The CD4 (T4) antigen is an essential component of the receptor for the AIDS retrovirus

Acquired immune deficiency syndrome (AIDS) is characterized by opportunistic infections and by 'opportunistic neoplasms' (for example, Kaposi's sarcoma). Persistent generalized lymphadenopathy (PGL) is epidemiologically associated with AIDS, especially in male homosexuals. A subset of T lymphocytes positive for the CD4 antigen (also termed T4 antigen), is depleted in AIDS and PGL patients. A retrovirus found in T-cell cultures from these patients is strongly implicated in the aetiology of AIDS because of the high frequency of isolation and the prevalence of specific antibodies in the patients. Here we have detected cell-surface receptors for the AIDS retrovirus (human T-cell leukaemia virus-III (HTLV-III) and lymphadenopathy-associated virus-1 (LAV-1) isolates) by testing the susceptibility of cells to infection with pseudotypes of vesicular stomatitis virus bearing retroviral envelope antigens, and by the formation of multinucleated syncytia on mixing virus-producing cells with receptor-bearing cells. Receptors were present only on cells expressing CD4 antigen; among 155 monoclonal antibodies tested, each of the 14 anti-CD4 antibodies inhibited formation of syncytia and blocked pseudotypes. Productive infection of CD4+ cells with HTLV-III or LAV-1 markedly reduced cell-surface expression of CD4. In contrast, receptors for HTLV-I and HTLV-II were not restricted to CD4+ cells, were not blocked by anti-CD4 antibodies; cells productively infected with HTLV-I and HTLV-II expressed surface CD4. Hence, we conclude that the CD4 antigen is an essential and specific component of the receptor for the causative agent of AIDS.

Frequent detection and isolation of cytopathic retroviruses (HTLV-III) from patients with AIDS and at risk for AIDS

Peripheral blood lymphocytes from patients with the acquired immunodeficiency syndrome (AIDS) or with signs or symptoms that frequently precede AIDS (pre-AIDS) were grown in vitro with added T-cell growth factor and assayed for the expression and release of human T-lymphotropic retroviruses (HTLV). Retroviruses belonging to the HTLV family and collectively designated HTLV-III were isolated from a total of 48 subjects including 18 of 21 patients wih pre-AIDS, three of four clinically normal mothers of juveniles with AIDS, 26 of 72 adult and juvenile patients with AIDS, and from one of 22 normal male homosexual subjects. No HTLV-III was detected in or isolated from 115 normal heterosexual subjects. The number of HTLV-III isolates reported here underestimates the true prevalence of the virus since many specimens were received in unsatisfactory condition. Other data show that serum samples from a high proportion of AIDS patients contain antibodies to HTLV-III. That these new isolates are members of the HTLV family but differ from the previous isolates known as HTLV-I and HTLV-II is indicated by their morphological, biological, and immunological characteristics. These results and those reported elsewhere in this issue suggest that HTLV-III may be the primary cause of AIDS.

Isolation of lymphocytopathic retroviruses from San Francisco patients with AIDS

Infectious retroviruses have been detected in 22 of 45 randomly selected patients with acquired immune deficiency syndrome (AIDS) and in other individuals from San Francisco. The AIDS-associated retroviruses (ARV) studied in detail had a type D morphology, Mg2+-dependent reverse transcriptase, and cytopathic effects on lymphocytes. The viruses can be propagated in an established adult human T cell line, HUT-78. They cross-react with antiserum to the lymphadenopathy-associated retrovirus isolated from AIDS patients in France. Antibodies to ARV were found in all 86 AIDS patients and in a high percentage of 88 other homosexual men in San Francisco. This observation indicates the widespread presence of these lymphocytopathic retroviruses and their close association with AIDS.

Delineation of a region of the human immunodeficiency virus type 1 gp120 glycoprotein critical for interaction with the CD4 receptor

The primary event in the infection of cells by HIV is the interaction between the viral envelope glycoprotein, gp120, and its cellular receptor, CD4. A recombinant form of gp120 was found to bind to a recombinant CD4 antigen with high affinity. Two gp120-specific murine monoclonal antibodies were able to block the interaction between gp120 and CD4. The gp120 epitope of one of these antibodies was isolated by immunoaffinity chromatography of acid-cleaved gp120 and shown to be contained within amino acids 397-439. Using in vitro mutagenesis, we have found that deletion of 12 amino acids from this region of gp120 leads to a complete loss of binding. In addition, a single amino acid substitution in this region results in significantly decreased binding, suggesting that sequences within this region are directly involved in the binding of gp120 to the CD4 receptor.

Activation of the HIV-1 LTR by T cell mitogens and the trans-activator protein of HTLV-I

To investigate the mechanism by which immune activation augments replication of the human immunodeficiency virus type 1 (HIV-1) in infected T cells, four different classes of T cell mitogens were evaluated for their effects on the HIV-1 long terminal repeat (LTR). Phytohemagglutinin (PHA), a mitogenic lectin; phorbol 12-myristic 13-acetate, a tumor promoter; ionomycin, a calcium ionophore; and tat-1, the trans-activator protein from the human T cell leukemia/lymphoma virus type I (HTLV-I) each stimulated the HIV-1 LTR. Studies of deleted forms of the LTR supported a central role in these responses for the HIV-1 enhancer, which alone was sufficient for mitogen inducibility, but also suggested that other 5' positive and negative regulatory elements contribute to the overall magnitude of the response. Synergistic activation of the HIV-1 LTR (up to several thousandfold) was observed with combinations of these mitogens and the HIV-1--derived tat-III protein. Cyclosporin A, an immunosuppressive agent, inhibited PHA-mediated activation of the HIV-1 LTR but was without effect in the presence of other mitogens. Thus, HIV-1 gene expression and replication appear to be regulated, via the HIV-1 LTR, by the same mitogenic signals that induce T cell activation.

Biological and biochemical characterization of a cloned Leu-3- cell surviving infection with the acquired immune deficiency syndrome retrovirus

Leu-3- cells that survive infection with the acquired immune deficiency syndrome (AIDS) retrovirus can be induced with IUdR to express infectious virus. A cellular clone (8E5), isolated by limiting dilution of a mass culture of survivor cells, was found to contain a single, integrated provirus that was constitutively expressed. Although IUdR treatment of 8E5 cells failed to induce infectious virus, cocultivation with Leu-3+ cells generated the characteristic syncytia associated with acute AIDS retrovirus infection. The single integrated copy of proviral DNA directs the synthesis of all major viral structural proteins except p64, as monitored by immunoblotting. The relationship of the 8E5 clone to viral latency and persistence is discussed.

The structure, function, and expression of interleukin-2 receptors on normal and malignant lymphocytes

Antigen or mitogen-induced activation of resting T cells induces the synthesis of interleukin-2 (IL-2) as well as the expression of specific cell surface receptors for this lymphokine. Failure of the production of either IL-2 or its receptor results in a failure of the T-cell immune response. The receptor is composed of a 33,000-dalton (251-amino acid) peptide precursor that is post-translationally glycosylated into the mature 55,000-dalton form. In contrast to resting T cells, human T-cell lymphotrophic virus I (HTLV-I)-associated adult T-cell leukemia cells constitutively express large numbers of IL-2 receptors. Because IL-2 receptors are present on the malignant T cells but not on normal resting cells, clinical trials have been initiated in which patients with adult T-cell leukemia are treated with a monoclonal antibody that binds to the IL-2 receptor.

Suramin protection of T cells in vitro against infectivity and cytopathic effect of HTLV-III

A recently discovered member of the human T-cell leukemia virus (HTLV) family of retroviruses has been etiologically linked to the acquired immune deficiency syndrome (AIDS). This virus, which has been designated HTLV-III, is tropic for OKT4-bearing (helper-inducer) T cells. Moreover, the virus is cytopathic for these cells. Suramin is a drug used in the therapy of Rhodesian trypanosomiasis and onchocerciasis, and it is known to inhibit the reverse transcriptase of a number of retroviruses. Suramin has now been found to block in vitro the infectivity and cytopathic effect of HTLV-III at doses that are clinically attainable in human beings.

Recombinant human interferon alfa-A suppresses HTLV-III replication in vitro

Recombinant human interferon alfa-A (rIFN alpha A) had a dose-related suppressive effect on human T lymphotropic virus type III (HTLV-III) replication in vitro in normal peripheral-blood mononuclear cells (PBMC). Both single-dose and multiple-dose regimens were inhibitory. Such inhibitory concentrations (4-1024 units/ml) were not toxic to PBMC in culture, and were within the ranges achievable in blood after injection. These studies suggest that clinical trials of rIFN alpha A in early HTLV-III infection are warranted.

AIDS-associated retroviruses (ARV) can productively infect other cells besides human T helper cells

We have examined the host range of AIDS-associated retroviruses (ARV) that are known to infect human T cells of the helper subset. We have observed that the virus cannot infect fibroblast and epithelial cell lines of many different animal species. It is infectious and replicates efficiently in peripheral mononuclear cells (PMC) of chimpanzee and at low levels in baboon and rhesus monkey PMC. Most importantly, it has been found to replicate in established lines of human B cells, monocytes, and promyelocytes. This ability to infect these other cell types appears to be associated, in most cases, with the presence of the Leu 3 T helper cell antigen on the cell surface. Other mechanisms for virus infection, however, may be involved. The results suggest that ARV will be found in other cells of AIDS patients, besides T cells, and that these cells could be the reservoir for continual virus spread in the host. Variations in the replicative ability of ARV isolates in human cells have also been noted; they could reflect potentially important pathogenic differences among these human retroviruses.

Identification of the putative transforming protein of the human T-cell leukemia viruses HTLV-I and HTLV-II

The human T-cell leukemia viruses HTLV-I and HTLV-II are unique among the transforming retroviruses of vertebrates in their ability to transform human T cells in vitro and in their close association with human malignancies (T-cell lymphomas and leukemia). Their genomes are relatively simple, containing the genes gag, pol, env, and a 3' region termed "X." This 3' region may be responsible for the transforming potential of the viruses. The existence of proteins encoded by the 3' region has been postulated on the basis of multiple open reading frames. In the present study this region is shown to contain a gene encoding a protein of 40 kilodaltons in HTLV-I and 37 kilodaltons in HTLV-II. It is proposed that these proteins be called, respectively, p40xI and p37xII.

The short arm of chromosome 11 is a "hot spot" for hypermethylation in human neoplasia

Inactivation of normally expressed genes may play a role in the formation and/or progression of human cancers. Methylation of cytosine in DNA could potentially participate in such alterations of gene expression. Abnormalities in DNA methylation are a consistent feature of human neoplasms, and we now show that these include not only previously recognized widespread genomic hypomethylation, but also regional increases in gene methylation. A hot spot for abnormal methylation of C + G-rich areas has been detected on the short arm of chromosome 11 in an area known to harbor tumor suppressor genes. This change occurs consistently in common forms of human cancer and appears early during the transformation of cells with viruses including members of the human T-cell leukemia (HTLV) family. Furthermore, in one chromosome 11 gene examined, calcitonin, the increased methylation in somatic tumor cells coincides with the presence of an "inactive" chromatin pattern in the transcriptional regulatory area. The increased regional DNA methylation demonstrated may then participate in or mark chromosomal changes associated with gene inactivation events that are central to the genesis and/or progression of human cancers.

The human interleukin-2 receptor: normal and abnormal expression in T cells and in leukemias induced by the human T-lymphotropic retroviruses

The human receptor for interleukin-2 (T-cell growth factor) plays a critical role in the growth of T cells and is required for full expression of the normal immune response. Through hybridoma and recombinant DNA techniques, the interleukin-2 receptor protein has been biochemically characterized and purified; full-length copies of its complementary DNA have been molecularly cloned, sequenced, and expressed in eukaryotic cells; and the receptor gene has been characterized. Transient expression of the interleukin-2 receptor gene occurs during normal T-cell activation, and high- and low-affinity forms of the membrane receptor exist. A naturally occurring, soluble receptor has also been isolated, and its levels in serum correlate with the activity of various diseases. Deregulation of interleukin-2 receptor expression occurs in T-cell leukemias produced by the human T-lymphotropic retroviruses types I and II (HTLV-I and -II) and has been causally linked to the action of the trans-activator (taf) gene of these viruses. Monoclonal antibodies specific for the interleukin-2 receptor are being evaluated in the treatment of HTLV-I-induced leukemias and other conditions involving the inappropriate function of activated T cells.

Ribavirin suppresses replication of lymphadenopathy-associated virus in cultures of human adult T lymphocytes

The in-vitro effect of ribavirin on the replication of lymphadenopathy-associated virus (LAV), one of the prototype viruses aetiologically associated with lymphadenopathy syndrome and acquired immunodeficiency syndrome, was tested. Ribavirin, a nucleoside, suppressed the replication of LAV in cultures of human adult T lymphocytes. Suppression occurred at ribavirin concentrations of 50 micrograms/ml or higher.

Human alpha- and beta-interferon but not gamma- suppress the in vitro replication of LAV, HTLV-III, and ARV-2

The effect of human interferons (IFNs) (alpha, beta, and gamma) on the in vitro replication of AIDS viruses (LAV, HTLV-III, and ARV-2) in human peripheral blood lymphocytes was investigated. At the time of peak virus production, IFN-alpha preparations (leukocyte, Namalwa, alpha 1, and alpha 2) at 100 U/ml, suppressed LAV, HTLV-III, and ARV-2 replication as measured by reverse transcriptase (RT) activity by greater than 50%. This suppression was dose dependent and high dosages (500 U/ml) of IFN-alpha resulted in almost complete suppression of RT activities (77-99%). A low dose (100 U/ml) of IFN-beta suppressed all three AIDS viruses by 75%. In contrast, human IFN-gamma at a dose range from 100 U/ml to 500 U/ml had no significant effect on the production of infectious viruses. These results indicate that only IFN-alpha and -beta are effective against LAV, HTLV-III, and ARV-2 replication. A continuous supply of IFN appeared to be essential for the constant suppression of RT activity. In fact, upon termination of single IFN treatment, enhanced virus production resulted.

T-cell growth factor gene: lack of expression in human T-cell leukemia-lymphoma virus-infected cells

Activated mature T cells require T-cell growth factor (TCGF) for continuous proliferation. However, many mature T cells infected with human T-cell leukemia-lymphoma virus grow independently of exogenously added TCGF. It is now reported that cells infected with this virus also lack detectable TCGF messenger RNA (less than one copy per cell) and thus do not produce their own growth factor. The results apparently rule out an autostimulation mechanism of growth control.

Neutralization of HTLV-III/LAV replication by antiserum to thymosin alpha 1

An antiserum prepared against thymosin alpha 1, a hormone secreted by the thymus gland, effectively neutralized the AIDS-associated virus [HTLV-III/LAV (clone BH-10)] and blocked its replication in H9 cells. Reverse transcriptase activity and expression of the HTLV-III/LAV antigens p15 and p24 were inhibited by purified immunoglobulin G preparations of antisera to thymosin alpha 1. The antiviral activity of the antiserum was found to be due to a region of homology between thymosin alpha 1 and p17, a product of the gag gene of HTLV-III/LAV. Comparison of the primary sequences of thymosin alpha 1 and the gag protein revealed a 44% to 50% homology in an 18-amino acid region, between positions 11 and 28 on thymosin alpha 1 and 92 and 109 on the gag protein. The effectiveness of the thymosin alpha 1 antiserum and of immunoglobulin G-enriched preparations in blocking replication of HTLV-III(BH-10) in H9 cells suggests a novel approach to the development of an AIDS vaccine. A vaccine directed against the gag protein might overcome the problem of genetic drift in the envelope region of the virus and be useful against all genetic variants of HTLV-III/LAV.

A new human retrovirus isolate of West African origin (SBL-6669) and its relationship to HTLV-IV, LAV-II, and HTLV-IIIB

A new human retrovirus of West African origin (SBL-6669) has been isolated from a patient with immunological and clinical signs of immunodeficiency. Using radioimmunoprecipitation assays (RIPA) and Western blot (WB) tests with human sera, the new virus isolate has been compared with HTLV-IV, LAV-II, and the HTLV-IIIB prototype strain of the human immunodeficiency virus (HIV). The West African isolates appeared to be members of the same virus group since their glycoproteins were antigenically indistinguishable. West African sera showed no detectable cross reaction with HTLV-IIIB glycoproteins. The external glycoprotein in the different virus strains only showed minor variations in size. The size of the transmembranous protein was not unambiguously defined. In the West African virus isolates a 30-35 kD protein was seen similar to the protein previously described possibly to represent this component. However, in SBL-6669 a distinct 41 kD protein was also identified. There were interstrain variations in the size of several viral proteins among the West African virus isolates. Only minor differences were seen between SBL-6669 and LAV-II. The variations were most pronounced in two core proteins corresponding to the 19 kD and 24 kD proteins of HTLV-IIIB. In addition, West African human retroviruses appear to differ in pathogenicity. LAV-II and SBL-6669 are associated with immunodeficiency, whereas HTLV-IV was isolated from healthy individuals. Since further spread of these viruses to other parts of the world is imminent, it is necessary to consider their antigenic and immunogenic properties in serodiagnosis of HIV infections and in planning for immunoprophylactic interventions.

Transactivation induced by human T-lymphotropic virus type III (HTLV III) maps to a viral sequence encoding 58 amino acids and lacks tissue specificity

The acquired immune deficiency syndrome (AIDS) retrovirus, HTLV-III/LAV, encodes a transacting factor which directly or indirectly stimulates the expression of genes linked to its LTR. To further dissect this phenomenon, we have cotransfected a biologically active molecular clone of HTLV-III and a recombinant plasmid containing an indicator gene, the bacterial gene for chloramphenicol acetyltransferase (CAT), under the control of the HTLV-III LTR. Amplified CAT activity was detected in both lymphoid cells and fibroblasts from a number of species in the presence of the proviral DNA. Deletion experiments confirm the previous assignment of the gene required for transactivation to a region immediately 5' to the envelope gene, and further narrow down the critical functional domain to a coding sequence of 58 codons.

Location of cis-acting regulatory sequences in the human T-cell leukemia virus type I long terminal repeat

The location of cis-acting regulatory regions within the long terminal repeat (LTR) of the human T-cell leukemia virus type I (HTLV-1) was determined. The sequences present between nucleotides -350 and -55 (cap site +1) contain an enhancer element that is active in lymphoid and nonlymphoid cell lines. The sequences located near the "TATA" and RNA initiation sites contain a promoter, the activity of which can be augmented by homologous and heterologous enhancer elements. A region responsive to trans-acting transcription factors present in HTLV-I- and HTLV type II-infected cells is located between nucleotides -159 and +315. HTLV-I LTR deletion mutants respond in a similar manner both to the trans-acting factors present in infected cells and to the tat protein encoded by the x-lor region of the genome, thus providing further evidence that the tat protein mediates transcriptional trans-activation of the LTR in HTLV-infected cells.

CD4 receptor binding peptides that block HIV infectivity cause human monocyte chemotaxis. Relationship to vasoactive intestinal polypeptide

The octapeptide Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr (peptide T) and two structural analogs are potent agonists of human monocyte chemotaxis, evincing identical rank potency orders as was previously shown for their inhibition of human immunodeficiency virus (HIV) envelope binding and T cell infectivity. Chemotactic activity could be inhibited by anti-CD4 monoclonal antibodies (Mabs), but not other mononuclear cell Mabs. The core peptide required for chemotactic activity is a pentapeptide related to the sequence Thr-Thr-Asn-Tyr-Thr. Homologous pentapeptides, identified by computer search, were detected in several other non-HIV-related viruses as well as the neuropeptide vasoactive intestinal polypeptide (VIP). The CD4 molecule, therefore, appears to be a recognition molecule for a small signal peptide ligand whose active sequence is a homolog of peptide T and which may be the neuropeptide VIP.

Activation of T cell-derived lymphokine genes in T cells and fibroblasts: effects of human T cell leukemia virus type I p40x protein and bovine papilloma virus encoded E2 protein

The effects of p40x, a product of an human T cell leukemia virus type I, on the activation of lymphokine genes were examined. The mouse GM-CSF and IL-3 genes were activated by cotransfection with a pX containing plasmid both in Jurkat and CV1 cells. Mouse GM-CSF gene was also activated by phytohaemagglutinin A (PHA)/phorbol myristate acetate (PMA) or PMA/calcium ionophore A23187 stimulation. The 5'-flanking region of the mouse GM-CSF gene which is required for activation by pX or mitogen was mapped within 226 bp upstream from the transcription initiation site. Action of pX was not restricted to T cells. pX activated exogenously added GM-CSF, IL-2, IL-3 and IL-4 genes in fibroblasts. Activation of the GM-CSF gene in fibroblasts appears to require the same regulatory region as in T cells. Similar results were obtained using bovine papilloma virus encoded E2 protein. We propose that pX or E2 protein, both in T cells and fibroblasts, activates cellular component(s) in the signal transduction pathway which results in the activation of lymphokine genes in the absence of extracellular stimuli.

Granulocyte-macrophage colony-stimulating factor. Sensitive and receptor-mediated regulation by 1,25-dihydroxyvitamin D3 in normal human peripheral blood lymphocytes

We show that 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), the most hormonally active metabolite of vitamin D3, modulates sensitively and specifically both the protein and messenger RNA accumulation of the multilineage growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF). The regulation of GM-CSF expression is seen in both normal human mitogen-activated T lymphocytes and T lymphocytes from a line (S-LB1) transformed with human T cell lymphotropic virus 1 (HTLV-1). In contrast, cells from a HTLV-1 transformed T lymphocyte line (Ab-VDR) established from a patient with vitamin D-resistant rickets type II with undetectable 1,25(OH)2D3 cellular receptors are resistant to the action of 1,25(OH)2D3. Inhibition of GM-CSF expression by 1,25(OH)2D3 can occur independently of interleukin 2 regulation and is probably mediated through cellular 1,25(OH)2D3 receptors. We conclude that 1,25(OH)2D3 may be important in the physiology of hematopoiesis.