biopsy looked minimally affected, immunohistochemical studies showed specific binding of IgM to the human peripheral nerve. Our patient also had high titer of antibody to human T-cell leukemia virus I (HTLV-I) in both serum and cerebrospinal fluid (CSF), which might activate B-cell-mediated immunity and facilitate the production of IgM antibody. The other unique feature is the reactivity of antibody to gangliosides. The patient had IgM antibody reactivities to gangliosides with disialosyl residue such as GT1b, GQ1b and GD3, but not to GD1b. IgM antibody to gangliosides with disialosyl residue has been reported in ataxic symptoms, but our patient failed to demonstrate ataxia. Without reactivity to GD1b, sensory ataxic neuropathy might not develop even in the presence of antibody reactive to other gangliosides with disialosyl residue.

Induction of adult T-cell leukemia-like lymphoproliferative disease and its inhibition by adoptive immunotherapy in T-cell-deficient nude rats inoculated with syngeneic human T-cell leukemia virus type 1-immortalized cells

Human T-cell leukemia virus type 1 (HTLV-1) has been shown to be the etiologic agent of adult T-cell leukemia (ATL), but the in vivo mechanism by which the virus causes the malignant transformation is largely unknown. In order to investigate the mechanisms of HTLV-1 leukemogenesis, we developed a rat model system in which ATL-like disease was reproducibly observed, following inoculation of various rat HTLV-1-immortalized cell lines. When previously established cell lines, F344-S1 and TARS-1, but not TART-1 or W7TM-1, were inoculated, systemic multiple tumor development was observed in adult nude (nu/nu) rats. FPM1 cells, newly established from a heterozygous (nu/+) rat syngeneic to nu/nu rats, caused transient tumors only at the injection site in adult nu/nu rats, but could progressively grow in newborn nu/nu rats and metastasize in lymph nodes. The derivative cell line (FPM1-V1AX) serially passed through newborn nu/nu rats acquired the potency to grow in adult nu/nu rats. These results indicated that only some with additional changes but not all of the in vitro HTLV-1-immortalized cell lines possessed in vivo tumorigenicity. Using the syngeneic system, we further showed the inhibition of tumor development by transferring splenic T cells from immunized rats, suggesting the involvement of T cells in the regression of tumors. This novel and reproducible nude rat model of human ATL would be useful for investigation of leukemogenesis and antitumor immune responses in HTLV-1 infection.

Physical and functional interaction between the human T-cell lymphotropic virus type 1 Tax1 protein and the CCAAT binding protein NF-Y

Tax1, a potent activator of human T-cell lymphotropic virus type 1 (HTLV-1) transcription, has been shown to modulate expression of many cellular genes. Tax1 does not bind DNA directly but regulates transcription through protein-protein interactions with sequence-specific transcription factors. Using the yeast two-hybrid system to screen for proteins which interact with Tax1, we isolated the B subunit of the CCAAT binding protein NF-Y from a HeLa cDNA library. The interaction of Tax1 with NF-YB was specific in that NF-YB did not interact with a variety of other transcription factors, including human immunodeficiency virus Tat, human papillomavirus E6, and Bicoid, or with the M7 (amino acids 29CP-AS) Tax1 mutant. However, NF-YB did interact with the C-terminal Tax1 mutants M22 (130TL-AS) and M47 (319LL-RS). We also show that in vitro-translated NF-YB specifically bound to a glutathione S-transferase-Tax1 fusion protein. Further, Tax1 coimmunoprecipitated with NF-Y from nuclear extracts of HTLV-1-transformed cells, providing evidence for in vivo interaction of Tax1 and NF-YB. We further demonstrate that Tax1 specifically activated the NF-Y-responsive DQbeta promoter, as well as a minimal promoter which contains only the Y-box element. In addition, mutation of the Y-box element alone abrogated Tax1-mediated activation. Taken together, these data indicate that Tax1 interacts with NF-Y through the B subunit and that this interaction results in activation of the major histocompatibility complex class II promoter. Through activation of this and other NF-Y driven promoters, the Tax1-NF-Y interaction may play a critical role in causing cellular transformation and HTLV-1 pathogenesis.

HTLV Tax gene expression in patients with lymphoproliferative disorders

AIMS

To study the expression of the human T lymphotropic virus (HTLV) Tax gene in peripheral blood mononuclear cells.

METHODS

Blood was collected from 72 patients with lymphoproliferative disorders. Serum from all patients was assayed for antibodies directed against HTLV-I structural proteins by ELISA and western blotting. RNA was purified from fresh blood cells and amplified by reverse transcription polymerase chain reaction (RT-PCR). After Southern blotting, the PCR products were hybridised with a 32P end-labelled probe specific for the Tax gene.

RESULTS

All samples were seronegative. A specific band for the Tax gene was found in five samples. Each of the patients positive for Tax gene expression had a different type of lymphoproliferative disorder.

CONCLUSIONS

Infection by HTLV-I cannot be assessed solely by immunological assays, particularly when only disrupted virions are used. Sensitive molecular biology assays are essential for detecting viral gene expression in fresh blood cells.

Do superantigens play a role in lymphoproliferation?

The T cell superantigens are infectious agents that interact with the T cell receptor and the MHC molecules outside their normal antigen-specific sites, with products of conserved sequences of the variable region chains. This non-specific interaction results in the massive stimulation of T cells (up to 20% of the total) as opposed to conventional antigenic stimulation, which is specific and limited to about 10,000 cells. B cell superantigens have recently been described, stimulating a restricted subset of B cells, those expressing the VH3 subgroup in their rearranged immunoglobulin genes. A number of murine malignancies have been shown to be due to T cell superantigens acting either on T cells or on B cells: the RCS B cell lymphomas in SJL mice, the radiation leukemia virus-induced T cell thymic lymphomas in C57BL/Ka mice and B cell lymphomas in the murine AIDS. We propose that some human B cell malignancies can be due to a similar type of interaction. B cell lymphomas in AIDS patients were recently suggested to be due to the HIV gp120 envelope glycoprotein, a newly recognized superantigen. It can be speculated that the low grade B cell gastric lymphomas of mucosa-associated lymphoid tissue (MALT) are the result of exposure to the H. pylori pathogen. EBV-related lymphocytic proliferation has also been shown to be related with a restricted repertoire and may constitute another example of superantigen driven proliferation. A classification of the various superantigen-driven lymphoproliferative states is proposed.

Mantle cell lymphoma with the features of mucosa-associated lymphoid tissue (MALT) lymphoma in an HTLV-I-seropositive patient

A case of small lymphocytic B-cell lymphoma with seropositivity for human T-cell leukemia virus type I (HTLV-I), whose clinical features were closely related to those of mucosa-associated lymphoid tissue (MALT) lymphoma, is presented. The neoplastic cells of the lymph node were immunologically positive for CD5, in addition to several B-cell markers, but negative for CD10, and cytogenetically carried a t(11;14)(q13;q32). These findings were fully consistent with so-called mantle cell lymphoma (MCL). In addition to the lymph nodes and bone marrow, multiple extranodal sites including lacrimal and salivary glands, lung and stomach (where MALT is present) were occupied by lymphoma cells. These extranodal lesions were immunologically identical to the lymph nodes (CD5(+), CD10(-)), but histologically showed lymphoepithelial lesions (LEL) characteristic of MALT lymphoma. These findings suggest a possible relationship between MCL and MALT lymphoma, and the neoplastic cells are thought to originate from the CD5-positive B cells, which are present near the areas across the mantle and marginal zones. Furthermore, HTLV-I-infection, which appears to create an immunodeficient state or modulate the B-cell response, is thought to play a role in B-cell lymphomagenesis.

Mechanisms of Tax Regulation of Human T Cell Leukemia Virus Type I Gene Expression

During the last several years, the human T cell leukemia virus type I (HTLV-I) has become recognized as an important cause for public health concern throughout the world. HTLV-I is the causative agent of a variety of clinical diseases, including an aggressive lymphoproliferative disorder named adult T cell leukemia. HTLV-I induces pathogenicity in the infected host cell through the synthesis of a virally encoded protein called Tax. Expression of Tax is critical to the life cycle of the virus, as the protein greatly increases the efficiency of HTLV-I gene transcription and replication. Furthermore, Tax has been shown to deregulate the transcription of many cellular genes, leading to the hypothesis that the presence of Tax promotes unchecked growth in the HTLV-I-infected cell. The mechanism of Tax trans-activation of HTLV-I gene expression is not known. Tax does not bind directly to the Tax-responsive promoter elements of the virus, but appears to function through interaction with certain cellular DNA binding proteins, including activating transcription factor 2 and cAMP response element binding protein that recognize these sequences. This review summarizes some of the recent work in the field aimed at elucidating the mechanism of Tax trans-activation of HTLV-I gene expression. Copyright 1995 S. Karger AG, Basel

Role of HTLV-I in development of non-Hodgkin lymphoma in Jamaica and Trinidad and Tobago. The HTLV Lymphoma Study Group

Human T-cell lymphotropic virus type I (HTLV-I) has been implicated in the aetiology of adult T-cell leukaemia/lymphoma in Japan and elsewhere, particularly the Caribbean. We have carried out parallel case-control studies in Jamaica and in Trinidad and Tobago to quantify the role of HTLV-I in the development of non-Hodgkin lymphoma (NHL). 135 cases of NHL were enrolled in Jamaica and 104 in Trinidad and Tobago. Controls were selected from patients treated in the same wards or clinics at the same time as the cases. Overall, patients with NHL were 10 times more likely than were controls to be seropositive for HTLV-I (Jamaica odds ratio 10.3 [95% CI 6.0-18.0], Trinidad and Tobago 14.4 [7.6-27.2]). In both countries the association between NHL and HTLV-I was greatest for T-cell lymphomas (18.3 [9.5-35.6] and 63.3 [25-167]). Among T-cell lymphomas especially, there was no significant difference between men and women in the association between NHL and HTLV-I, but there was a significant inverse relation between age and likelihood of HTLV-I seropositivity. B-cell lymphomas were predominant in the older age groups and were not associated with HTLV-I seropositivity. These findings are consistent with the hypothesis that early life exposure to HTLV-I is important for risk of subsequent ATL. Prevention of vertical transmission of HTLV-I could reduce by 70-80% cases of NHL in people under 60 years in this region.

Activation of the human T-cell leukemia virus type I enhancer is mediated by binding sites for Elf-1 and the pets factor

Infection with human T-cell leukemia virus type I (HTLV-I) is associated with adult T-cell lymphoma/leukemia. This disease occurs in only a small minority of people infected with HTLV-I and manifests itself many years after infection. Therefore, it appears that a fine balance exists between HTLV-I and the host T-cell factors with which it interacts. HTLV-I encodes a transactivating protein, Tax, which activates viral transcription via cellular mechanisms which are incompletely understood. As viral gene expression is negligible during latency, it is doubtful that Tax controls the initial transition to the replicative state. Tax-independent cellular factors which control HTLV-I transcription, and presumably latency, have received little study. Recently, the product of the chicken proto-oncogene ets-1 has been shown to bind to the HTLV-I enhancer and modestly activate transcription in certain cell types (S. C. Gitlin, R. Bosselut, A. Gégonne, J. Ghysdael, and J. N. Brady, J. Virol. 65:5513-5523, 1991). However, the functional significance of the ets-binding site in the intact enhancer has not previously been shown. We now demonstrate that site-specific mutation of the purine-rich ets-binding site significantly diminishes inducible enhancer function, but not Tax response, in the human Jurkat T-cell line. Similarly, mutation of the peri-ets (pets) site, not previously noted in the HTLV-I enhancer, markedly inhibits inducible enhancer function but not Tax response. Further, we show that the predominant protein binding the purine-rich HTLV-I enhancer element in human T cells is not ets-1 but Elf-1, a member of the ets family which is very similar to the Drosophila morphogen E74. Regulation of HTLV-I through Elf-1/pets enhancer motifs resembles that seen with human immunodeficiency virus type 2 (D. M. Markovitz, M. Smith, J. Hilfinger, M. C. Hannibal, B. Petryniak, and G. J. Nabel, J. Virol. 66:5479-5484, 1992; J. M. Leiden, C.-W. Wang, B. Petryniak, M. Smith, D. M. Markovitz, G. J. Nabel, and C. B. Thompson, J. Virol. 66:5890-5897, 1992), another human pathogenic retrovirus with a relatively long incubation period.

IgG-kappa-type plasmacytoma secreting salivary-type amylase in adult T-cell leukemia

A IgG-kappa-type plasmacytoma secreting salivary-type amylase ectopically is reported in a patient with smouldering adult T-cell leukemia(ATL). The patient had plasmacytomas in the distal region of the right femur, the proximal region of left tibia, and the left paranasal sinus. Both his serum and urine contained high levels of amylase. The presence of IgG-kappa and S-type amylase in the plasmacytoma cells was confirmed immunocytochemically. In addition, he was also positive for the antibody against the human T-cell leukemia virus type I (HTLV-I), and had abnormal lymphocytes with convoluted nuclei (ATL cells) in the peripheral blood. The monoclonal integration of HTLV-I proviral DNA was demonstrated in the leukemic cells of the peripheral blood, but not in the plasmacytoma cells. Our case suggested that not only can HTLV-I infection play a role in the development of ATL, but may also induce a B-cell malignancy in an indirect manner, and even an ectopic amylase producing plasmacytoma.

Large granular lymphocytosis in a patient infected with HTLV-II

HTLV-II has been associated with a variety of lymphoproliferative disorders, including atypical hairy cell leukemia, chronic T cell leukemia, T prolymphocytic leukemia, and large granular lymphocytic leukemia. However, a direct or indirect role for HTLV-II in these disorders is not yet firmly established. We studied a patient diagnosed as having leukemia of the large granular lymphocyte (LGL) type who was HTLV-II seropositive, to determine if the expanded cell population was infected. Two populations of CD3-CD16+ LGL were identified; one was CD8+, the other CD8-. Populations of cells with these surface markers as well as normal CD3+CD4+ and CD3+CD8+ cells were separated by flow cytometric methods, DNA extracted, and gene regions of HTLV-II pol and tax amplified, using the polymerase chain reaction, and probed after Southern blotting. HTLV-II was detected in the CD3+CD8+ population, and not in the CD3-CD16+ large granular lymphocyte population. This finding indicates that the role of HTLV-II, if any, in LGL proliferation is indirect.

Clinical, morphological and virological features of an HTLV-I-positive case of ATL in a white man from the Caucasus

An HTLV-I-associated case of adult T-cell leukemia (ATL) was described in a 51-year-old white man, native from Georgia, the former U.S.S.R. Clinical manifestation of the disease (enlarged lymph nodes, bone marrow and peripheral blood changes, CNS-involvement, cutaneous lesions and hypercalcemia) as well as laboratory findings were recognized to be very similar to those frequently observed in ATL patients from endemic regions. Mature T-helper surface phenotype detected on peripheral blood lymphocytes of the patient (OKT3-, OKT4+ and OKT8-) and aggressive course of the disease were also in favour of classical type ATL developed in the patient. The HTLV-I antibody presence in an ATL patient was repeatedly confirmed by serological tests (Abbott HTLV-I EIA and Serodia HTLV-I), immunofluorescence and Western blot assay. The latter revealed the presence of a large spectrum of HTLV-I-specific antibodies (to p19, p24, p26, p28, p32, p36, pr53, gp21, gp46, gp62 and gp68 of HTLV-1). The HTLV-I-specific antibodies have also been detected in serum samples of the patient's wife and son. The presence of HTLV-I provirus in the primary ATL patient's PBL was clearly demonstrated by PCR and Southern blot analysis. This case, with the HTLV-I infections detected in two other family members, suggests that in Europe, HTLV-I-positive cases of ATL can occur in virus-infected local people with much wider distribution than that hitherto supposed.

Immunoglobulin VH4 gene usage in B lymphoid leukaemias

VH4 gene rearrangements occur in a similar proportion of cases of B lineage acute lymphoblastic leukaemia (ALL) and B chronic lymphocytic leukaemia (B CLL). However, there may be differences in the pattern of VH4 gene usage between these disorders as is the case for VH1 gene rearrangements. To examine this, we analysed the sequences of 24 PCR-amplified clonal VH4 gene rearrangements from a series of 15 cases of ALL and nine cases of CLL. Five distinct groups of genes were rearranged, three of which (represented by V2-1, V71-2/V71-4, V4.21) have been described in rearranged form in normal B lymphoid tissues. The most frequently rearranged gene was V4.21 which is strongly associated with autoimmune reactivity. V71-2, V71-4 and V2-1 were more frequently rearranged in CLL than ALL. The remaining two groups (represented by V4.33, V4.35) have not previously been described in rearranged form. One of these, V4.35, was seen only in ALL rearrangements. Both V4.35 and a VH1 gene, 20P3, which is also preferentially rearranged in ALL, are located at the 3' end of the VH locus. The location of these genes suggests that their rearrangement may be developmentally regulated in ALL. The findings in this study confirm restricted repertoires of IgH gene rearrangement in ALL and CLL. Characterization of IgH repertoires provides a means of correlating these transformed B cell populations with normal B cell developmental compartments. Moreover, the distinctive repertoires in ALL and CLL may reflect important differences in the ontogenic timing and microenvironmental milieu of tumourigenesis in these disorders.

Extensive and selective mutation of a rearranged VH5 gene in human B cell chronic lymphocytic leukemia

B cell chronic lymphocytic leukemia (CLL) is the malignant, monoclonal equivalent of a human CD5+ B cell. Previous studies have shown that the VH and VL genes rearranged and/or expressed in CLL have few and apparently random mutations. However, in this study, we have found that the rearranged VH251 gene, one of the three-membered VH5 family, has extensive and selective mutations in B-CLL cells. Somatic mutation at the nucleotide level is 6.03% in B-CLLs whereas the somatic mutation levels are much lower in CD5+ and CD5- cord B cells, adult peripheral blood B cells, and Epstein-Barr virus-transformed CD5+ B cell lines (0.45, 0.93, and 1.92%, respectively). Complementary determining region 1 (CDR1) mutation in CLLs is particularly prevalent, and interchanges in CDRs often lead to acquisition of charge. Analysis of somatic mutations and mutations to charged residues demonstrated that the mutations in CLLs are highly selected.

Indications for the presence of antibodies cross-reactive with HTLV-I/II, but not HIV, in patients with myelodysplastic syndrome

Serological evidence is presented for the fact that patients with the myelodysplastic syndrome exhibit a statistically significant reactivity in confirmatory assays for antibodies to human T-lymphotropic viruses types I and II (HTLV-I/II). This antibody reactivity, evident by indirect immunofluorescence and Western blot, was not confined to HTLV core antigens but extended to native and recombinant envelope glycoproteins. The effect was also observed in cases of acute myeloic leukemia, albeit to a lesser degree. It was essentially absent from patients with chronic myeloic leukemia or lymphocytic leukemias and healthy or multitransfused controls. No antibodies to human immunodeficiency viruses types 1 or 2 were detected in any of the specimens. The investigated clinical population had no known risk factor for retroviral infection other than a history of multiple platelet transfusions, and none of the specimens was seropositive for HTLV-I or HTLV-II according to recommended criteria. The cause of this cross-reactivity remains to be determined.

Mapping of homologous, amino-terminal neutralizing regions of human T-cell lymphotropic virus type I and II gp46 envelope glycoproteins

Twelve synthetic peptides containing hydrophilic amino acid sequences of human T-cell lymphotropic virus type I (HTLV-I) envelope glycoprotein were coupled to tetanus toxoid and used to raise epitope-specific antisera in goats and rabbits. Low neutralizing antibody titers (1:10 to 1:20) raised in rabbits to peptides SP-2 (envelope amino acids [aa] 86 to 107), SP-3 (aa 176 to 189), and SP-4A (aa 190 to 209) as well as to combined peptide SP-3/4A (aa 176 to 209) were detected in the vesicular stomatitis virus-HTLV-I pseudotype assay. Higher-titered neutralizing antibody responses to HTLV-I (1:10 to 1:640) were detected with pseudotype and syncytium inhibition assays in four goats immunized with a combined inoculum containing peptides SP-2, SP-3, and SP-4A linked to tetanus toxoid. These neutralizing anti-HTLV-I antibodies were type specific in that they did not inhibit HTLV-II syncytium formation. Neutralizing antibodies in sera from three goats could be absorbed with peptide SP-2 (aa 86 to 107) as well as truncated peptides containing envelope aa 90 to 98, but not with equimolar amounts of peptides lacking envelope aa 90 to 98. To map critical amino acids that contributed to HTLV-I neutralization within aa 88 to 98, peptides in which each amino acid was sequentially replaced by alanine were synthesized. The resulting 11 synthetic peptides with single alanine substitutions were then used to absorb three neutralizing goat antipeptide antisera. Both asparagines at positions 93 and 95 were required for adsorption of neutralizing anti-HTLV-I antibodies from all three sera. Peptide DP-90, containing the homologous region of HTLV-II envelope glycoprotein (aa 82 to 97), elicited antipeptide neutralizing antibodies to HTLV-II in goats that were type specific. In further adsorption experiments, it was determined that amino acid differences between homologous HTLV-I and HTLV-II envelope sequences at HTLV-I aa 95 (N to Q) and 97 (G to L) determined the type specificity of these neutralizing sites. Thus, the amino-terminal regions of HTLV-I and -II gp46 contain homologous, linear, neutralizing determinants that are type specific.

Tumorigenesis mediated by an antigen receptor

The heavy chain variable region of the immunoglobulin receptors on cells of the B lymphoma NYC are almost identical to that of other independent B-cell tumors of B/W mice. NYC IgM binds a viral antigen produced by the tumor cells; and despite extensive screening, immunoglobulin-negative variants were never found in the NYC cells, suggesting that NYC loses the capacity to grow in culture when it does not synthesize surface immunoglobulin. These findings indicate that the interaction of endogenous antigen with surface IgM continuously stimulates growth and, thus, that the tumorigenesis of B lymphomas in B/W mice is mediated by antigen receptors.

Clonal evolution of a follicular lymphoma: evidence for antigen selection

The potential role antigens play in growth stimulation or in clonal selection of follicular lymphomas is unknown. To study this issue, we sequenced the immunoglobulin heavy chain variable region genes expressed by a follicular lymphoma from multiple biopsy specimens and also cloned and sequenced the corresponding germ-line variable gene from this patient. Comparison to the germ-line gene revealed numerous nucleotide substitutions in all of the lymphoma variable gene sequences. Some of the substitutions may have occurred in the nonmalignant precursor B cell that gave rise to this lymphoma because they were shared among all of the variable genes, but many of the mutations accumulated as the malignant clone expanded. The mutations were distributed in such a way that strongly suggested the majority of tumor cells had been positively selected through their antigen receptor. This was especially evident for the mutations that developed late in the clonal evolution of this lymphoma. These findings indicate that antigen stimulation may be involved in the growth of follicular lymphoma tumors.

Chronic leukaemias

In recent years many subtypes of CLL and some CML variants have been recognized throughout the world by means of careful clinical, epidemiological, immunological, molecular biological and viral studies. Most striking has been the establishment of a close association between certain immunophenotypical subtypes of CLL and infection with HTLV-I and possibly HTLV-II. CLL has consistently been shown to have a strong genetic component and a low incidence among Asians, but a growing body of evidence also links this major leukaemia type with environmental factors including solvents, unidentified farming and other occupational exposures. In contrast, CML is characterized by few genetic associations, relatively homogenous world-wide distribution, greater frequency in Blacks than in Whites, little evidence of viral aetiology, and evidence that exposures to ionizing radiation, benzene and possibly other chemical agents are important aetiological factors. Most studies suggest that acquired rather than genetic factors are of greater importance in the aetiology of CML, but this conclusion is somewhat difficult to reconcile with the relatively small variation in incidence rates internationally. Common to both disorders in most populations are an increasing incidence with age, male predominance, and stability of incidence, survival and mortality over the years, exclusive of improved survival of CML following allogeneic bone marrow transplantation.

Analysis of VH251 gene mutation in chronic lymphocytic leukemia (CLL) and normal B-cell subsets

B-cell chronic lymphocytic leukemia (CLL) is the malignant, monoclonal equivalent of a human CD5+ B cell. Previous studies have shown that the VH and VL genes rearranged and/or expressed in CLL have low and random mutations. In this study, however, we have found that the rearranged VH251 gene, one of the three-membered VH5 family, has extensive and selective mutations in B-CLL cells. Somatic mutation at the nucleotide level is 6.03%, and there is a high ratio of replacement to silent mutation in CDRs relative to FWRs. CDR1 mutation is particularly prevalent, and interchanges often lead to acquisition of charge. In VH251 rearranged in CD5+ and CD5- cord-blood B cells, adult peripheral-blood B cells and EBV-transformed CD5+ B-cell lines, the somatic mutation levels are much lower (0.45%, 0.93%, and 1.92%, respectively) with concomitantly lower replacement to silent ratios in CDRs relative to FWRs. The extensive and highly selective somatic mutation of VH251 used in CD5+ CLL cells strongly suggests that part of CLL is generated under the influence of antigen selection and stimulation.

HTLV-I induced extranodal lymphomas

HTLV-I induced not only nodal but also primary extranodal lymphomas. In this report we describe 12 patients with HTLV-I induced extranodal T-cell lymphoma collected from the literature and our institute experience. There were 5 males and 7 female patients of middle age positive for HTLV-I antibody. The sites of primary tumor were gastrointestinal, Waldeyer's ring, skin, facial sinuses, and the pleura. All of these were histologically diffuse lymphomas and most of them were found to be a helper/inducer T-cell phenotype, showing integration of HTLV-I proviral DNA. Late leukemic changes and skin infiltration often occurred, but hypercalcemia was rare. Survival time varied from 4 to 35 months, and late organ infiltrations were common. These HTLV-I induced extranodal lymphomas were compared with HTLV-I unrelated extranodal lymphomas or HTLV-I induced nodal lymphomas (lymphoma type ATL). Between 1981 and 1990, we had 110 ATL patients and of these, 5 (4.6%) were HTLV-I induced primary extranodal lymphomas. The frequency of HTLV-I induced extranodal lymphoma might be much higher than expected because until now attention has not been paid to this entity. From the present review, it is suggested that HTLV-I could cause primary extranodal lymphoma which may have some different characteristics from other types of lymphoma. Therefore, patients with T-cell extranodal lymphomas should be investigated further for the presence of HTLV-I antibody and the tumor cells should be examined for the integration of HTLV-I proviral DNA using Southern blot analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibodies and chemiluminescence immunoassay for detection of the surface protein of human T-cell lymphotropic virus

Monoclonal antibodies (MAbs) raised against human T-cell lymphotropic virus type I (HTLV-I) recognized five distinct antigenic domains of viral env gene-encoded proteins. By using recombinant env proteins and synthetic peptides as mapping antigens, it was determined that the most immunogenic region represented a central portion of the retroviral surface protein (domain 2; amino acids 165 to 191). However, only a single MAb was able to react strongly with native viral proteins. This antibody (clone 6C2) was directed to an epitope within domain 4 (amino acids 210 to 306) of the retroviral env gene and reacted with envelope proteins in both HTLV-I and HTLV-II, as determined by immunoprecipitation, solid-phase binding, and immunoblotting. No reactivity against envelope components of other human retroviruses, including human immunodeficiency virus types 1 and 2, was present. Flow cytometry data demonstrated that MAb 6C2 reacted with cell lines chronically infected with HTLV-I or HTLV-II and also with surface antigens expressed on fresh adult T-cell leukemia cells, following up-regulation with interleukin-2. By a chemiluminescence immunoassay procedure, picogram amounts of viral surface protein could be detected in the unconcentrated supernatants of HTLV-infected cell lines and in diagnostic cultures. Levels of env and gag proteins released by cells into culture supernatants were not directly related to percent expression of cell surface viral-coat proteins. Further, the molar ratio of p19 to gp46 in conditioned media varied from strain to strain, possibly reflecting differences in viral assembly or packaging mechanisms. MAb 6C2 will be of value in characterizing the biochemical and immunological behavior of retroviral env gene proteins and in studying the interaction of HTLV-I and HTLV-II with their receptors.