[Infection of peripheral blood lymphocytes in sheep with bovine leukemia virus in vitro]

Continuous cultivation of peripheral blood lymphocytes from healthy sheep was carried out in vitro with the help of human recombinant interleukin-2. Lymphocytes were concurrently cultivated with the lethally X-rayed BLV-producing FLK culture cells. Electron microscopy and dot-blot hybridization established that sheep peripheral blood lymphocytes were infected with BLV and a full cycle of replication takes place in them. Infection of sheep leukocytes in vitro can be used to study the mechanisms of leukogenesis in vitro.

Feline immunodeficiency syndrome--a comparison between feline T-lymphotropic lentivirus and feline leukemia virus

A feline T-lymphotrophic lentvirus (FTLV) has recently been isolated from a domestic cat free of feline leukemia virus (FeLV). This virus is distinct from FeLV (an oncornavirus), although they share a common denominator, namely, the ability to cause immunosuppression and induce lymphadenopathy and anemia. Their differences can be revealed by examining the following: the metal requirement for reverse transcriptase activity, the antigenic comparison by Western blot analysis, the different susceptibilities of a variety of feline cells, and the morphology based on electron microscopy. In the serological survey of 1,612 cats surveyed in the USA, 232 (14.4%) were seropositive for antibodies to FTLV, which was lower than for the 42 Canadian cats surveyed of which 8 (19%) were seropositive. Of the 61 cats positive for FeLV, 15 (25%) were also positive for FTLV, giving the impression that coinfection between these two retroviruses plays an important role in the cliniocpathological signs of what was previously thought to be solely an FeLV syndrome.

Different mechanisms account for the relative resistance of KG-1 and HL-60 cell lines to retrovirus infection

I infected three different human leukemic cell lines (K562, KG-1, and HL-60) with an amphotropic retrovirus vector (designated PA317/N2) which confers G418 resistance and contains the Moloney murine leukemia virus long terminal repeat. Compared with K562 cells, both KG-1 and HL-60 cells were relatively resistant to infection with this retrovirus vector. In HL-60 cells, this resistance appeared to result from diminished viral DNA synthesis, while in KG-1 cells there was a block to the genomic integration of the viral DNA.

Targets of v-myc tumorigenesis in the avian embryo depend on time and not on site of retroviral infection

The present study extends our previous data, showing that the v-myc oncogene induces heart tumors and skin anomalies in young avian embryos [Saule et al., Proc. Natl. Acad. Sci. USA 84, 7982-7986 (1987)]. We now report that the target cells which become transformed are the same, whether the MC29 retrovirus is injected at E3 in various sites of the embryo (coelom, heart, brain, lateral plate mesoderm) or deposited on the embryo. Furthermore we confirm, in the quail, the time-specific pattern previously observed in the chick. In the quail, the incidence of heart tumors falls from 100% to 28% when injection is delayed from E3 to E4. By contrast, the incidence of skin anomalies rises from 30% to 64% when injection is delayed from E3 to E4. The skin defect, which consists of the presence of bell-shaped cornified feathers, could be assigned to hyperkeratinization of the epidermis. Both the dermis and the epidermis displayed hyperproliferation, whereas skin muscle hypertrophy during the embryonic period could not be confirmed. The presence of myc gene products was investigated using an antibody that recognizes both the c- and v-myc proteins. In the skin of control embryos, nuclei were well stained at E12-E13. At E14 the signal had disappeared. In abnormal skin patches from infected embryos, the antibody still marked heavily epidermal and dermal nuclei at E18. Finally we injected MC29 through the chorioallantoic vein in E10 chickens. No tumors were found during embryonic life, but 81% of the chickens developed tumors of hemopoietic or endothelial origin from the 14th posthatching day onwards. Studies of MC29 integration sites demonstrated that these tumors were derived from only a few transformed cells. Thus, contrasting with in vitro experiments, in vivo this virus has a restricted number of targets varying with the time of injection.

Evidence for linkage between the caprine leucocyte antigen (CLA) system and susceptibility to CAE virus-induced arthritis in goats

The distribution of caprine leucocyte antigens (CLA) in goats from four different breeds (n = 546) affected by caprine arthritis-encephalitis virus (CAEV)-induced arthritis were determined and compared breed for breed with those of infected but clinically healthy controls (n = 402). Differences in frequencies of some of the CLA specificities between the affected and control groups were found, but after correction of the ordinary P values for number of observed alleles, only the CLA Be7 specificity in the Saanen breed showed a significant deviation at the 0.05 probability level. Animals of the Saanen breed carrying this specificity are less prone to develop arthritis after CAE virus infection than goats lacking this specificity. Eleven groups (multiple-case families or halfsibling groups with at least two informative diseased offspring/group) were analyzed for manifestation of the disease and segregation of the parental haplotypes. The results of the maximum likelihood test of association (P less than 0.005) and the calculated high lod score value of 5.70 give evidence for linkage between the locus encoding the determined class I CLA alleles and a hypothetical locus (i) coding for genes responsible for arthritis resistance/susceptibility. The particular class I CLA allele associated with the disease susceptibility varied from family to family, however. These data provide the first evidence that CAE virus-induced arthritis in the goat is genetically influenced by the MHC system; they also suggest that susceptibility/resistance genes are not directly associated with the determined class I gene products but rather are in close genetic linkage.

Inhibition of the development of tumors or leukemia in mice and rats after reduction of food intake. Possible implications for humans

Recent data referring to the influence of a restricted diet on the incidence of radiation-induced tumors and leukemia in rats and mice are reviewed. The incidence of tumors developing in rats exposed to total-body gamma irradiation was reduced from 93% to 35% in female rats and from 59% to 7% in male rats after restriction of food intake. In a similar study carried out on mice, the incidence of leukemia in irradiated mice of both sexes was reduced from 50% to 4% after restriction of food intake. Radiation-induced leukemia in mice is caused by a transmissible virus activated by total-body gamma irradiation. In most of the animal species investigated thus far, tumors, leukemia, and lymphomas were found to be caused by transmissible viruses. It appears that activation of some of these latent viruses could be prevented by restriction of food intake. If the results of experiments carried out on mice and rats are extrapolated for humans, it would follow that all of us (particularly those who have had multiple cases of cancer or leukemia among family members) should aim at holding our weight below the limits considered normal for our age, sex, and height. This appears particularly important for persons that have been exposed to large doses of ionizing radiation.

Alterations in the U3 region of the long terminal repeat of an infectious thymotropic type B retrovirus

We isolated and characterized a type B thymotropic retrovirus (DMBA-LV) which is highly related to mouse mammary tumor virus (MMTV) isolates and which induces T-cell thymomas with a high incidence and a very short latent period. Regions of nonhomology between the DMBA-LV genome and the MMTV genome were identified by heteroduplex mapping and nucleotide sequence studies. In the electron microscope heteroduplex mapping studies the EcoRI-generated 5' and 3' fragments of the DMBA-LV genome were compared with the corresponding fragments of the MMTV (C3H and GR) genome isolated from mammary tumors. The results indicated that DMBA-LV contained a region of nonhomologous nucleotide sequences in the 3' half of the U3 region of the long terminal repeat (LTR). Nucleotide sequence studies confirmed these results and showed that in this region 440 nucleotides of the MMTV (C3H) sequences were deleted and substituted with a segment of 122 nucleotides. This substituted segment in the form of a tandem repeat structure contained nucleotide sequences derived exclusively from sequences which flanked the substitution loop. The distal glucocorticoid regulatory element was unaltered, and two additional copies of the distal glucocorticoid regulatory element-binding site were present in the substituted region. The restriction endonuclease map of the reconstructed molecular clone of DMBA-LV was identical to that corresponding to unintegrated linear DMBA-LV DNA present in DMBA-LV-induced tumor cell lines. Since the nucleotide sequences of the LTRs present in four different DMBA-LV proviral copies isolated from a single thymoma were identical, we concluded that they were derived from the same parental virus and that this type B retrovirus containing an alteration in the U3 region of its LTR could induce thymic lymphomas. Thus, DMBA-LV represents the first example of a productively replicating type B retrovirus that contains an LTR modified in the U3 region and that has target cell and disease specificity for T cells.

Retroviruses

First brought to scientific attention as infectious cancer-causing agents nearly 80 years ago, retroviruses are popular in contemporary biology for many reasons. (i) The virus life cycle includes several events--in particular, reverse transcription of the viral RNA genome into DNA, orderly integration of viral DNA into host chromosomes, and utilization of host mechanisms for gene expression in response to viral signals--which are broadly informative about eukaryotic cells and viruses. (ii) Retroviral oncogenesis usually depends on transduction or insertional activation of cellular genes, and isolation of those genes has provided the scientific community with many of the molecular components now implicated in the control of normal growth and in human cancer. (iii) Retroviruses include many important veterinary pathogens and two recently discovered human pathogens, the causative agents of the acquired immunodeficiency syndrome (AIDS) and adult T cell leukemia/lymphoma. (iv) Retroviruses are genetic vectors in nature and can be modified to serve as genetic vectors for both experimental and therapeutic purposes. (v) Insertion of retroviral DNA into host chromosomes can be used to mark cell lineages and to make developmental mutants. Progress in these and other areas of retrovirus-related biology has been enormous during the past two decades, but many practical and theoretical problems remain to be solved.

Inoculation of baboons and macaques with simian immunodeficiency virus/Mne, a primate lentivirus closely related to human immunodeficiency virus type 2

A primate lymphotropic lentivirus was isolated on the human T-cell line HuT 78 after cocultivation of a lymph node from a pig-tailed macaque (Macaca nemestrina) that had died with malignant lymphoma. This isolate, originally designated M. nemestrina immunodeficiency virus (MnIV) and now classified as simian immunodeficiency virus (SIV/Mne), was inoculated intravenously into three juvenile rhesus monkeys (Macaca mulatta), three juvenile pig-tailed macaques (M. nemestrina), and two juvenile baboons (Papio cynocephalus). All six macaques became viremic by 3 weeks after inoculation, whereas neither of the baboons developed viremia. One pig-tailed macaque died at 15 weeks with suppurative peritonitis secondary to ulcerative, necrotizing colitis. Immunologic abnormalities included a marked decrease in CD4+ peripheral blood lymphocytes. Although five macaques mounted an antibody response to SIV/Mne, the animal that died at 15 weeks remained antibody negative. Three other macaques (two rhesus and one pig-tailed) died 66 to 87 weeks after inoculation after exhibiting progressive weight loss, anemia, and diarrhea. Histopathologic findings at necropsy included various manifestations of immune deficiency, nephropathy, subacute encephalitis, pancreatitis, adenocarcinoma, and lymphoid atrophy. SIV/Mne could be readily isolated from the spleens and lymph nodes of all necropsied macaques, and from the cerebrospinal fluid, brains, bone marrow, livers, and pancreas of some of the animals. SIV antigens were localized by avidin-biotin immunohistochemistry to pancreatic islet cells and to bone marrow endothelial cells. The data suggest that African baboons may be resistant to infection by SIV/Mne, whereas Asian macaques are susceptible to infection with this pathogenic primate lentivirus.

Variants of amphotropic type-C retrovirus isolated from cultures of Moloney- and Rauscher-MuLV-induced tumors

We isolated and characterized 2 strains of type-C retrovirus, R5NX and YACNX, from established lymphoid cell cultures derived from Rauscher-MuLV-induced lymphoma (RBL-5) in a C57BL/6 mouse, and Moloney-MuLV-induced lymphoma (YAC) in an A-strain mouse, respectively. The R5NX and YACNX viruses were compared with the prototype 4070A strain of amphotropic virus isolated from feral mice in California, and were found to belong to the same amphotropic virus class on the basis of viral interference, neutralization tests, and other biological properties. However, they were not quite identical with respect to viral neutralization antigens and restriction enzyme cleavage patterns of the proviral DNA. The possibility that these viruses may have been present in the original tumor together with the R-MuLV or M-MuLV as "exogenous" viruses rather than as contaminants of cell cultures by the 4070A virus is discussed. Although these 2 isolates were not pathogenic when inoculated into newborn C3H/HE mice, they could establish persistent infections in these mice.

Evolution of cancer genes as a mutation-driven process

Cancer is primarily a somatic genetic disease resulting from the accumulation of several precancerous mutations in a cell lineage. The evolution of highly oncogenic retroviruses has been used as a model for the evolution of a cancer cell. The properties of intermediates between one set of replication-competent retrovirus and protooncogene progenitors and the homologous highly oncogenic retrovirus were analyzed to differentiate between selection-driven and mutation-driven models of this evolution. In this case and in some other cases where sufficient data are available, it appears that the intermediates in the evolution of highly oncogenic retroviruses are not transforming, indicating that they were not formed in a purely selection-driven process. Furthermore, analysis of retrovirus mutation rates indicates that there is a high rate of mutation in retrovirus replication such that the evolution of highly oncogenic retroviruses could be mutation-driven. Other evidence is mentioned suggesting that oncogenesis in general is at least partially mutation-driven, although mutational mechanisms are involved that are different from those involved in the evolution of highly oncogenic retroviruses.

A single point mutation in the envelope gene is responsible for replication and XC fusion deficiency of the endogenous ecotropic C3H/He murine leukemia virus and for its repair in culture

The molecular basis has been determined for differences in infectivity and XC phenotype of endogenous ecotropic murine leukemia virus of the low-leukemia mouse strain C3H/He, its relative in the high-leukemia mouse strain AKR, and highly infectious, XC-positive C3H virus variants selected in vitro. Endogenous ecotropic type C virus induced by iododeoxyuridine from the nontransformed C3H/10T1/2 cell line is XC negative and replication deficient. In contrast, viruses produced late after iododeoxyuridine induction in chemically transformed C3H/10T1/2 cells (MCA5) are XC positive and infectious. XC-negative viruses can be converted to XC-positive viruses by being grown in certain transformed cell lines. We have cloned the endogenous ecotropic provirus of C3H/He from MCA5 cells, which is XC negative and replication deficient, as well as two XC-positive C3H proviruses derived by in vitro conversion. Fragment exchange between the XC-negative molecular clone p110 and the XC-positive AKR virus clone p623 revealed that the defect in p110 lies 3' of the SalI site located in the pol region. Nucleotide sequencing established that the C3H p110 provirus was integrated within the R region of an endogenous VL30 long terminal repeat (LTR) in reverse orientation and that the virus differed from the infectious AKR p623 provirus by a point mutation, substituting Lys for Arg at the potential precursor cleavage site for gp70 and p15E. In vitro-converted XC-positive C3H proviral clones 3211 and 4211 are identical to XC-negative C3H p110, except that they have Arg at this site and the normal cleavage site is thus regenerated in these clones. The XC-negative C3H p110 was blocked in processing of Pr85env, whereas clones 3211 and 4211 had normal cleavage of the env precursor into gp70. Both the XC-negative C3H provirus and the in vitro-converted XC-positive C3H proviruses had a single copy of a 99-base-pair enhancer element in the LTR, whereas two copies of this sequence are present in the AKR proviral LTR. Substitution of Arg for Lys at the envelope precursor processing site of C3H p110 by site-directed mutagenesis is sufficient by itself to convert the virus to the XC-positive replication-competent phenotype. Thus, we have established that a single point mutation at the processing site of the envelope precursor protein Pr85 is responsible for the difference in the infectivity and XC phenotype of endogenous ecotropic murine leukemia virus from C3H/He and AKR mice and that the basis for in vitro conversion is a mutation at this site.

Spumaviruses isolated from sources containing agents of non-A, non-B (NANB) hepatitis do not cause NANB hepatitis

Serum and liver tissue containing infective non-A, non-B hepatitis virus were shown to contain a retrovirus-like agent that replicated when inoculated into chimpanzee liver cell cultures in vitro. The virus appeared to assemble its core particles in association with tubular structures reminiscent of those characteristically seen in non-A, non-B hepatitis virus-infected chimpanzee liver in vivo, and produced syncytial cytopathic effects in a number of continuous and a primary mammalian liver cells. The agents were neutralized by acute and convalescent sera from human and chimpanzee cases of non-A, non-B hepatitis, as well as by antisera against simian spumavirus type 7, but not type 6. Aluminum chloride failed to abolish viral infectivity. There was no evidence of virus replication or hepatitis in chimpanzees inoculated with a seventh passage of one of the isolates. Thus the data suggest that the isolates are not causally related to non-A, non-B hepatitis, as was previously postulated.

Lentivirus-induced lymphoproliferative disease. Comparative pathogenicity of phenotypically distinct ovine lentivirus strains

For investigation of the pathogenicity of lentivirus strains, which have distinctly different cytopathic phenotypes in synovial membrane cell culture, plaque-purified, lytic, and nonlytic ovine lentivirus (OvLV) isolates were inoculated intratracheally into two groups of neonatal lambs. Twelve lambs were inoculated with a lytic OvLV isolate and 3 lambs each with two nonlytic OvLV isolates. Five control lambs were inoculated with either virus-free medium or were left uninoculated. In 8 of 12 lambs inoculated with a lytic OvLV isolate mild to severe lesions of lymphoid interstitial pneumonia (LIP) and pulmonary lymphoid hyperplasia developed, 6 of 12 lambs had lesions of pulmonary lymph node follicular hyperplasia, 3 of 9 female lambs had lesions of lymphoproliferative mastitis, 3 of 10 lambs had lesions of lymphocytic/plasmacytic synovitis, and 3 lambs had no lesions. In 3 of 6 lambs inoculated with nonlytic OvLV isolates only mild LIP lesions developed, without concurrent mammary gland or joint lesions. Bronchoalveolar lavage samples from OvLV-diseased lambs contained on average 1.5-fold more numbers of total leukocytes, and 4-fold more numbers of lymphocytes, compared with bronchoalveolar lavage samples of normal lambs. Monoclonal antibodies to ovine lymphocyte surface markers showed that the SBU-T8+ lymphocyte (CD 8 equivalent) was the predominant lymphocyte subset (mean of 65% of total lavaged lymphocytes) in bronchoalveolar lavage samples of 3 diseased lambs. Ovine lentivirus was reisolated from multiple tissues of both groups of OvLV-inoculated lambs, but the percentage of individual tissues infected was greater in lambs inoculated with the lytic viral isolate. Control lambs had no lesions and failed to produce OvLV-specific antibodies or yield OvLV from tissues. All OvLV-inoculated lambs produced either low or undetectable serum virus neutralizing antibodies. In contrast, lambs inoculated with either lytic or nonlytic OvLV produced precipitating antibodies to OvLV glycoprotein and group-specific protein. However, initial detection of precipitating antibodies to OvLV glycoprotein was earlier (mean, 5.8 weeks after inoculation) in OvLV-infected lambs in which severe lymphoproliferative disease developed and delayed (mean, 10.2 weeks after inoculation) in OvLV-infected lambs with mild or no lesions. Together, these results suggest that lentivirus isolates produced disease in a virus strain-dependent manner and suggest that humoral immune responses against OvLV failed to prevent lesion development in lentivirus-infected lambs.(ABSTRACT TRUNCATED AT 400 WORDS)