Nucleotide sequence analysis of a variant human T-cell leukemia virus (HTLV-Ib) provirus with a deletion in pX-I

Lobostemon trigonus (Thunb.) H. Buek, a medicinal plant from South Africa as a potential natural microbicide against HIV-1

ETHNOPHARMACOLOGICAL RELEVANCE

There have been different methods proposed to prevent the sexual transmission of HIV-1 and many of them have centered on the use of anti-retrovirals as microbicides. Given that a large section of the African population still relies on herbal medicine, Lobostemon trigonus (L. trigonus), a traditionally used medicinal plant in South Africa to treat HIV-1 was further investigated for its potential as a natural microbicide to prevent the sexual transmission of HIV-1.

METHODS

The aerial parts of L. trigonus were oven-dried at 80 °C, ground, extracted with boiling water for 30 min and then filtered. The aqueous extract produced was then bioassayed using different HIV-1 inhibition assays. The active components were purified and chemically profiled using ultra-performance liquid chromatography/quadrupole time-of flight mass spectrometry (UPLC-qTOF-MS). The mechanism of HIV-1 inhibition was determined by fusion arrest assay and time of addition assay. Molecular modelling and molecular dynamic simulations, using Schrödinger, were used to better understand the molecule's mechanism of entry inhibition by evaluating their docking affinity and stability against the gp120 of HIV-1.

RESULTS

The aqueous extract of this plant had a broad spectrum of activity against different subtypes of the virus; neutralizing subtype A, B and C in the TZM-bl cells, with IC₅₀ values ranging from 0.10 to 7.21 μg/mL. The extract was also inhibitory to the virus induced cytopathic effects in CEM-SS cells with an EC₅₀ of 8.9 μg/mL. In addition, it inhibited infection in peripheral blood mononuclear cells (PBMC) and macrophages with IC₅₀ values of 0.97 and 4.4 μg/mL, respectively. In the presence of vaginal and seminal simulants, and in human semen it retained its inhibitory activity albeit with a decrease in efficiency, by about 3-fold. Studies of the mode of action suggested that the extract blocked HIV-1 attachment to target cells. No toxicity was observed when the Lactobacilli strains, L. acidophilus, L. jensenii, and L. crispatus that populate the female genital tract were cultured in the presence of L. trigonus extract. UPLC-qTOF-MS analyses of the purified fraction of the extract, confirmed the presence of six compounds of which four were identified as rosmarinic acid, salvianolic acids B and C and lithospermic acid. The additional molecular dynamic simulations provided further insight into the entry inhibitory characteristics of salvianolic acid B against the HIV-1 gp120, with a stable pose being found within the CD4 binding site.

CONCLUSION

The data suggests that the inhibitory effect of L. trigonus may be due to the presence of organic acids which are known to possess anti-HIV-1 properties. The molecules salvianolic acids B and C have been identified for the first time in L. trigonus species. Our study also showed that the L. trigonus extract blocked HIV-1 attachment to target cells, and that it has a broad spectrum of activity against different subtypes of the virus; thus, justifying further investigation as a HIV-1 microbicide.

Molecular and phylogenetic analyses of 16 novel simian T cell leukemia virus type 1 from Africa: close relationship of STLV-1 from Allenopithecus nigroviridis to HTLV-1 subtype B strains

A serological survey searching for antibodies reacting with human T-cell leukemia virus type 1 (HTLV-1) antigens was performed on a series of 263 sera/plasma obtained from 34 monkey species or subspecies, originating from different parts of Africa. Among them, 34 samples exhibited a typical HTLV-1 Western blot pattern. Polymerase chain reaction was performed with three primer sets specific either to HTLV-1/STLV-1 or HTLV-2 and encompassing gag, pol, and tax sequences, on genomic DNA from peripheral blood mononuclear cells of 31 animals. The presence of HTLV-1/simian T-cell leukemia virus type 1 (STLV-1) related viruses was determined in the 21 HTLV-1 seropositive animals tested but not in the 10 HTLV-1 seronegative individuals. Proviral DNA sequences from the complete LTR (750 bp) and a portion of the env gene (522 bp) were determined for 16 new STLV-1 strains; some of them originating from species for which no STLV-1 molecular data were available as Allenopithecus nigroviridis and Cercopithecus nictitans. Comparative and phylogenetic analyses revealed that these 16 new sequences belong to five different molecular groups. The A. nigroviridis STLV-1 strains exhibited a very strong nucleotide similarity with HTLV-1 of the subtype B. Furthermore, four novel STLV-1, found in Cercocebus torquatus, C. m. mona, C. nictitans, and Chlorocebus aethipos, were identical to each other and to a previously described Papio anubis STLV-1 strain (PAN 503) originating from the same primate center in Cameroon. Our data extend the range of the African primates who could be permissive and/or harbor naturally STLV-1 and provide new evidences of cross-transmission of African STLV-1 between different monkey species living in the same environment and also of STLV-1 transmissions from some monkeys to humans in Central Africa.

Oligonucleotide treatment of ras-induced tumors in nude mice

Oligonucleotides have shown an ability to target specific oncogene transcripts and inhibit their expression in cells, but the degree to which sustained treatment can suppress the levels of an oncogenic protein enough to benefit a patient remains to be determined. This question has been studied in several ways. First, the relationship of antisense DNA inhibition to the predicted secondary structure of human H-RAS oncogene mRNA was examined in transformed mouse cells that form solid tumors. Inhibition of H-Ras expression was sequence-specific, dose-dependent, and correlated with inhibition of focus formation. The efficacy of the first intron antisense sequence in reducing H-Ras expression was greater than that of the initiation codon target. Second, H-RAS transformed solid tumor cells were pretreated in vitro with normal oligonucleotides, after which tumor growth from the treated cells was tested in nude mice. The three days of treatment with the first intron antisense DNA reduced H-Ras cellular levels by more than 90% whereas a nonspecific control DNA reduced H-Ras levels by approx 20%. Tumor growth of cells treated with H-RAS antisense oligonucleotide was significantly reduced for up to 14 d following the end of treatment and implantation into the mice, whereas the nonspecific control DNA had no significant effect. Third, H-RAS transformed bladder cancer cells were implanted into nude mice, after which the mice were treated for 31 d with oligonucleotide phosphorothioates. Tumor growth in mice treated with H-RAS 12th codon antisense oligonucleotide was reduced by about 80% throughout the treatment period, reiterating the sustained effect seen in pretreated tumor cells. However, the scrambled phosphorothioate control inhibited tumor growth by about 60%, illustrating some nonspecific inhibition. Fourth, K-RAS transformed pancreatic cancer cells were treated in culture and in nude mice. Inhibition of K-Ras expression with a phosphorothioate oligonucleotide directed against a 5'-UTR sequence was sequence-specific and dose-dependent. K-RAS transformed pancreatic cancer cells were implanted into nude mice, after which the mice were treated for 14 d with oligonucleotide phosphorothioates. Tumor growth in mice treated with K-RAS 5'-UTR antisense oligonucleotide was reduced by about 50% throughout the treatment period, reiterating the sustained effect seen with H-RAS transformed cells. In this case, the sense phosphorothioate control did not inhibit tumor growth, demonstrating that nonspecific inhibition is not a characteristic of all phosphorothioate sequences. The next logical steps include testing oligonucleotide efficacy against other tumor types, toxicological testing in higher species, and clinical trials in human subjects.

Chimeric matrix proteins encoded by defective proviruses with large internal deletions in human T-cell leukemia virus type 1-infected humans

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATLL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and other diseases. The mechanisms of virus pathogenesis are still obscure. The occurrence of defective proviruses in HTLV-1-infected cell lines and the peripheral blood mononuclear cells (PBMC) of infected individuals is a frequent feature of virus infection. We detected defective proviruses with large internal deletions in PBMC from ATLL and HAM/TSP patients and in asymptomatic HTLV-1 carriers. Seventeen PCR-amplified defective proviruses were sequenced, and three types of deletions were found. Besides truncated MA and the 5' end of the genome, truncated CA, truncated SU, and more frequently truncated TM linked to the pX region were detected. Reverse transcription-PCR analysis of PBMC from ATLL patients and asymptomatic carriers also revealed RNA transcripts with large internal deletions. Analysis of two RT-PCR cDNA clones confirmed a Gag-TM-pX structure of the transcripts. Most defective proviruses contained numerous internal stop codons, but some were capable of coding for the truncated MA linked to a variable out-of-frame peptide. Cloned defective proviruses with long open reading frames were subjected to in vitro transcription-translation followed by radioimmunoprecipitation, which showed expression of chimeric proteins between 8 and 12 kDa. Possible roles of defective proviruses and chimeric proteins are discussed, although there is no firm association with pathogenesis.

Simian T-lymphotropic virus type I infection among wild-caught Indonesian pig-tailed macaques (Macaca nemestrina)

Evidence for the presence of simian T-lymphotropic viruses (STLV-I) was identified in live-caught pig-tailed macaques from two locations in southern Sumatra, Indonesia. Of 60 animals tested, 13.3% of the animals showed seroreactivity to HTLV-I/II enzyme-linked immunosorbent assay (ELISA) antigens. Of these, 75% showed indeterminate reactivity and 25% showed positive reactivity to HTLV-I/II Western blot antigens. Polymerase chain reaction (PCR) analysis of 6 of 8 seroreactive monkeys' peripheral blood mononuclear cell (PBMC) DNA showed production of proper size molecular weight product that hybridized specifically to an STLV-I tax gene-specific probe. Phylogenic analyses of tax gene fragment sequences from the PCR products of two samples, 930287 and 930306, indicated that these animals were infected with retroviruses related to those of the Asian STLV-I clade.

Evolutionary inferences of novel simian T lymphotropic virus type 1 from wild-caught chacma (Papio ursinus) and olive baboons (Papio anubis)

A serological survey of 22 wild-caught South African (Transvaal) chacma baboons (Papio ursinus) and eight olive baboons (Papio anubis) from Kenya indicates that 13 P. ursinus and one P. anubis have antibodies reacting with human T cell leukemia/lymphoma virus type 1 (HTLV-1) antigens, whereas three P. ursinus had a indeterminate reactivity on Western blot analysis. With six primer sets specific to either HTLV-1-Simian T-cell leukemia virus type 1 (STLV-1) or HTLV-2 and encompassing long terminal repeat (LTR), gag, pol, env, and tax sequences, polymerase chain reaction was performed on genomic DNA from peripheral blood mononuclear cells of 18 animals, and the presence of HTLV-1-STLV-1-related viruses was determined in 13 seropositive and three seroindeterminate animals but not in the two HTLV seronegative individuals. Proviral DNA sequences from env (522 bp), pol (120 bp), and complete (755 bp) or partial (514 bp) LTR were determined for three STLV-1-infected P. ursinus and one P. anubis. Comparative and phylogenetic analyses revealed that P. anubis (Pan-486) sequence clusters with one (Pan-1621) of two previously described P. anubis STLV-1. Likewise, P. ursinus viruses (Pur-529, Pur-539, and Pur-543) form a distinct group, different from all known HTLV-1 but closely affiliated with two STLV-1 strains from South African vervets (Cercopithecus aethiops pygerythrus). This study, reporting the first STLV-1 sequences from wild-caught P. ursinus and P. anubis, corroborates the hypothesis of cross-species transmissions of STLV-1 in the wild. Further, phylogenetic analyses indicate that the known HTLV-1 strains do not share a common origin with nonhuman primates STLV in South Africa.

Quantification of human T-cell lymphotropic virus type 1 proviral load by quantitative competitive polymerase chain reaction

The polymerase chain reaction (PCR) has been established as a highly sensitive technique for detection of viral DNA or RNA. However, due to inherent limitations of PCR the amount of amplified product often does not correlate with the initial amount of template DNA. This is particularly true for PCR detection of viral infections that are characterized by low in vivo viral copy numbers in certain stages of the infection, such as human T-cell lymphotropic virus type 1 (HTLV-1) and simian T-cell lymphotropic virus type 1 (STLV-1). Therefore, we developed a quantitative competitive polymerase chain reaction (qcPCR) for detection of HTLV-1 and STLV-1 proviral DNA. The assay was optimized using an infectious HTLV-1 clone, ACH, HTLV-1 infected cell lines, MT-2.6 and HUT-102 and STLV-1 infected lines Kia and Matsu. Applicability of this system was demonstrated by determining HTLV-1 proviral load in peripheral blood mononuclear cells (PBMC) of human subjects with HTLV-1 associated diseases and an asymptomatic carrier as well as rabbits infected experimentally. This qcPCR method, the first designed specifically for HTLV-1 and STLV-1, will provide an important tool for pathogenesis studies of HTLV-1 and for evaluating the efficacy of antiviral drugs and vaccines against the viral infection using animal models.

Human T-cell leukemia virus type 1 pX-I and pX-II open reading frames are dispensable for the immortalization of primary lymphocytes

Human T-cell leukemia virus type 1 (HTLV-1) infects and transforms CD4+ T-lymphocytes both in vivo and in vitro. Although the Tax protein of HTLV-1 has been strongly implicated as a transforming agent, other virally encoded proteins may also play a role in the transformation process. In addition to the rex and tax genes, the pX region of the HTLV-1 genome contains two open reading frames (pX-I and pX-II) which encode the putative viral accessory proteins known as p12I, p30II, and p13II. Mutations in the ACH molecular clone of HTLV-1 that are predicted to abrogate the expression of p12I, p13II and p30II were constructed. These mutations had no effect on viral replication or the immortalization of primary lymphocytes. Although these proteins are dispensable for viral replication and immortalization in vitro, it remains possible that they alter infection in vivo.

Detection of simian T cell leukemia virus type I infection in seronegative macaques

Simian species of Asian and African origin are naturally infected with the simian T cell leukemia virus type I (STLV-I). Like the closely related human T cell leukemia virus type I (HTLV-I), STLV-I is primarily cell associated, and typical infections exhibit low viral burdens. Four macaques experimentally inoculated with a new STLV-I strain isolated from a sooty mangabey monkey were examined over extended periods of time for signs of infection by (1) commercial enzyme immunoassay and immunoblot assay for cross-reactive serum antibodies to HTLV-I, (2) commercial HTLV-I p24gag antigen-capture assay on supernatants from cocultures of macaque peripheral blood mononuclear cells (PBMCs) with human PBMCs, and (3) nested PCR amplification of proviral sequences in macaque PBMC DNA. The nested PCR assay was 100% specific and detected a single STLV-I copy in 150,000 PBMCs. In addition, our data show that experimental infection of macaques with STLV-I can be serologically silent for more than 43 months.

Variable Immortalizing Potential and Frequent Virus Latency in Blood-Derived T-Cell Clones Infected With Human T-Cell Leukemia Virus Type I

Human T-cell leukemia virus type I (HTLV-I)-infected T cells expanded in vitro by single-cell cloning provide a unique system for investigating virus-cell interactions in nonimmortalized T cells. By analysis of clones generated randomly from the blood of virus carriers, we confirm that CD4 T cells are the major reservoir of HTLV-I in vivo and show that most infected cells contain a single integrated provirus. Contrary to the situation in HTLV-I immortalized cell lines, the HTLV-I provirus was found to be transcriptionally silent in a high proportion of randomly generated T-cell clones and could not be reactivated by mitogenic stimulation. The spontaneous proliferation previously documented in HTLV-I–infected T-cell clones was not observed in silently infected cells, and therefore correlates directly with the expression of tax and other viral genes. The only cytokine mRNA found to be significantly elevated in the virus-producing clones was interleukin-6; however, receptor-blocking experiments argue against a role for IL-6 in the virus-induced cell proliferation. We observed a striking variation in the ability of individual HTLV-I–producing clones to immortalize fresh peripheral blood lymphocytes. This ability did not correlate with the levels of viral mRNA expression, gag p24 production, spontaneous proliferation, or tax-transactivation, possibly suggesting a role for host cell factors as determinants of viral infectivity or immortalization. Studies to elucidate the basis of this phenotypic heterogeneity should enhance our understanding of viral spread and pathogenesis.

A source of glycosylated human T-cell lymphotropic virus type 1 envelope protein: expression of gp46 by the vaccinia virus/T7 polymerase system

Heterologous expression of the human T-cell lymphotropic virus type 1 (HTLV-1) envelope surface glycoprotein (gp46) in a vaccinia virus/T7 polymerase system resulted in the production of authentic recombinant gp46. Five differentially glycosylated forms of the surface envelope protein were produced by this mammalian system, as demonstrated by tunicamycin inhibition of N-glycosylation and N-glycan removal with endoglycosidase H and glycopeptidase F. These studies revealed that all four potential N-glycosylation sites in gp46 were used for oligosaccharide modification and that the oligosaccharides were mannose-rich and/or hybrid in composition. Conformational integrity of the recombinant HTLV-1 envelope protein was determined by the ability to bind to various HTLV-1-infected human sera and a panel of conformational-dependent human monoclonal antibodies under nondenaturing conditions. Furthermore, this recombinant gp46 was recognized by a series of HTLV-2-infected human sera and sera from a Pan paniscus chimpanzee infected with the distantly related simian T-cell lymphotropic virus STLVpan-p. Maintenance of highly conserved conformational epitopes in the recombinant HTLV-1 envelope protein structure suggests that it may serve as a useful diagnostic reagent and an effective vaccine candidate.

Genetic variability and molecular epidemiology of human and simian T cell leukemia/lymphoma virus type I

In the past few years, numerous investigators have demonstrated that human T cell leukemia/lymphoma virus type I (HTLV-I) possesses a great genetic stability, and recent data indicate that viral amplification via clonal expansion of infected cells, rather than by reverse transcription, could explain this remarkable genetic stability. In parallel, the molecular epidemiology of HTLV-I proviruses showed that the few nucleotide changes observed between isolates were specific for the geographical origin of the patients but not for the type of the associated pathologies (adult T cell leukemia/lymphoma, tropical spastic paraparesis/HTLV-I-associated myelopathy). Thus, based on sequence and/or restriction fragment length polymorphism analysis of more than 250 HTLV-I isolates originating from the main viral endemic areas, three major molecular geographical subtypes (or genotypes) emerged, strongly supported by phylogenetic analysis (high bootstrap values). Each of these genotypes (Cosmopolitan, Central African, and Melanesian) appeared to arise from ancient interspecies transmission between monkeys infected with simian T cell leukemia/lymphoma virus type I and humans. Furthermore, careful sequences analyses indicate that, within (or alongside) these three main genotypes, there are molecular subgroups defined clearly by several specific mutations but not always supported by phylogenetic analyses. Thus in Japan, there is evidence for two ancestral HTLV-I lineages: the classical Cosmopolitan genotype, representing approximately 25% of the HTLV-I present in Japan and clustering in the southern islands; and a related subgroup that we called the Japanese group. Similarly, within the Central African cluster, there are molecular subgroups defined by specific substitutions in either the env or the long terminal repeat. Furthermore, recent data from our laboratory indicate the presence of a new molecular phylogenetic group (fourth genotype) found among inhabitants of Central Africa, particularly in Pygmies. While geographical subtypes vary from 2 to 8% between themselves, HTLV-I quasi-species present within an individual appear to be much lower, with a variability of < 0.5%.

Tax mutation associated with tropical spastic paraparesis/human T-cell leukemia virus type I-associated myelopathy

Tumaco, Colombia, is an area with elevated rates of tropical spastic paraparesis/human T-cell leukemia virus type I (HTLV-I)-associated myelopathy (TSP/HAM). We have identified a mutation in nucleotide 7959 of the tax gene of 14 Tumaco HTLV-I isolates (14 positive of 14 tested) that was present in 5 of 14 (35%) TSP/HAM patients from Japan and in 8 of 11 (72%) TSP/HAM patients from other geographic locations. In contrast, this mutation was found in only 2 of 21 (9.5%) HTLV-I-infected subjects outside of Tumaco who did not have TSP/HAM. tax clones with nucleotide mutations including one at nucleotide 7959 showed a greater ability to transactivate the HTLV-I U3 promoter. However, this effect was not observed when two clones that differed only in nucleotide 7959 were compared. These results suggest that HTLV-I-infected individuals carrying isolates with this tax mutation are at higher risk for developing TSP/HAM.

Nucleotide sequence analysis of a full-length human T-cell leukemia virus type I from adult T-cell leukemia cells: a prematurely terminated PX open reading frame II

Human T-cell leukemia virus type 1 (HTLV-1) is etiologically associated with adult T-cell leukemia/lymphoma (ATL). The prototypic HTLV-1, ATK, is the only full-length provirus cloned from uncultured leukemic cells and completely sequenced prior to this study. We have determined the complete nucleotide sequence of another full-length HTLV-1 provirus cloned directly from leukemic cells. A premature termination codon was found in the second open reading frame (orf II) of the pX region. Our finding indicates that open reading frame II of the HTLV-1 pX region is not required for outgrowth of ATL leukemic clones in vivo.

Human T-cell leukemia virus type II nucleotide sequences between env and the last exon of tax/rex are not required for viral replication or cellular transformation

Human T-cell leukemia virus types I (HTLV-I) and II (HTLV-II) and bovine leukemia virus contain a region of approximately 600 nucleotides located 3' to the env gene and 5' to the last exon of the tax and rex regulatory genes. This region was originally termed nontranslated or untranslated (UT) since it did not appear to be expressed. Several studies have identified novel mRNAs in HTLV-I-, HTLV-II-, a bovine leukemia virus-infected cells that splice into open reading frames (ORFs) contained in the UT region and, thus, have the potential to produce proteins that might contribute to the biological properties of these viruses. The HTLV-II infectious molecular clone pH6neo has several ORFs in the UT region (nucleotides 6641 to 7213) and a large ORF which overlaps the third exon of tax/rex. To investigate the importance of these ORF-containing sequences on viral replication and transformation in cell culture, proviral clones containing deletions in UT (pH6neo delta UT) or a stop codon insertion mutation (pH6neoST) were constructed. Lymphoid cells were transfected with mutant proviral constructs, and stable cell clones, designated 729pH6neo delta UT and 729pH6neoST, were characterized. Viral protein production, reverse transcriptase activity, and the capacity to induce syncytia were indistinguishable from cells transfected with the wild-type clone. Finally, 729pH6neo delta UT- and 729pH6neoST-producer cells cocultured with primary blood T lymphocytes resulted in cellular transformation characteristic of HTLV. These results indicate that putative protein-coding sequences between env and the last exon of tax/rex are not required for viral replication or transformation in cell culture.

The transactivator gene of human T-cell leukemia virus type I is more variable within and between healthy carriers than patients with tropical spastic paraparesis

Human T-cell leukemia virus type I (HTLV-1) causes T-cell leukemia and tropical spastic paraparesis (TSP) in a minority of infected people, whereas the majority remain healthy. No association between a particular HTLV-I sequence and disease manifestation has been found in previous studies. We studied here the sequence variability of the gene for the HTLV-I Tax protein, which is the dominant target antigen of the very strong cytotoxic T-lymphocyte response to the virus. In HTLV-I infection, the intraisolate nucleotide variability is much greater than the variability between isolates. The predicted protein sequence of Tax was significantly more variable in the healthy seropositive individuals' provirus than in those of the patients with TSP. Thus, tax sequence heterogeneity, rather than the presence of particular sequences, distinguishes healthy HTLV-I-seropositive individuals from patients with TSP.

Nucleotide sequence analysis of human T cell leukemia virus, type II (HTLV-II) isolates

A study by Hall et al. (J Virol 1992;66:2456-2463; Ref. 11) has suggested the existence of two closely related molecular subtypes of HTLV-II, which were tentatively designated HTLV-IIa and HTLV-IIb. To confirm this nucleotide sequence analysis of 986 bp of the env gene region encoding the entire surface glycoprotein, gp46, and the amino terminus of the transmembrane glycoprotein, gp21, of 10 HTLV-II isolates was carried out. The results clearly established the existence of two subtypes and demonstrated a 4.3% divergence in sequence in this region. Analysis of other gene regions of the provirus, including the pol (1544 bp), gag (448 bp), and the entire LTR (743 bp) of two representative isolates of each subtype, showed a sequence divergence of 3.8 to 5.7%, with greatest divergence occurring in the LTR. In addition to single nucleotide changes, the gag regions encoding the structural protein, p19, of the HTLV-IIb isolates were also found to have a 66-bp deletion that would be expected to result in a p19 protein having a 22-amino acid deletion in the carboxy-terminus region. Attempts to exploit this to differentiate the two subtypes serologically were unsuccessful in that recombinant p19 proteins of both subtypes were found to be antigenically cross-reactive. The finding of two molecular subtypes of HTLV-II may have important implications for a better understanding of the biological and pathogenic properties of the virus, and will be useful in characterizing the viruses present in endemic foci in American Indian populations.

Characterization of the antibody response to three different versions of the HTLV-I envelope protein expressed by recombinant vaccinia viruses: induction of neutralizing antibody

Recombinant vaccinia viruses (RVV) designated RVV E1, RVV E2, and RVV E3, were constructed to express three different versions of the human T cell leukemia virus type I (HTLV-I) envelope proteins to determine which configuration elicits an optimal antibody response. RVV E1 expressed the native HTLV-I envelope proteins gp46 (surface protein) and gp21 (transmembrane protein), while RVV E2 expressed the envelope precursor with the proteolytic cleavage site deleted. The RVV E3 construct expressed only the external surface glycoprotein, gp46. Radioimmunoprecipitation and FACS analysis confirmed that the appropriate envelope proteins were expressed by RVV E1-, E2-, and E3-infected cells. Immunization studies were carried out using Balb/c, A/J, and C57BL/6 strains of mice. Balb/c mice responded poorly to immunization with all of the three RVV constructs. C57BL/6 mice produced neutralizing antibodies in response to immunization with all three constructs, whereas A/J mice developed neutralizing antibodies only when immunized with the RVV E1s construct. The results indicate that the humoral immune responses depend on the form of HTLV-I envelope proteins expressed by each RVV.

Nucleotide sequence analysis of an HTLV-I isolate from a Chilean patient with HAM/TSP

Isolates of HTLV-I have been characterized from a number of different regions of the world; however, there has not been a nucleotide sequence analysis of an HTLV-I isolate from a South American country. Reported here is an individual from Chile identified with the HTLV-I-associated neurological disease HAM/TSP. The sera and the nucleic acid sequence of the HTLV-I present in peripheral blood lymphocytes from this Chilean HAM/TSP patient over a two year period are characterized. During this time, the patient's condition grew progressively worse. While the serological profile of this patient was unremarkable in comparison with other HAM/TSP patients previously described, nucleic acid sequence analysis identified two nucleotide positions which contained nucleotides unique to this Chilean isolate. The nucleotide sequence analysis also indicates that the Chilean HTLV-I isolate is more closely related to Caribbean and Japanese isolates of HTLV-I than to the African and U.S. isolates described so far.

Low degree of human T-cell leukemia/lymphoma virus type I genetic drift in vivo as a means of monitoring viral transmission and movement of ancient human populations

We have studied the genetic variation of human T-cell leukemia/lymphoma virus type I (HTLV-I) isolates in the same individuals over time, as well as of HTLV-I isolates from various parts of the world. The viral DNA fragment studied encodes the carboxy terminus of gp46 and almost all of gp21, both of which are envelope glycoproteins. Samples were obtained from native inhabitants of five African countries, two South American countries, China, the French West Indies, and Haiti and included 14 patients with tropical spastic paraparesis/HTLV-I-associated myelopathy, 10 patients with adult T-cell leukemia, 1 patient with T-cell non-Hodgkin's lymphoma, and 3 healthy HTLV-I-seropositive individuals. DNA analyses of HTLV-I sequences demonstrated that (i) little or no genetic variation occurred in vivo in the same individual or in different hosts from the same region carrying the same virus, regardless of their clinical statuses; (ii) changes in nucleotide sequences in some regions of the HTLV-I genome were diagnostic of the geographical origin of the viruses; (iii) HTLV-I sequences from West African countries (Mauritania and Guinea Bissau) and some from the Ivory Coast and Central African Republic were virtually identical to those from the French West Indies, Haiti, French Guyana, and Peru, strongly suggesting that at least some HTLV-I strains were introduced into the New World through infected individuals during the slave trade events; and (iv) the Zairian HTLV-I isolates represent a separate HTLV-I cluster, in which intrastrain variability was also observed, and are more divergent from the other HTLV-I isolates. Because of the low genetic variability of HTLV-I in vivo, the study of the proviral DNA sequence in selected populations of infected individuals will increase our knowledge of the origin and evolution of HTLV-I and might be useful in anthropological studies.

Multiple isolates and characteristics of human T-cell leukemia virus type II

Human T-cell leukemia (or lymphotropic) virus type II (HTLV-II) was isolated from eight HTLV-seropositive patients, six of whom were also infected with human immunodeficiency virus, by cocultivation of peripheral blood mononuclear cells (PBMCs) with BJAB, a continuous B-cell line. Restriction endonuclease mapping of the proviruses demonstrated consistent differences among isolates, and two distinct physical map patterns were observed. The results suggest the existence of two closely related molecular subtypes of HTLV-II, which are tentatively designated HTLV-IIa and HTLV-IIb. This finding was supported by preliminary nucleotide sequence analysis of the env gene region encoding the transmembrane glycoprotein gp21, which showed consistent differences between the two proposed virus subtypes. Exploitation of differences in restriction endonuclease sites allowed polymerase chain reaction amplification to detect and differentiate the two subtypes in fresh PBMCs of HTLV-seropositive intravenous drug abusers (IVDAs). The results of these studies confirm that HTLV-II infection is the prominent HTLV infection in seropositive IVDAs and also show that infection with both subtypes occurs. The finding of genetic heterogeneity in the HTLV-II group of viruses may have important implications for studies on its role in human disease and will be useful in characterizing the viruses present in newly discovered endemic foci in New World indigenous populations.

Geographical subtypes demonstrated by RFLP following PCR in the LTR region of HTLV-I

It has been demonstrated that specific mutations, localized in the long terminal repeat (LTR) region of HTLV-I, allowed to propose the existence of three HTLV-I subtypes. Because some of these mutations created or suppressed the restriction sites for ApaI, NdeI, DraI, SacI, MaeIII, and MaeII enzymes, these endonucleases were used for characterization of further 30 HTLV-I isolates. Seventeen proviral DNA from Japan, five from the Caribbean, one each from French Guyana, the United States, and China, two from Ivory Coast, and three from Zaire were tested. The DNA used were extracted from 26 in vivo peripheral blood mononuclear cell samples and from four cell lines obtained from two Japanese, one Chinese, and one North American patients. Digestions were performed on amplified DNA of the LTR region (nucleotides 31-768). The results confirm the existence of three subtypes of HTLV-I according to LTR sequences. Subtype I was observed only in patients from the Ivory Coast and Zaire. Subtype II was found in the patient from the French West Indies, and in 33% of the samples from Japan. Subtype III was most often observed in the Japanese but also in the Zairian patients.

HIV-1 ancestry primordial expansions of RRE and RRE related sequences

The human T-lymphotropic retroviruses HTLV-I and HIV-1/-2 share a complementary patchwork homology in which the RRE regions of HIV-1 and -2 cover 78.1% of a 169 nucleotide (nt) region (PX1,2) positioned precisely between open reading frames PX I and PX II of ATLV (HTLV-I). The sequence character of the PX1,2 region is shown to be influenced by a primordial expansion, CTC2T, originating several hundred nucleotides upstream. A second primordial expansion, AGCU(U/C), is identified and shown to represent 52.1% of the HIV-1 RRE region. It is argued that prior to the present AIDS pandemic the efficiency of the rev receptor was enhanced by an ancestral recombination event.

Comparative biological responses of rabbits infected with human T-lymphotropic virus type I isolates from patients with lymphoproliferative and neurodegenerative disease

An experimental rabbit model was used to determine host responses to infection by various human T-lymphotropic virus type-I (HTLV-I) strains. Seven groups of 4 to 5 rabbits each were inoculated with lethally-irradiated HTLV-I-infected cell lines derived from patients with adult T-cell leukemia/lymphoma or from patients with HTLV-I-associated myelopathy. Four separate control groups of 2 rabbits each were inoculated with similarly prepared HTLV-I-negative cells derived from rabbits or humans. Anti-viral antibody responses were assessed by immunoblot assay and hematologic parameters were measured using automated cell counters and cytologic staining. The virologic status of challenged rabbits was determined by co-culture and HTLV-I antigen capture assay, as well as by polymerase chain reaction (PCR) amplification of HTLV-I DNA from peripheral blood mononuclear cells (PBMC) or tissues. The HTLV-I inocula could be separated into groups based upon their infectivity to rabbits: highly infectious strains elicited intense serologic responses and were detected frequently in tissues by antigen and PCR assays, while other strains were moderately to poorly infectious, induced weak antibody responses and were infrequently detected by antigen and PCR assays. Overall, PBMC appeared to have the greatest quantity of HTLV-I containing cells, while bone marrow was a poor source of virus. No clinical or hematologic abnormalities were evident during the 24-week course of infection. Taken together, our results suggest there is heterogeneity in the biological response to HTLV-I infection which is, in part, dependent on the infecting strain of virus.

DNA sequence analysis of the gene encoding the HTLV-I p21e transmembrane protein reveals inter- and intraisolate genetic heterogeneity

DNA sequence analysis was performed on a 235-bp region of the p21 e transmembrane protein gene of the human T-cell lymphoma/leukemia virus type I (HTLV-I) which encompassess the putative immunosuppressive peptide. Polymerase chain reaction-based amplification was used to generate multiple molecular clones from isolates derived from fresh or cultured cells from 19 individuals. A dendrogram was constructed using the p21e DNA sequence information to compare the sequences among isolates in the current study and other previously published HTLV-I isolates including strains from Africa and Papua New Guinea. Examination of multiple clones from individual isolates revealed the presence of multiple genotypes in patients with tropical spastic paraparesis/HTLV-I-associated myelopathy and adult T-cell leukemia/lymphoma. These findings suggest that HTLV-I, like HIV, may be present as a quasispecies in vivo. Our studies, however, failed to identify specific sequence motifs that segregated exclusively with the lymphoproliferative or neurological forms of the disease.

Nucleotide sequence analysis of isolates of human T-lymphotropic virus type 1 of diverse geographical origins

Nucleotide sequences for long terminal repeat (LTR), gag, the protease gene, and pol of a human T-lymphotropic virus type 1 (HTLV-1) isolate of probable Caribbean origin (HTLV-1CH) and a Zairian isolate (HTLV-1EL) were determined providing complete proviral sequences for these isolates. These sequences were compared with those available from previously analyzed isolates. Nucleotide sequence differences of 1.2-3.3% were identified among isolates for which complete genetic information was available. Nucleotide sequence diversity was distributed relatively evenly over the genome with 1.3-5.2% differences in the LTR, 1.1-2.9% differences in gag, 0.7-2.1% differences in the protease gene, 0.9-2.5% differences in pol, 0.9-2.4% differences in env, 0.0-1.4% differences in rex, and 0.1-2.6% differences in tax. There were 1.2-2.3% amino acid differences overall, with 0.8-1.6% nonconservative amino acid alterations. Nucleotide differences were not found in regions of the LTR which are important for transcriptional activity or Tax response. Within the Rex-response element, nucleotide differences were found predominantly in loop rather than stem structures, thus, maintaining the overall secondary structure necessary for Rex activity. Evolutionary tree analysis of the sequence differences suggests a predominant clustering of different HTLV1 strains according to geographical origin. An open reading frame was also identified on the minus DNA strand situated between the env and rex/tax genes which exhibits 0.1-6.9% nucleotide sequence variation among HTLV1 strains. The limited sequence variation among HTLV-1 strains is in striking contrast to the extensive heterogeneity seen among human immunodeficiency virus (HIV) strains.

HTLV-1 envelope sequences from Brazil, the Caribbean, and Romania: clustering of sequences according to geographic origin and variability in an antibody epitope

We sequenced the envelope genes of Human T-cell leukemia type I viruses (HTLV-I) derived from five Brazilian, two Caribbean, and one Romanian case of adult T-cell leukemia after amplification of the complete env gene by PCR. A comparison with previously reported HTLV-I sequences revealed that, although highly homologous, no two env sequences were identical. All envelope sequences differed from each other by 0.3-2.1% nucleotide differences. The five Brazilian sequences clustered together and were about as different from each other (0.5-0.75% nucleotide difference) as were three previously reported Japanese sequences (0.7-0.95%). In contrast, sequences of Caribbean origin were less homogeneous (0.5-1.9% nucleotide differences within this group). The Romanian sequence was not significantly more divergent than any of the others and was closest to our two Caribbean sequences. We observed two changes in a region (aa 176-209) which has previously been shown to contain a linear antibody epitope recognized by most human sera from seropositive individuals. One of these changes affects the binding of monoclonal antibodies to this epitope demonstrating the variability of an antibody epitope in the HTLV-I envelope.

Temporal regulation of viral and cellular gene expression during human T-lymphotropic virus type I-mediated lymphocyte immortalization

An autocrine mechanism of proliferation may play a significant role in the leukemogenesis of adult T-cell leukemia, a mature T-cell malignancy caused by human T-lymphotropic virus type I (HTLV-I). To further delineate the role of HTLV-I and the interleukin 2 (IL2) system in the transformation process, human primary lymphocytes were infected by cocultivation with lethally X-irradiated MT2 cells in the presence or absence of human rIL2; the polymerase chain amplification reaction was used to examine quantitatively the expression of HTLV-I, IL2, and IL2R alpha mRNAs during early and late proliferation phases that displayed polyclonal (days 7 to 49) and oligoclonal (days 100 to 150) proviral integration, respectively. IL2 mRNA and IL2 activity were transiently expressed during the polyclonal phase but were undetectable at later time points. IL2R alpha mRNA expression remained at a constitutively high level throughout the examined time course. Viral transcripts were detectable at each time point. Expression of the tax-rex mRNA was inversely related to IL2 mRNA levels; it was low early in the polyclonal phase but increased 30-fold with the development of oligoclonality. In addition, paraformaldehyde-fixed HTLV-I-producing cells activated peripheral blood lymphocytes. These data suggest that HTLV-I activates human T lymphocytes. However, IL2 expression is transient, indicating a limited involvement of an IL2 autocrine growth loop in the transformation process. Lastly, another viral determinant, in addition to the trans activator tax, may be important in HTLV-I-induced T-cell proliferation.

Deleted HTLV-I provirus in blood and cutaneous lesions of patients with mycosis fungoides

Mycosis fungoides, a rare form of cutaneous T cell leukemia/lymphoma, is suspected of having a viral etiology on the basis of certain similarities to adult T cell leukemia, which is associated with human T cell leukemia/lymphoma virus type I (HTLV-I) infection. Cell lines were established from peripheral blood mononuclear cells (PBMC) of an HTLV-I-seronegative patient with mycosis fungoides. DNA hybridization analysis revealed the presence of HTLV-I-related sequences with unusual restriction endonuclease sites. Sequence analysis of subcloned fragments demonstrated the presence of a monoclonally integrated provirus with a 5.5-kilobase deletion involving large regions of gag and env and all of pol. Additional evidence for the presence of deleted proviruses was found by polymerase chain reaction (PCR) amplification of DNA from cutaneous lesions of five other HTLV-I-seronegative patients. The findings suggest that HTLV-I infection may be involved in the etiology of at least certain cases of mycosis fungoides.

In vivo genomic variability of human T-cell leukemia virus type I depends more upon geography than upon pathologies

To investigate the geography- and disease-associated genomic variation of human T-cell leukemia virus type I (HTLV-I), we studied ex vivo DNA from peripheral blood lymphocytes from nine patients by polymerase chain reaction and direct DNA sequencing. For each viral strain, 1,917 bp was sequenced, including parts of the long terminal repeat, the env gene, and the px II, px III, and px IV coding frames of the px region. The number of genomic variations observed in the U3 region of the long terminal repeat was higher than that seen in the env and px genes. Very few mutations were present in the px II and px III genes. In contrast, the px IV open reading frame exhibited numerous single point mutations. While no specific mutation could be linked to any pathology (adult T-cell leukemia/lymphoma or tropical spastic paraparesis/HTLV-I-associated myelopathy), variations among HTLV-I isolates from different geographic areas (Ivory Coast, Caribbean, and Japan) existed. The Ivory Coast HTLV-I appeared to represent a group by itself.

Relative prevalence and risk factors of HTLV-I and HTLV-II infection in US blood donors

The clinical significance of human T-cell lymphotropic virus type II (HTLV-II) infection, unlike that of HTLV-I, is unknown, and the major known association of HTLV-II seropositivity is with intravenous drug abuse. Screening of blood donors for HTLV-I, now routine in North America, does not distinguish this retrovirus from HTLV-II. To find out more about the seroepidemiology of and risk factors for HTLV I and II, blood from 480,000 volunteer donors in five geographically separate US urban centres was tested for antibodies to HTLV-I/II and HIV-1. Confirmed HTLV-I/II seropositive donors were then followed up by DNA amplification to distinguish type I from type II and by interviews focusing on possible risk factors. HTLV seroprevalence was 3.3 times greater than that for HIV-1 (0.043% vs 0.013%). DNA amplification on 65 of the 207 HTLV-I/II seropositive donors revealed that 34 (52%) had HTLV-II infection and 28 (43% had HTLV-I; 3 samples were uninformative. Interviews of 49 donors showed that whereas HTLV-I was principally associated with donor origin from endemic regions, the major risk factor for HTLV-II infection was intravenous drug use. The surprisingly high rate of HTLV-II infection in US blood donors raises important public health and donor counselling issues since HTLV-I infection is associated with adult T-cell leukaemia and a neurological disorder while the pathogenicity of HTLV-II is as yet unclear.

Comparative analysis of nucleotide sequences of the partial envelope gene (5' domain) among human T lymphotropic virus type I (HTLV-I) isolates

Human T-cell lymphotropic virus type I (HTLV-I) is associated with adult T-cell leukemia/lymphoma (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The nucleotide sequences of 640 bp of the proviral genome (positions 5158-5797) derived from 11 HTLV-I-infected persons were analyzed using the polymerase chain reaction and M13-based sequencing techniques. Patterns of single nucleotide substitutions were characterized from the extracellular domain of the envelope gene (gp46). Compared with other retroviruses, the nucleotide sequences of the HTLV-I external envelope gene are highly conserved among the genotypes studied. We found no evidence of dual infections with HTLV-II among the seropositive asymptomatic persons or in patients with either ATL or HAM/TSP. No unique sequence differences were observed in the envelope gene of the HTLV-I isolates derived from patients coinfected with human immunodeficiency virus type 1 (HIV-1). However, comparative analysis of these data and other published HTLV-I envelope sequences indicated the presence of four subtypes of HTLV-I in relation to their geographic origin.

Limited sequence variation in human T-lymphotropic virus type 1 isolates from North American and African patients

Nucleotide sequences were determined from the env genes of three HTLV-I clones derived from two North American patients and one African patient with adult T-cell leukemia/lymphoma (ATLL). In addition, sequences from the pX region, between env and the 3'LTR, were determined from one of these isolates. These data were compared to sequences derived from HTLV-I isolates of two Japanese ATLL patients, a Japanese patient with HTLV-I-associated myelopathy or tropical spastic paraparesis (HAM/TSP) and a Caribbean ATLL patient. Nucleotide sequence variation was found to be less than 6% in coding and noncoding regions. Predicted amino acid sequences varied between 0.6 and 1.8% in the envelope, 0-3.7% in rex, 0.8-2.5% in the tax gene product, and 3-14.0% in the pX-I open reading frame. Comparisons of the predicted amino acid sequences of the surface envelope protein (SU-gp46) suggest that the variation between isolates of different geographical origins is greater than that between isolates obtained from the same region of the world.

Robustness of maximum likelihood tree estimation against different patterns of base substitutions

In the maximum likelihood (ML) method for estimating a molecular phylogenetic tree, the pattern of nucleotide substitutions for computing likelihood values is assumed to be simpler than that of the actual evolutionary process, simply because the process, considered to be quite devious, is unknown. The problem, however, is that there has been no guarantee to endorse the simplification. To study this problem, we first evaluated the robustness of the ML method in the estimation of molecular trees against different nucleotide substitution patterns, including Jukes and Cantor's, the simplest ever proposed. Namely, we conducted computer simulations in which we could set up various evolutionary models of a hypothetical gene, and define a true tree to which an estimated tree by the ML method was to be compared. The results show that topology estimation by the ML method is considerably robust against different ratios of transitions to transversions and different GC contents, but branch length estimation is not so. The ML tree estimation based on Jukes and Cantor's model is also revealed to be resistant to GC content, but rather sensitive to the ratio of transitions to transversions. We then applied the ML method with different substitution patterns to nucleotide sequence data on tax gene from T-cell leukemia viruses whose evolutionary process must have been more complicated than that of the hypothetical gene. The results are in accordance with those from the simulation study, showing that Jukes and Cantor's model is as useful as a more complicated one for making inferences about molecular phylogeny of the viruses.

Molecular evolution of human T-cell leukemia virus

Phylogenetic trees for the human T-cell leukemia virus type I (HTLV-I) and its related viruses were constructed by use of nucleotide sequences of the long terminal repeat (LTR) and the tax gene. The trees showed that the viruses diverged from a common ancestral virus and that they are classified into two groups whose hosts are either primates or bovines. However, the topology of the trees for the viruses differed from that for the hosts. This suggests that HTLV-I and HTLV-I-related viruses evolved independently of host-species divergence and that interspecies transmission between human and monkeys occurred in the past. The nucleotide diversity of the tax genes of HTLV-I was estimated to be 0.025. This value is more than 10 times larger than that of human globin genes, but it is about 20 times smaller than that of hemagglutinin genes of influenza A viruses. Thus, the genetic variability of the HTLV-I genes seems to be higher than that of nuclear genes but much lower than the genes of typical RNA viruses. Furthermore, we examined functional constraints on the overlapping region of the rex and tax genes. The results obtained imply that for the overlapping region, the tax gene has much stronger constraints against amino acid changes than the rex gene.

Detection of HTLV-I proviral sequences in CD30-positive large cell cutaneous T-cell lymphomas

To investigate the possibility that cutaneous T-cell lymphomas of large cell type may be associated with human T-cell leukemia/lymphoma virus type I infection in nonendemic regions, tissue samples from six cases of large cell cutaneous T-cell lymphoma and four cases of small cell cutaneous T-cell lymphoma were screened for the presence of integrated proviral human T-cell leukemia/lymphoma virus type I DNA. Combined use of Southern blot hybridization and enzymatic DNA amplification revealed human T-cell leukemia/lymphoma virus type I-specific sequences in all cases of large cell cutaneous T-cell lymphoma and in none of the cases of small cell cutaneous T-cell lymphoma. These results suggest that in nonendemic areas, a significant proportion of large cell cutaneous T-cell lymphoma cases are associated with human T-cell leukemia/lymphoma virus type I.

Familial adult T-cell leukemia/lymphoma

Clinical and laboratory data are described for two siblings who both developed adult T-cell leukemia/lymphoma resulting from infection by human T lymphotropic virus type I (HTLV-I). These findings suggest that genetic factors or virus-specific factors may determine which HTLV-I-infected individuals will develop leukemia.

Sequence variants of human T-cell lymphotropic virus type I from patients with tropical spastic paraparesis and adult T-cell leukemia do not distinguish neurological from leukemic isolates

We have amplified and sequenced DNA in the envelope (env) and long terminal repeat (LTR) regions of human T-cell lymphotropic virus type I (HTLV-I) proviruses from the peripheral blood of 10 HTLV-I-seropositive patients with tropical spastic paraparesis (TSP) and two patients with adult T-cell leukemia. The aim was to examine variation in these regions and to test the hypothesis that the sequences of leukemogenic HTLV-I isolates differ from those causing the neurological disease TSP. In 5 of the 12 HTLV-I-seropositive patients, more than one HTLV-I sequence variant was identified in the same individual. No two individuals shared identical sequences in either env or LTR U3. Sequence variations were found at 73 positions in 1,416 bases amplified in env. Sequence variability was found throughout the LTR-U3 region, including the sequences of two transcriptional enhancers. Several nucleotide changes common to both Caribbean and Japanese HTLV-I isolates allowed us to identify a consensus sequence that differs from the HTLV-I prototype sequence (M. Seiki, S. Hattori, Y. Hirayama, and M. Yoshida, Proc. Natl. Acad. Sci. USA 80:3618-3622, 1983). No sequence in the env or LTR U3 region was found to be characteristic of isolates from TSP patients. Although each isolate was distinct at the nucleotide level, the predicted protein sequence of HTLV-I env is less variable than that of human immunodeficiency virus env, suggesting that these lymphotropic retroviruses use different strategies to evade host immune responses.

Amplification of HTLV-1-related sequences among patients with neurological disorders in highly endemic Nagasaki: lack of evidence for association of HTLV-1 with multiple sclerosis

We studied DNA sequences homologous to HTLV-1 in peripheral blood mononuclear cells (PBMC) of 30 patients with neurological disorders in Kyushu, where HTLV-1 is highly endemic. The regions of HTLV-1 amplified by means of polymerase chain reaction (PCR) included U3, U5, gag, pol, env and pX. Our system specifically detected HTLV-1 sequences only from HTLV-1-positive cells and was sufficiently sensitive to detect one proviral copy per 10(3) PBMC. All PCR-positive cases were seropositive, including 4 cases of tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM) (4/4), and one case each of myasthenia gravis (1/7) and multiple sclerosis (1/8). The PCR-positive rate of patients, excluding 4 TSP/HAM cases, was 8% (2/26), which is similar to the seroprevalence of the adult population in the area. The data suggest that multiple sclerosis is not associated with prototype HTLV-1.

Identification of HTLV-I gag protease and its sequential processing of the gag gene product

The full-length provirus of human T-cell leukemia virus type I (HTLV-I) was isolated from MT-2, a lymphoid cell line producing HTLV-I. In transfected cells, structural proteins of HTLV-I, the gag and env products, were formed and processed in the same manner as observed in MT-2 cells. The nucleotide sequence was determined for a region between the gag and pol genes of the proviral DNA clone containing an open-reading frame. The deduced amino acid sequences show that this open-reading frame encodes a putative HTLV-I protease. The protease gene (pro) of HTLV-I was investigated using a vaccinia virus expression vector. Processing of 53k gag precursor polyprotein into mature p19, p24, and p15 gag structural proteins was detectable with a recombinant plasmid harboring the entire gag- and protease-coding sequence. We demonstrated that the protease processed the gag precursor polyprotein in a trans-action. A change in the sequence Asp(64)-Thr-Gly, the catalytic core sequence among aspartyl proteases, to Gly-Thr-Gly was shown to abolish correct processing, suggesting that HTLV-I protease may belong to the aspartyl protease group. The 76k gag-pro precursor polyprotein was identified, implying that a cis-acting function of HTLV-I protease may be necessary to trigger the initial cleavage event for its own release from a precursor protein, followed by the release of p53 gag precursor protein. The p53 gag precursor protein is then processed by the trans-action of the released protease to form p19, p24, and p15.

Translation of gag, pro, and pol gene products of human T-cell leukemia virus type 2

Sequence analysis of human T-cell leukemia proviral DNA revealed three open reading frames arranged at a -1 position relative to one another. On the basis of homology to other retroviruses, these open reading frames were assigned to the gag, pro, and pol genes. To characterize the primary protein products of these genes and their modes of synthesis, a DNA clone of human T-cell leukemia virus type 2 was transcribed and translated in vitro. Analysis of the viral proteins revealed three polyproteins with molecular masses of 58, 75, and 112 kilodaltons at relative frequencies of 100:13:0.9, respectively. These proteins were mapped on the viral genome by both internal deletions and 3'-end truncations at gag, pro, and pol, respectively. The results indicate that translation of the pol gene requires two independent frameshift events, and the readthrough frequencies at the two frameshift sites appeared to be similar.

High rate of HTLV-II infection in seropositive i.v. drug abusers in New Orleans

Confirmed infection with HTLV-II (human T cell leukemia virus type II) has been described only in rare cases. The major limitation to serological diagnosis of HTLV-II has been the difficulty of distinguishing HTLV-II from HTLV-I (human T cell leukemia virus type I) infection, because of substantial cross-reactivity between the viruses. A sensitive modification of the polymerase chain reaction method was used to provide unambiguous molecular evidence that a significant proportion of intravenous drug abusers are infected with HTLV, and the majority of these individuals are infected with HTLV-II rather than HTLV-I. Of 23 individuals confirmed by polymerase chain reaction analysis to be infected with HTLV, 21 were identified to be infected with HTLV-II, and 2 were infected with HTLV-I. Molecular identification of an HTLV-II--infected population provides an opportunity to investigate the pathogenicity of HTLV-II in humans.

Labeling of DNA probes with a photoactivatable hapten

A photoactivatable reagent for introducing haptens onto DNA probes has been prepared using a commercially available bifunctional linker arm reagent and amino-derivatized 2,4-dinitrophenyl (DNP). The resulting compound (photo-DNP) couples efficiently to DNA using an ordinary sunlamp. Under optimum conditions, about 7-23 DNP molecules per 1000 bases are incorporated into the DNA. Hybridization experiments demonstrate that as little as 1.5 x 10(5) copies of target DNA can be detected by filter hybridization with a photo-DNP-labeled probe and immunochemical detection.

Processing of gag precursor polyprotein of human T-cell leukemia virus type I by virus-encoded protease

The biological activity encoded in the putative protease gene (pro) of human T-cell leukemia virus type I was investigated by using a vaccinia virus expression vector. The 53-kilodalton gag precursor polyprotein was processed into the mature p19, p24, and p15 gag proteins when the gag and protease-coding sequence was expressed under the control of a vaccinia virus promoter, suggesting that the protease may be synthesized through the mechanism of ribosomal frame shifting. The processing defect of a protease mutant could be complemented by cointroduction of a wild-type construct into the cell, demonstrating that the pro gene encodes the biologically active protease molecules which are capable of processing the gag precursor polyprotein in vivo in trans. A study involving the use of a variety of mutants constructed in vitro revealed that the protease consists of a nonessential carboxy-terminal region and a part essential for its activity, including the putative catalytic residue, aspartic acid. Furthermore, a cluster of adenine residues positioned at the overlapping region between the gag and pro genes was shown to be involved in the ribosomal frameshifting event for the synthesis of protease. To mimic the formation of the 76-kilodalton gag-pro precursor polyprotein formed by ribosomal slipping, the coding frames of the gag and pro gene were adjusted. The processing of the gag-pro precursor polyprotein depended on an intact protease gene, implying that a cis-acting function of human T-cell leukemia virus type I protease may be necessary to trigger the initial cleavage event that leads to the release of protease from the precursor protein.

Two major subgroups of human T-cell leukemia virus-1 in Japan

T lymphocytes of patients with human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy (HAM) were cultured. After cultivating for several months, HAM-derived cell lines were tested for the presence of HTLV-1 proviral genome. We have found two major subgroups, the SacI type and the PstI type, of HTLV-1 by the restriction map analysis. They were almost equally distributed among HAM patients. We have also found two types of the provirus in DNA derived from fresh peripheral blood lymphocytes (PBL) or lymph node cells of adult T-cell leukemia/lymphoma (ATL) patients. The PstI type proviruses were predominant in ATL patients. It was concluded that two major subgroups of HTLV-1 exist in Japan and both types have an ability to cause either of two diseases, ATL or HAM.