Cell-free transmission of Fv-4 resistance gene product controlling Friend leukemia virus-induced leukemogenesis in mice

Fv-4 is a mouse gene that dominantly confers resistance to infection by ecotropic murine leukemia virus (MuLV). The Fv-4' env antigen that binds to the cell surface of Fv-4'-bearing C3H cells was found in sera from normal Fv-4'-bearing C4W mice. The serum Fv-4' env antigen binds to ecotropic MuLV receptors, shown by specific binding to transfectant cells expressing ecotropic MuLV receptors but not to parental mink cells. To determine whether the binding of Fv-4' env antigen to the putative MuLV receptors would block FLV infection, C3H thymocytes or spleen cells that had been preincubated with C4W serum were mixed with FLV and the subsequent production of MuLV specific antigens was examined. C3H thymocytes or spleen cells treated with C4W serum became refractory to binding by FLV. These results provide evidence that the Fv-4' env antigen is released from C4W-derived cells in vivo and binds to cells expressing surface receptors for ecotropic MuLV, thereby protecting them from infection with FLV. The implication of these findings for gene therapy of retrovirus-induced disease such as acquired immune deficiency syndrome (AIDS) is discussed.

Models of HTLV-I-induced diseases. Infectious transmission of HTLV-I in inbred rats and HTVL-I env-pX transgenic rats

To examine the pathogenic roles of HTLV-I in HTLV-I-induced diseases, we developed two models; namely HTLV-I carrier rats and HTLV-I env-pX transgenic rats. Among life long HTLV-I carriers in seven rat strains, only WKAH rats with the RT1k haplotype developed chronic progressive myeloneuropathy, resembling HAM/TSP clinically and histologically in humans, designated as HAM rat disease and after long incubation periods. Apoptosis of myelin forming cells, oligodendrocytes and Schwann cells associated with HTLV-I infection appears to be the primary cause of HAM rat disease. Local activation of the pX gene and TNF alpha gene was evident in these rats. WKAH rats transgenic for HTLV-I env-pX gene were established and at age 5 weeks, swelling of the bilateral ankle joints began to develop and histological features of the affected joints resembled findings in cases of rheumatoid arthritis (RA): high-titers of rheumatoid factors were present in these rats. A series of vascular collagen diseases such as polyarteritis nodosa-like angiitis, polymyositis, myocarditis, and Sjögren's syndrome-like sialodenitis together with RA were present, even in one individual animal. These transgenic rats as well as HAM rats appear to be suitable animal models for elucidating pathogenic mechanisms implicated in HTLV-I-induced diseases and also various demyelinating vascular collagen diseases of unknown etiology.

Alveolar macrophages produce the Env protein of a human endogenous retrovirus, HERV-E 4-1, in a subgroup of interstitial lung diseases

We investigated whether intraalveolar inflammatory cells such as alveolar macrophages or lymphocytes produced the gene product of a type-C human endogenous retrovirus (HERV), HERV-E 4-1, which might initiate an immune response resulting in interstitial lung disease. We evaluated HERV-E 4-1 Env protein production by bronchoalveolar lavage fluid (BALF) cells and PBL in 109 patients with sarcoidosis, idiopathic pulmonary fibrosis (IPF), lung cancer, and rheumatoid lung disease as well as 26 normal control individuals. Production of HERV-E 4-1 Env protein by alveolar macrophages was observed using indirect immunofluorescence in 3 IPF patients and 3 sarcoidosis patients (6/135). No peripheral blood lymphocytes showed HERV-E 4-1 Env protein production. Antibodies to HERV-E 4-1 Env protein were detected in the BALF of all six patients by immunoblot analysis, while none of the normal control individuals showed HERV-E 4-1 Env protein antibody in the BALF. All examined BALF cells showed HERV-E 4-1 env mRNA transcript expression by reverse transcription-polymerase chain reaction. No significant influence of point mutation or DNA polymorphism on HERV-E 4-1 Env protein production was recognized. In conclusion, local production of HERV-E 4-1 Env protein and defective tolerance of HERV gene products with resultant antibody production may contribute to the pathogenesis of IPF or sarcoidosis in some patients.

Tissue and differentiation specific expression on the endogenous retrovirus ERV3 (HERV-R) in normal human tissues and during induced monocytic differentiation in the U-937 cell line

ERV3 (HERV-R) is a complete, single copy human endogenous retrovirus located on the long arm of chromosome 7. The open reading frame in its envelope gene has been conserved during evolution but the gag and pol genes contain in-frame termination codons. To find a suitable experimental model system for analysis of the functions of the ERV3 genome, an extensive screening study of different normal and neoplastic human tissues was performed. Most tissues express low levels of the ERV3 env mRNA although high expression levels are observed in placenta, sebaceous glands, adrenals, testis, bronchial, epithelium and the monocytic cell line U-937. In U-937 cells the ERV3 env expression varied in a manner related to the differentiation status of the cells; being highest in the terminally differentiated non proliferating cells. U-937 cells can be induced to differentiate from the monoblastic to the mature monocyte/macrophage stage upon stimulation by several substances such as phorbolesters (TPA), Vitamin D3, Retinoic Acid (RA) and combinations of some cytokines. We conclude that the ERV3 locus is expressed in a tissue and differentiation specific way and that the U-937 cell line is a suitable model system to further analyze the proposed functions of ERVs such as immunomodulation, cell fusion and protection against exogenous retroviral infections.

HTLV-I env-pX transgenic rats: prototype animal model for collagen vascular diseases

To evaluate the function of HTLV-I env-pX gene in vivo, we developed two lines of transgenic rats (env-pX rats) that expressed env-pX gene products, under control of own LTR promotor. In various tissues of the rats, env and pX mRNAs were constitutively expressed, irrespective of age. At age 5 weeks, swelling of the bilateral ankle joints histologically showing synovial lining hyperplasia, severe chronic inflammation, erosion of the joint cartilage, and bone destruction with pannus formation began to develop in these env-pX rats. These histologic features resemble those of rheumatoid arthritis (RA) in man. High titered rheumatoid factors and low anti-dsDNA antibodies and hyper-gamma globulinemia were detected. Necrotizing arteritis resembling polyarteritis nodosa, polymyositis, myocarditis and Sjögren syndrome-like sialoadenitis developed, together with RA-like arthritis even in one individual animal. Thymic atrophy with low body weight was also observed. The evidence indicates that env-pX rats appear to be suitable animal models for elucidating pathogenetic mechanisms involved in not only HTLV-I related diseases but also various collegen vascular and autoimmune diseases of unknown etiology in man.

Production of env-deficient rous sarcoma virus (RSV) early after infection

Production of defective virus particles during the early stage of Rous sarcoma virus (RSV) infection of chicken embryo fibroblasts (CEF) was examined. RSV harvested 2 days post infection (2pi) had 10 to 30 times lower specific infectivity (focus forming units/unit reverse transcriptase activity) than 5pi harvest. Virus particles produced on day 2 contained less env proteins than particles harvested on day 5. The amount of other viral proteins was equal in particles harvested on day 2 and day 5. Analysis of infected cells revealed that these cells synthesized less env proteins on day 2 than on day 5. RSV RNA in infected cells was spliced normally on day 2. Infection at a low multiplicity of infection (moi) prolonged the production of defective particles. When infection was initiated by a low moi (0.01), particles harvested on day 5 had the same characteristics as 2pi particles after infection with a high moi (1.0). We conclude that the low infectivity of early harvest is due to the reduced amount of env proteins in virus particles, which is a consequence of the reduced env protein synthesis.

A structured retroviral RNA element that mediates nucleocytoplasmic export of intron-containing RNA

A common feature of gene expression in all retroviruses is that unspliced, intron-containing RNA is exported to the cytoplasm despite the fact that cellular RNAs which contain introns are usually restricted to the nucleus. In complex retroviruses, the export of intron-containing RNA is mediated by specific viral regulatory proteins (e.g., human immunodeficiency virus type 1 [HIV-1] Rev) that bind to elements in the viral RNA. However, simpler retroviruses do not encode such regulatory proteins. Here we show that the genome of the simpler retrovirus Mason-Pfizer monkey virus (MPMV) contains an element that serves as an autonomous nuclear export signal for intron-containing RNA. This element is essential for MPMV replication; however, its function can be complemented by HIV-1 Rev and the Rev-responsive element. The element can also facilitate the export of cellular intron-containing RNA. These results suggest that the MPMV element mimics cellular RNA transport signals and mediates RNA export through interaction with endogenous cellular factors.

Systemic T cell-independent tumor immunity after transplantation of universal receptor-modified bone marrow into SCID mice

Gene modification of hematopoietic stem cells (HSC) with antigen-specific, chimeric, or "universal" immune receptors (URs) is a novel but untested form of targeted immunotherapy. A human immunodeficiency virus (HIV) envelope-specific UR consisting of the extracellular domain of human CD4 linked to the zeta chain of the T cell receptor (CD4 zeta) was introduced ex vivo into murine HSC by retroviral transduction. After transplantation into immunodeficient SCID mice, sustained high level expression of CD4 zeta was observed in circulating myeloid and natural killer cells. CD4 zeta-transplanted mice were protected from challenge with a lethal dose of a disseminated human leukemia expressing HIV envelope. These results demonstrate the ability of chimeric receptors bearing zeta-signaling domains to activate non-T cell effector populations in vivo and thereby mediate systemic immunity.

Production of infectious recombinant Moloney murine leukemia virus particles in BHK cells using Semliki Forest virus-derived RNA expression vectors

We describe a heterologous, Semliki Forest virus (SFV)-driven packaging system for the production of infectious recombinant Moloney murine leukemia virus particles. The gag-pol and env genes, as well as a recombinant retrovirus genome (LTR-psi (+)-neoR-LTR), were inserted into individual SFV1 expression plasmids. Replication-competent RNAs were transcribed in vitro and introduced into the cytoplasm of BHK-21 cells using electroporation. The expressed Moloney murine leukemia virus structural proteins produced extracellular virus-like particles. In these particles the gag precursor was processed into mature products, indicating that the particles contained an active protease. The protease of the gag-pol fusion protein was also shown to be active in a trans-complementation assay using a large excess of Pr65gag. Moreover, the particles possessed reverse transcriptase (RT) activity as measured in an in vitro assay. Cotransfection of BHK-21 cells by all three SFV1 constructs resulted in the production of transduction-competent particles at 4 x 10(6) colony-forming units (cfu)/ml during a 5-hr incubation period. Altogether, 2.9 x 10(7) transduction-competent particles were obtained from about 4 x 10(6) transfected cells. Thus, this system represents the first RNA-based packaging system for the production of infectious retroviral particles. The facts that no helper virus could be detected in the virus stocks and that particles carrying the amphotropic envelope could be produced with similar efficiency as those that carry the ecotropic envelope make the system very interesting for gene therapy.

Specific infection of CD4+ target cells by recombinant rabies virus pseudotypes carrying the HIV-1 envelope spike protein

A recombinant rabies virus (RV) mutant deficient for the surface spike glycoprotein (G) gene was used to study the incorporation of envelope proteins from HIV-1 expressed from transfected plasmids. A hybrid HIV-1 protein in which the cytoplasmic domain was replaced with that of RV G was incorporated into the virus envelope and rescued the infectivity of the RV mutant. The RV(HIV-1) pseudotype viruses could infect only CD4+ cells, and their infectivity was neutralized specifically by anti-HIV-1 sera. In contrast to the chimeric protein, wild-type HIV-1 envelope protein or mutants with truncated cytoplasmic domains failed to produce pseudotyped particles. This indicates the presence of a specific signal in the RV G cytoplasmic domain, allowing correct incorporation of a spike protein into the envelope of rhabdovirus particles. The possibility of directing the cell tropism of RV by replacement of the RV G with proteins of defined receptor specificity should prove useful for future development of targetable gene delivery vectors.

Inhibition of melanoma-associated antigen expression and ecotropic retrovirus production in B16BL6 melanoma cells transfected with major histocompatibility complex class I genes

We have previously reported that expression of the melanoma-associated antigen (MAA) recognized by MM2-9B6 monoclonal antibody in B16 melanoma was closely associated with C-type ecotropic retroviral particle production. Our present data show that this MAA is encoded by the env gene of an ecotropic retrovirus produced by B16 melanoma cells. Transfection of H-2Kb or H-2Kd genes into two individual clones isolated from B16BL6 melanoma, BL6-8 (H-2Kb-, H-2Db+) and BL6-2 (H-2Kb-, H-2Db-), resulted in a loss of MAA expression. Electron immunohistochemical analysis of melanoma cells and reverse transcriptase assay revealed that the loss of MAA expression in the H-2K gene-transfected cells paralleled the elimination of retroviral particles. In contrast, expression of the endogenous H-2Db gene or transfection with the H-2Dd or H-2Ld gene had no effect on MAA expression or retrovirus production. Northern blot analysis showed equivalent retroviral messages in retrovirus-producing and -nonproducing BL6 melanoma clones. Southern blot analysis revealed that H-2Kb-negative BL6 melanoma cells contain at least four different ecotropic retroviruses with different insertion sites that somatically emerged during malignant transformation or progression. Restriction enzyme analysis showed various changes in proviral DNAs from the H-2Kb- and H2Kd-transfected cells that failed to produce retroviral particles. The observed alterations in the patterns of PstI- and HindIII-digested proviral DNA were found to be due to the appearance of PstI and loss of HindIII restriction sites in the pol region as a result of several nucleotide substitutions. Thus, BL6 melanoma cells produce melanoma-specific ecotropic murine leukemia viruses that encode serologically detectable cell surface MAA. The transfection of BL6 melanoma cells with H-2Kb or H2Kd genes but not H-2Dd or H-2Ld genes resulted in a loss of MAA expression that was attributed to the changes in proviral DNA and loss of melanoma-specific ecotropic retrovirus particle production.

Role of calmodulin in HIV-potentiated Fas-mediated apoptosis

The recently demonstrated extraordinary rate of turnover of T cells in human immunodeficiency virus (HIV)-1-infected patients and the apparently concomitant high rate of viral production and death are consistent with a large amount of cell death directly due to infection. Apoptosis may be one of the major forms of T cell death in HIV-1 infection. Many apoptotic pathways depend on calcium and therefore would be expected to involve calmodulin. As the HIV-1 envelope glycoprotein, gp160, contains two known calmodulin-binding domains, we investigated the possibility that the cytoplasmic domain of the HIV-1 envelope protein gp160 could enhance Fas-mediated apoptosis, the major form of apoptosis in lymphocytes. Our studies have shown that 1) transfection of H9 and MOLT-4 cells with a non-infectious HIV proviral clone, pFN, which expresses wild-type gp160, leads to enhanced Fas-mediated apoptosis, 2) transfection of MOLT-4 cells with a pFN construct pFN delta 147, which expresses a carboxyl-terminally truncated gp160 lacking the calmodulin-binding domains, produces less Fas-mediated apoptosis than transfection with pFN, and 3) the calmodulin antagonists trifluoperazine and tamoxifen completely inhibit the pFN enhancement of Fas-mediated apoptosis in MOLT-4 cells. We have replicated all of these results using the vectors pSRHS and pSRHS delta 147, which express wild-type gp160 and truncated gp160, respectively, in the absence of other viral proteins. These investigations provide a mechanism by which HIV-1 may induce apoptosis and a possible intracellular target for future therapeutics.

Peripheral blood mononuclear cells from sheep infected with a variant of bovine leukemia virus synthesize envelope glycoproteins but fail to induce syncytia in culture

Peripheral blood mononuclear cells (PBMCs) infected with the oncogenic retrovirus bovine leukemia virus (BLV) produce virus when cultured briefly. BLV can be transmitted in cocultures to adherent susceptible cells, which become infected, express viral proteins, and fuse into multinucleated syncytia several days later. PBMCs from 3 of 10 BLV-infected sheep displayed a lifelong deficiency in induction of syncytium formation among indicator cells in culture, although large numbers of PBMCs synthesized viral transcripts or capsid protein. Since the infected, syncytium-deficient PBMCs were > or = 97% B cells, the deficiency could not be attributed to altered host cell tropism. The syncytium-deficient phenotype was recapitulated in newly infected sheep, demonstrating that this property is regulated by the viral genotype. The alteration in the BLV genome delayed but did not prohibit the establishment of BLV infection in vivo. Envelope glycoproteins were synthesized in syncytium-deficient PBMCs, translocated to the cell surface, and incorporated into virions. However, monoclonal antibodies specific for the BLV surface glycoprotein did not stain fixed PBMCs of the syncytium-deficient phenotype. Moreover, an animal with syncytium-deficient PBMCs had lower titers of neutralizing antibodies throughout the first 5 years of infection than an animal with similar numbers of infected PBMCs of the syncytium-inducing phenotype. The syncytium-deficient variant productively infected indicator cells at greatly reduced efficiency, showing that the alteration affects an early step in viral entry or replication. These results suggest that the alteration maps in the env gene or in a gene whose product affects the maturation or conformation, and consequently the function, of the envelope protein complex.

Translation initiation in GB viruses A and C: evidence for internal ribosome entry and implications for genome organization

GB viruses A and C (GBV-A and GBV-C) are two recently described RNA viruses which appear to be members of the Flaviviridae. Although both viruses appear to contain long 5' nontranslated regions, the sites of polyprotein initiation and the presence of core-like proteins remain to be determined. Translation studies were undertaken to determine the mechanism and sites of polyprotein initiation in GBV-A and GBV-C. Rabbit reticulocyte lysates programmed with monocistronic RNAs containing 5' ends of GBV-A or GBV-C fused in-frame with the chloramphenicol acetyltransferase (CAT) open reading frame generated GBV-CAT fusion proteins in vitro. Site-specific mutagenesis and N-terminal sequencing located the sites of translation initiation immediately upstream of the putative signal sequence for the GBV E1 envelope glycoproteins. Efficient translation of the monocistronic GBV-CAT RNAs required the inclusion of GBV coding sequences. This, coupled with the presence of at least 523 nucleotides of 5' nontranslated RNA containing multiple AUG codons, suggests that translation initiation of these RNAs did not utilize a ribosome scanning mechanism. Translation of bicistronic RNAs containing 5' nontranslated sequences within the intercistronic space was consistent with the presence of a weakly active internal ribosome entry site in both GBV-A and GBV-C. Secondary structure predictions indicate that the 5' ends of these viruses assume similar complex structures distinct from those identified in the internal ribosome entry site-containing picornaviruses, pestiviruses, and hepatitis C viruses. The data indicate that GBV-A and GBV-C are unique members of the Flaviviridae that do not contain core-like proteins at the N termini of their putative polyproteins.

Identification of domains in the simian immunodeficiency virus matrix protein essential for assembly and envelope glycoprotein incorporation

The matrix domain (MA) of the simian immunodeficiency virus (SIV) is encoded by the amino-terminal region of the Gag polyprotein precursor and is the component of the viral capsid that lines the inner surface of the virus envelope. To define domains of the SIV MA protein that are involved in virus morphogenesis, deletion and substitution mutations were introduced in this protein in the context of a gag-protease construct and expressed in the vaccinia virus vector system. The MA mutants were characterized with respect to synthesis and processing of the Gag precursor, assembly and release of virus-like particles, and incorporation of the envelope (Env) glycoprotein into particles. We have identified two regions of the SIV MA which are critical for particle formation. Both domains are located in a central hydrophobic alpha-helix of the SIV MA, according to data on the structure of this protein. In addition, we have characterized a domain whose mutation impairs the incorporation of SIV Env glycoproteins with long transmembrane cytoplasmic tails into particles. Interestingly, these mutant particles retained the ability to associate with SIV Env proteins with short cytoplasmic tails.

The rev-responsive element negatively regulates human immunodeficiency virus type 1 env mRNA expression in primate cells

The human immunodeficiency virus type 1 (HIV-1) Rev protein mediates the accumulation of unspliced and singly spliced viral transcripts within the cytoplasm of infected cells, late in the infection cycle, leading to the expression of the viral structural proteins, Gag, Pol, and Env. Rev binds to a complex RNA structure, the Rev-responsive element (RRE), present in all Rev-responsive viral transcripts, relieving their nuclear sequestration. The precise mechanism by which RRE-containing transcripts are retained within the nucleus in the absence of Rev protein is not well understood. We previously demonstrated that the RRE alone plays a crucial role in the nuclear retention of RRE-containing env transcripts in stably transfected Drosophila cells. Here we extend our previous observations and demonstrate that the RRE is a principal determinant of nuclear retention for envelope transcripts in primate cells and, in particular, human CD4+ T cells.

Increased envelope spike density and stability are not required for the neutralization resistance of primary human immunodeficiency viruses

Previous observations that the gp120 envelope glycoprotein contents of some primary, clade B human immunodeficiency virus type 1 (HIV-1) isolates were higher than those of laboratory-passaged HIV-1 isolates suggested the hypothesis that increased envelope glycoprotein spike density or stability contributes to the relative neutralization resistance of the primary viruses. To test this, the structural, replicative, and neutralization properties of a panel of recombinant viruses with HIV-1 envelope glycoproteins from divergent clades were examined in an env complementation assay. In this system, although the spike density and stability of envelope glycoproteins from primary HIV-1 isolates were not greater than those from a laboratory-adapted isolate, relative resistance to neutralizing antibodies and soluble CD4 was observed for the viruses with primary envelope glycoproteins. Thus, neither high envelope glycoprotein spike density nor stability is necessary for the relative neutralization resistance of primary HIV-1 viruses.

Mutational analysis of the envelope protein of spleen necrosis virus

Spleen necrosis virus (SNV) is an amphotropic type C retrovirus originally isolated from a duck. The envelope protein is related to that of type D retroviruses, and SNV appears to use the same receptor as do simian retroviruses. However, little is known about envelope-receptor interactions of SNV. We constructed a series of envelope mutants to characterize the SU peptide of SNV. Point mutations were introduced throughout SU in regions that are conserved among all retroviruses belonging to the same receptor interference group. The biological and biochemical properties of these mutants were analyzed. All mutants were transported efficiently to the cell surface. Almost all mutations in the amino-terminal one-third caused a conformational change of the envelope and a significant drop in infectivity and abolished the ability to confer superinfection interference. Similar observations were made with only two of seven mutants with mutations in the middle of SU. Four mutations in this region had little or no effect on biological activity. One mutant envelope protein (Asp to Arg at position 192) was processed normally but showed little infectivity and had no ability to confer superinfection interference. A detailed mutational analysis suggested that this amino acid forms a hydrogen bond to its cellular receptor. Mutations within the carboxy-terminal part of SU had very little or no effect on biological function. Aberrantly processed envelope proteins were proteolytically cleaved at a new point upstream of and differing in sequence from the conserved retroviral SU/TM cleavage site. Surprisingly, these mutants still retained some infectivity (0.01 to 1% of that of the wild type). Our data indicate that the envelope of SNV behaves in a manner very different from that of the envelopes of other studied retroviruses.

Genetics of intracisternal-A-particle-related envelope-encoding proviral elements in mice

Intracisternal-A-particle-related envelope-encoding (IAPE) proviral elements in the mouse genome encode and express an envelope-like protein that may allow transmission of IAPEs as infectious agents. To test IAPE mobility and potential transmission in mice, we have analyzed the distribution of IAPE elements in the genomes of Mus spretus and Mus musculus inbred strains and wild-caught animals. Potential full-length (IAPE-A) proviral elements are present as repetitive copies in DNA from male but not female animals of M. musculus inbred strains and Mus musculus castaneus. Analysis of IAPE-cellular junction fragments indicates that fixation of most IAPEs in the germ line occurred in M. musculus and M. spretus after speciation but before M. musculus inbred strains were derived.

Expression of the endogenous retrovirus ERV3 (HERV-R) during induced monocytic differentiation in the U-937 cell line

ERV3 (HERV-R) is a complete human endogenous retrovirus located on the long arm of chromosome 7. LTR-env-gene-spliced mRNA of 9 and 3.5 Kb is widely expressed in human tissues and cells, but gag-pol mRNA has not been found. Further, the env gp70 gene contains an open reading frame throughout its length and its expression has recently been detected as a full-length protein. The highest expression of ERV3 detected so far is in placenta and the lowest in cytotrophoblasts and choriocarcinoma cell lines. In this report we have studied ERV3 mRNA and protein expression in the human monoblastic cell line U-937 during differentiation into monocytes/macrophages. Differentiation of U-937 cells was induced by 1,25a-dihydroxyvitamin D3 (vitD3), retinoic acid (RA), gamma interferon (IFN-gamma) and phorbol-myristate-acetate (PMA-TPA). The expression of ERV3 env mRNA was found to be differentiation-associated, with high expression detected in the late stages of monocytic development. Using TPA, the expression of ERV3 env was detected as 9- and 3.5-kb transcripts by Northern blotting, as mRNA by in situ hybridization and as a cytoplasmic 65-kDa protein by immunofluorescence and Western blots. Low levels of basal expression were found, with up-regulation of both message and protein at 24 to 48 hr after addition of TPA. Induction with vitD3, IFN-gamma and RA produced higher levels of mRNA at earlier time points. It is concluded that the U-937 cell line represents an excellent model system for further studies to study the relationship between ERV3 expression and cellular differentiation.

Uncleaved env gp160 of human immunodeficiency virus type 1 is degraded within the Golgi apparatus but not lysosomes in COS-1 cells

The fate of newly synthesized human immunodeficiency virus type 1 env gp160 was examined in COS-1 cells. The results of morphological chase experiments involving cycloheximide demonstrated that gp160 was retained in the Golgi apparatus for longer than the half-life of the molecule. The degradation of gp160 was insensitive to both bafilomycin A1 and leupeptin (< 0.2 mM), which block lysosomal proteolysis. However, degradation was effectively suppressed by leupeptin at higher concentrations, maximally at 1.7 mM. Furthermore, undegraded gp160 was accumulated in the Golgi apparatus, but was not detected in lysosomes. These results indicate that in COS-1 cells gp160 is not degraded in lysosomes, but rather that degradation takes place in the Golgi apparatus.

Construction of recombinant extended single-chain antibody peptide conjugates for use in the diagnosis of HIV-1 and HIV-2

The construction, expression and evaluation of recombinant scFv based HIV diagnostic reagents are described. In a whole-blood, erythrocyte agglutination assay format, recombinant scFv antibodies (expressed in Escherichia coli), linked to a spacer domain and HIV-gp36 or -gp41 peptides, were shown to be able to detect efficiently natural antibodies against HIV in human serum. Performance in trials suggests that these single chain reagents have potential as alternatives to existing Fab-peptide chemical conjugates. We also report the construction of an inducible expression vector, pGC, which can be used both in laboratory experiments and in large-scale fed-batch fermentations. It was found that while the base scFv reagent (lacking a spacer) functioned as well as the Fab peptide conjugate in assays where whole (negative) blood was spiked with mouse monoclonal anti-HIV antibodies (IgG or IgM), clinical assays using human sera showed lower sensitivities and increased false negatives. This deficiency was overcome by inclusion of the natural 1C3 kappa (light) chain domain as a spacer arm between the scFv and HIV peptide tags. This spacer was thought to overcome steric constraints which would otherwise prevent efficient interaction between the reagent (once bound to the surface of red blood cells) and the various serum antibodies against the respective C-terminal peptide epitopes. As a result of this important modification, performance of the extended scFv reagent (for both HIV-1 and HIV-2) equalled that of the current commercial technology in limited trials.

Cytolytic response to HIV in patients with HIV disease treated with extracorporeal photochemotherapy: preliminary study

Extracorporeal photochemotherapy (photopheresis), an immunomodulatory therapy that targets circulating T helper lymphocytes, has been applied to the management of human immunodeficiency virus (HIV) disease. Any therapy that exerts its actions on CD4+ T cells has the potential of exacerbating HIV infection. Therefore, it was necessary to observe immune function during treatment. Because cytotoxic T lymphocytes (CTL) and natural-killer cells are thought to play an important role in the response against HIV infection, we examined the effect of photopheresis on HIV cytolytic activity. The study group consisted of seven patients with late-stage HIV disease who had not received any previous treatment for HIV infection. Patients were treated exclusively with photopheresis on two consecutive days each month for 14-32 months (average, 25 months). Peripheral lymphocytes, collected at various points during treatment, were used as effectors in a 51Cr release assay. Epstein-Barr virus (EBV)-transformed autologous B cell lines transfected with recombinant vaccinia vectors that expressed the HIV env (gp120, gp41) and gag (p24) proteins were used as target cells. All seven patients demonstrated relatively constant levels of cytolysis (>10% above controls) during treatment in the context of stable CD4+ T cell counts and a stable clinical status. These results suggest that extracorporeal photochemotherapy did not impair the cytolytic response to HIV infection and may have enhanced it in some patients.

Vaginal transmission of chimeric simian/human immunodeficiency viruses in rhesus macaques

Chimeric simian/human immunodeficiency viruses (SHIVs) that express the env genes derived from distinct HIV type 1 (HIV-1) isolates were tested for the ability to infect rhesus macaques following intravaginal inoculation. SHIVs containing either the HIV-1 HXBc2 or the HIV-1 89.6 envelope glycoproteins were capable of replicating in intravenously inoculated rhesus macaques. However, intravaginal inoculation of animals with these two SHIVs resulted in infection only with the SHIV containing the HIV-1 89.6 glycoprotein. Thus, properties conferred by the envelope glycoproteins in the chimeric virus affect the ability of particular SHIVs to initiate a systemic infection following vaginal inoculation. These results provide indirect support for the hypothesis that the selection of specific viral variants occurs in the genital tracts of individuals exposed to HIV by sexual contact.

Targeted infection of human cells via major histocompatibility complex class I molecules by Moloney murine leukemia virus-derived viruses displaying single-chain antibody fragment-envelope fusion proteins

As an approach to cell targeting by retroviruses, the lack of which constitutes one major limitation of retroviral vector technology, we engineered the Moloney murine leukemia virus ecotropic envelope glycoprotein. When inserted between amino acids 6 and 7 of the latter, a single-chain antibody fragment (ScFv) specific for human major histocompatibility complex class I molecules was shown to be able to redefine the tropism of ecotropic Moloney murine leukemia virus-derived retroviral particles by allowing infection of major histocompatibility complex class I-positive human cells. At variance with other recently described experimental systems, the type of modification adopted here allowed targeted infection in the absence of coexpressed wild-type env-encoded protein molecules. Interestingly, the chimeric ScFv-env protein also retained the ability to recognize the ecotropic receptor and allowed infection of murine cells, albeit at a reduced efficiency.