The infiltration kinetics of simian immunodeficiency virus-specific T cells drawn to sites of high antigenic stimulation determines local in vivo viral escape.

Despite vigorous cell-mediated immune responses to human and simian immunodeficiency viruses (HIV/SIV) the immune system is unable to clear latently infected resting T cells. These infected cells are reactivated by antigenic stimulation, leading to viral replication. By using the SIV/macaque model of HIV pathogenesis, the dynamics of T cell infiltration into delayed type hypersensitivity sites specific for the purified protein derivative of bacillus Calmette-Guérin have been studied. Early viral mRNA synthesis coincided with the infiltration of antigen-specific T cells. When the infiltration of anti-SIV-specific T cells was rapid compared with the kinetics of viral assembly, the sites were sterilized before the transition to late viral mRNA synthesis occurred. When their infiltration was slow, ephemeral foci of replication were identified. These findings were paralleled by plasma viremia; low viremia coincided with rapid sterilization of the delayed type hypersensitivity sites, whereas high load was found in association with local replication and delayed sterilization. These data suggest that although effective local control of SIV is possible once antiviral T lymphocytes have arrived on site, the slower deployment of these T cells may allow the virus to escape and thus to reseed the pool of memory T cells.

Enhancement of humoral immunity to SIVenv following simultaneous inoculation of mice by three recombinant adenoviruses encoding SIVenv/poliovirus chimeras, Tat and Rev.

A means of inducing gene expression by simultaneous infection with three recombinant adenoviruses (Ad) is described. The simian immunodeficiency virus (SIV) envelope-coding region was placed under the control of the human immunodeficiency virus type 1 (HIV-1) Tat and Rev proteins provided in trans by distinct Ad vectors (Ad-tat; Ad-rev). Coinfection of cells with the three recombinant adenoviruses led to induction of high levels of SIV env mRNA and protein synthesis, while inoculation of mice elicited anti-Env antibodies. Insertion of the poliovirus VP1 neutralization epitope (C3) in the V1 hypervariable region of SIV envelope not only proved to be highly immunogenic for the poliovirus epitope but also enhanced the kinetics of anti-SIV Env antibody production. By contrast, insertion in V4 elicited no anti-C3 response and only normal anti-Env responses.

Residual expression of reporter genes in constructs mimicking HIV genome organization.

Plasmids were constructed whereby the expression of a reporter gene, either the cDNA corresponding to the secreted form of human alkaline phosphatase (SEAP) or the herpes simplex virus type 1 (HSV1) thymidine kinase (tk) gene, was rendered dependent upon the expression of the human immunodeficiency virus type 1 (HIV1) tat and rev proteins. The SEAP or tk genes were placed between HIV1 splice donor and acceptor sites. One SEAP construct carried a series of alternating splice donor and acceptor sites. In all cases, the rev response element mapped within an intron. Despite such mimicry of the HIV1 genome, residual expression of the reporter gene in the absence of tat and rev was observed. These results, as well as non-specific T-cell recruitment, suggest limits to the specificity of using HIV-activated toxic gene expression to kill HIV-infected cells.

Complex intrapatient sequence variation in the V1 and V2 hypervariable regions of the HIV-1 gp 120 envelope sequence.

Human immunodeficiency virus (HIV) quasi-species fluctuate both in time and in space. In general intrapatient variation is less extensive than interpatient variation. The V1 and V2 hypervariable regions of the envelope gene were analyzed for patient samples harboring highly divergent genomes in other loci. Proviral sequences were amplified by PCR, cloned, and sequenced. It was concluded that intrapatient variation may exceed interpatient variation but the presence of two clearly distinct populations was not confirmed. The env hypervariable regions appeared to be evolving independently of one another, cautioning against extrapolation of data, particularly from the V3 region. Virus typing and the assessment of HIV superinfection by genetic methods will prove difficult and experimental approaches will have to be carefully designed.

Independent fluctuation of human immunodeficiency virus type 1 rev and gp41 quasispecies in vivo.

The human immunodeficiency virus type 1 (HIV-1) overlapping rev and env coding sequences have been examined from sequential peripheral blood mononuclear cell DNA samples from one individual. These were the same DNA samples from which sequence data for the tat and nef/long terminal repeat loci have been derived and span a 4-year period. The rev/env sequences were established by sequencing cloned polymerase chain reaction products. The structure of the populations of rev protein sequences increased in complexity with disease, while those of the corresponding env sequences remained complex. This suggests that the rev and env populations evolved differently, probably reflecting different selection pressures. No defective rev variants encoded substitutions in residues 76 through 79, indicating that the experimental finding of down regulation of rev activity by competitive inhibition may not necessarily occur in vivo. After having analyzed three HIV loci (15% of the genome) from the same individual over 4 years, it is clear that no two loci evolved similarly, indicating the difficulties in comparing data from different loci.

LAV revisited: origins of the early HIV-1 isolates from Institut Pasteur.

Two of the first human immunodeficiency virus type-1 (HIV-1) strains isolated were authenticated by reanalyzing original cultured samples stored at the Collection Nationale de Culture des Microorganismes as well as uncultured primary material. Cloned polymerase chain reaction products were used to analyze coding sequences of the V3 loop in the gp120 glycoprotein. The original isolate HIV-1 Bru, formerly called LAV, was derived from patient BRU. HIV-1 Lai was derived from patient LAI and contaminated a HIV-1 Bru culture between 20 July and 3 August 1983. The culture became, in effect, HIV-1 Lai, identifiable by a unique motif in the V3 loop. Because of this contamination two, rather than one, HIV-1 isolates were sent to the Laboratory of Tumor Cell Biology at the National Cancer Institute on 23 September 1983. Original HIV-1 Bru was indeed present in the sample marked JBB/LAV. However the M2T-/B sample harbored HIV-1 Lai, a strain capable of growing on established cell lines. The striking similarity between HIV-1 Lai (formerly LAV-Bru) and HTLV-3B sequences remains.

Enhancement of gene expression by somatic hybridization with primary cells: high-level synthesis of the hepatitis B surface antigen in monkey Vero cells by fusion with primary hepatocytes.

Vero cells transfected with the S gene encoding the surface antigen (HBsAg) of the hepatitis B virus (HBV) synthesize HBsAg at low levels. We have obtained a large increase in S gene expression by somatic hybridization of Vero cells with primary hepatocytes, which are the natural target cells for HBV infection. Fusion with cells other than hepatocytes did not enhance expression of the S gene. The Vero/hepatocyte hybrid clones analyzed are stable and have maintained a high level of HBsAg synthesis over prolonged periods. Hybrid cell lines may be of general interest for the high-level synthesis of proteins using cloned genes.

Multiple subsets of HIV-specific cytotoxic T lymphocytes in humans and in mice.

The human immunodeficiency virus type 1 (HIV-1) induces a strong cytotoxic T lymphocyte (CTL) response in humans following infection. HIV-specific CTL can be detected directly in the blood and lungs of infected patients, and can be expanded in vitro by stimulation with autologous HIV-infected lymphoblasts. Furthermore, CTL specific for HIV envelope glycoprotein gp160 have been obtained in mice by immunization with recombinant vaccinia virus (VV) that carry the HIV env gene. In this study, we show that mice also produce strong CTL responses to gag and nef proteins following immunization with VV recombinants, thus providing a convenient model system to study T lymphocyte immunity to defined HIV antigens. To determine the specificity of circulating HIV-immune CTL in humans, a panel of doubly transfected mouse P815 tumor cells was produced which express the human HLA-A2 or HLA-A3 transplantation antigen gene and one HIV-1 gene (env, gag or nef). Using these cells as targets to CTL, we show that HIV-infected humans carry co-existing CTL sub-populations of different specificities. Each subpopulation appears to vary in intensity among different individuals. Surprisingly, CTL specific for regulatory, non-structural nef protein appear to be a major constituent of the human immune response to HIV.

An expression vector for high-level protein synthesis in Vero cells.

We have constructed two new multi-purpose cloning vectors, pNI1 and pNI2, that carry the Escherichia coli gene Ecogpt encoding the enzyme xanthine-guanine phosphoribosyl transferase as a dominant selective marker. The Ecogpt gene is under the control of either the long-terminal-repeat promoter of mouse mammary tumor virus, pNI1, or the simian virus 40 early promoter, pNI2. Another feature of the vectors is a polylinker preceded by the human metallothionein IIA promoter. We have used pNI2 for the synthesis of the hepatitis B surface antigen (HBsAg) at a high level in monkey Vero cells. We show that gene amplification and a concomitant stable increase of HBsAg synthesis can be achieved in these cells using modified selective medium containing hypoxanthine, aminopterin and thymidine, i.e., increasing the aminopterin and decreasing the hypoxanthine concentrations.

Cytotoxic T lymphocytes in HIV-induced disease: implications for therapy and vaccination.

The immune response to HIV in infected humans leads to the production of HIV-specific cytotoxic T lymphocytes (CTL) which circulate in high frequencies. The presence of these CTL and their eventual protective activities have been studied by various laboratories, and correlations have been made with certain immunopathological manifestations of HIV infections. It seems probable that HIV-immune CTL participate in the induction of certain disorders by initiating inflammatory reactions in the lungs, central nervous system and lymph nodes. Various virus antigens recognized by HIV-immune CTL on the surface of the infected cell have been identified, and molecular definition of the epitopes recognized is well under way. Likewise, numerous HLA transplantation antigens that regulate HIV antigen recognition by CTL have been identified. These data are discussed with regard to the eventual development of a vaccine and of functional immunotherapies.

Insertions in the hepatitis B surface antigen. Effect on assembly and secretion of 22-nm particles from mammalian cells.

The envelope protein of hepatitis B virus carrying the surface antigen, HBsAg, has the unique property of mobilizing cellular lipids into spherical or elongated particles, about 22 nm in diameter, which are secreted from mammalian cells. We have created mutant envelope proteins by insertion of various sequences of different lengths into two regions of the S gene encoding the major envelope protein. S genes carrying inserts in phase with HBsAg were expressed in mouse L cells from the simian virus 40 early promoter. Various single or double inserts in the two major hydrophilic domains of HBsAg were compatible with secretion of 22-nm particles. In all mutant envelope proteins studied, the HBsAg domains required for intracellular aggregation appeared to be intact. However, assembly into particles was not sufficient to assure transport into the extracellular space. The 22-nm HBsAg particle may be a useful vehicle for the export and presentation of foreign peptide sequences.

Amplifiable expression vectors for mammalian cell lines.

We have constructed a prototype of a general expression vector for mammalian cells, which carriers a strong promoter active in a variety of tissues and animal species for expression of the gene of interest and a truncated gene for amplification in selective medium. Expression of the S gene of HBV encoding the surface antigen was used to evaluate various versions of this vector. The human metallothionein IIA promoter was found to be particularly efficient for expression of this gene, both in mouse L and monkey Vero cells. Including a promoterless tk gene in the vector led to gene amplification in Ltk- cells by selection of TK+ variants in selective medium containing hypoxanthine, aminopterine and thymidine (HAT medium). Concomitant increases of the S gene expression levels were initially 50-100 fold. Although many clones were unstable, even in selective medium, some maintained the high expression levels for over one year.

A poliovirus neutralization epitope expressed on hybrid hepatitis B surface antigen particles.

The hepatitis B virus (HBV) envelope protein carrying the surface antigen (HBsAg) is assembled with cellular lipids in mammalian cells into empty viral envelopes. In a study to evaluate the capacity of such particles to present foreign peptide sequences in a biologically active form, in-phase insertions were created in the S gene encoding the major envelope protein. One of the sequences inserted was a synthetic DNA fragment encoding a poliovirus neutralization epitope. Mammalian cells expressing the modified gene secreted hybrid particles closely resembling authentic 22-nanometer HBsAg particles. These particles reacted with a poliovirus-specific monoclonal antibody and induced neutralizing antibodies against poliovirus. The results indicate that empty viral envelopes of HBV may provide a means for the presentation of peptide sequences and for their export from mammalian cells.

[Expression of the hepatitis B virus surface antigen gene by rat hepatocyte X mouse hepatoma hybrid cells]. / Etude de l'expression du gène S du virus de l'hépatite B dans les cellules hybrides hépatocytes de rat X hépatome de souris.

The expression of the S gene of hepatitis B virus has been studied in the somatic hybrid cells resulting from the fusion between rat hepatocytes in primary culture and cells of the mouse hepatoma line BWTG3, and in the parental line BWTG3. The DNA of the S gene inserted into the plasmids pAC Tk+ and pNY4 has been co-transfected into these cells with a plasmid DNA bearing a resistance gene to aminoglycoside. The level of expression of the S gene among the co-transfected resistant clones was estimated by radioimmunoassay. The results show that a high number of the co-transfected cellular hybrid clones express the S gene, whereas it is found, by contrast, that the S gene is poorly expressed in the mouse hepatoma cells. The level of expression of the S gene (as the amount of HBs Ag synthesized) is high in the hybrid clones and the synthesis of the HBs antigen is stable in time. These observations suggest for the first time in cell cultures in vitro, the role which is probably played by the normal hepatocyte genome in the expression of the S gene of HBV.

Nucleotide sequence and expression of the diphtheria tox228 gene in Escherichia coli.

The complete nucleotide sequence of the diphtheria tox228 gene encoding the nontoxic serologically related protein CRM228 has been determined. A comparison of the predicted amino acid sequence with the available amino acid sequences from the wild-type toxin made it possible to deduce essentially the entire nucleotide sequence of the wild-type tox gene. The signal peptide of pro-diphtheria toxin and the putative tox promoter have been identified, a highly symmetrical nucleotide sequence downstream of the toxin gene has been detected; this region may be the corynebacteriophage beta attachment site (attP). The cloned toxin gene was expressed at a low level in Escherichia coli.

[Transfection and expression of the S gene of hepatitis B virus in hepatocytes of adult rats in primary culture]. / Transfection et expression du gène S du virus de l'hépatite B dans les hépatocytes de Rat adulte en culture primaire.

The feasibility of gene transfer in differentiated mammalian cells in primary culture, has been worked out in isolated adult rat hepatocytes. The calcium phosphate technique has been applied to the hepatocytes after 3 to 5 days of culture. The DNA of a plasmid carrying the gene S of HBV has been used in the transfection experiments. The transcription of the gene S in the transfected hepatocytes, characterized by the synthesis of the gene product (the surface antigen HBs Ag) has been demonstrated by radioimmunoassay and cytologic visualization by immunofluorescence.

Transcription of the hepatitis B surface antigen gene in mouse cells transformed with cloned viral DNA.

Mouse L cells transformed with recombinant plasmids carrying hepatitis B virus (HBV) DNA fragments were used to study the transcription of the viral surface antigen gene (gene S). An HBV-specific, polyadenylated, 2.3-kilobase RNA was mapped on the HBV genome. This RNA hybridized with approximately 75% of the genome and excluded the region of the HBV core antigen gene (gene C). The 2.3-kilobase RNA species was present only in cell lines that produced hepatitis B surface antigen. An HBV-specific 2.3-kilobase RNA was also detected in human hepatoma cell line PLC/PRF/5 which produced hepatitis B surface antigen. A study of gene S expression in the transformed mouse L cells allowed us to localize the regions of initiation and termination of gene S transcription. Our results strongly suggest that the 2.3-kilobase RNA molecule is the mRNA of the major polypeptide of the envelope, which carries the viral surface antigen determinants.