The intracytoplasmic domain of the Env transmembrane protein is a locus for attenuation of simian immunodeficiency virus SIVmac in rhesus macaques

The human and simian immunodeficiency virus (HIV-1 and SIVmac) transmembrane proteins contain unusually long intracytoplasmic domains (ICD-TM). These domains are suggested to play a role in envelope fusogenicity, interaction with the viral matrix protein during assembly, viral infectivity, binding of intracellular calmodulin, disruption of membranes, and induction of apoptosis. Here we describe a novel mutant virus, SIVmac-M4, containing multiple mutations in the coding region for the ICD-TM of pathogenic molecular clone SIVmac239. Parental SIVmac239-Nef+ produces high-level persistent viremia and simian AIDS in both juvenile and newborn rhesus macaques. The ICD-TM region of SIVmac-M4 contains three stop codons, a +1 frameshift, and mutation of three highly conserved, charged residues in the conserved C-terminal alpha-helix referred to as lentivirus lytic peptide 1 (LLP-1). Overlapping reading frames for tat, rev, and nef are not affected by these changes. In this study, four juvenile macaques received SIVmac-M4 by intravenous injection. Plasma viremia, as measured by branched-DNA (bDNA) assay, reached a peak at 2 weeks postinoculation but dropped to below detectable levels by 12 weeks. At over 1.5 years postinoculation, all four juvenile macaques remain healthy and asymptomatic. In a subsequent experiment, four neonatal rhesus macaques were given SIVmac-M4 intravenously. These animals exhibited high levels of viremia in the acute phase (2 weeks postinoculation) but are showing a relatively low viral load in the chronic phase of infection, with no clinical signs of disease for 1 year. These findings demonstrated that the intracytoplasmic domain of the transmembrane Env (Env-TM) is a locus for attenuation in rhesus macaques.

Nucleotide sequence analyses of partial envgp46 gene of human T-lymphotropic virus type I from inhabitants of Fujian Province in Southeast China

Partial sequences from the env(gp46) gene of two human T-lymphotropic virus type I (HTLV-I) isolates (LIN and WEN) obtained from inhabitants of Fujian Province in southeast China were analyzed. A phylogenetic tree was constructed from these sequence data and those of other known HTLV-I isolates from all over the world. Comparisons of the LIN and WEN nucleotide sequences with other HTLV-I isolates showed diversity ranging from 0.73 to 7.00% for LIN and from 0.87 to 7.00% for WEN. Sequences of isolates LIN, WEN, MT-2, TSP1, and CH were most closely related, and the phylogenetic tree showed that all belong to the widespread subtype A of the cosmopolitan group. These preliminary data indicate that HTLV-I isolates from Fujian Province, China are closely related to HTLV-I strains from Japan and the Caribbean.

Enhanced susceptibility to lupus contributed from the nonautoimmune C57BL/10, but not C57BL/6, genome

Genes from New Zealand Black and New Zealand White mice have been implicated in the development of a disease similar to human systemic lupus erythematosus. In an attempt to define the MHC class II genes involved in disease, we previously studied similarly designed backcrosses of New Zealand Black mice with C57BL/6 (B6) mice transgenic for Ez genes or with C57BL/10 (B10) mice transgenic for Az genes. Although the transgenes showed no effect on the development of autoantibody production or lupus nephritis in either backcross, surprisingly, there was greatly increased expression of these disease traits in the backcrosses involving B10 compared with B6 mice. These studies therefore implicated genetic contributions in B10 vs B6 backgrounds, despite their 98% identity. A genome-wide linkage analysis uncovered a B10 locus on mid-chromosome 13, which enhanced nephritis and was strongly linked with the production of pathogenic retroviral gp70-anti-gp70 immune complexes when contributed by B10, but not B6, mice. The subsequent identification of a single marker polymorphic between B10 and B6, along with the extreme genetic similarity between the two strains in this region, is likely to permit expedited identification of the lupus-susceptibility gene from this nonautoimmune strain.

Establishment of monoclonal anti-retroviral gp70 autoantibodies from MRL/lpr lupus mice and induction of glomerular gp70 deposition and pathology by transfer into non-autoimmune mice

Several strains of mice, including MRL/MpJ mice homozygous for the Fas mutant lpr gene (MRL/lpr mice), F(1) hybrids of New Zealand Black and New Zealand White mice, and BXSB/MpJ mice carrying a Y-linked autoimmune acceleration gene, spontaneously develop immune complex-mediated glomerulonephritis. The involvement of the envelope glycoprotein gp70 of an endogenous xenotropic virus in the formation of circulating immune complexes and their deposition in the glomerular lesions have been demonstrated, as has the pathogenicity of various antinuclear, antiphospholipid, and rheumatoid factor autoantibodies. In recent genetic linkage studies as well as in a study of cytokine-induced protection against nephritis development, the strongest association of serum levels of gp70-anti-gp70 immune complexes, rather than the levels of antinuclear autoantibodies, with the development and severity of glomerulonephritis has been demonstrated, suggesting a major pathogenic role of anti-gp70 autoantibodies in the lupus-prone mice. However, the pathogenicity of anti-gp70 autoantibodies has not yet been directly tested. To examine if anti-gp70 autoantibodies induce glomerular pathology, we established from unmanipulated MRL/lpr mice hybridoma clones that secrete monoclonal antibodies reactive with endogenous xenotropic viral env gene products. Upon transplantation, a high proportion of these anti-gp70 antibody-producing hybridoma clones induced in syngeneic non-autoimmune and severe combined immunodeficiency mice proliferative or wire loop-like glomerular lesions. Furthermore, deposition of gp70 in glomeruli and pathological changes were observed after intravenous injection of representative clones of purified anti-gp70 immunoglobulin G, demonstrating pathogenicity of at least some anti-gp70 autoantibodies.

The envelope protein of an endogenous murine retrovirus is a tumor-associated T-cell antigen for multiple murine tumors

Recently, significant progress has been made in identifying specific tumor-associated antigens recognized by T cells and defining the specific peptide epitopes within these proteins that are processed and presented on class I major histocompatibility antigens. Most of these antigens have been identified in human melanoma, where many of them appear to be tissue-specific, nonmutated proteins expressed by melanoma and normal melanocytes but not by other tissues. There has been much less progress in identifying the tumor antigens on murine tumors that are recognized by T cells, and this has restricted the development of preclinical animal models for immunotherapy. The authors previously described a method for generating tumor-reactive T cells from murine tumors (tumor infiltrating lymphocytes) that are CD8+ T cells recognizing autologous tumor and that can inhibit established tumor on adoptive transfer. Here the authors show that the envelope protein of an endogenous murine retrovirus of the AKV family, found in the germline of the C57BL/6 mouse, is recognized by tumor-infiltrating lymphocytes from two histologically different tumors syngeneic to that mouse strain. Furthermore, the authors identify the specific 9-amino acid peptide from the p15E transmembrane component of this envelope protein that is recognized in the context of major histocompatibility complex Kb, show that it is naturally presented and recognized on several other H-2b tumors, and that cytotoxic T lymphocytes specific for this epitope are therapeutic for these antigen-expressing tumors on adoptive transfer.

Antiviral activity of an intracellularly expressed single-chain antibody fragment directed against the murine leukemia virus capsid protein

We have addressed the possibility that intracellularly expressed miniantibodies directed against the viral capsid protein can be used as antiretroviral agents in gene transfer experiments. R187 is a rat monoclonal antibody that has been reported to recognize the MuLV p30gag capsid polypeptide. We report here that it also binds to the Pr65gag precursor polyprotein. R187 has been cloned and expressed in the form of a single-chain variable fragment (scFv) that shows the same binding specificity as the parental antibody. When expressed intracellularly, the R187 scFv favors the production of viral particles showing reduced infectivity. It, however, exerts no detectable protective effect against infection. This was observed both when using replication-incompetent MuLV-derived vector and replication-competent wild-type MuLV. Although the intimate mechanism of the inhibition is not clear, this work raises the possibility that gene engineering of anti-capsid protein scFvs may offer an additional lead for gene therapy of severe retrovirus-linked diseases.

Interaction and specificity of Rel-related proteins in regulating Drosophila immunity gene expression

NF-kappaB/Rel family proteins regulate genes that are critical for many cellular processes including apoptosis, inflammation, immune response, and development. NF-kappaB/Rel proteins function as homodimers or heterodimers, which recognize specific DNA sequences within target promoters. We examined the activity of different Drosophila Rel-related proteins in modulating Drosophila immunity genes by expressing the Rel proteins in stably transfected cell lines. We also compared how different combinations of these transcriptional regulators control the activity of various immunity genes. The results show that Rel proteins are directly involved in regulating the Drosophila antimicrobial response. Furthermore, the drosomycin and defensin expression is best induced by the Relish/Dif and the Relish/Dorsal heterodimers, respectively, whereas the attacin activity can be efficiently up-regulated by the Relish homodimer and heterodimers. These results illustrate how the formation of Rel protein dimers differentially regulate target gene expression.

Influence of amino acid substitutions on antigenicity of immunodominant regions of the HTLV type I envelope surface gylcoprotein: a study using monoclonal antibodies raised against relevant peptides

By the use of sera of human T cell leukemia virus type I (HTVL-I)-infected individuals it was shown that amino acid substitutions at positions 192 (proline to serine) and 250 (serine to proline) in major immunodominant regions (175-199 and 239-261) of the surface envelope glycoprotein (gp46) of the virus may influence the humoral response. Since human sera are polyclonal in nature, one cannot readily discriminate between an immunoglobulin-specific recognition and multiple bindings of diverse antibodies. To overcome this difficulty we generated murine monoclonal antibodies to synthetic peptides mimicking all or portions of these gp46 regions. The reactivity of some of these antibodies to synthetic peptides harboring (or not harboring) the preceding amino acid substitutions at position 192 or 250, to denatured gp46 by Western blotting, and to live (variously substituted) HTLV-I-infected cells, combined with blocking experiments with various peptides, allow us to conclude that the major epitopes (positions 183-191, 190-197, 190-199, and 246-252) in the two immunodominant regions may elicit different antibody responses according to their sequences. It is worth noting that in a reporter gene inhibition assay, it was found that a neutralizing monoclonal antibody (MF1), the epitope for which is located between residues 190 and 197, had a high level of activity when cells (2060) harboring a gp46 with proline at position 192 were used and had no activity toward cells (1010) with a serine at this position. Therefore our results establish that certain amino acid substitutions of gp46 may drastically affect the antigenicity of the molecule and the biological activity of the antibodies elicited.

The humoral immune response to human T-cell lymphotropic virus type 1 envelope glycoprotein gp46 is directed primarily against conformational epitopes

Individuals infected with human T-cell lymphotropic virus type 1 (HTLV-1) develop a robust immune response to the surface envelope glycoprotein gp46 that is partially protective. The relative contribution of antibodies to conformation-dependent epitopes, including those mediating virus neutralization as part of the humoral immune response, is not well defined. We assess in this report the relationship between defined linear and conformational epitopes and the antibodies elicited to these domains. First, five monoclonal antibodies to linear epitopes within gp46 were evaluated for their ability to abrogate binding of three human monoclonal antibodies that inhibit HTLV-1-mediated syncytia formation and recognize conformational epitopes. Binding of antibodies to conformational epitopes was unaffected by antibodies to linear epitopes throughout the carboxy-terminal half and central domain of HTLV-1 gp46. Second, an enzyme-linked immunoadsorbent assay was developed and used to measure serum antibodies to native and denatured gp46 from HTLV-1-infected individuals. In sera from infected individuals, reactivity to denatured gp46 had an average of 15% of the reactivity observed to native gp46. Third, serum antibodies from 24 of 25 of HTLV-1-infected individuals inhibited binding of a neutralizing human monoclonal antibody, PRH-7A, to a conformational epitope on gp46 that is common to HTLV-1 and -2. Thus, antibodies to conformational epitopes comprise the majority of the immune response to HTLV-1 gp46, and the epitopes recognized by these antibodies do not appear to involve sequences in previously described immunodominant linear epitopes.

Syncytium-inhibiting monoclonal antibodies produced against human T-cell lymphotropic virus type 1-infected cells recognize class II major histocompatibility complex molecules and block by protein crowding

Four new monoclonal antibodies (MAbs) that inhibit human T-cell lymphotropic virus type 1 (HTLV-1)-induced syncytium formation were produced by immunizing BALB/c mice with HTLV-1-infected MT2 cells. Immunoprecipitation studies and binding assays of transfected mouse cells showed that these MAbs recognize class II major histocompatibility complex (MHC) molecules. Previously produced anti-class II MHC antibodies also blocked HTLV-1-induced cell fusion. Coimmunoprecipitation and competitive MAb binding studies indicated that class II MHC molecules and HTLV-1 envelope glycoproteins are not associated in infected cells. Anti-MHC antibodies had no effect on human immunodeficiency virus type 1 (HIV-1) syncytium formation by cells coinfected with HIV-1 and HTLV-1, ruling out a generalized disruption of cell membrane function by the antibodies. High expression of MHC molecules suggested that steric effects of bound anti-MHC antibodies might explain their inhibition of HTLV-1 fusion. An anti-class I MHC antibody and a polyclonal antibody consisting of several nonblocking MAbs against other molecules bound to MT2 cells at levels similar to those of class II MHC antibodies, and they also blocked HTLV-1 syncytium formation. Dose-response experiments showed that inhibition of HTLV-1 syncytium formation correlated with levels of antibody bound to the surface of infected cells. The results show that HTLV-1 syncytium formation can be blocked by protein crowding or steric effects caused by large numbers of immunoglobulin molecules bound to the surface of infected cells and have implications for the structure of the cellular HTLV-1 receptor(s).

Establishment of monoclonal antibody, gp21-34, against HTLV-II envelope protein (p20E)

A monoclonal antibody (MAb), gp21-34, specifically reactive with human T-lymphotropic virus type-II (HTLV-II) transmembranous envelope glycoprotein (p20E) was developed by immunization with a recombinant protein fused with thioredoxin moiety at the N-terminal portion. This MAb, which belongs to the IgG1 kappa subclass, reacted with HTLV-II infected cell lines (TON-1, C3-44, and Si-IIA) by IFA, but not with HTLV-I infected cell lines (TCL-Kan and MT-2). By Western blot analysis, this MAb reacted with p20E of HTLV-II lysates but not with HTLV-I lysates. Some epitope analyses with synthetic peptides were carried out to look for a plausible linear epitope in the C-terminal region of p20E.

Epitope mapping of HTLV envelope seroreactivity in LGL leukaemia

Sera from approximately 50% of patients with large granular lymphocyte (LGL) leukaemia react with a recombinant human T-cell leukaemia/lymphoma virus (HTLV) transmembrane envelope protein, p21e. Two immunodominant epitopes within env p21e have been defined by reactivity against recombinant proteins GD21 and BA21. In this study sera from 41 patients with LGL leukaemia were examined for reactivity against these recombinant HTLV env proteins. Overall, 21/41 (51%) sera reacted to p21e. Only two sera reacted to GD21. The predominant immunoreactivity against p21e was directed against the BA21 epitope, with 19/41 (46%) sera being BA21 positive. Seroconversion to BA21 protein was also documented. PCR analyses confirmed the low incidence of protypical HTLV sequences (2/41, 5%). These data document an association between BA21 seroreactivity and LGL leukaemia. This finding raises the possibility that such BA21 seroreactivity could be due to cross-reactivity to a cellular or retroviral antigen sharing some amino acid homology with the transmembrane glycoprotein of HTLV.

Human CD4+ T lymphocytes recognize a highly conserved epitope of human T lymphotropic virus type 1 (HTLV-1) env gp21 restricted by HLA DRB1*0101

HTLV-1 causes two distinct human diseases, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukaemia/lymphoma (ATL). Persistently infected individuals carry a risk of <1% of developing either disease. These basic epidemiological data imply that virus-host interactions, especially immunogenetic factors, influence the outcome of infection. Several studies showed that the HLA class II DR1 DQ5 haplotype is over-represented in HAM/TSP, but rare in ATL. Therefore, we selected four patients with HAM/TSP and one seronegative control who all carried the HLA DR1 DQ5 haplotype. We analysed the CD4+ T lymphocyte response against eight synthetic peptides of HTLV-1 envelope (env) glycoprotein gp21, a crucial target antigen in HAM/TSP. The first of two immunodominant epitopes corresponded to a domain of the HTLV-1 envelope protein which had previously been shown to be essential for HTLV-1 envelope function. The second immunodominant epitope overlapped a highly conserved sequence of the retroviral transmembrane envelope protein. DR1 (DRB1*0101)-restricted T lymphocytes were activated by the conserved peptide sequence in nanomolar concentrations. In contrast, this conserved sequence can also induce non-specific, cAMP-mediated immunosuppressive effects on T cells when added in micromolar concentrations to culture media, as shown by Haraguchi S, Good RA, James-Yarish M, Cianciolo GJ, Day NK, Proc Natl Acad Sci USA 1995; 92:5568-71. Hence, HTLV-1 env gp21 might exert either stimulating immunological or immunosuppressive effects in HTLV-1-infected individuals, depending on the level of its expression and the presence of HLA DRB1*0101.

Characterization of a simian T-lymphotropic virus from a wild-caught orang-utan (Pongo pygmaeus) from Kalimantan, Indonesia

In a recent serological survey among 143 ex-captive orang-utans two individuals were found that reacted positive in an ELISA detecting antibodies which cross-react with human T-lymphotropic virus type I (HTLV-I) antigens. Infection of both animals with an HTLV-I or simian T-lymphotropic virus (STLV)-like virus was confirmed by Western blot analysis. A third wild-caught animal, which was not part of the original serological survey, was also found to be infected with an HTLV-related virus in a diagnostic PCR assay and Western blot assay. Nucleotide sequence analysis of the 709 bp PCR fragment from the tax/rex region of the HTLV/STLV genome confirmed infection of orang-utans with an STLV similar to but clearly distinct from other Asian STLVs.

Immunogenicity and conformational properties of an N-linked glycosylated peptide epitope of human T-lymphotropic virus type 1 (HTLV-I)

The identification and characterization of epitopes of human T-lymphotropic virus type 1 (HTLV-I), which elicit an effective humoral or cell-mediated immune response, remains a central obstacle to the development of a peptide-based vaccine against the virus infection. The objective of the studies presented here was to examine the influence of N-linked glycosylation on peptide structure and immunogenicity. We engineered the 233-253 sequence of gp46 of HTLV-I to contain an N-acetylglucosamine (GlcNAc) residue at Asn244. Secondary structure prediction using computer algorithms indicated that this peptide may contain a beta-turn at residues 242-246. Recent work with model glycopeptides suggests that beta-turn conformation in peptides may be induced, and probably is stabilized, by the presence of even a single sugar residue. In the present study, the structures of the 233-253 peptide, SC1, and the 233-253(Asn244-GlcNAc) glycopeptide, SC2, were determined. Similar conformation was exhibited by both the glycosylated and nonglycosylated peptide displaying a beta-turn at residues 243-246 and extended-chain structure at the peptide/glycopeptide termini. Both peptides were engineered into chimeric constructs with a promiscuous T-cell epitope from measles virus and were used as immunogens in rabbits. Both chimeric peptides were highly immunogenic in rabbits, producing high-titered antibodies as early as primary + three weeks. The antibodies generated against either construct were able to bind to whole virus (ELISA) and to gp46 (radioimmunoprecipitation assay). Additionally, human sera of individuals known to be positive for HTLV-I recognized both the glycosylated and nonglycosylated constructs. It appears that the 233-253 peptide is able to adopt a conformation that mimics the structure in native gp46, and addition of a GlcNAc residue at Asn244 does not affect the conformational preference or stability of this construct; nor does glycosylation alter immunogenicity but instead appears to enhance immune recognition.

Selective cytotoxicity of two rodent T cell lymphomas to rat yolk sac tumours involves a retroviral envelope protein expressed by the lymphoma

A Gross virus induced rat T cell lymphoma G1-Tc1 and a Moloney virus induced mouse T cell lymphoma YAC-1 are shown to exert a strong cytotoxic activity against rat yolk sac tumours but not to various types of rat, mouse or human normal cells or tumour cell lines including carcinomas, sarcomas, lymphomas and gliomas. Both lymphomas are CD3+, CD4-, CD8- and T-cell receptor (TCR) alpha beta +. The cytotoxicity was not MHC restricted or dependent on the density of MHC class I of the target cells, and the mouse lymphoma killed the rat yolk sac tumour target. The cytotoxic action was fast and up to 80% specific killing was observed in 4-h 51Cr release assays. A rat B cell hybridoma was established from a Wistar/Furth (WF) rat immunized with the syngeneic lymphoma G1-Tc1 producing an immunoglobulin (Ig)G2c monoclonal antibody (MoAb) 1F2. This binds to the lymphomas G1-Tc1 and YAC-1 and also to a murine non-cytolytic Rauscher lymphoma RMA, but not to any other of several rat, mouse or human cell types tested. The 1F2 completely inhibited the killing of rat yolk sac tumours by the two cytolytic lymphomas, but did not interfere with the killing mediated by natural killer (NK) cells or cytolytic lymphokine-activated killer (LAK) cells. Immunochemical analysis of solubilized cell membranes of the lymphoma G1-Tc1 demonstrates that the 1F2 antibody recognizes an epitope on a retroviral gp 70 envelope protein. This indicates that a retroviral protein is involved in the lytic activity of the two lymphomas.

Circulating levels of IL-10 are critically related to growth and rejection patterns of murine mastocytoma cells

Previously tumorigenic P815 tumor cells are rejected by histocompatible mice after transfection with a mutated retroviral gene, and the host is made resistant to subsequent challenge with tumorigenic (control) cells transfected with the nonmutated sequence. To functionally characterize the class I-restricted response to the tumor cell vaccine, we have assessed the in vitro (by CD8+ cells) and in vivo production of type 1 or type 2 cytokines in mice injected with either type of transfected P815 derivative. IL-12 and IL-10 were selectively or preferentially expressed by the regressor mice, and this correlated with the detection of functional type 1 reactivity in vivo (i.e., delayed-type hypersensitivity). Other cytokines were produced by the regressor mice only in vitro (IFN-gamma) or were not detected at all with either type of tumor recipient (IL-4). By means of monoclonal antibody-mediated neutralization or enhancement of endogenous cytokine levels, IL-10 was found to serve an important role in the growth and rejection patterns of the transfected P815 derivatives. In addition to previous evidence for an IL-12 requirement in promoting anti-P815 reactivity, these data establish IL-10 as an important cytokine in permitting optimal expression of this reactivity, which apparently develops in the absence of a strong bias toward a type 1 or type 2 cytokine response.

DNA binding and transcriptional activation by the Ski oncoprotein mediated by interaction with NFI

The Ski oncoprotein has been found to bind non-specifically to DNA in association with unindentified nuclear factors. In addition, Ski has been shown to activate transcription of muscle-specific and viral promoters/enhancers. The present study was undertaken to identify Ski's DNA binding and transcriptional activation partners by identifying specific DNA binding sites. We used nuclear extracts from a v-Ski-transduced mouse L-cell line and selected Ski-bound sequences from a pool of degenerate oligonucleotides with anti-Ski monoclonal antibodies. Two sequences were identified by this technique. The first (TGGC/ANNNNNT/GCCAA) is the previously identified binding site of the nuclear factor I (NFI) family of transcription factors. The second (TCCCNNGGGA) is the binding site of Olf-1/EBF. By electophoretic mobility shift assays we find that Ski is a component of one or more NFI complexes but we fail to detect Ski in Olf-1/EBF complexes. We show that Ski binds NFI proteins and activates transcription of NFI reporters, but only in the presence of NFI. We also find that homodimerization of Ski is essential for co-activation with NFI. However, the C-terminal dimerization domain of c-Ski, which is missing in v-Ski, can be substituted by the leucine zipper domain of GCN4.

Synthesis and CD studies of an 88-residue peptide containing the main receptor binding site of HTLV-I SU-glycoprotein

Essential HTLV-1 biological functions, like host-cell receptor recognition, depend on the structural motives on the surface glycoprotein gp46. We defined a peptide of 88 amino acids [Arg147-Leu234] corresponding to the central part of the protein sequence, where major neutralizing epitopes are localized. After evaluating the feasibility of its chemical synthesis, the chosen sequence was realized using the stepwise solid-phase methodology. Multiple chromatographic purification steps were required to obtain a sample suitable for structural analysis. Correct folding was supported by strong binding of monooclonal antibodies, recognizing known exposed immunodominant regions. Circular dichroism studies confirmed a non-random conformation of at least 70-80% of the synthetic peptide. Investigation of the 3D-structure of the synthetic peptide will provide useful information for future vaccine and drug-design strategies.

Neutralizing human monoclonal antibodies to conformational epitopes of human T-cell lymphotropic virus type 1 and 2 gp46

Ten human monoclonal antibodies derived from peripheral B cells of a patient with human T-cell lymphotropic virus (HTLV)-associated myelopathy are described. One monoclonal antibody recognized a linear epitope within the carboxy-terminal 43 amino acids of HTLV gp21, and two monoclonal antibodies recognized linear epitopes within HTLV type 1 (HTLV-1) gp46. The remaining seven monoclonal antibodies recognized denaturation-sensitive epitopes within HTLV-1 gp46 that were expressed on the surfaces of infected cells. Two of these antibodies also bound to viable HTLV-2 infected cells and immunoprecipitated HTLV-2 gp46. Virus neutralization was determined by syncytium inhibition assays. Eight monoclonal antibodies, including all seven that recognized denaturation-sensitive epitopes within HTLV-1 gp46, possessed significant virus neutralization activity. By competitive inhibition analysis it was determined that these antibodies recognized at least four distinct conformational epitopes within HTLV-1 gp46. These findings indicate the importance of conformational epitopes within HTLV-1 gp46 in mediating a neutralizing antibody response to HTLV infection.

Resistance to fas-mediated apoptosis of peripheral T cells in human T lymphocyte virus type I (HTLV-I) transgenic mice with autoimmune arthropathy

Transgenic mice carrying the env-pX region of human T lymphocyte virus type I (HTLV-I) develop autoimmune arthropathy in high incidence. Adopting the approach that Fas-mediated apoptosis has a critical function in the elimination of self-reactive T cells, we examined the involvement of this apoptosis in the induction of autoimmunity in HTLV-I transgenic mice. Splenic T cells derived from the transgenic mice were more resistant to apoptosis induced by anti-Fas mAb than those of the nontransgenic mice, whereas no appreciable difference in apoptosis was detected for thymocytes from either mouse's type. The resistance of transgenic T cells may be due to Tax coded in the pX region, since Tax mediates the inhibition of anti-Fas- induced apoptosis in mature T cell line, Jurkat. Among the transgenic mice, the extent of the resistance to Fas-mediated apoptosis was further enhanced in transgenic T cells with disease. These results suggest that the escape of self-reactive T cells from Fas-mediated apoptosis in the periphery, is critical for the development of autoimmune arthropathy in HTLV-I transgenic mice.

SIV DNA vaccine trial in macaques: post-challenge necropsy in vaccine and control groups

In this study we describe the histopathologic findings from nine macaques in a simian immunodeficiency virus (SIV) DNA vaccine trial evaluating the ability of a 5-plasmid DNA vaccine to protect against an uncloned SIVmac251 challenge (Lu et al., J. Virol. 1996, 70, 3978-3991). Three vaccinated and one control macaque developed disease and were euthanized in the first year following challenge. The other four vaccinated and one control macaque remained clinically normal and were euthanized at the end of the trial (60 weeks post-challenge). The necropsy data revealed that both diseased and clinically normal macaques had developed typical SIV-related lymphoid changes, inflammatory disorders and opportunistic infections. All animals had variable degrees of follicular and/or paracortical lymphoid hyperplasia suggesting immune activation. All but one vaccinated macaque and both control macaques had SIV-associated opportunistic infections. Within the small groups of animals, the ability to contain opportunistic infections was superior, and the overall lymphoid changes less severe, in the macaques that had received vaccine DNAs by three routes of inoculation (intravenous, intramuscular and gene gun) than in those that had received control DNAs or vaccine DNAs by gene gun only. In the future it will be important to further test how the route and method of DNA inoculation impact the efficacy of immunodeficiency virus vaccines.

Preferential recognition of synthetic peptides from HTLV-I gp21 envelope protein by HLA-DRB1 alleles associated with HAM/TSP (HTLV-I-associated myelopathy/tropical spastic paraparesis)

To determine CD4+ T-cell epitopes of HTLV-I-envelope protein recognized by the HLA alleles associated with HAM/TSP, we established 20 CD4+ T-cell lines from peripheral blood mononuclear cells (PBMCs) of naive healthy donors using a panel of synthetic peptides spanning the entire length of HTLV-I-envelope proteins, gp46 and gp21. We quantitated the precursor frequencies of HTLV-1-envelope specific CD4+ T-cells and analyzed epitope specificity in the context of HLA alleles. The precursor frequencies ranged from 3.0 to 10.6 per 10(7) PBMCs in the naive healthy donors. The CD4+ T-cell epitopes of HTLV-I-envelope protein were clustered in amino acids 76 to 90, 136 to 160, 171 to 185 and 196 to 210 of gp46, and in amino acids 366 to 400 and 436 to 485 of gp21. The CD4+ T-cell epitopes of gp21 were preferentially recognized by HLA-DRB1 0101 and 1502 which were known to be associated with HAM/TSP. Thus, it was suggested that HTLV-I gp21 might contain the major CD4+ T-cell epitopes recognized by HLA-DRB1 alleles of HAM/TSP.