Infective transmission and characterisation of a C-type virus released by cultured human myeloid leukaemia cells

Human retroviruses in leukaemia and AIDS: reflections on their discovery, biology and epidemiology

The study of retroviruses has had a profound impact by unveiling an unusual form of viral replication: the multiplication of RNA viruses via a proviral DNA, for which Jan Svoboda provided the experimental model over forty years ago. In 1970 Temin, Mizutani and Baltimore discovered that this group of viruses contains a unique enzyme catalysing the synthesis of a DNA copy of the viral RNA: reverse transcriptase (RT). The discovery of RT has itself had an enormous impact on molecular biology in general, but also stimulated many premature claims of its detection in human disease. Claims by Gallo's laboratory that the cytoplasm of human leukaemia cells contained RT proved to be unfounded, as did his report in collaboration with Weiss that myeloid leukaemia contained HL23 virus, this organism proving not to be human but a laboratory contaminant of three monkey viruses. Conclusive demonstration of a retroviral involvement in human leukaemia was first provided in 1981 by Hinuma and his associates, showing that adult T-cell leukaemia (ATL), a rare form of leukaemia endemic to south-west Japan, is caused by a new retrovirus (ATLV). Other publications in December 1980 and through 1981 claimed the discovery of a new human T-cell leukaemia virus involved in mycosis fungoides (MF) and Sézary's syndrome (SS). This virus was termed HTLV by Gallo. The nucleotide sequence of ATLV is strongly conserved, that of my 1983 isolate from a black British ATL patient being practically identical with the Japanese virus isolates. After AIDS was recognised in 1981 by Gottlieb and coworkers as a new human disease, several papers were published by Gallo and his associates during 1983-4, invoking the oncovirus responsible for adult T-cell leukaemia as the cause of AIDS. In 1983 the French scientist Barré-Sinoussi and her colleagues succeeded in isolating a new agent in the disease, a lentivirus, which they named LAV. The French immunologist Klatzmann and his colleagues discovered that LAV killed CD4+ T-cells, furnishing an explanation for the pathogenesis of AIDS and providing a mechanism for how AIDS developed. For some time Gallo continued to suggest leukaemia virus involvement, claiming that his independent isolate of the AIDS virus, termed HTLV-III, was closely related to HTLV-I (the Japanese ATLV). Although this created considerable confusion among researchers for a period, the relationship was eventually disproved. Unlike ATLV, whose nucleic acid sequence is very stable, the AIDS virus (now termed HIV by international agreement) is extraordinarily unstable, the sequences of independent HIV isolates being quite unique: this made it possible to establish conclusively that both HTLV-III and another independent isolate CBL-1, from Weiss' laboratory, were actually LAV isolates from the French laboratory. It has been shown by Hayami and his associates that only African primates are infected with similar lentiviruses to HIV which explains why AIDS started in Africa. Further research has clarified the origin of HIV-1 to be a chimpanzee lentivirus and HIV-2 to be the sooty mangabey lentivirus, which began to spread in humans perhaps no more than fifty years ago. The infection has spread rapidly, primarily through sexual intercourse, but also by transmission through blood and its products as well as contaminated needles and syringes. Sexual intercourse has now spread the virus around the World; and there are probably some 70 million infected. 90% of those infected with HIV develop the deadly disease of AIDS within ten years of infection: the death toll from the disease has been enormous. By contrast, HTLV-1 has been infecting man in isolated areas probably for hundreds of years; but it has not spread widely. HTLV causes leukaemia in only less than 1% of those infected. The prime mode of transmission of HTLV-1 is between mother and neonate; infections can be reduced by stopping breast-feeding by infected mothers. The isolation of HIV enabled screening tests to be developed for contaminated blood. However, due to the peculiar biology of HIV infection, unfortunately all efforts to develop an effective vaccine have so far failed.

HIV antibodies: further questions and a plea for clarification

The existence of specific antibody/protein reactions is the crucial assumption underlying proof of HIV isolation, proof of HIV infection and the causative role of HIV in AIDS. However, since 1. antibodies which react with the 'HIV' proteins arise following allogenic stimuli in non-HIV-infected animals and humans, as well as in mice and humans with autoimmune disorders; antibodies to antigens from both mycobacteria and yeasts cross-react with HIV env and gag proteins; 2. individuals belonging to the AIDS risk groups are subjected to allogenic stimuli and have high levels of autoimmune antibodies, while the vast majority of patients in the AIDS risk groups are infected with either or both mycobacteria or yeasts; the evidence for the existence of HIV and its putative role in AIDS must be reappraised.

A novel mechanism of retrovirus inactivation in human serum mediated by anti-alpha-galactosyl natural antibody

Type C retroviruses endogenous to various nonprimate species can infect human cells in vitro, yet the transmission of these viruses to humans is restricted. This has been attributed to direct binding of the complement component C1q to the viral envelope protein p15E, which leads to classical pathway-mediated virolysis in human serum. Here we report a novel mechanism of complement-mediated type C retrovirus inactivation that is initiated by the binding of "natural antibody" [Ab] (anti-alpha-galactosyl Ab) to the carbohydrate epitope Gal alpha 1-3Gal beta 1-4GlcNAc-R expressed on the retroviral envelope. Complement-mediated inactivation of amphotropic retroviral particles was found to be restricted to human and other Old World primate sera, which parallels the presence of anti-alpha-galactosyl natural Ab. Blockade or depletion of anti-alpha-galactosyl Ab in human serum prevented inactivation of both amphotropic and ecotropic murine retroviruses. Similarly, retrovirus was not killed by New World primate serum except in the presence of exogenous anti-alpha-galactosyl Ab. Enzyme-linked immunosorbent assays revealed that the alpha-galactosyl epitope was expressed on the surface of amphotropic and ecotropic retroviruses, and Western blot analysis further localized this epitope to the retroviral envelope glycoprotein gp70. Finally, down-regulation of this epitope on the surface of murine retroviral particle producer cells rendered them, as well as the particles liberated from these cells, resistant to inactivation by human serum complement. Our data suggest that anti-alpha-galactosyl Ab may provide a barrier for the horizontal transmission of retrovirus from species that express the alpha-galactosyl epitope to humans and to other Old World primates. Further, these data provide a mechanism for the generation of complement-resistant retroviral vectors for in vivo gene therapy applications where exposure to human complement is unavoidable.

Viral and cellular factors governing hamster cell infection by murine and gibbon ape leukemia viruses

Hamster cells are resistant to infection by most retroviruses, including Moloney murine leukemia virus (MoMLV) and gibbon ape leukemia viruses (GaLVs). We have constructed MoMLV-GaLV hybrid virions to identify viral and cellular determinants responsible for the inability of GaLV and MoMLV to infect hamster cells. The substitution of MoMLV core components for GaLV core components circumvents the resistance of hamster cells to infection by GaLV, demonstrating that hamster cells have receptors for GaLV but are not efficiently infected by this primate retrovirus because of a postpenetration block. In contrast, hamster cells are apparently resistant to MoMLV infection because although they bear a receptor for MoMLV, the receptor is nonfunctional. Treatment of CHO K1 or BHK 21 hamster cells with the glycosylation inhibitor tunicamycin allows the cells to be infected by MoMLV. The construction of MoMLV-GaLV hybrid virions that can efficiently infect resistant cells has allowed the identification of viral and cellular factors responsible for restricting infection of hamster cells by MoMLV and GaLV.

Retrovirus-like particles associated with myeloproliferative disease in the dog

A case of granulocytic myeloproliferative disease with hypercalcaemia of malignancy in a 6-year-old Golden Retriever dog is described. Numerous retrovirus-like budding particles were observed at the cell surface of the neoplastic granulocytes, suggesting the presence of a new oncogenic virus. Several attempts by other workers to demonstrate the presence of an oncogenic retrovirus in canine lymphosarcoma have produced minimal results. This study suggests that non-lymphoid canine myeloproliferative disorders warrant further investigation.

RNA tumor virus in human thymomas and thymus hyperplasias

Human thymomas and thymus hyperplasias were examined for retroviruses. Most of these patients were complicated by systemic immunological diseases such as myasthenia gravis and pure red cell aplasia. The thymus cells were co-cultured with allogenic B cells or peripheral blood lymphocytes (PBL) pretreated with mitomycin C. Retrovirus-like particles were demonstrated in cultured thymus cells in all cases of thymomas and thymus hyperplasias examined by electron microscopy. In most cases, these particles were detected in thymus epithelial cells. Reverse transcriptase activity sedimenting at a density of 1.15-1.17 gm/cm3 in sucrose density gradients was eluted in the culture fluids. Retrovirus-like particles were demonstrated in human T cells infected with these particles. Antibodies to virus-infected T cells were detected in sera of the patients with thymoma and thymus hyperplasia. These results suggest that in thymomas and thymus hyperplasias, retroviruses that can be induced, following a proliferative stimulus, may be involved in the genesis of thymic disorders and in the pathogenesis of systemic immunological diseases.

Isolation of HTLV derived from Japanese adult T-cell leukemia patients in human diploid fibroblast strain IMR90 and the biological characters of the infected cells

HTLV was isolated in the human diploid fibroblast strain IMR90 directly from the leukemic cells of the Japanese ATL-patients. The infection was checked by the presence of virus-specific p24 and proviral DNA. The isolation was successful in three of four patients. The patient whose virus isolation was unsuccessful contained only a defective viral genome in his leukemic cells. The infected cells produced polykaryons when co-cultured with catS + L-cells. Human leukemia HL60 cells formed clusters adherent to the infected IMR90 cells but not to uninfected IMR90 cells. The former phenomenon was blocked by the ATLL patients' serum.

Detection of lymphocytes producing a human retrovirus associated with adult T-cell leukemia by syncytia induction assay

Recently 10 T-cell lines were established from patients with adult T-cell leukemia (ATL). During establishment of these cell lines, it was found that when T-cell lines expressing the ATL-associated retroviral antigen were cocultivated with 8C cat cells, multinucleated syncytia were formed. Retroviral antigen-negative T-cell lines did not induce syncytia. Peripheral blood lymphocytes obtained from ATL patients did not express the retroviral antigen before cultivation in vitro but became positive for the retroviral antigen after cultivation for a short period; these retroviral antigen-positive lymphocytes, but not retroviral antigen-negative lymphocytes, induced syncytia upon cocultivation with 8C cells. Peripheral blood lymphocytes isolated from patients with chronic lymphocytic leukemia of T-cell origin or Sézary syndrome or from normal adults and lymph node cells from a patient with immunoblastic lymphadenopathy-like T-cell lymphoma did not express the retroviral antigen even after cultivation in vitro and did not induce syncytia upon cocultivation with 8C cells. Thus, there was complete agreement between the presence of the retroviral antigen in established T-cell lines or freshly isolated peripheral blood lymphocytes and their ability to induce syncytia. Syncytia formation was enhanced 5- to 20-fold by the presence of Polybrene and inhibited by addition of plasma of ATL patients to the cocultures. Syncytia were detected within 4 hr on cocultivation of 8C cells with the retroviral antigen-positive T-cells, indicating that most syncytia were formed by early polykaryocytosis. After cocultivation, a clone of 8C cells that harbored the ATL virus genome and had syncytia-inducing activity was isolated. These findings indicate that the retrovirus associated with ATL has syncytia-inducing activity. Syncytia induction assay using 8C cells will be useful for detection and characterization of human retrovirus associated with T-cell malignancies.

Isolation of a unique retrovirus, MNV-1, from Macaca nemestrina

Cell cultures established from the spleen of a Macaca nemestrina with enzootic retroperitoneal fibromatosis (ERF) spontaneously released a unique retrovirus. Throughout 14 serial passages, the spleen cell cultures remained fibroblastic and no cytopathic effect was evident. The virus incorporates [3H]uridine, contains an RNA-dependent DNA polymerase (RDDP), has a buoyant density of 1.15 g/cm3 in sucrose, and was designated MNV-1. Virion-associated reverse transcriptase showed no preference for either Mg2+ or Mn2+ in standard RDDP assays. Complementary DNA (cDNA) transcribed from polyadenylated MNV-1 RNA hybridized to genomic DNA and RNA extracted from diseased tissues but not to nucleic acids from normal tissues of a healthy Macaca nemestrina or a Macaca mulatta. MNV-1 is therefore exogenous to these species. MNV-1 had no detectable homology to the endogenous macaque virus isolates MAC-1 and MMC-1. Liquid hybridization of MNV-1 cDNA to viral RNA derived from exogenous and endogenous subhuman primate retroviruses (SiSV(SSAV), GALV-SF, BaEV-M7, and BILN) did not reveal any significant sequence homologies. In addition, MNV-1 does not share homology with bovine leukemia virus or Mason-Pfizer monkey virus as determined by Southern blot hybridization. We conclude that MNV-1 is a unique retrovirus which has not previously been described. As the ultrastructure of virions in in vitro cell cultures, as well as disease involved tissue, show some particles with type C morphology and others with type D morphology, MNV-1 may be comprised of more than one component.

Use of vesicular stomatitis virus pseudotypes to map viral receptor genes: Assignment of RD114 virus receptor gene to human chromosome 19

Vesicular stomatitis virus pseudotypes bearing envelope glycoproteins of the endogenous feline type C retrovirus, RD114, were used to assay the expression of receptors specific to RD114 on the surfaces of mouse-human hybrid cells carrying different human chromosomes. These studies show that the gene encoding the RD114 receptor is located on human chromosome 19.

Relationship of retroviruses isolated from human leukemia tissues to the woolly monkey-gibbon ape leukemia viruses

Retroviruses have been isolated from the tissues of human leukemia patients. Previous studies have shown that these isolates share some antigenic determinants with the family of viruses isolated from the woolly monkey and gibbon ape and that they exhibit partial nuclei acid homology with this same group of viruses. We have compared the RNAs of the viruses by two-dimensional polyacrylamide gel electrophoresis of the large RNase T1-resistant oligonucleotides. The degree of sequence identity between the RNAs was determined by the similarity of their RNase T1-resistant oligonucleotide pattern on gels, fingerprints, and in some cases by partial sequence analysis of individual oligonucleotides. This technique permits us to determine the degree of sequence identity among related RNA species. From our studies we conclude that viruses isolated from the tissues of two human leukemia patients, A1476 and SKA 21-3, as well as some subcultures of a virus isolated from the leukemic tissues of a third patient, HL23V, are closely related to the wooly monkey virus. However, the fingerprints of other HL23 viral isolates are very similar to that of GaLVSF, a gibbon ape leukemia virus isolated from a lymphosarcoma.

Viruses and lymphocytes in rheumatoid arthritis. I. Studies on cultured rheumatoid lymphocytes

Synovial fluid lymphocytes from patients with rheumatoid arthritis have been examined for evidence of a productive infection with retroviruses by electron microscopy, labelling with 3H-uredine, growth in soft agar, and culturing in conditioned medium. No such viruses were detected. In addition, the synovial lymphocytes were activated before fusion and cocultivation with several cell lines which have proved permissive for primate retroviruses. Monitoring these cultures subsequently by reverse transcriptase assay, labelling with 3H-uridine, and membrane immunofluorescence gave no indication that retroviruses were present.

Viruses and lymphocytes in rheumatoid arthritis. II. Examination of lymphocytes and sera from patients with rheumatoid arthritis for evidence of retrovirus infection

The possible involvement of retroviruses in the aetiology of rheumatoid arthritis (RA) was investigated. Retrovirus antigens were not expressed on rheumatoid synovial and peripheral blood lymphocytes as judged by membrane immunofluorescence, radioimmunoassay, and complement-mediated cytotoxicity. The specific antiretroviral (anti-RD-144 and anti-SSAV) sera used in this study were produced in rabbits immunised with viral antigens grown in a homologous system (rabbit cells and medium supplemented with normal rabbit serum), avoiding non-specific immunofluorescence previously detected with donated antiretroviral sera. Immune complexes lodged in the rheumatoid synovial membranes did not contain, and other cells within the membranes did not express, retroviral antigens. Antibodies cross-reacting with primate retrovirus antigens were sought in sera from patients with 'autoimmune' diseases by means of solid phase radioimmunoassay. There were no retrovirus antibodies in the 3 groups of patients studied, that is, those with rheumatoid arthritis, systemic lupus erythematosus, and with non-RA conditions. Absorption of rheumatoid factor did not alter this conclusion. These results give little support to the hypothesis that activation of endogenous human retroviruses or an infection with horizontally transmitted retroviruses is associated with the rheumatoid process.

Characterization of a type-C virus produced by co-cultures of human leukemic bone-marrow and fetal canine thymus cells

The putative human helper virus SKA-21/A204V, isolated by Nooter et al. in 1977 from human leukemic bone-marrow cells following co-culture with normal fetal canine thymus cells, Cf2th, has been characterized with respect to its major viral core protein, reverse transcriptase, and nucleic acid sequences. The results of these analyses show that this virus is not distinguishable from the woolly monkey type-C virus, SSAV-1, by the techniques employed.

Mason-Pfizer like virus in kidney grafted patients

Lymphocytes from a kidney grafted patient were specifically stimulated to incorporated thymidine in vitro by mitomycin C treated Hela cells infected with a Mason-Pfizer like virus (MPV). The thermolabile mutant of vesicular stomatitis virus (VSV tl) grown in leukocytes of this patient produced pseudotypes which were neutralized by the patient's sera and boy rabbit anti-MPV sera. Coculture of the patients leukocytes with SIRC cells yielded virus populations with dual properties; those of MPV plus those of another virus which was not typed serologically but possessed the biological properties of typical C particles. The patient also had neutralizing antibodies to MPV, which were detected by inhibition of syncytium formation on KC cells and by neutralization of VSV tl (MPV) pseudotypes. Preliminary results on the frequency of similar findings in other kidney grafted patients are presented.

Biology and virology of the human malignant lymphomas: 1st Milford D. Schulz Lecture

Permanent cell lines have been established from twelve diffuse histiocytic lymphomas (SU-DHL-1 to -12), three American Burkitt's lymphomas (SU-AmB-1 to -3), two acute lymphoblastic leukemias (SU-ALL-1 and -2), and three diffuse undifferentiated lymphomas (SU-DUL-1, -2, and -3). The cultured cells displayed neoplastic characteristics, as manifested by heterotransplantability in congenitally athymic nude mice and by the presence of cytogenetic abnormalities in early passage generations. Functional and marker studies revealed that the three American Burkitt's lymphomas, as well as several of the diffuse histiocytic and undifferentiated lymphomas, were of B-lymphocytic origin, whereas the two acute lymphoblastic leukemias were both of T-lymphocytic origin. Two of the cell lines, SU-DHL-1 and -2, appeared to be of true histiocytic origin; two others exhibited no markers and were designated as "null" cells. All ten of the DHL cell lines studied to date, as well as SU-DUL-1, have been devoid of Epstein-Barr virus (EBV) genomes by the EBNA test, whereas two of the three American Burkitt's lymphoma cell lines were positive. Spontaneous production of a C-type RNA virus was first detected in post-mitochondrial cytoplasmic fractions and culture fluids of the SU-DHL-1 cell line. Screening assays for the detection of reverse transcriptase-positive particles in the culture fluids of the other cell lines indicate that eight of the fifteen cell lines tested to date have spontaneously initiated C-type RNA virus production. After partial purification by ion-exchange and affinity chromatography, the reverse transcriptases of the virus isolated from SU-DHL-1 cells is partially inhibited by antibodies to the reverse transcriptases of C-type viruses of subhuman primate and endogenous feline, but not of murine, origin. Conversely, antibody prepared against the purified SU-DHL-1 viral reverse transcriptase, at concentrations which maximally inhibit the homologous enzyme, partially inhibits the reverse transcriptases of subhuman primate C-type viruses, but has little or no inhibitory activity against the reverse transcriptases of feline or murine leukemia viruses. The viruses produced by the SU-DHL-1 and SU-AmB-3 cell lines have been shown to be infectious for normal human peripheral blood mononuclear cells, normal human bone marrow cells, and certain human lymphoblastoid cell lines. After infection by these viruses, normal human peripheral blood mononuclear cells and human bone marrow cells have exhibited striking changes in growth behavior and morphology which, though not permanently sustained, have many of the features of abortive transformation.

Search for type-C oncornavirus-related genetic information in tissues from patients with systemic lupus erythematosus

Single-stranded 3H-DNA probes complementary to the RNA of Rauscher murine leukemia virus and of simian sarcoma virus were prepared using techniques that permitted complete transcription of the viral genome of each virus. These probes were used in DNA-DNA hybridization studies with the cellular DNA from uncultured specimens of spleens and placentas of patients with systemic lupus erythematosus (SLE). No proviral DNA sequences related to these viruses were detected in these tissues. The results presented here do not support previously reported antigenic data implicating type-C oncornavirus infection of these organs in SLE.

Neoplastic transformation of canine embryo cells in vitro by N-methyl-N'-nitro-N-nitrosoguanidine

A cell line derived from a normal beagle embryo was treated in vitro with various levels of N-methyl-N'-nitro-N-nitrosoguanidine or dimethyl sulfoxide (control). Cells treated only with the carcinogen underwent morphologic alteration in vitro, and one of these altered cell lines produced tumors subcutaneously when injected into NIH nude mice. The tumorigenic transformed line formed larger cell aggregates and grew in this aggregate form when suspended in liquid growth medium above an agar base.

Search for infective mammalian type-C virus-related genes in the DNA of human sarcomas and leukemias

DNA was extracted from two human sarcoma cell lines, TE-32 and TE-418, and the leukemic cells from five children with acute myelocytic leukemia, three children with acute lymphocytic leukemia and four adults with acute myelocytic leukemia. The DNAs, assayed for infectivity by transfection techniques, induced no measurable virus by methods which would detect known mammalian C-type antigens or RNA-directed DNA polymerase in TE-32, D-17 dog cells and other indicator cells, nor did they recombine with or rescue endogenous human or exogenous murine or baboon type-C virus. Model systems used as controls were human sarcoma cells, TE-32 and HT-1080, and human lymphoma cells TE-543, experimentally infected with KiMuLV, GaLV or baboon type-C virus, all of which released infectious virus and whose DNAs were infectious for TE-32 and D-17 dog cells. Other model systems included two baboon placentas and one embryonic cell strain spontaneously releasing infectious endogenous baboon virus and yielding DNAs infectious for D-17 dog cells but not for TE-32 cells. Four other baboon embryonic tissues and two embryonic cell strains, releasing either low levels of virus or no virus, did not yield infectious DNA.

Immunologic approaches toward detection of type C viral expression in man

Type C RNA viruses have been isolated from a large number of mammalian species. These agents may be horizontally transmitted as infectious cancer-inducing agents, or vertically transmitted from one generation to the next, often in an unexpressed form, within the host genome. To date, the translational products of three viral genes have been identified. With purified virus-coded proteins as probes, sensitive and highly specific radioimmunologic assays have been developed for the detection of antibodies and antigens related to the known type C viruses. These techniques have proved valuable in sero-epidemiologic studies of the horizontally transmitted oncogenic viruses of cats, cattle, and gibbons, and have been used to detect translational products of endogenous viruses in tissues of species from which complete virus has yet to be isolated. This review describes the application of radioimmunoassays in the search for immunologic evidence of type C virus expression in man.

Structural biochemistry 15--mass spectrometry of permethylated nucleotides

Techniques have been summarized for the permethylation and mass spectral characterization of selected nucleotide monophosphates. The electron impact induced mass spectra are reproduced, and the fragmentation pathways observed are discussed in detail.

The viral etiology of cancer: a realistic approach

The etiology of cancer resembles that of many other diseases in that multiple factors may be required. Because of this, the role or viruses in the etiology of human cancers is especially difficult to assess. When animal tumor systems were used as models, the roles of various predisposing characteristics in virus oncogenesis were elucidated. Extrapolation of these findings to the human diseases suggests the importance of genetics, age, hormones, immune competence, and stress in determining susceptibility to tumor development in individuals infected with an oncogenic virus. The importance of cofactors in induction of those human tumors most strongly associated with virus infection, including Burkitt's lymphoma, nasopharyngeal carcinoma, cerviccal carcinoma, acute myelogenous leukemia, and breast cancer, is reviewed. Understanding of the role of these cofactors in virus carcinogenesis may lead to disease prevention through elimination of one or more of the cofactors.

Nucleic acid sequences of primate type C viruses in normal and neoplastic human tissues

Recent reports on the isolation of type C viruses from human cells have generated considerable controversy because of the close relationship of the viruses to the type C viruses of subhuman primates. These findings have been interpreted as evidence for contamination despite the repeated isolation of some type C viruses from separate clinical specimens or from separate frozen primary cell stocks of the same donor. Our laboratory has described a type C virus which is released from the HEL-12 strain of normal human embryonic lung fibroblasts. The HEL-12 virus is related immunologically to simian sarcoma (woolly monkey fibrosarcoma) virus (SiSV) and the endogenous type C viruses of baboons and domestic cats. To demonstrate that the HEL-12 virus is not an adventitious contaminant, fresh human tissues were examined for antigenic cross-reactivity with HEL-12 virus antigens. Some patients with myelogenous leukemia contain circulating immunoglobulins which specifically inhibit the reverse transcriptases of HEL-12 virus and primate type C viruses. In addition, the glomerular immune complexes in patients with systemic lupus erythematosus contain antigens related to HEL-12 virus proteins. Using the techniques of molecular hybridisation, we demonstrate here that HEL-12 cells contain proviral DNA sequences before antigen expression or spontaneous virus release can be detected. We also present evidence for the existence of nucleic acid sequences homologous to HEL-12 viral RNA in the DNAs from certain cancer patients.

The epidemiology of the feline leukemia virus (FeLV)

Clustering of cases of feline lymphosarcoma (LSA) has been observed by veterinarians for many years. In 1964 it was discovered that feline LSA was caused by an oncornavirus, the feline leukemia virus (FeLV). In 1970, a simple, indirect immunoflourescent antibody (IFA) test for FeLV was developed which enabled large numbers of cats, living in their natural (household) environments, to be tested for the virus. In one study, over 2,000 cats were tested and the results showed conclusively that FeLV is a contagious agent for cats. This finding was independently confirmed by several other investigators using different testing procedures. After discovering the contagious nature of FeLV a test and removal program was devised which successfully prevents the spread of FeLV and the development of FeLV diseases in the pet cat population. There is, at present, no evidence that FeLV infects humans living with FeLV infected cats.

Detection of human C-type "helper" viruses in human leukemic bone marrow with murine sarcoma virus-transformed human and rat non-producer cells

Bone-marrow cells from two leukemic children were co-cultivated with the leukemic children A 7573. In early passages, C-type oncornaviruses were released as detected by extracellular reverse transcriptase assay. Co-cultivation of the infected canine cells with the non-producing cell lines R-970-5 (human) or K-NRK (rat) both transformed by Kirsten mouse sarcoma virus (MSV) yielded a new pseudotype of MSV that could transform rat embryo, rabbit SIRC and human kidney cells but not mouse embryo cells. The focur formation could be inhibited by an antiserum to the simian sarcoma virus but not by a serum directed against murine leukemia virus. A cell line derived from a focus of transformed cells became a highe virus is related to the simian sarcoma virus. It is concluded that the leukemic bone-marrow cells produce a C-type oncornavirus that can serve as a helper virus to the defective MSV.

Survey of human lymphoblastoid cell lines and primary cultures of normal and leukaemic leukocytes for oncornavirus production

Velocity sedimentation of uridine-labelled cultures was found to be more reliable than isopycnic sedimentation in detecting oncornavirus production in lymphoid cells. Of 13 cell lines (including six derivea from Burkitt's lymphomas and two from leukaemic leukocytes) only one, the leukaemia-derived, Epstein-Barr virus-producing line QIMR-WIL, showed any activity. The nature of the QIMR-WIL particles was further defined by isolation of uridine-labelled 70S RNA and by the simultaneous assay for reverse transcriptase and 70S RNA, but production of such particles was detected in only three of 10 assays. Pretreatment of cells with 5'-iododeoxyuridine or culture in arginine-free medium did not induce particle production. Syncytia assays using XC cells were negative. Of 13 primary cultures (nine samples of leukaemic leukocytes and four of cord leukocytes) treated with mitogens and subjected to inducing conditions, one (leukocytes from a patient with acute myelogenous leukaemia) showed evidence in successive assays of oncornavirus synthesis. The low and transient yield of oncornavirus-like particles obtained in this work parallels that reported in previous studies of fresh lymphoid cells and primary cultures.