Attenuated multi-mutated herpes simplex virus-1 for the treatment of malignant gliomas

We have created a double mutant of the herpes simplex virus (HSV) type 1 (termed G207) with favourable properties for treating human malignant brain tumours: replication-competence in glioblastoma cells (and other dividing cells), attenuated neurovirulence, temperature sensitivity, ganciclovir hypersensitivity, and the presence of an easily detectable histochemical marker. G207 has deletions at both gamma 34.5 (RL1) loci and a lacZ gene insertion inactivating the ICP6 gene (UL39). G207 kills human glioma cells in monolayer cultures. In nude mice harbouring subcutaneous or intracerebral U-87MG gliomas, intraneoplastic inoculation with G207 causes decreased tumour growth and/or prolonged survival. G207 is avirulent upon intracerebral inoculation of mice and HSV-sensitive non-human primates. These results suggest that G207 should be considered for clinical evaluation in the treatment of glioblastomas.

Involvement of a spliced and defective human foamy virus in the establishment of chronic infection

Human foamy retrovirus (HFV) is found as two proviruses (HFV and delta HFV) which differ by a splice-induced deletion within the bel1 transactivator gene. The defective delta HFV (which lacks a functional Bel1 but harbors an intronless bet gene) is predominantly found in nonlytic infections in vitro as well as in vivo. Here, we show that infection of cell lines stably transduced by delta HFV DNA with the highly lytic HFV leads to chronic infections characterized by an absence of lysis, a balanced ratio of HFV to delta HFV, and a persistent Bet expression accompanied by a shutoff of structural genes. While this system only partially reflects the natural situation, in which target cells are infected by HFV and delta HFV simultaneously, it strongly suggests that delta HFV is a defective interfering retrovirus. Accordingly, previous or concomitant exposure to delta HFV viruses greatly enhances the formation of lysis-resistant clones in culture after HFV infection. The inability of delta HFV proviruses encoding a mutated bet gene to induce chronic infection suggests a role for Bet in this process. Through a specific, splice-induced, genomic deletion, resulting in a switch from Bel1 to Bet expression, the lytic properties of HFV are progressively lost. Such programmed inactivation of a key gene represents a new regulatory mechanism of gene expression in retroviruses.

Nef stimulates human immunodeficiency virus type 1 proviral DNA synthesis

The Nef protein of human immunodeficiency virus type 1 (HIV-1) stimulates viral infectivity. The mechanism of this phenotype was investigated. Viruses containing disrupted nef genes were 4 to 40 times less infectious than wild-type HIV-1 in a single-round infection. The Nef-mediated stimulation HIV-1 infectivity was dependent on the association of Nef with the plasma membrane and could be observed when Nef was provided in trans in the virus producer but not target cells. The impaired infectiousness of nef-defective (delta Nef) virions was observed whether or not CD4 was present in either of these cells. Furthermore, it was independent of the mode of viral entry, since it was not rescued by pseudotyping Env- HIV-1 virions with the amphotropic murine leukemia virus envelope glycoproteins. As predicted from this result, wild-type and delta Nef virions entered cells with equal efficiencies. However, despite their normal content in viral genomic RNA and reverse transcriptase activity, delta Nef viruses were limited in their ability to perform reverse transcription once internalized in several cell types, including peripheral blood lymphocytes. Since Nef does not appear to be abundant in virions, these results suggest that Nef acts in producer cells to allow the generation of particles fully competent for completing steps that follow entry, leading to efficient reverse transcription of the HIV-1 genome. Using a trans complementation assay, we found that Nef proteins from a number of primary HIV-1 isolates as well as, to a milder degree, those from HIV-2ST and SIVMAC239 could enhance the infectivity of delta Nef HIV-1. This indicates that the Nef-mediated stimulation of proviral DNA synthesis is highly conserved and likely plays an important role in vivo.

Persistence of replication-deficient adenovirus-mediated gene transfer in lungs of immune-deficient (nu/nu) mice

To evaluate the role of cell-mediated immunity during gene transfer to the respiratory epithelium, the time course of luciferase activity was assessed after intratracheal administration of Av1Luc1, an E1a-E3-deleted adenoviral (Ad5) vector expressing firefly luciferase, to FVB/N, BALB/c and BALB/c-nu/nu adult mice. Adenovirus-mediated luciferase activity was rapidly lost from the respiratory tract between 2 and 14 days after treatment of both FVB/N and BALB/c wild-type mice. In the wild-type mice, loss of luciferase activity was associated with an early inflammatory response consisting of infiltration with macrophages and polymorphonuclear leukocytes and a more prolonged response characterized by lymphocytic infiltration. In the immune-deficient nu/nu mice, luciferase activity was maintained at higher levels than in immune-competent mice after exposure to virus and was associated with a distinct pattern of inflammation, consisting primarily of macrophages and polymorphonuclear cells but lacking the lymphocytic infiltrates typical of the inflammation in wild-type mice. Adenoviral DNA was rapidly cleared from the lungs of both nu/nu and wild-type mice. Markedly increased expression of proliferating cell nuclear antigen (PCNA) was observed in bronchiolar and alveolar epithelial cells and in inflammatory cells after exposure to Av1LUc1. The proliferative response of the respiratory epithelium was more extensive and persistent in wild-type than in nu/nu mice. To assess further the impact of the immune system on adenovirus-mediated gene expression, cotton rats treated with cyclosporin A or dexamethasone were exposed to Av1Luc1. Both agents decreased lung inflammation and significantly increased lung luciferase activity. The loss of lung luciferase activity is dependent, in part, on the immune-mediated clearance of respiratory epithelial cells, which may limit the extent and duration of gene expression with recombinant adenoviral vectors.

Erythroleukaemia induction by the Friend spleen focus-forming virus

The Friend spleen focus-forming virus has been a valuable tool for understanding the molecular events involved in the multiple stages of leukaemia. As summarized in Figure 3, the primary effect of SFFV, which occurs within days, is to cause a polyclonal proliferation of erythroid precursor cells that can proliferate in the absence of their normal regulator erythropoietin. This is the direct result of the unique envelope glycoprotein encoded by SFFV, which is transported to the cell surface and apparently interacts with the EpoR or another component of the multimeric EpoR complex, resulting in the constitutive activation of the Epo signal transduction pathway. Within this proliferating population of erythroid cells is a rare cell that has undergone several genetic changes due to the integration of the viral genome in specific sites in the mouse DNA. This leads to the activation of a gene encoding the PU.1 transcription factor, whose high expression in erythroid cells may be the cause of the block in differentiation that is characteristic of SFFV-transformed erythroid cells. SFFV integration can also lead to the inactivation of the p53 tumour supressor gene, giving these cells a growth advantage in the mouse. The disease induced by SFFV in mice is very similar to polycythaemia vera in humans (Golde et al, 1981). The major clinical feature of polycythaemia vera is the continuous expansion of the number of mature red blood cells in the presence of low serum Epo levels. Also, BFU-E and CFU-E from these patients can form in the absence of Epo like the analogous cells from SFFV-infected mice (Casadevall et al, 1982). It is possible that haematopoietic cells from individuals suffering from this disease express a protein similar to the envelope glycoprotein of SFFV that can interact with the EpoR and lead to its constitutive activation. Alternatively, these patients may contain a mutant EpoR gene that is constitutively activated like the mutant EpoR described earlier. As we understand more fully how the SFFV envelope protein constitutively activates te EpoR complex, we can begin to design therapies to counteract its action that can then be applied to treating patients with polycythaemia vera or other human diseases associated with uncontrolled erythropoiesis.

Inflammatory effects of gene transfer into the CNS with defective HSV-1 vectors

The use of viral vectors which infect and express genes in post-mitotic neurons is a potential strategy for the treatment of disorders affecting the central nervous system (CNS). However, the inflammatory consequences of such strategies have yet to be systematically examined. Preparations of non-replicating defective herpes simplex virus type 1 (HSV-1) amplicon vectors containing the lacZ gene were obtained by standard methods and stereotaxically injected into the adult rat dentate gyrus (DG). The consequent gene expression and inflammatory effects following microinjection were investigated. beta-Galactosidase activity was detected in neurons of the DG from 24 h to at least 12 days after vector injection. A strong inflammatory response developed within 2 days, characterized by diffuse up-regulation of major histocompatibility complex (MHC) class I antigens and the activation of microglia. After 4 days the recruitment of MHC class II+ cells, activated T lymphocytes and macrophages was detected. These features persisted for at least 31 days. Of importance was the finding of beta-galactosidase activity in a bilateral group of neurons in the supramammillary nuclei (SMN) of the posterior hypothalamus, known to send afferent projections to the DG. The onset of inflammation at this secondary site was delayed, but its cellular characteristics resembled those found at the primary site of injection. Thus, the use of preparations of defective HSV-1 vectors for gene transfer in the CNS has immunological implications both at primary and secondary sites within the CNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of mpl cytoplasmic domain sequences required for myeloproliferative leukemia virus pathogenicity

v-mpl is a truncated form of a receptor-like chain which belongs to the cytokine receptor superfamily. This sequence has been transduced in the myeloproliferative leukemia virus as an env-mpl fusion gene responsible for an acute myeloproliferative disorder in mice. We constructed a series of viral mutants in the mpl sequence. Analysis of their oncogenic potential in vivo indicated that a critical 69-amino-acid-long cytoplasmic domain of v-Mpl is required for myoproliferative leukemia virus pathogenicity. We also developed an in vitro assay and showed that expression of the env-mpl gene confers growth factor independence to murine as well as to human hematopoietic growth factor-dependent cell lines. These findings strongly suggest that v-Mpl delivers a constitutive proliferative signal through a limited region of its cytoplasmic domain.

Inactivation of E2a in recombinant adenoviruses improves the prospect for gene therapy in cystic fibrosis

Although first generation recombinant adenoviruses, deleted of sequences spanning E1a and E1b, have been useful for in vivo applications of gene therapy, expression of the recombinant gene has been transient and often associated with the development of inflammation. We show that with first generation adenovirus-mediated gene transfer to the mouse lung, viral proteins are expressed leading to destructive cellular immune responses and repopulation of the lung with nontransgene containing cells. Second generation E1 deleted viruses further crippled by a temperature sensitive mutation in the E2a gene were associated with substantially longer recombinant gene expression and less inflammation. Stable expression of human CF transmembrane conductance regulator has been achieved in lungs of CF mice instilled with a second generation virus.

Human oropharyngeal lesions with a defective Epstein-Barr virus that disrupts viral latency

The Epstein-Barr virus (EBV), a human herpesvirus that is predominantly latent after infection, can be induced to replicate by deleted, rearranged EBV DNA from cultures of laboratory strain P3HR-1. Because mucosal surfaces are permissive of EBV replication, 101 oral biopsies from 70 Chinese and 5 American patients were examined for natural counterparts to tissue culture defective virus (WZhet), using as marker the abnormal juxtaposition of BamHI W and Z EBV DNA restriction fragments. Of the 49 oral biopsies that contained EBV DNA, 12 (24%) had the rearranged WZ fragment by polymerase chain reaction analysis: 3 (42%) of 7 EBV-positive epithelial dysplasias or carcinomas, 6 (38%) of 16 hairy leukoplakias, and 3 (12%) of 25 nonmalignant salivary gland biopsies. Accompanying viral replication was confirmed by in situ cytohybridization and demonstration of the linear configuration of the genome in select WZhet-positive lesions. These findings indicate that defective EBV with the unusual property of disrupting EBV latency is prevalent in natural infections and may contribute to EBV's pathogenic diversity.

The MA (p15) and p12 regions of the gag gene are sufficient for the pathogenicity of the murine AIDS virus

Inoculation of the replication-defective retrovirus DEF27 (BM5d), packaged as an amphotropic virus pseudotype, into C57BL/6J mice leads to development of murine AIDS. Disease development showed a long incubation period (20 to 24 weeks), was associated with amplification of the BM5d provirus in splenocytes and lymph nodes, and was independent of the presence of exogenous or endogenous replication-competent helper viruses. However, both the onset of disease and amplification of the defective provirus were significantly enhanced by coinfection with the replication-competent B-cell-tropic ecotropic helper virus BM5e. The part of the BM5d viral genome that was essential for the pathogenicity was determined by making precisely engineered alterations in the reading frame of the gag and pol genes of BM5d proviral DNA and examining the ability of the altered amphotropic BM5d pseudotypes to induce the disease in C57BL/6J mice. The results show that expression of the MA (p15) and p12 regions of the gag gene is sufficient for pathogenicity of the BM5d retrovirus.

Delayed cytopathicity of a feline leukemia virus variant is due to four mutations in the transmembrane protein gene

Two molecularly cloned, replication-defective variants of feline leukemia virus, called 61B and 61C, have both been shown to cause fatal immunodeficiency in cats when coinfected with a replication-competent, minimally pathogenic helper virus, but 61B exhibits a longer latency period between infection and disease (J. Overbaugh, E. A. Hoover, J. I. Mullins, D. P. W. Burns, L. Rudensey, S. L. Quackenbush, V. Stallard, and P. R. Donahue, Virology 188:558-569, 1992). Infection of the 3201 feline T-cell line with 61B plus helper virus also results in longer time from infection to cytopathic effect compared with 61C plus helper virus, providing an in vitro system with which to study the mechanism for this difference. We report that the primary determinant of cytopathicity of 61B maps to gp70, the extracellular envelope glycoprotein. The long latency of 61B, on the other hand, maps to the extracellular portion of the envelope transmembrane protein, in which there are only four predicted amino acid differences between 61B and 61C. These differences render 61B replication defective, and two of the predicted amino acid changes lie in a region that is highly conserved among many retroviruses. The eventual onset of 61B cytopathicity in cell culture was associated with the outgrowth of an apparent recombinant virus that encodes the pathogenic gp70 of 61B and replaces the transmembrane protein of 61B with that of the helper virus. Thus, during in vitro infection, a cytopathic virus evolved from a replication-defective virus and a nonpathogenic virus, suggesting that recombination between multiple variants in natural infection may influence progression of feline leukemia virus-associated immunodeficiency disease.

In vitro characterization of a herpes simplex virus type 1 ICP22 deletion mutant

We report the construction of a deletion mutant (del22Z) that is unable to synthesize any detectable messenger RNA or protein products from the herpes simplex virus type 1 (HSV-1) immediate early ICP22 gene upon infection. The del22Z deletion mutant lacks all but 18 nucleotides of the ICP22 coding sequence and carries the bacterial lacZ gene at the site of the deletion. No other known open reading frames or flanking sequences were disrupted. Del22Z was able to infect Vero cells productively but was severely restricted in human and rodent cells that were permissive for the parental HSV-1(F). The yield of del22Z was not enhanced significantly, either by increasing the multiplicity of infection or by increasing the duration of the infection. There was a prolonged expression of some early gene products and a delayed appearance of some late gene products in both permissive and restrictive cells. This phenotype of cell-line restricted growth and alteration of the normal gene expression cascade maps specifically to the ICP22 coding region.

Recombination between human immunodeficiency viruses (HIV) type 1 and 2 results in generation of defective hybrid viruses

Dual infection by HIV-1 and HIV-2 is already documented. To test if this could lead to recombination and generation of altered viruses, recombination between HIV-1 and HIV-2 DNAs was studied. Release of recombinant viruses was detected following cotransfection of human rhabdomyosarcoma cells with truncated versions of these proviral DNAs. Linearization of plasmid DNAs was required for virus production. Analysis of viral particles by hybridization revealed the presence of viral RNA. However viral replication was not evident. A computer search of the overlap region between the substrate DNAs revealed 66% homology despite an overall genomic sequence homology of only 35%. These data suggest possible generation of replication-deficient hybrid viruses as a result of recombination between HIV-1 and -2.

The 'WS motif' common to v-mpl and members of the cytokine receptor superfamily is dispensable for myeloproliferative leukemia virus pathogenicity

Several motifs are conserved in the extracellular domain of the cloned chains of the recently described cytokine receptor superfamily. One of them, usually close to the transmembrane region, is the 'WS motif'. Its function remains unknown, but it has been recently shown that the integrity of this motif is essential for interleukin 2 receptor beta-chain and erythropoietin receptor activity [Miyazaki, T., Maruyama, M., Yamada, G., Hatakeyama, M. & Taniguchi, T. (1991). EMBO J., 10, 3191-3197; Watowich, S.S., Yoshimura, A., Longmore, G.D., Hilton, D.J., Hoshimura, Y. & Lodish, H.R. (1992). Proc. Natl. Acad. Sci. USA, 89, 2140-2144]. This WS motif is present in the v-mpl oncogene, which has been transduced in the myeloproliferative leukemia virus (MPLV). v-mpl encodes a truncated transmembrane protein that belongs to this growth factor receptor family. We demonstrate that determinants of MPLV pathogenesis are encoded by the env-mpl fusion gene and that the complete deletion of the WS motif does not abolish MPLV oncogenic properties.

The induction of cataracts by HIV-1 in transgenic mice

OBJECTIVE

To elucidate the tissue specificity of the expression of HIV-1 genes in an animal and its pathological effects on these tissues.

DESIGN AND METHODS

Transgenic mice carrying a defective HIV-1 genome were bred in order to overcome the host-range barrier of this virus.

RESULTS

mRNA specific to the transgene was detected in the eyes and the spleen, and, in smaller quantities, in the thymus and the brain. Interestingly, many of the transgenic mice developed cataracts at 3-6 months of age. Swelling and vacuolation of the lens fiber cells were marked, but the epithelial cells of the lens were less affected. HIV antigens were detected in the lens fiber cells and the retina by immunological staining. Accumulation of large amounts of p24 Gag antigen was demonstrated in the affected lens by immunoblot analysis, while negligible Env or other viral proteins was detected. Although accumulation of the Gag protein was also detected in the skin and the brain, no apparent abnormality was observed in these tissues.

CONCLUSIONS

Preferential expression of the HIV genes in the eyes, skin, brain and lymphoid tissues was demonstrated. The accumulation of the Gag protein is suggested to have detrimental effects on lens fiber cells, causing cataracts.

High frequency of transmission of murine AIDS virus in C57BL/10 mice via mother's milk

Maternal transmission of a murine leukemia virus (MuLV) mixture named LP-BM5 MuLV, which is knwon to induce murine AIDS (MAIDS), was investigated. Adult female C57BL/10 mice were inoculated intraperitoneally with LP-BM5 MuLV. When the virus-inoculated female mice developed splenomegaly or lymphadenopathy, they were mated with normal C57BL/10 male mice. Of 56 offspring born to MAIDS mothers, 14 appeared to develop MAIDS, as assessed by the occurrence of splenomegaly or lymphadenopathy as well as the mitogen response of spleen cells. The occurrence of MAIDS in offspring was found to be accompanied by the maternal transmission and expansion of a defective virus genome from which almost the entire pol and env regions are deleted. On the other hand, the ecotropic helper virus genome was detected in all offspring regardless of the occurrence of MAIDS. To examine the mode of maternal transmission of LP-BM5 MuLV, foster-nursing experiments were conducted. The ecotropic helper viruses were found in all normal offspring nursed by a MAIDS mother, and some of them developed MAIDS. In contrast, none of offspring born to a MAIDS mother that were nursed by an uninfected foster mother either carried the LP-BM5 MuLV or developed MAIDS. Finally, both the defective and the ecotropic helper viruses were detected in LP-BM5 MuLV-infected mother's milk. These results indicated that maternal transmission of LP-BM5 MuLV occurs with a high frequency and is mediated by mother's milk.

Fulminant hepatitis related to transmission of hepatitis B variants with precore mutations between spouses

A precore defective variant of hepatitis B virus has been indicated to cause fulminant hepatitis in various instances such as intrahospital outbreaks or mother-to-child transmission of hepatitis B virus. To learn whether similar variants are involved in interspouse transmission, we analyzed three cases of fulminant hepatitis B that developed in formerly healthy subjects whose only exposure to hepatitis B virus was contact with their longtime spouses, who were carriers of HBV and positive for antibody to HBe. The DNA clones for precore and S genes were propagated from patients and spouses and sequenced. Because of the conservation of S-gene sequences and the identity of subtypes between patient and spouse, it was suggested that patients were infected with hepatitis B virus from their spouses, not from other sources. A TGG-to-TAG mutation at the 28th codon of the precore gene of hepatitis B virus was commonly observed in all DNA clones from patients with fulminant hepatitis and from their spouses. A 29th-codon GGC-to-GAC mutation was additionally evident in DNAs from one patient-and-spouse couple. A significant rise in the circulating hepatitis B virus concentration was transiently observed in the index spouse of this case just before development of fulminant hepatitis in her husband. The increase in circulating HBV DNA was associated with a rise in abundancy of variants with mutations at both the 28th and 29th codons, compared with variants with only a 28th-codon mutation. The double mutation in hepatitis B virus DNA may either help the virus escape immune surveillance or replicate at a higher rate than before.

Demonstration of two distinct cytopathic effects with syncytium formation-defective human immunodeficiency virus type 1 mutants

The mechanism of human immunodeficiency virus type 1 (HIV-1) cytopathicity is poorly understood and might involve formation of multinucleated giant cells (syncytia), single-cell lysis, or both. In order to determine the contributions of the fusion domain to syncytium formation, single-cell lysis, and viral infectivity and to clarify the molecular details of these events, insertion mutations were made in the portion of env encoding this sequence in the functional HIV-1 proviral clone HXB2. Viruses produced from these mutant clones were found to have a partial (F3) or complete (F6) loss of syncytium-forming ability in acutely infected CEM, Sup T1, and MT4 T-cell lines. During the early stage of acute infection by F6 virus, there was a loss of the syncytial cytopathic effect, which resulted in increased cell viability, and a 1.9- to 2.6-fold increase in virus yield in the cell lines tested. In the late stage of acute infection, the single-cell cytopathic effect of F6 virus was similar to that of the parental HXB2 virus. The F3 and F6 viruses were also found to have a 1.7- to 43-fold reduction in infectivity compared with the HXB2 virus. The mutant F3 and F6 and parental HXB2 envelope proteins were expressed in vaccinia virus, and the mutant envelope proteins were observed to be defective in their ability to form syncytia. BSC-40 cells infected with vaccinia virus recombinants revealed no differences in kinetics of cleavage, cell surface expression, or CD4 binding capacity of the mutant and parental envelope proteins. These results demonstrate that a loss of syncytium formation results in an attenuation of infectivity and a loss of the syncytial cytopathic effect without a loss of single-cell lysis. These mutants may reflect in tissue culture the changes observed in the HIV isolates in vivo during disease progression, which exhibit marked differences in syncytium production.

An unusual transmissible agent--MaTu

MaTu is an agent, believed to be derived from a human mammary carcinoma, which displayed several extraordinary properties. These were: RIP and PAGE revealed in MaTu-infected cells only a single protein band of Mr 58 k, the gp 58. This gp 58 was immunoprecipitated by antibodies present in some human sera as well as in some sera of rabbits, sheep, and cattle. MaTu had an extremely restricted host range: it was transmissible only to HeLa cells, but not to human embryo fibroblasts, to three human tumour cell lines (T 47 D, T 24, and HMB 2) or to monkey Vero and rabbit SIRC cells. A retrovirus with a broad host range, used as a helper (X-MLV) enabled the transmission of MaTu to human fibroblasts, but not to Vero or SIRC, which are also permissive for X-MLV. These observations, together with our previous reports, support the view that MaTu might either be a novel type of defective virus, or even a non-viral autonomous genetic element.

The specificity of the disease induced by defective murine retroviruses containing abl, fos, or Ha-ras is usually not determined by their LTR

The long terminal repeats (LTR) of the defective murine sarcoma viruses (MSV) containing v-abl, v-Ha-ras, or v-fos were exchanged for LTRs from other retroviruses having different tissue tropism. The new chimeric MSV were found to induce the same diseases as the parental viruses, indicating that sequences outside the LTR, most likely those of the oncogene, are responsible for the disease specificity of these defective MSV.

Evidence against a requisite role for defective virus in the establishment of persistent hepadnavirus infections

The factors involved in the establishment of persistent hepadnavirus infection are poorly understood. Recent findings demonstrate that the sequence of the genome of hepatitis B virus (HBV) is variable in infected individuals and that, in some cases, virus mutants predominate. Our objectives in the present study were to analyze the variability of woodchuck hepatitis virus (WHV) genomes in an infected animal and to determine whether sequence heterogeneity played a critical role in the ability of WHV to induce chronic infection. We cloned and determined the complete nucleotide sequence of three supercoiled genomes from an animal that became infected after inoculation with a standardized WHV serum pool (i.e., the WHV7 virus pool). We found that there were four nucleotide substitutions among the three genome sequences as well as a 73-nucleotide deletion in one of the recombinants. DNA transfection experiments revealed that only one of the three recombinants was capable of independent replication. These data suggest that a significant proportion of replicative templates in woodchucks that are infected with WHV are defective virus genomes. Next, we compared the outcome of acute infection after inoculation with a serum pool containing a uniform population of replication competent virus (i.e., the WHV7R pool) with a serum pool composed of WHV genomes of variable sequence. The WHV7R serum pool originated from a woodchuck that became a chronic carrier after in vivo transfection of the liver with the infectious WHV7 recombinant. Neonatal woodchucks were inoculated with 5 x 10(6) WHV genome equivalents of either the WHV7 pool or the WHV7R pool. All animals in the study became acutely infected with WHV. Of the animals infected with the WHV7 serum pool, 65% became chronic carriers, while 80% of the animals infected with the WHV7R serum pool developed chronic infection. Thus, infection of woodchucks with a serum pool containing defective virus resulted in a rate of chronic WHV infection that was similar to, or even lower than, a rate from a pool containing only wild-type virus. This suggests that the presence of defective virus in the inoculum is not a prerequisite for the establishment of persistent hepadnavirus infections.

Defective viral DNA in Epstein-Barr virus-associated oral hairy leukoplakia

Defective Epstein-Barr virus (EBV) has a deleted and rearranged genome (termed het DNA) that disrupts latency and induces standard EBV to replicate in vitro. We used the polymerase chain reaction to detect, in 2 of 10 patient samples, the junction of abnormally juxtaposed EBV DNA fragments BamHI W and Z, a genomic rearrangement responsible for the biologic activity of het DNA. By sequence analysis, the junction in wild-type defective DNA appears to be similar but not identical to the recombination in the DNA of laboratory strain P3HR-1. The presence of this marker for het DNA in the epithelial lesions of two patients suggests a role for defective EBV in a human pathologic process.

Immunodeficiency and clonal growth of target cells induced by helper-free defective retrovirus

The murine acquired immunodeficiency syndrome is induced by a defective retrovirus. To study the role of virus replication in this disease, helper-free stocks of defective Duplan virus were produced. These stocks were highly pathogenic in absence of detectable replicating murine leukemia viruses (MuLVs) other than xenotropic MuLV. They induced expansion of the infected cell population (over 1000-fold), and this cell expansion was oligoclonal in origin and, most likely, arose through cell division. These results suggest that this defective virus is oncogenic, inducing a primary neoplasia associated with an acquired immunodeficiency syndrome as a paraneoplastic syndrome. These data emphasize the need to determine whether virus replication is necessary for the progression of other immunodeficiency diseases, including acquired immunodeficiency syndrome, and whether these diseases also represent paraneoplastic syndromes.

[The SSPE model: suggestions for an explication of viral persistence]

The detection of a latent viral flora intrinsic to the central nervous system (CNS) raises the problem to know if some neuropathogenic strains have the property of initiating persistent infections or if the persistence is the result of the immune response particularities at the CNS level. A review is done of the pathogenic explanations of virus persistence in SSPE, followed by the discussion about two pathogenic alternatives issues from the author's studies: the antigenic "drift" hypothesis and the one of the defective interfering particles preferential synthesis.

Defective virus is associated with induction of murine retrovirus-induced immunodeficiency syndrome

C57BL/6 mice infected with a mixture of murine leukemia viruses (MuLV) develop a syndrome characterized by lymphoproliferation and profound immunodeficiency. Analyses of this viral mixture (LP-BM5 MuLV) showed that it includes replication-competent ecotropic and mink cell focus-inducing MuLV and defective viruses with genome sizes of 3.8-6.5 kilobases. The ecotropic and mink cell focus-inducing MuLV biologically cloned from the mixture did not induce disease, whereas viral preparations containing the ecotropic MuLV and 4.8-kilobase defective virus were active. Cells producing the 4.8-kilobase defective virus expressed an unusual gag-encoded polyprotein of Mr 60,000.

Thymic lymphoma induction by the AKT8 murine retrovirus

The directly transforming murine retrovirus, AKT8, was isolated from a spontaneous AKR thymoma and carries the cell-derived viral oncogene, akt. We have now shown that this virus produces thymic lymphomas after inoculation of susceptible mouse strains. The presence of the AKT8 genome in the DNA of the virus-induced tumors was demonstrated by Southern blotting using an akt-specific probe. These results establish the in vivo pathogenicity of the AKT8 virus and its akt oncogene, and imply a potential role for the cellular akt proto-oncogene in tumor development.

Heart tumors specifically induced in young avian embryos by the v-myc oncogene

To determine if expression of the v-myc oncogene had any effect during ontogeny, we injected avian myelocytomatosis virus strain MC29 into avian embryos at various stages of development. The injection of MC29 at embryonic day 2 (E2) or 3 (E3) caused, about 10 days later, rhabdomyosarcomas of the heart and, in some cases, skin muscle hypertrophy. When the injection was performed at E4 or E5, the number of heart tumors declined, whereas the number of skin muscle tumors increased significantly. The p110gag-myc protein was found in all tumors analyzed. When the virus was injected intravenously into E10 embryos, no tumors appeared during embryonic life, in striking contrast to the results obtained from injections at earlier stages. The monoclonal antibody 13F4, which is specific for the myogenic lineage, bound strongly to tumoral heart tissue, whereas it bound weakly to normal cardiac cells. Comparison of the peaks of tumor incidence in relationship to the timing of injection suggests that the v-myc product could interfere in vivo with an early step of the muscle lineage differentiation program. In addition, we show that the p58c-myc protein, which is supposed to play an important role in the control of cell proliferation, is only faintly detected in the heart of normal E3 embryos, in contrast to limb and tail buds, which readily express detectable levels of p58c-myc.

Infection of the central nervous system of mice by standard Sendai virus, defective interfering Sendai virus and the mixture of both: comparison of virus multiplication and pathogenicity

The intracerebral (i.c.) infection of newborn mice with standard Sendai virus (SV), defective interfering Sendai virus (DV) and their mixture (SV + DV) has been used as a model for the possible role of defective interfering particles of paramyxoviruses in several chronic degenerative diseases of central nervous system (CNS). The dynamics of Sendai virus multiplication and virus distribution in CNS of mice, as well as the histological changes and the clinical symptoms were evaluated for up to 112 days post-infection (p.i.). The infectious virus was detected in the brains of animals inoculated i.c. either with SV, or DV, or SV + DV as soon as by 5 hr p.i., with maximum infectivity titre at 24 hr p.i. In brains of animals inoculated with SV, the virus was detected until 5th day p.i.; nevertheless in those, inoculated with SV + DV or DV, low infectious titres could be detected even at later intervals. In mice inoculated i.c. with DV, traces of Sendai virus were detected in subpassages, as late as 3 months p.i.

B cell activation by the nontransforming P3HR-1 substrain of the Epstein-Barr virus (EBV)

The P3HR-1 substrain of Epstein-Barr virus does not transform B cells. This defect is known to be determined by the loss of the coding sequence for the nuclear antigen EBNA-2. The virus can attach to and enter resting B cells. The initial events after EBV infection are reminiscent of those induced by polyclonal B cell activators. Similar to the effect of these, P3HR-1 virus lowers membrane IgD expression on B cells and abrogates the transient elevation of activation markers BB-1 and LB-1 induced by the culture conditions. An important event of B cell activation is the acquisition of competence to respond to specific growth factors produced by T cells. This was induced by the P3HR-1 virus. The infected B cells had elevated [3H]thymidine incorporation when exposed to the supernatant of PHA-treated T cells. The EBV receptor is identical with the complement receptor CR2. Ligand binding to CR2 has been shown both with mouse and human B cells to deliver certain activation signals. Therefore, it is possible that the early step of activation by EBV is initiated through the binding to the receptor and is thus a cell surface event.

Infection of the adrenal gland as a route to the central nervous system after viraemia with herpes simplex virus in the mouse

Intravenous inoculation of 4-week-old female NIH (inbred) mice with herpes simplex virus type 1 (HSV-1) strain P2C6 (defective in thymidine kinase) produced bilateral hind limb paralysis in nearly all animals by the 5th day after inoculation; very few mice died. In male mice the incidence and severity of paralysis was considerably lower than in females. The parental strain, CL(101), produced similar paralysis but all mice died by day 7. Observations on paralysis and death after intravenous inoculation are given for other strains of HSV-1 and HSV-2. By day 1 after inoculation of P2C6 significant virus replication had occurred in the adrenal glands but in none of the other organs tested. Titres of virus were similar in the adrenal glands of male and female mice. Histology of the adrenals showed most extensive replication in the cortex with some involvement of the medulla, particularly at the corticomedullary junction. By the 2nd and 3rd days, virus was detected in the lower thoracic spinal cord of both male and female animals but clearance was possibly quicker from males. Adrenalectomy proved that virus reached the cord via the adrenals. In the cord the infection was associated with bilateral demyelination in the ventral white matter as early as day 3.

Round cell variant of measles virus: neurovirulence and pathogenesis of acute encephalitis in newborn hamsters

A subacute sclerosing panencephalitis (SSPE) strain of measles virus has been previously shown to be composed of two interrelated but separable viral variants. One of these, the syncytiagenic or S variant, resembles defective, cell-associated strains of measles virus; while the other, the round cell inducing or RC variant, induces a highly productive infection in cell culture. It is now reported that the S variant is more neurovirulent in newborn hamsters than the RC variant and that viral replication in infected CNS tissues occurs in two phases. Early in the infection cell-free virus, composed primarily of the RC variant, is produced. Later, coincident with the appearance of antiviral antibody, cell-free virus rapidly disappears, leaving behind only cell-associated virus which resembles the S variant. Quantification of viral antigen expression in the infected tissues suggests that this change in the state of infection is not associated with antigenic modulation, but rather is the result of preferential elimination of RC variant infected cells.

[Pathogenicity of the Lassa virus for laboratory mice]

Pathogenicity for randombred and inbred mice of various age groups of the standard Lassa virus and the virus enriched with defective interfering particles (DIP) was studied. The standard Lassa virus inoculated intracerebrally caused 100% death of C3H/Sn mice aged up to 4 weeks and 60%-70% death of randombred white mice aged 3-4 weeks. BALB/C mice were found to be nonsusceptible to the virus, and its lethality for C57BL/6 and AKR mice varied within the range of 30%-60%. Lassa virus enriched with DIP caused no death of the susceptible animals and showed poor protective activity against the standard virus.

Round cell variant of measles virus: spontaneous conversion from productive to cell-associated state of infection

A subacute sclerosing panencephalitis strain of measles virus was found to be composed of two viral variants distinguishable by their cytopathic effects in Vero cells. One of the variants was similar to defective cell-associated measles virus strains, whereas the other was highly productive of viral progeny but did not induce cell fusion. Cloning of the variants by an agarose plaque procedure revealed a consistent and rapid interconversion of the variants into one another. While the mechanism of this interconversion remains unknown, analysis of the expression of viral antigens by the variants using indirect immunofluorescence with monoclonal antibodies specific for measles structural antigens suggested that the interconversion involved modulation of the expression of the viral matrix or M antigen.

Growth of defective subacute sclerosing panencephalitis viruses in human neural cells and their neurovirulence in mice

A defective subacute sclerosing panencephalitis (SSPE) virus which had been passaged in human embryonic lung cells was transferred to cultures of three neural cell types: neuroblastoma, oligodendroglioma and glioblastoma. The growth characteristics of the virus in these cells were essentially similar to those in non-neural cells. On the other hand, a marked difference in neurovirulence was noticed for the virus grown in neural cells when examined by intracerebral inoculation into mice. The virus passaged in neuroblastoma and oligodendroglioma cells showed high neurovirulence, inducing an acute encephalitis, whereas the virus passaged in human embryonic lung cells and that in glioblastoma cells did not show neurovirulence. These results suggest that the virus recovered its neurovirulence after passage in certain human neural cells.

Variation in homotypic and heterotypic interference by defective interfering viruses derived from different strains of Semliki Forest virus and from Sindbis virus

There was strong interference between various virulent and avirulent strains of Semliki Forest virus (SFV) and their respective defective interfering (DI) viruses but in other combinations interference was variable: it could be equally strong, weak or could not be demonstrated. On passage, this spectrum of interfering activity changed, some combinations showing greater interference than before and others less. Heterotypic interference between DI SFV, DI Sindbis virus and standard viruses was clearly demonstrated although this was strongest between DI SFV preparations and Sindbis standard virus than in the reciprocal combinations. Variation in interference between DI SFVs and different SFV strains was similar in magnitude to that between DI SFVs and Sindbis virus, suggesting that a similar DI RNA sequence is recognized by both viruses.

Properties of host and virus which influence defective interfering virus mediated-protection of mice against Semliki Forest virus lethal encephalitis. Brief report

Variation of the mouse strain, the amount of defective interfering (DI) virus and the amount of infectious Semliki Forest virus (SFV) are all factors which affect the efficiency with which DI SFV prevents the SFV-mediated lethal encephalitis.

[Immunologic analysis of the pathology developing in mice as a results of intrauterine infection with the influenza virus]

The progency of C57BL/6 mice consisting of three groups: with signs of slow influenza infection ("dwarf"), "nude-like" resembling nude mice, and "nude-like" with spontaneous fur growth, was examined. The slow influenza infection in "dwarf" mice was found to be characterized by marked immunosuppression manifested by a sharp reduction of the number of antibody- and rosette-forming cells and blasttransformation of spleen lymphocytes into T- and B-mitogens. The most marked immuno-suppression was found in the "dwarfs" born to the females infected with the virus enriched with standard virions. "Nude-like" animals also had marked immunosuppression (particularly with regard to the rosette-formation), however, the "dwarfs" appeared to have more marked affection of B-cells as compared with "nude-like" mice. Gradual restoration of fur in a portion of "nude-like" animals (spontaneous growth) was due to sharp stimulation of immune responsiveness in them as manifested by a two-fold (as compared with the controls) increase in the number of antibody- and rosette-forming cells and normalization of spleen cell response to T- and B-mitogens. Differences between nude and "nude-like" mice consisting in the latter in the affection of not only T- but also B-link of immunity are discussed.

[Persistence of the Japanese encephalitis virus in L929 cells. Correlation of viral and cellular factors]

The paper presents the results of the study of the first stage of Japanese encephalitis (JE) virus persistence in cultures of L929 cells. The main parameters of the establishment and development of JE virus persistence in these cells characterizing the system as a chronically infected one. A possible role in the mechanism of persistence of various cellular and viral factors: interferon, ts-mutants, defective particles, was studied. Interferon was shown to be the main factor of virus carrier state perpetuation in the L-JE system. The role of defective particles, ts-mutants, and possible association of JE virus genome with nuclear DNA of L929 cells in the mechanism of persistence is discussed.

Is progressive multifocal leukoencephalopathy a chronic disease because of defective interfering particles or temperature-sensitive mutants of JC virus?

JC virus was examined for temperature sensitivity and for evidence of defective interfering particles as a means of explaining the slow chronic nature of progressive multifocal leukoencephalopathy (PML). JC virus direct from the brain tissue of seven persons with PML was not temperature sensitive as indicated by in vitro assay at 37 and 39 degrees C. In fact, more cells contained viral antigen at 39 than at 37 degrees C. The amount of infectious virus also was increased at 39 degrees C. Virions isolated directly from diseased brain tissue had a higher buoyant density than did virus from the same PML patient passaged in culture and containing genomic deletions. In contrast to DNA from culture-passed virus, DNA extracted from virions direct from brain tissue was homogeneous in length. In 13 separate cases examined, the viral DNA direct from the brain was homogeneous although variations in length were noted among DNAs from different cases. Restriction enzyme cleavage patterns identified all as JC virus DNA. It was concluded that neither temperature sensitivity nor DI particles can be used to explain the slow, progressive nature of PML.