Human T-lymphotropic retroviruses

Direct activation of resting T lymphocytes by human T-lymphotropic virus type I

The mitogenic or antigenic stimulation of T lymphocytes in the presence of accessory cells results in the synthesis of interleukin-2 (IL-2), which, on interacting with de novo synthesized receptors on the membrane, induces the proliferation and differentiation of T cells. T lymphocytes are the preferential target cells of human T-lymphotropic virus type I (HTLV-I). This virus was isolated from leukaemic cells of patients with adult T-cell leukaemia. No viral transcription was detected in these leukaemic cells, indicating that consistent expression of HTLV-I is not needed for maintenance of the neoplastic state. After a short time in culture, these leukaemic cells produce viral particles which immortalize normal T cells. Hence, HTLV-I might be an important agent not only in the development, but also in the initiation, of this lymphoproliferative disease. This possibility was sustained by our previous observations indicating that normal T lymphocytes incubated with HTLV-I are able to form colonies in soft agar, seven days later, in the absence of exogenous IL-2. These results led us to explore further the immediate effects of viral infection on purified resting T lymphocytes. Here, we present evidence that HTLV-I is able to activate T lymphocytes. Indeed, binding of viral particles to these cells induces IL-2 production and IL-2 receptor expression, and triggers T-cell proliferation. This initial activation, which appears to be independent of accessory cells, may be relevant in understanding the role of HTLV-I in the aetiology of adult T-cell leukaemia.

Regulation of the human interleukin-2 receptor alpha chain promoter: activation of a nonfunctional promoter by the transactivator gene of HTLV-I

We have characterized regulatory regions of the human IL-2 receptor alpha chain (IL2R alpha) promoter. 5' deletion constructs extending to -327 directed CAT expression in HTLV-I-infected T cells, which express IL2R alpha constitutively, and in Jurkat cells, which express IL2R alpha only after induction. Deletions to -267 and -265 were active only in HTLV-I-transformed T cells, but their activity in Jurkat cells was restored by cotransfection of a construct expressing the HTLV-I transactivator protein (tat-I). However, HTLV-I-infected human osteosarcoma cells do not express IL2R alpha-CAT constructs. Thus cell-type-specific factors are required for IL2R alpha expression, and direct or indirect interaction(s) between tat-I and a specific region of the IL2R alpha promoter may cause altered regulation. Tat-I also augments IL2-CAT expression under some conditions, suggesting possible autocrine or paracrine mechanisms for HTLV-I-induced leukemogenesis.

Long-term inhibition of human T-lymphotropic virus type III/lymphadenopathy-associated virus (human immunodeficiency virus) DNA synthesis and RNA expression in T cells protected by 2',3'-dideoxynucleosides in vitro

We report that 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine inhibit retroviral DNA synthesis and mRNA expression in T cells exposed to the virus that causes acquired immunodeficiency syndrome, and afford such cells long-term protection in vitro under conditions of substantial viral excess. Both 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine appear to completely block reverse transcription from viral RNA to viral DNA. Viral mRNA expression is also not detected in cells protected by the drugs throughout 30 days of culture following exposure to the virus. Purine and pyrimidine analogues as 2',3'-dideoxynucleoside-5'-triphosphate serve as substrates for the human T-lymphotropic virus type III/lymphadenopathy-associated virus reverse transcriptase to elongate a DNA chain by one residue, after which the chain is terminated. Cloned normal helper/inducer T cells exposed to a cytopathic dose of the virus, but protected by the drugs, respond normally to specific antigen in vitro. These results suggest that the drugs could be promising agents for further studies in the experimental treatment of patients infected with retroviruses.

HTLV-I antibody and cell-mediated immunity status in sickle cell anemia

Patients with sickle cell anemia (SCA) had an abnormal susceptibility to infections. In Martinique (French West Indies), a human T-cell leukemia/lymphoma virus type I (HTLV-I) endemic area, we found that 17 (10%) of 173 SCA patients had antibodies to HTLV-I. The possible relationship between HTLV-I seropositivity and altered immunity was studied in 13 SCA patients with HTLV-I antibodies compared with 13 matched SCA patients without HTLV-I antibodies. The immunological results, as evaluated by the T-cell subsets analysis, the lymphocyte proliferation responses analyzed after activation with concanavalin A, phytohemagglutinin, or pokeweed mitogen, and the natural killer activity were not statistically different in these two groups of patients (SCA HTLV-I positive vs SCA HTLV-I negative). These data suggest that HTLV-I infection did not result in a major alteration of cellular immunity in this population.

Serum reactivity to human T-cell leukaemia/lymphoma virus type I proteins in patients with large granular lymphocytic leukaemia

To investigate the possibility that the recently recognised syndrome, leukaemia of large granular lymphocytes, could be associated with human T-cell leukaemia/lymphoma virus type I (HTLV-I), sera from 12 patients with this type of leukaemia were tested by the use of western-blot techniques for IgG antibodies to proteins related to human T-cell leukaemia/lymphoma virus type I (HTLV-I). Sera from 6 patients, including 2 patients with rheumatoid arthritis, reacted with p19 or p24 retroviral proteins or both. In contrast, no sample from 32 patients with uncomplicated rheumatoid arthritis, 27 with Felty's syndrome, 11 with other connective tissue disorders, or 21 normal individuals reacted with HTLV-I. The results suggest that leukaemia of large granular lymphocytes may be associated with a retrovirus related to HTLV-I.

Transmission dynamics of HIV infection

Simple mathematical models of the transmission dynamics of human immunodeficiency virus help to clarify some of the essential relations between epidemiological factors, such as distributed incubation periods and heterogeneity in sexual activity, and the overall pattern of the AIDS epidemic. They also help to identify what kinds of epidemiological data are needed to make predictions of future trends.

Expression of the T4 molecule (AIDS virus receptor) by human brain-derived cells

Three human cell lines of astrocytic origin were evaluated for expression of a human T-lymphocyte surface glycoprotein, T4, which also serves as a cellular receptor for the human immunodeficiency virus (AIDS virus, HIV). T4 antigen was detected on the cell surface of 2 of these cell lines using monoclonal OKT-4 antibody and flow cytometry. Gene transcripts encoding the T4 molecule were detected by a ribonuclease protection assay in surface T4-positive and -negative cells. Our results suggest that astrocytes may serve as targets for HIV infection in the brain.

Susceptibility of human glial cells to infection with human immunodeficiency virus (HIV)

Three human brain-derived cell lines (including two of astrocytic origin) were exposed in vitro to the human immunodeficiency virus (HIV), the etiologic agent of immunodeficiency in AIDS. In all three lines, HIV transcripts were detected by in situ hybridisation in 20-30% of cells 48 h after infection. Synthesis of virus gag gene products p24 and p55 was demonstrated by immunoblotting. No cytopathic effects typical of HIV-infected human T lymphocytes were observed. Our data indicate that HIV is neurotropic, and support the hypothesis that this virus may infect astrocytes in the brain.

Epidemiology of AIDS--statistical analyses

Some central questions concerning the epidemiology of AIDS are addressed by statistical analyses. Applying standard maximum likelihood theory to reported cases of transfusion-associated AIDS in the US, the mean and standard deviation of incubation time for AIDS are estimated to be about 60 and 19 months, respectively. If these parameters are applied to the data from the San Francisco CDC cohort study, we find a good correspondence between estimated and reported cases of AIDS when the probability factor p is 0.27-meaning that about 27% of those infected with HIV are expected to develop AIDS during a period of 8-10 years. Application of the incubation time model and the probability factor p to the data on transfusion-associated AIDS makes it possible to estimate the number of transfusion-associated infections with HIV from 1978 to 1984. These estimates give an exponential increase in the number of cases, with a relative increase of 2.74 each year. It seems reasonable to assume that this increase reflects the spread of the virus within this period.

Acquired immune deficiency syndrome in childhood: impaired production of interleukin-2 by HIV (LAV/HTLV III) infected patients

The phenotype and functions of T lymphocytes and of natural killer (NK) cells have been investigated in four children and five adults from three Italian families infected with HIV (LAV/HTLV III). The results show a heterogeneous pattern of immunological derangements involving distribution of T and natural killer subsets, proliferation in response to T cell mitogens and natural killer activity. However, all infected patients tested showed a very low or absent phytohaemagglutinin induced interleukin-2 production regardless of age and clinical conditions, while concanavalin A-induced interleukin-2 production was within the normal range. The impaired interleukin-2 production in response to phytohaemagglutinin in some patients is not related to phytohaemagglutinin-induced proliferation, to clinical conditions or to a defective distribution of T cell subsets. These results suggest that, in our patients, both adults and children, HIV (LAV/HTLV III) has an "early" tropism for a subset of T cells involved in interleukin-2 production.

Epidemiology of feline leukaemia virus infections

In cats the commonest cause of leukaemia and lymphomas is infection with feline leukaemia virus (FeLV). Following infection with this retrovirus some cats eliminate the virus and produce neutralizing antibody whereas others remain latently infected. A final group become persistently infected, and eventually succumb to neoplastic or non-neoplastic diseases induced by the virus. The proportion of cats falling into these different post-infection states depends on the age of exposure and the dose of virus received. In breeding colonies where the virus is endemic, up to 40% may be persistently infected, whereas in surveys of urban or suburban cats, only 1% are found to be infected for life. An important epidemiological feature of FeLV infection is that the majority of cats die from anaemia or immunosuppression rather than from leukaemia. Recent studies of the molecular biology of FeLV have shown that T cell tumour induction involves either transduction or insertional mutagenesis of the myc gene. Recombination between FeLV and FeLV related sequences present in all cat cells also appears to be important in generating different subgroups of the virus.

Development of antiretroviral therapy for the acquired immunodeficiency syndrome and related disorders. A progress report

We review the rationale for, and progress in, the development of antiviral therapy for the acquired immunodeficiency syndrome (AIDS). A consideration of the replicative cycle of the human immunodeficiency virus (HIV) can lead to the identification of several steps that represent potential targets for antiretroviral therapy, and several substances that can inhibit the replication of HIV in vitro have already been identified. The 2',3'-dideoxynucleosides are a class of nucleoside analogues in which the 3'-hydroxy group is modified so that it cannot form phosphodiester linkages for nucleic acid chains. Some are potent in vitro inhibitors of HIV replication, possibly acting as chain terminators of viral DNA during reverse transcription. One of these dideoxynucleoside analogues, 3'-azido-2',3'-dideoxythymidine (AZT), has now been administered for up to 18 months to patients with AIDS. The drug has been shown to improve immunologic function, to reverse, at least partially, HIV-induced neurologic dysfunction in some patients, and to improve certain other clinical abnormalities associated with AIDS. The principal toxic effect associated with AZT is dose-dependent suppression of bone marrow, resulting particularly in anemia and leukopenia; however, most patients in whom this toxic effect occurs can subsequently tolerate a lower dose of the drug. The demonstration that AZT can be beneficial in patients with AIDS has removed some of the uncertainty about the rationale for an antiretroviral intervention in HIV infection.

Endemic tropical spastic paraparesis associated with human T-lymphotropic virus type I: a clinical and seroepidemiological study of 25 cases

Tropical spastic paraparesis (TSP) is a common myeloneuropathy with primary and predominant involvement of the pyramidal tract and minimal sensory loss. The epidemic form of TSP is related to toxic nutritional factors, but the endemic form occurs in clusters in tropical areas, especially in India, Africa, the Seychelles, Colombia, and areas of the Caribbean. We describe the clinical and epidemiological features of 25 TSP patients from Martinique (French West Indies) with serum antibodies to human T-lymphotropic virus type I (HTLV-I). Furthermore, all 11 patients who were seropositive for HTLV-I had specific HTLV-I antibodies in their CSF. All were women. The age of onset varied from 25 to 60 years (mean, 45 years). The main clinical features are spastic paraparesis or paraplegia with spasticity of the upper limbs, minimal sensory loss, and bladder dysfunction. Minimal estimated incidence and prevalence are 1 per 100,000 inhabitants per year and 8 per 100,000, respectively. Seventeen percent of the relatives of patients with HTLV-I-associated TSP have HTLV-I antibodies (1 husband and 7 children). In Martinique, the prevalence of HTLV-I antibodies in the general population is about 2% and reaches 10% for neurological disorders other than TSP. Since our initial report, the association between spastic paraparesis and HTLV-I has been confirmed in Jamaica, Colombia, and Japan, suggesting the neurotropism of this lymphotropic human retrovirus.

Epidermal Langerhans cells--a target for HTLV-III/LAV infection

Langerhans cells (LC) are bone marrow-derived, Ia+, CD1+, CD4+, ATPase+ dendritic antigen-presenting cells within the human epidermis. Since the CD4 molecule has been implicated as a receptor structure for HTLV-III/LAV (human T-cell leukemia virus/lymphadenopathy-associated virus), we asked whether LC from HTLV-III/LAV-seropositive individuals display signs of HTLV-III/LAV infection. In skin biopsies from 7/40 HTLV-III/LAV-infected persons (1 asymptomatic carrier, 2 patients with acquired immunodeficiency syndrome (AIDS)-related complex and 4 patients with AIDS), LC were the only epidermal cells to react with a monoclonal antibody specific for the HTLV-III core protein p17. A varying percentage of p17+ LC were morphologically altered with blunt dendrites and poorly demarcated cellular contours. In one of these biopsies, the presence of LC-associated viral particles characteristic of HTLV-III/LAV as well as cytopathic changes in approximately one-third of the LC population were demonstrated by electron microscopy. These results strongly suggest that LC may harbor HTLV-III/LAV. The infection of LC with this retrovirus may have deleterious consequences for the immunologic functions of this cell system and may thus contribute to both the acquisition of immunodeficiency and the infectious and neoplastic complications of AIDS.

Fine structure of human immunodeficiency virus (HIV) and immunolocalization of structural proteins

Ultrathin section and surface replica electron microscopy were applied in combination with immunoelectron microscopy to elucidate the fine structure of HIV. The shell of the tubular core shows p24 antigenicity, while p17 is located at the inner leaflet of the lipid membrane. The virus particle is studded with 70-80 protrusions. These knobs have a diameter of 15 nm, a height of 9 nm, and are probably arranged in a T = 7 I symmetry. The major envelope protein gp120 is spontaneously shed from the viral surface. A possible role of released gp120 in pathogenesis is discussed.

Therapy of acquired immune deficiency syndrome with recombinant interleukin-2

Recombinant human interleukin-2 (rIL-2) was administered to 87 patients with the acquired immune deficiency syndrome (AIDS) to test the hypothesis that this lymphokine would correct the underlying qualitative and quantitative deficiency in cellular immunity. Patients were divided into two groups by the presence or absence of Kaposi's sarcoma and subjects within each of these groups received intravenous rIL-2 three times weekly for eight weeks. Subjects received one of several doses which ranged from 1,000 to 2,000,000 units per square meter body surface area. Toxicity at high doses consisted of flu-like symptoms and hypotension at highest doses. Partial objective tumor regression was observed in three patients with Kaposi's sarcoma. Seventeen patients had progression of disease (new opportunistic infection or increase in Kaposi's sarcoma) during therapy. No improvement in immunologic status was observed. This study does not suggest a role for single-agent rIL-2 therapy of established AIDS but its use in less symptomatic persons or in conjunction with antiretroviral agents such as azidothymidine should be investigated.

Interaction of viral and cellular factors with the HTLV-III LTR target sequences in vitro

The location of cis-acting regulatory sequences within the long terminal repeat (LTR) of the human T-cell lymphotropic virus type III was determined by eukaryotic cell transfection and chloramphenicol acetyltransferase (CAT) assay or in vitro cell-free transcription. A 160 base pair (bp) region of the LTR at position - 104 to 56 is required for trans-activation (cap site 1). A 24 bp enhancer element (EHE) capable of increasing the rate of transcription, irrespective of orientation, is located between nucleotides -105 to -80. It contains two 10 bp repeats. Three Sp1 binding sites (Sp1 III-I) are located between -78 and -45. A deletion of Sp1 III allowed for limited TATIII response while the presence of a functional enhancer restored the activity in HTLV-III infected cells. Complete loss of transcriptional activity and CAT gene expression could be attributed to the absence of EHE and Sp1 III-I at position -48. However, reinsertion of the enhancer restored accurate initiation but at a decreased level suggesting that the presence of a Sp1 binding site is not a prerequisite for the accurate initiation of transcription but is required for transcriptional activation independent of a promoter. The presence of a negative regulatory element (NRE) has been demonstrated by removal of the 5' part of U3 to position -117. Nucleotide sequences around the cap site and poly (A) site contain a trans-activator response element (TRE) and could be arranged into a unique secondary structure. A deletion of four nucleotides TCTGAGCCTGGGAGCTC causes a loss of three dimer linkage sequence binding. The CAT gene enzyme expression is completely abolished but transcriptional activity remains at reduced level.

Immunoreconstitution of T-cell impairments in asymptomatic male homosexuals by thymic humoral factor (THF)

The feasibility of using Thymic Humoral Factor (THF) for immunomodulation in asymptomatic male homosexuals was evaluated in a study on fifteen subjects with T-cell impairments, selected on the basis of a 2SD reduction in T helper/inducer (T4+) cells and one additional lymphocytic defect. Following two biweekly courses of treatment, mean relative increments of T4+ (P less than 0.002), T3+ (P less than 0.02) and total lymphocyte (P less than 0.05) populations of the group receiving THF (n = 7) were significantly increased when compared to the placebo group (n = 8). In addition, a transient increase in T4+ lymphocytes was observed after the first course in the two individuals of the THF-treated group who were seropositive for HTLV-III/LAV but not in those who were seronegative. No difference was found between the groups in fluctuations of serum interferon (IFN) or proliferation of peripheral mononuclear cells to mitogens. The results of this limited trial demonstrate that THF is capable of correcting T-cell impairments that may predispose asymptomatic homosexuals to infection by HTLV-III, without affecting IFN production. These findings suggest that future strategies for AIDS prevention in high-risk groups should include institution of large controlled trials in immunodeficient, asymptomatic, HTLV-III/LAV-seronegative male homosexuals to study the potential of selective immunoreconstitution as a preventive measure against HTLV-III/LAV infection.

Genomic diversity of Zairian HIV isolates: biological characteristics and clinical manifestation of HIV infection

We describe here several African isolates of HIV, compare them to U.S.-European prototype isolates and to each other, correlate the number of isolates with serological results, and provide insights into the disease spectrum associated with HIV infection in Africa. Three of 25 healthy Zairian donors and 54 of 87 Zairian patients selected for specific pathology and hospitalized in the internal medicine department of the University Clinic of Kinshasa, Zaire, were HIV positive over a six month period in 1985 either by serum antibody (42 cases) or virus isolation (40 cases). The virus positive cases showed a decrease in number of T4 cells and interleukin-2 (IL2) production by mononuclear cells. Restriction endonuclease analysis of HIV sequences from these isolates showed that genomic diversity is also observed in the Zairian isolates but closely related viruses could also be found, similar to the spectrum of diversity among isolates obtained from the U.S. and Europe. A number of isolates (12 of 40) were obtained from serum antibody negative adults. These results are difficult to explain by viral antigenic diversity alone since hybridization with a HTLV-III-B (clone BH10) probe under stringent conditions indicated an overall high degree of relatedness. Rather, these results indicate that some African HIV infected patients fail to make detectable antibodies to HIV or the antibodies were bound in immune complexes not detectable by current techniques.

Analysis of human serum antibodies to human immunodeficiency virus (HIV) using recombinant ENV and GAG antigens

Recombinant proteins representing gag and env amino acid sequences of the Human Immunodeficiency Virus (HIV) (HTLV-IIIb) were produced in Escherichia coli and used to analyze sera for the presence of antibodies to HIV. ENV-9 is a protein representing the carboxy terminus of gp120 and part of gp41 which is highly immunoreactive. GAG-1 represents 83% and GAG-55 100% of the amino acids of the gag open reading frame. The purified proteins allow sensitive detection by enzyme linked immunosorbent assay (ELISA) of antibodies directed against either env or gag of HIV. We have determined the reactivity of sera from several HIV exposed individuals, either form high risk populations or with clinically defined conditions, in the ENV-9, GAG-55, and GAG-1 assays and found that two major seropositive groups are observed. The quantitative analysis of sera with env and gag antigens by ELISA showed AIDS patients had very low gag reactivity while retaining high env reactivity. Results obtained with authentic p24 viral protein in both ELISA and radioimmunoassay correlated to those from the GAG-55 ELISA. This correlation and the analysis of sera with both the ENV and GAG ELISAs indicate that the antibodies reactive to gag are specifically affected relative to env reactivity and that different levels of antibodies to separate viral components in these sera may correlate with disease state.

AIDS and the neurosurgeon

AIDS is a fatal viral infection transmitted by body fluids, primarily blood, which is becoming more common in the U.K., and if the gloomiest predictions are true will affect millions in the next decade. Most, if not all, of these patients will at stage develop neurological manifestations: therefore the neurosurgeon will find it difficult to avoid close contact with the syndrome. As the presentation may mimic a number of neurological conditions, or patients with AIDS may suffer head injury, subarachnoid haemorrhage, or other common conditions, it is probably wise to assume all patients have AIDS and to modify operating technique and other procedures where blood may be spilt to minimise the risks of acquiring the infection.

Establishment of bovine leukemia virus-producing and -nonproducing B-lymphoid cell lines and their proviral genomes

We have established four cell lines in vitro from peripheral leukemic cells of four independent enzootic bovine leukosis (EBL) cattle. All cell lines exhibited differentiated B-cell characters. Two of them produced infectious bovine leukemia virus (BLV), but the others did not. Nonproducer cell lines contained single copies of defective BLV proviral genomes with the same integration profiles as the uncultured cells. On the other hand, numerous proviral copies were detected in producer cell lines. One of the producer cell lines, BL407, whose original uncultured cell contained complete and defective proviral genomes retained the original two copies and had increased only complete genomes in different integration sites after long term culture. These findings suggest that the monoclonal leukemic cells from EBL cases are preferentially established in vitro irrespective of their proviral structures, and the producer B-lymphoid cells amplify their proviral copies by reinfection with viruses re-expressed from the cells during in vitro cultivation.

Molecular characterization of human immunodeficiency virus from Zaire: nucleotide sequence analysis identifies conserved and variable domains in the envelope gene

To examine the genetic relatedness of human immunodeficiency viruses (HIV) from different geographic locations, we molecularly cloned the genome of HIV isolated from a Zairian AIDS patient. Restriction mapping of the recombinant clone, designated HIV-Zr6, revealed both common (as observed in other HIV isolates) and unique restriction sites. The DNA clone of HIV-Zr6, shown to give rise to infectious cytopathic virus after transfection of cultured lymphoid cells, was sequenced in several regions. The long terminal repeat (LTR), open reading frame 1 (ORF1), C-terminal envelope (env) gene domain, and ORF2 showed less than 6% difference in nucleotide sequence when compared to other HIV isolates including human T-lymphotropic virus-type III (HTLV-III) clone B10, lymphadenopathy-associated virus-1 (LAV-1), and AIDS-associated retrovirus-2 (ARV-2). About 15% difference in nucleotide sequences was noted in the N-terminal env gene domain. Alignments of env gene sequences revealed conserved, moderately variable, and hypervariable stretches in the predicted amino acid sequences. This model provides a basis for assessing the significance of sequence variation on properties controlled by the viral Env glycoproteins such as cell tropism and immunogenicity.

Persistent HIV antigenaemia and decline of HIV core antibodies associated with transition to AIDS

Sequential serum samples from 13 homosexual men who seroconverted for antibodies to human immunodeficiency virus (HIV) were tested for HIV antigen. In one of these men, who developed the acquired immune deficiency syndrome (AIDS), HIV antigenaemia preceded the onset of AIDS by more than a year and persisted throughout the course of the disease. This antigenaemia was accompanied by the disappearance of IgG antibody reactivity to the major HIV core protein p24. In none of the 12 others, who all remained without serious disease, were serum concentrations of HIV antigen detected, except on one occasion in one man. All their serum samples showed strong IgG antibody reactivity to p24. Nine children who were infected with HIV in 1981 by plasma transfusion from a single donor were also followed up for HIV antigenaemia. HIV antigen was almost constantly present in the serum (26 of 28 samples) of five children who developed AIDS related complex or AIDS and less often in the serum (four of 10 samples) of four children who remained free of symptoms. The two children who developed AIDS showed a virtual absence of antibody reactivity to p24. These results indicate that increased HIV gene expression is a contributing factor to the development of AIDS and also provide evidence for a switch from latent to active HIV infection.

Lentivirus genomic organization: the complete nucleotide sequence of the env gene region of equine infectious anemia virus

The nucleotide sequence of the envelope (env) gene region of equine infectious anemia virus (EIAV), a member of the lentivirus subfamily of retroviruses, has been determined from a clone of integrated proviral DNA for which the gag and pol sequences have been reported previously. The env gene is 859 codons in length and the sequence reported here is consistent with the published biochemical properties of EIAV glycoproteins. The env gene region of EIAV shares considerable structural similarities but negligible sequence homologies with the env genes of other members of the lentivirus subfamily, visna virus, and human T-lymphotropic virus (HTLV-III) or lymphadenopathy virus (LAV). As in visna virus and HTLV-III, the polymerase (pol) and env genes of EIAV do not overlap. EIAV contains two short open reading frames (orf) of 50 and 66 codons in the pol-env intergenic region. However, unlike the orf Q regions reported for visna virus and HTLV-III, neither EIAV orf overlaps the 3' terminus of the adjacent pol gene. The EIAV genome also contains a third short open reading frame of 135 codons which is contained completely within the env gene, in contrast to the 3'-orf/orf F gene reported for HTLV-III/LAV which extends beyond the env gene terminus. These results provide a detailed description of the env gene region of EIAV and describe a number of characteristic features of genomic organization in lentiviruses which contrast with the genomic organization of oncogenic retroviruses.

The epidemiology of the human immunodeficiency virus infection

It is nearly six years since the first evidence of the AIDS epidemic was seen, with the report of five cases of Pneumocystis carinii pneumonia diagnosed in young, otherwise healthy homosexual men in Los Angeles. The report was surprising, for although P. carinii is a common human commensal, the pneumonia essentially occurs only in the presence of severe immune suppression. Similar reports quickly followed from New York City and San Francisco, with the additional observation that Kaposi's sarcoma—a malignancy usually seen only in elderly men in this country—was also occurring epidemically among young homosexual men.

Since then, the epidemic has evolved at a relentless pace to a reported 32,000 cases in the United States by March 1987. The epidemic has sparked a massive multidisciplinary scientific effort, resulting in the successful identification of the causal agent—the human immunodeficiency virus (HIV)—within two years from the first report and producing a commercially available antibody test within four years.

Infection of the HTLV-II-bearing T-cell line C3 with HTLV-III/LAV is highly permissive and lytic

The recent discovery that HTLV-I infected T-cells have an enhanced susceptibility to HTLV-III/LAV infection with concurrent cell lysis (S. Harada, Y. Koyanagi, and N. Yamamoto (1985) Science, 229, 563-566) led us to investigate a possible role for HTLV-II infected T cells in this respect. HTLV-II-bearing C3 cells were exposed to HTLV-III/LAV and the subsequent infection monitored by indirect immunofluorescence (IIF) of cells, reverse transcriptase (RT) activity in culture fluids, and hemacytometer cell counts. HTLV-III/LAV antigen expression was detected within 2 days whereas RT activity was detected within 3 days postinfection. The presence of immunofluorescent positive cells and RT activity was accompanied by cell lysis. Double infection of C3 cells was confirmed by IIF using a goat polyclonal antibody directed against the core p24 protein for detecting HTLV-II, and high titer serum from a pre-AIDS patient for detecting HTLV-III/LAV. We conclude that HTLV-I and HTLV-II infected T-cells share an enhanced susceptibility to HTLV-III/LAV infection with the promotion of cell lysis.

Elevated levels of mRNA can account for the trans-activation of human immunodeficiency virus

The genome of human immunodeficiency virus encodes a protein that dramatically elevates amounts of viral proteins. The precise mechanism of this trans-activation remains to be established. It has been reported that trans-activation can occur without major changes in the levels of mRNA. We constructed recombinant plasmids containing those viral sequences required in cis for trans-activation linked to the chloramphenicol acetyltransferase gene. These plasmids were introduced into cultured cells in either the presence or absence of a second plasmid that directed expression of the viral trans-activator protein. Expression of the chloramphenicol acetyltransferase gene was measured at the level of protein (by enzymatic assay) and RNA (by ribonuclease protection and primer extension). Our results demonstrate that trans-activation is accompanied by large increases in mRNA levels; these increases may be sufficient to explain the elevated levels of trans-activated protein.

A sequence homology between the pX genes of HTLV-I/II and the murine IL-3 gene

Searching the protein sequence database for amino acid sequences homologous to the x-lor sequence in the pX region of human T-cell leukemia virus types I and II (HTLV-I/II), we found that there is a region of 38 amino acids where the murine interleukin 3 (IL-3) sequence has a 40% homology with the x-lor sequence. A statistical analysis shows that this homology is highly significant with a probability of 1.57 X 10(-10). The biological implication of this homology is discussed.

Induction of anti-HIV neutralizing antibodies by synthetic peptides

Two synthetic peptides containing amino acid sequences analogous to the envelope glycoprotein of human T-lymphotropic virus (HTLV) type III (HTLV-III) and lymphadenopathy associated virus (LAV) were produced and used to immunize rabbits. The subsequent rabbit antisera neutralized HTLV-III infectivity in vitro. The two synthetic peptides corresponded to regions associated with the gp120 or gp41 subunits respectively, of human immunodeficiency virus (HIV). This data indicates that at least two neutralizing epitopes are present on the envelope glycoprotein of HIV and these epitopes are associated with two distinct virus envelope glycoproteins. Antisera generated against these peptides neutralized infectivity of two different isolates of HTLV-III. The data is discussed in terms of possible strategy for developing an effective vaccine against the etiologic agents of acquired immune deficiency syndrome (AIDS).

Structure of a human retroviral sequence related to mouse mammary tumor virus

Human sequences that are related to the mouse mammary tumor virus (MuMTV) genome were cloned from breast tumor cell DNA. Of 100 recombinants, only 1 hybridized with two different probes from separate regions of the MuMTV genome (gag-pol and long terminal repeat [LTR]). This sequence, NMWV 4, was shown to have a proviruslike structure. Hybridization to digests of normal and tumor cell DNA indicated that NMWV 4 and a few closely related sequences are endogenous to the human genome. The regions that contain homology to the MuMTV LTR were sequenced. Long repeated sequences with the hallmarks of retroviral LTRs were identified. The NMWV 4 LTR contains transcription initiation and termination signals and is flanked by a polypurine tract (5' LTR) and a primer-binding site (3' LTR). The primer-binding site is complementary to tRNA lysine, the primer used by MuMTV and HTLV-III. The polypurine tract is also similar to those of these two retroviruses.

Molecular cloning and primary nucleotide sequence analysis of a distinct human immunodeficiency virus isolate reveal significant divergence in its genomic sequences

In an effort to evaluate data on genomic relatedness among the various human immunodeficiency viruses (HIVs), we have molecularly cloned a virus isolate designated HIV (CDC-451). Preliminary characterization of the HIV (CDC-451) clone indicated that the restriction enzyme map was distinct from those of other known HIV isolates. Analysis of the primary nucleotide sequence of the regions encoding the structural proteins and comparison with sequences known for other HIV isolates indicated substantial differences for HIV (CDC-451). The sequences encoding the group-specific antigen gene, although they showed some variation, were conserved to a greater extent than were those encoding envelope proteins. In the envelope gene sequences, most of the changes (up to 24.5% divergence) were located in the amino-terminal region encoding a glycoprotein with a Mr of 120,000. The carboxyl-terminal region, encoding a protein of Mr 41,000, was more highly conserved. The variation in the sequences encoding envelope proteins may have important implications for the antigenic properties and/or pathogenicity of the disease and for its detection and ultimate eradication.

Isolation of a new virus, HBLV, in patients with lymphoproliferative disorders

A novel human B-lymphotropic virus (HBLV) was isolated from the peripheral blood leukocytes of six individuals: two HTLV-III seropositive patients from the United States (one with AIDS-related lymphoma and one with dermatopathic lymphadenopathy), three HTLV-III seronegative patients from the United States (one with angioimmunoblastic lymphadenopathy, one with cutaneous T-cell lymphoma, and one with immunoblastic lymphoma), and one HTLV-III seronegative patient with acute lymphocytic leukemia from Jamaica. All six isolates were closely related by antigenic analysis, and sera from all six virus-positive patients reacted immunologically with each virus isolate. In contrast, only four sera from 220 randomly selected healthy donors and none from 12 AIDS patients without associated lymphoma were seropositive. The virus selectively infected freshly isolated human B cells and converted them into large, refractile mono- or binucleated cells with nuclear and cytoplasmic inclusion bodies. HBLV is morphologically similar to viruses of the herpesvirus family but is readily distinguishable from the known human and nonhuman primate herpesviruses by host range, in vitro biological effects, and antigenic features.

Cell killing by ultraviolet-inactivated human immunodeficiency virus

Extensive cell killing and cytopathology were observed within 24 hr after exposure of a clonal cell line of human T-4 lymphocytes (RH9) to culture supernatants containing human immunodeficiency virus (HIV). Ultraviolet-irradiated HIV-containing culture fluids were also capable of killing RH9 cells and of inducing specific cytopathic effects which were indistinguishable from those induced by unirradiated virus-containing preparations. The uv-irradiated HIV was incapable of forming proviral DNA using the endogenous virion genomic RNA as a template. The RH9 cells persistently infected with HIV did not release soluble cytotoxic factors to account for the cell killing observed when culture supernatants were added to uninfected RH9 cells. The fraction involved in cell killing had the hydrodynamic properties of a retrovirus. These results suggest that a virion component is responsible for cell killing by HIV.

STLV-I antibodies in feral populations of East African vervet monkeys (Cercopithecus aethiops)

Serum samples from feral populations of African green monkeys (Cercopithecus aethiops) were screened for antibodies to the simian T-lymphotropic virus, type I (STLV-I). Blood samples had been collected from 336 monkeys in 4 regions of central and southern Kenya in 1978 and 1979, from 114 monkeys in central Ethiopia in 1973, and from 85 monkeys from the Kampala region of Uganda in 1966. A total of 178/535 monkeys (33%) were seropositive (STLV-I+). Only 4/114 monkeys (4%) from Ethiopia were seropositive compared to 25/85 Ugandan monkeys (29%) and 149/336 Kenyan monkeys (44%). Epidemiological analysis of the Kenyan monkeys showed that 37% of the males and 54% of the females were STLV-I+, and that there was a progressive increase in the proportion of STLV-I+ monkeys of both sexes with age, rising from an average of 16% in infants (less than 9 months) to an average of 69% in adults (greater than 42 months). The proportion of STLV-I+ monkeys was higher among females in each age category. Seropositivity for antibodies to STLV-I had no apparent effect on the health of monkeys, and no association with the occurrence of Hepatocystis parasitemia was seen in this species. The analysis of data from infants of STLV-I+ mothers showed that seroconversion had occurred in 1 of 3 cases, suggesting that vertical transmission of the STLV-I virus is not an inevitable consequence for infants of seropositive mothers.

Demonstration of virus-specific transcriptional activator(s) in cells infected with HTLV-III by an in vitro cell-free system

Human T cell lymphotropic viruses (HTLV's) differ from most other retroviruses based on the presence of trans-regulatory genes for virus expression. In this study, using an in vitro cell-free transcription system, we demonstrate that nuclear extracts obtained from cells infected with HTLV-III (human immunodeficiency virus, HIV) contain a factor(s) that stimulates transcription specifically from the HTLV-III promoter. Present studies indicate that this activation is mainly involved in the initiation of transcription from the HTLV-III promoter.