Immunoinformatics, molecular docking and dynamics simulation approaches unveil a multi epitope-based potent peptide vaccine candidate against avian leukosis virus

Lymphoid leukosis is a poultry neoplastic disease caused by avian leukosis virus (ALV) and is characterized by high morbidity and variable mortality rates in chicks. Currently, no effective treatment and vaccination is the only means to control it. This study exploited the immunoinformatics approaches to construct multi-epitope vaccine against ALV. ABCpred and IEDB servers were used to predict B and T lymphocytes epitopes from the viral proteins, respectively. Antigenicity, allergenicity and toxicity of the epitopes were assessed and used to construct the vaccine with suitable adjuvant and linkers. Secondary and tertiary structures of the vaccine were predicted, refined and validated. Structural errors, solubility, stability, immune simulation, dynamic simulation, docking and in silico cloning were also evaluated.The constructed vaccine was hydrophilic, antigenic and non-allergenic. Ramchandran plot showed most of the residues in the favored and additional allowed regions. ProsA server showed no errors in the vaccine structure. Immune simulation showed significant immunoglobulins and cytokines levels. Stability was enhanced by disulfide engineering and molecular dynamic simulation. Docking of the vaccine with chicken's TLR7 revealed competent binding energies.The vaccine was cloned in pET-30a(+) vector and efficiently expressed in Escherichia coli. This study provided a potent peptide vaccine that could assist in tailoring a rapid and cost-effective vaccine that helps to combat ALV. However, experimental validation is required to assess the vaccine efficiency.

The coinfection of ALVs causes severe pathogenicity in Three-Yellow chickens

The coinfection of ALVs (ALV-J plus ALV-A or/and ALV-B) has played an important role in the incidence of tumors recently found in China in local breeds of yellow chickens. The study aims to obtain a better knowledge of the function and relevance of ALV coinfection in the clinical disease of avian leukosis, as well as its unique effect on the pathogenicity in Three-yellow chickens. One-day-old Three-yellow chicks (one day old) were infected with ALV-A, ALV-B, and ALV-J mono-infections, as well as ALV-A + J, ALV-B + J, and ALV-A + B + J coinfections, via intraperitoneal injection, and the chicks were then grown in isolators until they were 15 weeks old. The parameters, including the suppression of body weight gain, immune organ weight, viremia, histopathological changes and tumor incidence, were observed and compared with those of the uninfected control birds. The results demonstrated that coinfection with ALVs could induce more serious suppression of body weight gain (P < 0.05), damage to immune organs (P < 0.05) and higher tumor incidences than monoinfection, with triple infection producing the highest pathogenicity. The emergence of visible tumors and viremia occurred faster in the coinfected birds than in the monoinfected birds. These findings demonstrated that ALV coinfection resulted in considerably severe pathogenic and immunosuppressive consequences.

Molecular characteristics and pathogenicity of a Tibet-origin mutant avian leukosis virus subgroup J isolated from Tibetan chickens in China

Tibetan chicken is found in China Tibet (average altitude; ˃4500 m). However, little is known about avian leukosis virus subgroup J (ALV-J) found in Tibetan chickens. ALV-J is a typical alpharetrovirus that causes immunosuppression and myelocytomatosis and thus seriously affects the development of the poultry industry. In this study, Tibet-origin mutant ALV-J was isolated from Tibetan chickens and named RKZ-1-RKZ-5. A Myelocytomatosis outbreak occurred in a commercial Tibetan chicken farm in Shigatse of Rikaze, Tibet, China, in March 2022. About 20% of Tibetan chickens in the farm showed severe immunosuppression, and mortality increased to 5.6%. Histopathological examination showed typical myelocytomas in various tissues. Virus isolation and phylogenetic analysis demonstrated that ALV-J caused the disease. Gene-wide phylogenetic analysis showed the RKZ isolates were the original strains of the previously reported Tibetan isolates (TBC-J4 and TBC-J6) (identity; 94.5% to 94.9%). Furthermore, significant nucleotide mutations and deletions occurred in the hr1 and hr2 hypervariable regions of gp85 gene, 3'UTR, Y Box, and TATA Box of 3'LTR. Pathogenicity experiments demonstrated that the viral load, viremia, and viral shedding level were significantly higher in RKZ-1-infected chickens than in NX0101-infected chickens. Notably, RKZ-1 caused more severe cardiopulmonary damage in SPF chickens. These findings prove the origin of Tibet ALV-J and provide insights into the molecular characteristics and pathogenic ability of ALV-J in the plateau area. Therefore, this study may provide a basis for ALV-J prevention and eradication in Tibet.

Chicken CH25H inhibits ALV-J replication by promoting cellular autophagy

Autophagy plays an important role in host antiviral defense. The avian leukosis virus subgroup J (ALV-J) has been shown to inhibit autophagy while promoting viral replication. The underlying autophagic mechanisms, however, are unknown. Cholesterol 25-hydroxylase (CH25H) is a conserved interferon-stimulated gene, which converts cholesterol to a soluble antiviral factor, 25-hydroxycholesterol (25HC). In this study, we further investigated the autophagic mechanism of CH25H resistance to ALV-J in chicken embryonic fibroblast cell lines (DF1). Our results found that overexpression of CH25H and treatment with 25HC promoted the autophagic markers microtubule-associated protein 1 light chain 3 II (LC3II) and autophagy-related gene 5(ATG5), while decreased autophagy substrate p62/SQSTM1 (p62) expression in ALV-J infection DF-1 cells. Induction of cellular autophagy also reduces the levels of ALV-J gp85 and p27. ALV-J infection, on the other hand, suppresses autophagic marker protein LC3II expression. These findings suggest that CH25H-induced autophagy is a host defense mechanism that aids in ALV-J replication inhibition. In particular, CH25H interacts with CHMP4B and inhibits ALV-J infection in DF-1 cells by promoting autophagy, revealing a novel mechanism by which CH25H inhibits ALV-J infection. Although the underlying mechanisms are not completely understood, CH25H and 25HC are the first to show inhibiting ALV-J infection via autophagy.

TRIM25 participates in the fibrous tissue hyperplasia induced by ALV-J infection in chickens by targeting 14-3-3σ protein

ALV-J-SD1005 strain was subcutaneously inoculated into the necks of 1-day-old HY-Line Brown chickens and caused severe growth retardation, viremia and subcutaneous fibrosarcomas in the necks of all infected chickens from 14 days post inoculation (DPI) to 21 DPI, and also significantly increased the expressions of TRIM25, P53, etc., but significantly decreased the expressions of 14-3-3σ, etc. Overexpression of chicken TRIM25 (chTRIM25) significantly promoted cell proliferation and improved the expressions of P53, CDC2, and CDK2 tumor factors; and significantly inhibited the expression of 14-3-3σ in ALV-J-SD1005-infected DF1 cells; but knockdown of chTRIM25 caused the opposite effects. The results of co-immunoprecipitation (Co-IP) and confocal microscopy confirmed that chTRIM25 can recognize and bind 14-3-3σ protein in ALV-J-SD1005-infected cells, and they were co-located in the cytoplasm. It can be concluded that chTRIM25 participates in the fibrous tissue hyperplasia induced by ALV-J-SD1005 infections in chickens by binding 14-3-3σ protein and regulating the expressions of 14-3-3σ, P53, CDC2, and CDK2.

Isolation, identification and pathogenicity of a ALV-K strain from Chinese indigenous chicken breed

Subgroup K avian leukosis virus (ALV-K) is a new subgroup of avian leukosis virus (ALV) first identified in Chinese indigenous chickens in recent years. In this study, an ALV-K strain was isolated from Luhua chicken in Shandong province, China, and designated SD20LH01. The full-length genomic sequence of SD20LH01 was 7491 bp, which had the highest homology with ALV-K reference strains GDFX0601, GDFX0602 and GDFX0603. The nucleotide homology of env gene of SD20LH01 with reference strains of subgroup A, B, C, D, E, and J was ranged from 57.1 to 93.2%, while 94.1 to 99.4% with other ALV-K reference strains. The nucleotide difference of SD20LH01 mainly clustered with gp85 gene and U3 sequence when compared with the reference strain of ALV-K. In order to investigate the pathogenicity of SD20LH01, SPF chicken embryos were infected by yolk sac inoculation, and 1-day-old chickens were infected by intraperitoneal inoculation of SD20LH01. The results showed that yolk sac inoculation of SD20LH01 could induce persistent viremia, growth retardation and reduce the immune response to NDV and AIV-H9 vaccines. However, intraperitoneal inoculation in 1-day-old chickens could only induce a low level of viremia. In addition, no tumors were found in infected chickens during the animal experiments. This study enriched the genomic sequence data of ALV-K isolated in Chinese indigenous chickens, and laid a foundation for further study on the pathogenesis and prevention of ALV-K.

Avian Leucosis Virus-Host Interaction: The Involvement of Host Factors in Viral Replication

Avian leukosis virus (ALV) causes various diseases associated with tumor formation and decreased fertility. Moreover, ALV induces severe immunosuppression, increasing susceptibility to other microbial infections and the risk of failure in subsequent vaccination against other diseases. There is growing evidence showing the interaction between ALV and the host. In this review, we will survey the present knowledge of the involvement of host factors in the important molecular events during ALV infection and discuss the futuristic perspectives from this angle.

Preparation of a novel monoclonal antibody against Avian leukosis virus subgroup J Gp85 protein and identification of its epitope

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that has caused huge economic losses in the poultry industry due to its great pathogenicity and transmission ability. However, the continuous emergence of new strains would bring challenges to diagnosis and control of ALV-J. .This study focuses on preparing the monoclonal antibody (MAb) against ALV-J Gp85 and identifying its epitope. The truncated ALV-J gp85 gene fragment was amplified and then cloned into expression vectors. Purified GST-Gp85 was used to immune mice and His-Gp85 was used to screen MAb. Finally, a hybridoma cell line named J16 that produced specific MAb against the ALV-J. Immunofluorescence assay showed that MAb J16 specifically recognized ALV-J rather than ALV-A or ALV-K infected DF-1 cells. To identify the epitope recognized by MAb J16, fourteen partially overlapping ALV-J Gp85 fragments were prepared and tested by Western blot. The results indicated that peptide 150-LIRPYVNQ-157 was the minimal epitope of ALV-J Gp85 recognized by MAb J16. Alignment analysis of Gp85 from different ALV subgroups showed that the epitope keep high conservation among 36 ALV-J strains, but significant different from that of ALV subgroup A, B, C, D, E and K. Overall, we prepared a MAb specific against ALV-J and identified peptide 150-LIRPYVNQ-157 as a novel specific epitope of ALV-J Gp85, which may assist in laying the foundation for specific ALV-J detection methods.

Research Note: A novel recombinant subgroup E isolate of the avian leukosis virus with a subgroup B-like Gp85 region in China

The avian leukosis virus (ALV) strain DL00766 was isolated from a farm in China. The phylogenetic analysis showed that env had the highest homology with the E subgroup reference strain, ranging from 94.5% to 94.9%, whereas gp85 had the highest homology with the B and E subgroups, which were 89.0% to 91.3% and 91.3% to 91.8%. In addition, point mutation analysis of gp85 showed that a 400 bp long fragment in gp85 of DL00766 had the highest homology with subgroup B, ranging from 90.1% to 97.5%, and only 82.7% to 83.1% with E subgroup. These results indicate, DL00766 may be an AVL subgroup E isolate with a subgroup B-like gp85 region. This is also the first finding that the E subgroup is used as a recombinant subject, and the subgroup B provides a recombinant virus of an exogenous gene.

ALV-J-contaminated commercial live vaccines induced pathogenicity in Three-Yellow chickens: one of the transmission routes of ALV-J to commercial chickens

One avian leukosis virus of subgroup J (ALV-J) strain GX14YYA1 was isolated from a commercial bivalent Newcastle disease (ND)–infectious bronchitis (IB) vaccine in our previous study. To evaluate the pathogenicity of the ALV-J-contaminated vaccine on commercial chickens, day-old Three-Yellow chicks in group I were vaccinated with ALV-J-contaminated bivalent ND-IB live vaccine by intranasal and eye drop at 1-day-old for the primary vaccination and at 7-day-old for the secondary vaccination. Groups II and III were kept as the normal vaccination group with the noncontaminated ND-IB vaccine and blank control groups, respectively. The birds of different groups were maintained separately in isolators for 175 d. The first viremia was detected at 4 wk of age and 20% (2/10) of the birds maintained viremia during 11 to 25 wk of age. At the same time, the birds in group I experienced a significant suppression of body weight gain when compared with those of groups II and III (P < 0.05). In addition, the birds in group I showed obvious ALV-J hemangioma-type anatomical lesions in the liver and tumors were observed in the abdominal cavity. The results demonstrated that the ALV-J contaminated commercial live vaccines can induce pathogenicity in commercial Three-Yellow chickens and indicate that ALV-J-contaminated commercial live vaccines could be one of the transmission routes of ALV-J to commercial chickens.

Selection for avian leukosis virus integration sites determines the clonal progression of B-cell lymphomas

Avian leukosis virus (ALV) is a simple retrovirus that causes a wide range of tumors in chickens, the most common of which are B-cell lymphomas. The viral genome integrates into the host genome and uses its strong promoter and enhancer sequences to alter the expression of nearby genes, frequently inducing tumors. In this study, we compare the preferences for ALV integration sites in cultured cells and in tumors, by analysis of over 87,000 unique integration sites. In tissue culture we observed integration was relatively random with slight preferences for genes, transcription start sites and CpG islands. We also observed a preference for integrations in or near expressed and spliced genes. The integration pattern in cultured cells changed over the course of selection for oncogenic characteristics in tumors. In comparison to tissue culture, ALV integrations are more highly selected for proximity to transcription start sites in tumors. There is also a significant selection of ALV integrations away from CpG islands in the highly clonally expanded cells in tumors. Additionally, we utilized a high throughput method to quantify the magnitude of clonality in different stages of tumorigenesis. An ALV-induced tumor carries between 700 and 3000 unique integrations, with an average of 2.3 to 4 copies of proviral DNA per infected cell. We observed increasing tumor clonality during progression of B-cell lymphomas and identified gene players (especially TERT and MYB) and biological processes involved in tumor progression.

The Avian Leukosis Virus (ALV) is a simple retrovirus that causes cancer in chickens. The virus integrates its genome into the host genome and induces changes in expression of nearby genes. Here, we determine the sites of viral integrations and their role in the progression of tumors. We report pathways and novel gene players that might cooperate and play a role in the progression of B-cell lymphomas. Our study provides new insights into the changes during lymphoma initiation, progression, and metastasis, as a result of selection for specific ALV integration sites.

Transduction of rhesus macaque hematopoietic stem and progenitor cells with avian sarcoma and leukosis virus vectors

Genome-wide integration site analyses showed that Moloney murine leukemia virus (MoMLV)- and lentivirus-derived vectors integrate preferentially into the coding regions of genes, posing a risk of insertional mutagenesis. Avian sarcoma and leukosis viruses (ASLVs) were previously reported to have a weak preference for gene-coding regions in a cell line study as compared with human immunodeficiency virus and MoMLV; however, thus far these vectors have not been studied for their potential efficacy in transduction of hematopoietic progenitor and stem cells. In this study we investigated for the first time the ability of ASLV-derived RCAS (replication-competent ALV LTR [avian leukosis virus long terminal repeat] with a splice acceptor) vectors to transduce rhesus macaque hematopoietic progenitors and long-term repopulating cells, in an autologous transplantation model. RCAS vectors can efficiently and stably transduce rhesus macaque CD34+ hematopoietic progenitor cells with an efficiency of transduction of up to 34% ex vivo. In two animals transplanted with RCAS vector-transduced autologous CD34+ cells, highly polyclonal hematopoietic reconstitution with sustained gene-marking levels in myeloid and lymphoid lineages was observed up to 18 months post-transplantation. These findings are encouraging and suggest that this vector system should be explored and further optimized for gene therapy applications targeting hematopoietic stem and progenitor cells.

Development and validation of a PCR-RFLP assay to evaluate TVB haplotypes coding receptors for subgroup B and subgroup E avian leukosis viruses in White Leghorns

The cellular receptor of subgroup B avian leukosis virus (ALVB) is encoded by a gene at the tumour virus B (TVB) locus. TVB alleles encode specific receptors permitting infection by exogenous ALVB or avian leukosis virus subgroup D (ALVD) as well as endogenous avian leukosis virus subgroup E (ALVE), and thus susceptibility is dominant to resistance. Two single nucleotide polymorphisms at the TVB locus have been reported distinguishing three TVB alleles (TVB*S1, TVB*S3 and TVB*R). We have developed a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay using the two single nucleotide polymorphisms to define three observed allelic haplotypes and to identify the six possible TVB genotypes consisting of the three haplotypes in defined laboratory strains of chickens. One additional potential allelic haplotype and four genotypes were also briefly discussed. Chickens from parents heterozygous for different TVB alleles were challenged with Rous sarcoma viruses of subgroup ALVB and ALVE to induce wing-web tumours. Tumour incidences were evaluated between chickens of the genotypes determined with this newly developed PCR-RFLP assay. Importantly, chickens typed with this assay as TVB*S3/*S3 were resistant to infection by ALVE only, and those TVB*R/*R were resistant to both ALVE and ALVB. Furthermore, a vast majority of chickens with the susceptible TVB*S1/- genotypes developed a tumour. This PCR-RFLP assay enables a relatively rapid assessment of all six anticipated TVB genotypes in experimental strains of chickens undergoing segregation for TVB*S1, TVB*S3, and TVB*R alleles. This non-infectious assay should be further evaluated for the capacity to select and breed commercial chickens for genetic resistance to infections by ALVB, ALVD and ALVE.

Dissection of the c-Kit signaling pathway in mouse primordial germ cells by retroviral-mediated gene transfer

Establishment of the mammalian germ line is a prerequisite for fertility of the adult animal but we know surprisingly little about the molecular mechanisms regulating germ-line development in mammals. Signaling from the c-Kit receptor tyrosine kinase is essential for primordial germ cell (PGC) growth both in vivo and in vitro. Many downstream effectors of the c-Kit signaling pathway have been identified in other cell types but how these molecules control PGC survival and proliferation are unknown. Determination of the c-Kit effectors acting in PGCs has been hampered by the lack of effective methods to easily manipulate gene expression in these cells. We overcame this problem by testing the efficacy of retroviral-mediated gene transfer for manipulating gene expression in mammalian germ cells. We found that PGCs can be successfully infected with a variety of types of retroviruses. We used this method to demonstrate an important role for the AKT kinase in regulating PGC growth. Such technology for manipulating gene expression in PGCs will allow many of the molecular mechanisms regulating germ cell growth, behavior, and differentiation to be comprehensively analyzed.

Blocked B cell differentiation and emigration support the early growth of Myc-induced lymphomas

Avian leukosis virus induces lymphoma in chickens after proviral integration within the c-Myc gene, and subsequent expansion of Myc-overexpressing lymphocytes within transformed bursal follicles. The clonal expansion of these follicles allowed us to examine how Myc influences cell differentiation, growth, and apoptosis in lymphoid progenitors soon after the onset of Myc overexpression. Immunohistochemical analysis of developmental markers established that Myc overexpression consistently blocks lymphocyte differentiation at a late embryonic stage. Myc-transformed follicles also grow much more rapidly than normal follicles. This rapid growth is not mediated by suppression of apoptosis, as normal and Myc-transformed follicles showed similar rates of cell death by TUNEL immunohistochemical analysis of cells undergoing DNA degradation. Measurements of DNA synthesis and mitotic index showed modest effects of Myc to increase lymphocyte proliferation, as normal lymphocytes already divide rapidly. The major mechanism mediating rapid growth of transformed follicles instead involved failure of myc-overexpressing lymphocytes to emigrate from transformed follicles, while normal lymphocytes actively emigrate after hatching, as measured by BrdU pulse-chase labeling and immunohistochemical measurements. This failure to undergo the normal program of differentiation and subsequent bursal retention of lymphocytes accounts for most of the growth of transformed follicles, while Myc-induced proliferation makes a smaller contribution.

In vivo events of retroviral long terminal repeat integration into Marek's disease virus in commercial poultry: detection of chimeric molecules as a marker

The present study demonstrated, for the first time, that not only in vitro, but also in vivo, coinfections with Marek's disease virus (MDV) and each of the three avian retroviruses (reticuloendotheliosis virus [REV], avian lymphoid leukosis virus [ALV], and ALV-J) lead to retroviral long terminal repeat (LTR) integration into MDV. A total of 306 chicken and 59 turkey commercial flocks, submitted for differential avian oncogenic virus diagnosis, served to evaluate the flock mixed virus infection rate, the rate of birds with a multiple virus infection, and the issue of retroviral LTR integration into MDV in vivo. About a quarter of the tumor-bearing commercial flocks carried a mixed MDV and retrovirus infection. A total of 2926 DNA samples were analyzed, including 2428 chicken and 498 turkey DNA samples. Of these, 991 DNAs originated from flocks with a multiple virus infection. In 103 DNA preparations from that group (103/991, 10.4%), including 38 and 56 from chicken blood and tumor tissues, respectively, and nine samples from turkey blood, multiple virus sequences were detected by polymerase chain reaction (PCR). Fifty-six of the 103 samples were further analyzed by the previously developed hot spot-combined (HS-cPCR assay, of which 48% (27/56) contained chimeric MDV and retroviral LTR molecules. When extrapolated to the total samples derived from the flocks with multiple virus infection, that rate implies that about 5% of the DNA samples would carry MDV-retrovirus integration events. Several birds held a variety of chimeric molecules, indicating that several recombination events occurred simultaneously. The validation of the MDV and retroviral LTR chimeric constitution of these molecules was derived by the MDV and retroviral heterologous primers used for their creation by the HS-cPCR assay, Southern blotting and their detection by retroviral LTR probes, and LTR amplification from the gel-purified chimeric molecules. From several molecules, the LTR was sequenced, and a 161-bp retroviral LTR sequence was demonstrated. Our biochemical data imply that a recent integration occurred in the birds. The viability of recombinant viruses represented by the chimeric molecules will be further approached.

Retroviral vectors preloaded with a viral receptor-ligand bridge protein are targeted to specific cell types

Successful targeting methods represent a major hurdle to the use of retroviral vectors in cell-specific gene-delivery applications. We recently described an approach for retroviral targeting with a retroviral receptor-ligand bridge protein that was bound to the cognate cell-surface ligand receptors before viral challenge. We now report a significant improvement made to this viral targeting method by using a related bridge protein, designated TVB-EGF, comprised of the extracellular domain of the TVB receptor for subgroup B avian leukosis virus fused to epidermal growth factor (EGF). The most important activity of TVB-EGF was that it allowed specific viral entry when preloaded onto virions. Furthermore, virions preloaded with TVB-EGF were thermostable and could be produced directly from virus- packaging cells. These data suggest an approach for targeting retroviral vectors to specific cell types by using virions preloaded with a retroviral receptor-ligand bridge protein and indicate that these types of bridge proteins may be useful reagents for studying the normal mechanism of retroviral entry.

An avian sarcoma/leukosis virus-based gene trap vector for mammalian cells

RCASBP-M2C is a retroviral vector derived from an avian sarcoma/leukosis virus which has been modified so that it uses the envelope gene from an amphotropic murine leukemia virus (E. V. Barsov and S. H. Hughes, J. Virol. 70:3922-3929, 1996). The vector replicates efficiently in avian cells and infects, but does not replicate in, mammalian cells. This makes the vector useful for gene delivery, mutagenesis, and other applications in mammalian systems. Here we describe the development of a derivative of RCASBP-M2C, pGT-GFP, that can be used in gene trap experiments in mammalian cells. The gene trap vector pGT-GFP contains a green fluorescent protein (GFP) reporter gene. Appropriate insertion of the vector into genes causes GFP expression; this facilitates the rapid enrichment and cloning of the trapped cells and provides an opportunity to select subpopulations of trapped cells based on the subcellular localization of GFP. With this vector, we have generated about 90 gene-trapped lines using D17 and NIH 3T3 cells. Five trapped NIH 3T3 lines were selected based on the distribution of GFP in cells. The cellular genes disrupted by viral integration have been identified in four of these lines by using a 5' rapid amplification of cDNA ends protocol.

Electron microscopic study of the ATPase activity of the BAI strain A (myeloblastosis) avian tumor virus

Thymus glands of chicks with leukemia induced by BAI strain A (myeloblastosis) virus were fixed in cold 4 per cent formaldehyde-sucrose. Frozen sections were incubated in the ATPase medium of Wachstein and Meisel and studied by light microscopy and electron microscopy. The ATPase activity of the virus is localized to the outermost membrane of the virus. The membrane of the blast-like cells of the thymus cortex from which the virus emerges, by budding, also possesses such activity. It appears likely that the outermost membrane of the virus is derived from the plasma membrane of these cells.

Rearrangement of c-myc gene in rapidly induced avian lymphoid leukosis tumors

Southern blot hybridization of DNA samples from 9 primary tumors of avian lymphoid leukosis (LL) rapidly induced by ALV infection 27-74 days post inoculation was carried out to search for rearrangement of the c-myc gene with human c-myc gene exon III as a probe. Rearrangement of the c-myc gene was detected by appearance of new EcoRI fragments in 7 out of 9 tumors examined. The size of the fragments ranged from 3.1 to 4.0 kilobases (kb). In addition to these fragments, two fragments (9.0 kb and 13 kb) were observed in one tumor, and a faint fragment (3.5 kb) was observed in another tumor. Rearrangement of the c-myc gene was not detected in the remaining two tumors kept in unsuitable condition. These results suggest that rearrangement of c-myc gene was induced even in rapidly induced LL as well as that induced after long incubation period. This is the first report of involvement of c-myc gene in rapidly induced B-cell lymphoma (LL).

Lineage commitment of transformed haematopoietic progenitors is determined by the level of PKC activity

Our previous work showed that haematopoietic precursors transformed by the E26 avian leukemia virus undergo multilineage differentiation in response to the phorbol ester phorbol 12-myristate 13-acetate (PMA). Treatment of the cells with high concentrations of PMA (100 nM) favours myelomonocytic differentiation, while lower concentrations (20 nM) induce predominantly eosinophil differentiation. Here we have investigated the role of protein kinase C (PKC) in this process and found that 100 nM, but not 20 nM, PMA dramatically down-regulates total cellular PKC activity, indicating that high PMA concentrations result in less efficient signalling than lower PMA concentrations. Consistent with these findings is the observation that very low PMA concentrations (1 nM), which presumably only moderately activate PKC, induce myeloid differentiation. This suggests the existence of two PKC thresholds which play a role in lineage commitment. To test the model, alpha- and epsilon-PKC isoforms were expressed in E26-transformed progenitors. These cells exhibited myelomonocytic differentiation even in the absence of PMA, while treatment with concentrations of PMA as high as 100 nM led to the differentiation of predominantly eosinophils and failed to downregulate the exogenous PKC. Our results suggest that different levels of PKC activity result in three different phenotypes: (i) no PKC activity maintains the progenitor phenotype; (ii) low PKC activity favours myelomonocytic differentiation; (iii) high PKC favours eosinophil differentiation.

Safety of biopharmaceuticals: a current perspective

The impetus for this conference comes in large measure from the continuing development of the ICH Viral Safety document concerned with testing and evaluation of the viral safety of biotechnology products derived from characterized cell lines of human or animal origin [1]. My opening remarks for this conference were, I think, suggested by the organizers in the belief that George Santayana's quote, "Those who cannot remember the past are condemned to repeat it" has validity for this effort. In this brief review I have tried to recall some past unfortunate episodes and outline the lessons that they might have for us. I have also attempted to outline a number of issues which I believe are critical to the success of efforts to guarantee, as much as humanly possible, the safety that we seek balanced against our ability to develop and use important new products.

Effect of serotype 2 and 3 Marek's disease vaccines on the development of avian leukosis virus-induced pre-neoplastic bursal follicles

The effect of serotype 2 and 3 Marek's disease virus (MDV) vaccines on the development of pre-neoplastic bursal lesions induced by two strains of subgroup A avian leukosis virus (ALV) was studied. Chickens of line 15I5 x 7(1) susceptible to ALV-induced lymphoma were inoculated at hatch with Rous-associated virus-1 (RAV-1) or strain RPL-40 of subgroup A ALV. All chickens, except for negative controls, were also inoculated at hatch with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpesvirus (HVT), a serotype 3 MDV. At 11 and 14 weeks of age, serial sections of bursal tissues from chickens in various treatment groups were stained with methyl green pyronin and examined for ALV-induced pre-neoplastic bursal lesions, also known as hyperplastic follicles. At 6 days and at 11 and 14 weeks of age, bursal tissues from groups of chickens inoculated with serotype 2 MDV and ALV at hatch were also examined for the presence of MDV genome by in situ hybridization. The number of ALV-induced hyperplastic follicles was significantly higher in chickens inoculated with serotype 2 MDV than in unvaccinated chickens or in chickens vaccinated with HVT. In contrast, the lowest number of hyperplastic follicles was noted in chickens vaccinated with HVT, regardless of strain of ALV used. These results suggest that enhancement of lymphoid leukosis may result from an increase in the number of ALV-induced hyperplastic follicles caused by the MDV and also that the enhancing effect of MDV on ALV-induced lymphomagenesis may occur at the stage of formation of hyperplastic follicles in the bursa.

Retrovirus-induced B cell neoplasia in the bursa of Fabricius

The chicken bursa provides a revealing experimental model system which has helped unravel some of the mysteries surrounding induction of neoplasia by retroviruses lacking dominant viral oncogenes. Analysis of this system continues to provide opportunities for further insight into mechanisms underlying some of the essential characteristics of neoplastic change including maturation arrest, prolonged cell survival, and genetic instability. The deregulation of c-myc expression induced by nearby proviral integration appears to initiate preneoplastic change in a specific window of development, i.e., the bursal stem cell. The generation of large numbers of these preneoplastic stem cells, and the ability for further amplification by transplantation technology, may provide an opportunity to address questions such as how and why myc oncogenes produce preneoplastic maturation arrest or why stem cells are selective targets for these effects. Among the unexplained consequences of this preneoplastic state appears to be genetic instability which leads, inevitably, to formation of invasive bursal neoplasms. It is at least conceivable that the observed myc-induced enhancement of the remarkable capacity for apoptotic cell death present in bursal cells plays a role in this instability. DNA strand breakage is a very early feature of bursal cell apoptosis. If such breakage could occur in sublethal form it might provide a mechanism for increased frequency of genetic change (deletions, rearrangement, and recombination). Among the changes that seem required for successful tumor cell growth outside of follicles is the suppression of cell death induced by loss of cell-cell contact which is characteristic of normal and preneoplastic bursal cells. Several genes in the bcl-2 family are potentially important in the modulation of cell death events central to the evolution of these neoplasms. Their role, if any, remains to be established.

Subcellular localization and partial purification of the 25-hydroxyvitamin D3 1-hydroxylation reaction in the chick myelomonocytic cell line HD-11

Hypercalcemia in human granuloma-forming diseases like sarcoidosis results from the endogenous overproduction of 1,25-dihydroxyvitamin D [1,25-(OH)2D] by disease-activated tissue macrophages. The recent identification of an immortalized chick myelomonocytic cell line, HD-11, that constitutively expresses a 25-hydroxyvitamin D (25-OHD) 1-hydroxylation reaction has alleviated dependence on studying primary macrophage cultures with no replicative potential in vitro. In these experiments we established conditions for the maximal expression of the HD-11 cell 25-OHD3-1-hydroxylation reaction and localized this activity to the mitochondrial fraction. On a per cell basis, the activity of HD-11 cell 25-OHD3 1-hydroxylation reaction was comparable to that in primary cultures of chick renal tubular epithelial cells, which express the authentic renal 25-OHD3 1-hydroxylase. Maximal product yield was achieved after incubation of HD-11 cells with 200 nM 25-OHD3 for 3 h. Although adherent monolayers possessed 3- to 4-fold more capacity for hormone production than cells in suspension, suspended cells exhibited easily detectable 25-OHD3 catalytic activity (0.58 +/- 0.08 pmol per 10(6) cells per h; +/- SEM), 50% of which remained solubilized in a sonicate of suspended cells cleared of nuclei and plasma membrane. Subcellular localization disclosed 91% of the residual activity to be concentrated in the mitochondrial subfraction. A detergent-solubilized extract of this mitochondrial subfraction contained 1.9 +/- 0.3 pmol 1,25-(OH)2D3 synthetic capacity per mg protein. The catalytic activity (1-hydroxylase activity) was concentrated 20.2-fold after chromatography on octyl-amino agarose and was associated with 0.054 nmol cytochrome P450 per mg protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Chicken "erythroid" cells transformed by the Gag-Myb-Ets-encoding E26 leukemia virus are multipotent

The E26 avian leukemia virus encodes a transcriptional activator-type oncoprotein consisting of Gag, Myb, and Ets domains, and transforms early erythroid cells as well as myeloblasts. Surprisingly, we have found that "early erythroid" transformants obtained in culture are multipotent, since they can be induced to differentiate into myeloblasts and eosinophils after superinfection with retroviruses containing kinase-type or ras oncogenes. In addition, TPA is an efficient inducer that generates predominantly eosinophils at low concentrations and myeloblasts at high concentrations. The determination process involves the complete extinction of erythroid/thrombocytic markers and the subsequent activation of myelomonocytic/eosinophilic properties, including the acquisition of specific growth factor requirements. "Erythroleukemic" cells from virus-infected animals were likewise found to be multipotent, making this a unique system to study the genesis of stem cell leukemias and the molecular basis of lineage commitment during hematopoiesis.

Expression of immunoglobulin genes in the avian embryo bone marrow revealed by retroviral transformation

Analysis of the early stages of avian B lymphocyte differentiation has been hampered by the low frequency of extra-bursal B lineage cells in sites of hematopoiesis. Consequently, little is known about B lineage precursors prior to their migration into the bursa of Fabricius. Colonization of the bursa typically occurs between about days 8 and 14 of embryonic (e) development, although cells which can colonize the bursa, functionally defined as pre-bursal stem cells, can be demonstrated in embryo bone marrow up until about the time of hatch. As a novel approach to analyzing early stages of avian B lymphocyte development, we show here that transformed B lineage cells can be derived from chick embryo bone marrow after infection in vitro with the replication-defective retrovirus REV-T produced in the context of the non-cytopathic CSV helper virus. Thus, exposure of day 14e-15e chick embryo bone marrow cells to REV-T (CSV) results in the generation of transformed, polyclonal lines of cells. From these lines, cells expressing cell surface immunoglobulin were readily isolated by flow cytometric cell sorting and single cell cloning. Analysis of the phenotype of REV-T(CSV)-transformed clones with a panel of monoclonal antibody reagents demonstrated that transformation by v-rel likely leads to marked changes in cell surface antigen expression. Nonetheless, clones expressing cell surface immunoglobulin expressed apparently normal mRNA for immunoglobulin mu and light chain and contained apparently normal immunoglobulin heavy and light chain gene rearrangements. Furthermore, no evidence for chromosomal deletions or aberrations of the Ig loci was detected among either sIg+ or sIg- REV-T(CSV)-transformed clones.

MC29-immortalized clonal avian heart cell lines can partially differentiate in vitro

We established quail clonal heart muscle cell lines from cardiac rhabdomyosarcomas developed in embryos injected in ovo with the MC29 virus containing the v-myc oncogene. These clones were characterized by means of antibodies detecting markers of striated muscle cells. Two clones were selected for further characterization on the basis of a distribution of myogenic markers similar to that in normal early embryonic cardiac muscle cells. However, these muscle markers progressively disappeared with time in culture. Cardiomyocytic differentiation could be reinduced in culture, by associating the avain cardiac cells with 3T3 cells in a defined synthetic medium. Muscle markers were then reexpressed in all cardiac cells as soon as Day 1 after coculture. Multiplication of cardiac cells continued at the same time. This is characteristic of cardiac clones since MC29-infected quail myoblasts and MC29-infected quail fibroblasts exhibited a split response to 3T3 association, i.e., decreased growth and enhanced differentiation. The cardiac clones were maintained in vitro for more than 60 generations (6 months) without morphological changes. To our knowledge, this is the first description of clonal embryonic avian heart cell lines.

Interactions between endogenous virus loci ev6 and ev21. 2. Congenital transmission of EV21 viral product to female progency from slow-feathering dams

The influence of the endogenous virus ev6 on congenital transmission of EV21, the infectious viral product encoded by locus ev21, and the immune response to exogenous avian leukosis virus (ALV) infection was studied in rapid-feathering (RF) female progeny from four classes of slow-feathering (SF) (ev21+ and RF (ev21-) dams with and without ev6. Apart from transmitting infectious EV21 and ev6 to progency, dam ev genotype did not influence the immune response or shedding of RPL-40. The endogenous virus envelope glycoprotein encoded by ev6, however, completely restricted shedding and congenital transmission of infectious endogenous virus EV21, from SF dams. After 19 wk of exposure to ALV strain RPL-40 infected cage mates, only 11% of the congenitally infected female progeny mounted neutralizing antibodies against RPL-40, whereas 73% of their noncongenitally infected sisters seroconverted. More ev6+ female progeny, however, were shedders of RPL-40 and developed tumors than ev6- sisters. Among progeny from the four classes of dams, EV21 congenitally infected hens had the highest incidence (31%) of RPL-40-induced tumors.

Infrequent involvement of c-fos in avian leukosis virus-induced nephroblastoma

To determine whether c-fos is involved in avian leukosis virus-induced nephroblastoma, 28 tumors from chickens were analyzed for novel fos fragments. DNA from 1 of 16 clonal outgrowths (in chicken 6561) contained novel fos-related EcoRI and KpnI fragments which hybridized to both v-fos and viral probes. Oncogenicity tests using filtered 6561 tumor cell homogenates did not reveal a tumor-inducing transduction of c-fos. We conclude that c-fos is only an occasional target for proviral insertions or new transductions in avian leukosis virus-induced nephroblastoma. The results also identify a polymorphism in c-fos in K28 chickens and demonstrate that unintegrated viral DNA is not a general characteristic of avian leukosis virus-induced nephroblastoma.

[Effect of a mixed viral infection on the development of neoplasms induced by oncogenic viruses]

Data are presented concerning the stimulating effect of vaccinia and herpes simplex type 2 viruses on the development of leukemia in BALB/C, C57BL/6, and AKR mice. Mixed infection with PAB-49 and Marek disease virus of brown leghorn chickens was shown to increase the frequency of lymphomas development.

Absence of missense mutations in activated c-myc genes in avian leukosis virus-induced B-cell lymphomas

We have determined the nucleotide sequences of two independent DNA clones which contained the activated c-myc genes from avian leukosis virus-induced B-cell lymphomas. Neither of these c-myc genes contained missense mutations. This strongly supports the notion that the c-myc proto-oncogene in avian leukosis virus-induced B-cell lymphomas can be oncogenically activated by altered expression of the gene without a change in the primary structure of the gene product.

Cytoplasmic poly(ADP-ribose) polymerase and poly(ADP-ribose) glycohydrolase in AEV-transformed chicken erythroblasts

Poly(ADP-ribose) polymerase and poly(ADP-ribose) glycohydrolase activities were both investigated in chicken erythroblasts transformed by Avian Erythroblastosis Virus. Respectively 21% and 58% of these activities were found to be present in the post-mitochondrial supernatant (PMS). Fractionation of the PMS on sucrose gradients and poly(A+) mRNA detection by hybridization to [3H] poly(U) show that cytoplasmic poly(ADP-ribose) polymerase is exclusively localized in free mRNP. The glycohydrolase activity sedimented mostly in the 6 S region but 1/3 of the activity was in the free mRNP zone. Seven poly(ADP-ribose) protein acceptors were identified in the PMS in the Mr 21,000-120,000 range. The Mr 120,000 protein corresponds to automodified poly(ADP-ribose) polymerase. A Mr 21,000 protein acceptor is abundant in PMS and a Mr 34,000 is exclusively associated with ribosomes and ribosomal subunits. The existence of both poly(ADP-ribose) polymerase and glycohydrolase activities in free mRNP argues in favour of a role of poly(ADP-ribosylation) in mRNP metabolism. A possible involvement of this post translational modification in the mechanisms of repression-derepression of mRNA is discussed.

The cause of Kaposi's sarcoma: an avian retroviral analog

Changes in the epidemiologic patterns of Kaposi's sarcoma prior to and during the epidemic of acquired immunodeficiency suggest that a virus transmitted similarly to the human immunodeficiency virus (HIV) may be responsible. We propose a natural avian model for Kaposi's sarcoma. Hemangiomatosis of fowls corresponds clinically and pathologically to the human disease, with characteristics including predilection for distal skin, multicentricity with organ involvement, bleeding and recurrence after excision. Pathologic stages are also similar and include initial dissection of collagen by benign endothelial cells, the formation of large blood-filled spaces, spindle cell growth, and progression to fibrosarcomalike tumors. Avian hemangiomatosis is induced by a retrovirus of the lymphoid leukosis group and has been associated with laboratory transmission of lymphomatosis. An etiopathologic parallel should be sought in man.