Three novel genes of human T-lymphotropic virus type III: immune reactivity of their products with sera from acquired immune deficiency syndrome patients

Antisense Transcripts and Antisense Protein: A New Perspective on Human Immunodeficiency Virus Type 1

It was first predicted in 1988 that there may be an Open Reading Frame (ORF) on the negative strand of the Human Immunodeficiency Virus type 1 (HIV-1) genome that could encode a protein named AntiSense Protein (ASP). In spite of some controversy, reports began to emerge some years later describing the detection of HIV-1 antisense transcripts, the presence of ASP in transfected and infected cells, and the existence of an immune response targeting ASP. Recently, it was established that the asp gene is exclusively conserved within the pandemic group M of HIV-1. In this review, we summarize the latest findings on HIV-1 antisense transcripts and ASP, and we discuss their potential functions in HIV-1 infection together with the role played by antisense transcripts and ASPs in some other viruses. Finally, we suggest pathways raised by the study of antisense transcripts and ASPs that may warrant exploration in the future.

The activity of Nef on HIV-1 infectivity

The replication and pathogenicity of lentiviruses is crucially modulated by “auxiliary proteins” which are expressed in addition to the canonical retroviral ORFs gag, pol, and env. Strategies to inhibit the activity of such proteins are often sought and proposed as possible additions to increase efficacy of the traditional antiretroviral therapy. This requires the acquisition of an in-depth knowledge of the molecular mechanisms underlying their function. The Nef auxiliary protein is expressed uniquely by primate lentiviruses and plays an important role in virus replication in vivo and in the onset of AIDS. Among its several activities Nef enhances the intrinsic infectivity of progeny virions through a mechanism which remains today enigmatic. Here we review the current knowledge surrounding such activity and we discuss its possible role in HIV biology.

Inhibition of splicing by serine-arginine rich protein 55 (SRp55) causes the appearance of partially spliced HIV-1 mRNAs in the cytoplasm

We have previously shown that SRp55 inhibits splicing from HIV-1 exon 3, thereby generating partially spliced mRNAs encoding HIV-1 vpr. Here we show that SRp55 also inhibits splicing from HIV-1 exon 5 to generate HIV-1 vpu/env mRNA, albeit with lower efficiency. We also show that inhibition of HIV-1 splicing by SRp55 causes the appearance of partially spliced vpu, env and vpr mRNAs in the cytoplasm. SRp55 could also induce production of extracellular p24gag from a rev-defective HIV-1 provirus. These results indicate that SRp55 aids in the generation of partially spliced and unspliced HIV-1 mRNAs.

Serine- and arginine-rich proteins 55 and 75 (SRp55 and SRp75) induce production of HIV-1 vpr mRNA by inhibiting the 5'-splice site of exon 3

HIV-1 non-coding exon 3 can either be spliced to exons 4, 4a, 4b, 4c, and 5 to generate tat, rev, and nef mRNAs or remain unspliced to produce the 13a7 vpr mRNA. Here we show that serine- and arginine-rich proteins 55 and 75 (SRp55 and SRp75) inhibit splicing from the 5'-splice site of exon 3 thereby causing an accumulation of the partially unspliced 13a7 vpr mRNA. In contrast, serine- and arginine-rich protein 40 (SRp40) induces splicing from exon 3 to exon 4, thereby promoting the production of the 1347 tat mRNA. We demonstrate that SRp55 stimulates vpr mRNA production by interacting with the previously identified HIV-1 splicing enhancer named GAR and inhibiting its function. This inhibition requires both serine arginine-rich and RNA-binding domains of SRp55, indicating that production of HIV-1 vpr mRNA depends on the interaction of SRp55 with an unknown factor.

Prospects for antisense peptide nucleic acid (PNA) therapies for HIV

Since the discovery and synthesis of a novel DNA mimic, peptide nucleic acid (PNA) in 1991, PNAs have attracted tremendous interest and have shown great promise as potential antisense drugs. They have been used extensively as tools for specific modulation of gene expression by targeting translation or transcription processes. This review discusses the present and future therapeutic potential of this class of compound as anti-HIV-1 drugs.

Expression of human immunodeficiency virus type 1 tat from a replication-deficient herpes simplex type 1 vector induces antigen-specific T cell responses

Herpes simplex type-1 virus (HSV-1) based vectors have been widely used in different gene therapy approaches and also as experimental vaccines against HSV-1 infection. Recent advances in the HSV-1 technology do support the use of replication defective HSV-1 as vaccine vectors for delivery of foreign antigens. We have examined the ability of a recombinant replication-defective HSV-1 vector expressing the HIV-1 Tat protein to induce long-term Tat-specific immune responses in the Balb/c murine model. The results showed that vector administration by the subcutaneous route elicits anti-Tat specific T-cell mediated immune responses in mice characterized by the presence of the Tat-specific cytotoxic activity and production of high levels of IFN-gamma.

HIV-1 pathogenesis

Despite considerable advances in HIV science in the past 20 years, the reason why HIV-1 infection is pathogenic is still debated and the goal of eradicating HIV-1 infection remains elusive. A deeper understanding of the interplay between HIV-1 and its host and why simian immunodeficiency virus (SIV) is nonpathogenic in some natural hosts may provide a few answers.

Docking studies reveal a selective binding of D-penicillamine to the transactivator protein of human immunodeficiency virus type 1

DOCK and Affinity studies were carried out to study the binding of D- and L-penicillamine to the transactivator protein (tat) of human immunodeficiency virus type 1 (HIV-1). These studies reveal a selective binding of D-penicillamine to the cysteine-rich region covering amino acid residues 20-38 of the tat protein. A careful analysis of the components of the binding energy of the D- and L-isomers reveals that the D-isomer has a more favorable van der Waals interaction resulting from an optimal placement of the dimethylthiomethyl side chain in the binding site. This observation matches the experimental data that D-penicillamine is a more potent inhibitor of tat-mediated transactivation than the L-isomer. The docking and experimental data offer an interesting approach to design structural molecules with potential application to block signal functions of the tat protein in HIV-1 pathogenesis.

Intercellular traffic of human immunodeficiency virus type 1 transactivator protein defined by monoclonal antibodies

Monoclonal antibodies (mAbs) directed against the amino-terminal region (N-terminal sequence 2-19) of transactivator protein (tat) of HIV-1 have been shown to inhibit intercellular transactivation mediated by the extracellular tat protein. The intracellular transactivation was not significantly affected by anti-tat mAbs. The specificity of anti-tat mAbs in abolishing the transactivating potential of extracellular tat is documented by studies with mAbs to HIV-1 reverse transcriptase, or to a human mammary cancer protein. None of these antibodies showed any inhibitory effect on intercellular transactivation. Specific interaction of anti-tat IgG with tat protein expressed in Jurkat cells is further supported by experiments on immunoblotting. Extracellular tat is responsible for signals which induce a variety of biological responses in HIV-infected cells, as well as in uninfected cells. The fact that anti-tat mAbs can abolish the intercellular traffic of tat protein offers a unique strategy in the development of vaccines against AIDS.

Development of genetic vaccines for pathogenic genes: construction of attenuated vif DNA immunization cassettes

OBJECTIVE

To develop a putative immunization cassette using HIV-1 vif accessory gene derived from HIV-1 clinical specimens as a component of a DNA vaccine for HIV-1.

METHODS

vif genes were cloned from HIV-1-infected patients and the sequence variation present within the patients was analyzed. Prototypic genetic variants were selected and the ability of these clones to induce humoral and cellular immune responses was studied in animals. The selected protective genetic variants were biologically characterized through transcomplementation assays using primary cells infected with a vif-defective HIV-1 proviral clone.

RESULTS

Analysis of vif variants from different patients revealed that vif is highly conserved with the open reading frame remaining intact in vivo. It was shown that attenuated vif clones from HIV-1-infected subjects can effectively induce both humoral and cellular responses against Vif protein in mice. Evaluation of the cellular responses in vitro using human cellular targets infected with a clinical HIV-1 isolate showed that vif clones could induce cellular responses capable of destroying the virus.

CONCLUSIONS

The vif variants developed in this study exhibited non-productive phenotypes, yet were capable of inducing specific immune responses against HIV-1. These constructs could be used as part of a DNA vaccine strategy for HIV-1. This vaccine adaptation strategy could be used for the development of immunogens for any pathogen resulting in cross-reactive immunity and attenuated gene pathogenesis.

A novel, highly efficient peptide-HLA class I binding assay using unfolded heavy chain molecules: identification of HIV-1 derived peptides that bind to HLA-A*0201 and HLA-A*0301

A novel cell-free, highly automated peptide-HLA binding assay has been designed during which a mixture of unfolded recombinant HLA heavy chain molecules, beta 2-microglobulin and a fluorescent labeled standard peptide is allowed to form peptide-HLA complexes. The binding of a peptide of interest is monitored as the ability to inhibit the formation of fluorescent peptide-HLA complexes. The assay was validated using published, known HLA-A* 0201 and HLA-A* 0301 binding peptides. In addition a selected set of HIV-1LAI reverse transcriptase derived 10-mer peptides, that had been selected on the basis of HLA-A* 0201 or HLA-A* 0301 binding motifs, were tested for HLA-A* 0201/A* 0301 binding. In that set we identified 8 peptides which bound with high affinity to HLA-A* 0201 and 5 peptides which bound with high affinity to HLA-A* 0301. The major advantage of the use of denatured heavy chain is the improved economy and efficiency, as unfolded protein material is in principle easily accessible by recombinant technology.

Prevalence of anti-vif antibodies in HIV-1 infected individuals assessed using recombinant baculovirus expressed vif protein

A 630 base pair fragment of the HIV-1 genome encompassing the entire vif open reading frame has been produced by the polymerase chain reaction and cloned into the baculovirus transfer vector pAcYM1. Extracts from insect cells infected with a recombinant baculovirus expressing the HIV-1 vif gene product were used in a radioimmunoassay to analyse 238 sera from HIV infected individuals for the presence of anti-vif antibodies. The overall prevalence of anti-vif antibodies in this group of patients was 25.3%. Stratification of the group according to CD4 levels showed that anti-vif antibodies were more prevalent in patients with CD4 counts below the median of the group (155 x 10(6) cells/L; P = 0.005). A significant increase in anti-vif antibodies was observed in patients with CD4 levels less than 280 x 10(6) cells/L (P < 0.01) and in patients with symptomatic HIV infection (P = 0.0003). However, there was no significant difference in the prevalence of anti-vif antibodies in patients stratified according to p24 antigen status. The implications of these findings in the context of HIV replication are discussed.

Analysis of human immunodeficiency virus type 1 mRNA splicing patterns during disease progression in peripheral blood mononuclear cells from infected individuals

HIV-1 produces more than 20 mRNAs encoding the viral proteins. We have used a sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) approach to determine HIV-1 transcriptional patterns during the course of viral infection in unstimulated peripheral blood mononuclear cells (PBMCs) from different patients. Several sets of PCR primers, used in parallel reactions, allowed the amplification and specific detection of almost all individual HIV-1 transcripts. We investigated the transcriptional profile in two individuals during primary acute and early chronic infection. In these individuals, HIV-1 mRNA expression was elevated at the first time points examined and declined over time. In addition, we performed a detailed study of HIV-1 expression in several individuals over a minimum of 7 years following seroconversion. We found that long-term asymptomatic individuals had undetectable or low levels of the three classes of HIV-1 transcripts (unspliced, singly spliced, and multiply spliced). Individuals who demonstrated disease progression showed either a general increase in the amount of expression of all transcripts or elevated levels of unspliced transcripts in late-stage disease. The splicing pattern in each patient was conserved over the years and differed among the different individuals. No evidence of major changes in the splicing pattern was found during disease progression within the same individual. Thus, HIV-1 transcriptional patterns are viral strain specific rather than disease stage specific. These results indicate that high-level expression of any class of HIV-1 transcripts is associated with clinical progression. Our analysis also demonstrates the importance of using more than one set of primers to evaluate HIV-1 RNA expression, since virus in patient PBMCs showed sequence heterogeneity in conserved regions.

Vacuolar myelopathy in transgenic mice expressing human immunodeficiency virus type 1 proteins under the regulation of the myelin basic protein gene promoter

Vacuolar myelopathy is a common neurological complication in AIDS patients. The pathogenesis of this spinal cord white matter disease remains unclear and it is still debated whether infection of spinal cord with the human immunodeficiency virus type 1 (HIV-1) is causing the disease. We have generated transgenic mice expressing the entire HIV-1 genome under the regulation of an oligodendrocyte-specific promoter. These mice develop spinal cord vacuolar lesions similar to those found in AIDS patients. This animal model provides in vivo evidence linking the expression of HIV-1 proteins in oligodendrocytes to the spinal cord damage found in vacuolar myelopathy.

Cell-free HIV-1Zr6 vif mutants are defective in binding to peripheral blood mononuclear cells and in internalization

The vif gene of the human immunodeficiency virus (HIV-1) is required for productive virus infection of primary blood mononuclear cells (PBMCs) and macrophages in vitro. Replication of HIV-1 vif- mutants in T-lymphoid cell lines varies and is dependent on the cell line used for virus production. To further understand the role of Vif in HIV-1 infection, we constructed to vif deletion mutants from a molecular clone derived from an African patient (HIV-1Zr6). Cell-free Zr6 vif- virus pools made from transfected rhabdomyosarcoma (RD) cells do not replicate when added to cultures of stimulated PBMCs. However, vif mutants were able to spread from transfected RD cells to PBMCs if cell-to-cell contact was permitted. By Western blot analysis, viral structural proteins expressed after transfection of RD cells by wild-type or vif mutant proviruses were indistinguishable. However, binding of vif mutants to PBMCs or to purified CD4 and virus internalization were significantly reduced when compared with wild-type virus. The defects in cell-free infection, CD4 binding, and internalization were rescued by transcomplementation using a vif expression plasmid. Our results suggest a novel level at which the HIV-1 vif gene product acts to enhance cell-free infection and indicate that vif plays an important role in promoting HIV-1 binding and internalization. Combined with the previous reports of vif's effect at other steps in infection, this suggests that vif is a pleuripotent gene product that affects multiple stages of the infective process.

Antibody against human immunodeficiency virus type 1 (HIV-1) Tat protein may have influenced the progression of AIDS in HIV-1-infected hemophiliac patients

Retrospective analysis of serum samples from a group of hemophiliac patients who became infected with human immunodeficiency virus type 1 (HIV-1) between 1984 and 1985 has shown that, at variance with other HIV-1-infected patients, at the onset, or at least at a very early phase of HIV-1 infection, they constantly have elevated levels of antibodies against HIV-1-transactivating Tat protein and an absent or barely detectable p24 antigenemia. Anti-Tat antibodies in initial serum samples from hemophiliac patients were probably the consequence of the passive administration of immunoglobulins present in low- or intermediate-purity clotting factor concentrates prepared from HIV-1-infected blood. Furthermore, the analysis of serial serum samples obtained during the course of the disease, in which passively acquired anti-Tat antibodies were substituted by actively produced antibodies, demonstrated an inverse relationship between anti-Tat antibody and p24 anti-genemia levels throughout the observation period. These data seem to suggest that anti-Tat antibody may have some influence on the course of HIV-1 infection.

The Vif protein of human and simian immunodeficiency viruses is packaged into virions and associates with viral core structures

The vif gene of human and simian immunodeficiency viruses (HIV and SIV) encodes a late gene product that is essential for viral infectivity in natural target cells. Virions produced in the absence of Vif are abnormal in their ultrastructural morphology and are severely impaired in the ability to complete proviral DNA synthesis upon entry into new target cells. Because previous studies failed to detect Vif protein in virus particles, Vif is believed to influence virus infectivity indirectly, by affecting virion assembly, release, and/or maturation. In this report, we reexamined the possibility that Vif is a virion-associated protein. Utilizing high-titer Vif-specific antibodies, a sensitive immunoblot technique, and highly concentrated virus preparations, we detected a 23-kDa Vif-reactive protein in wild-type HIV type 1 (HIV-1) and a 27-kDa Vif-reactive protein in wild-type SIVSM virions. Neither protein was present in virions derived from vif-deficient HIV-1 and SIVSM proviral constructs. Vif protein content was similar among different strains of HIV-1 and was independent of the cell type (permissive or nonpermissive) used to produce the virus. To determine the subvirion localization of Vif, HIV-1 virions were treated with proteinase K or Triton X-100 to remove virion surface proteins and the viral membrane, respectively, purified through sucrose, and analyzed by immunoblot analysis. Vif protein content was not affected by the removal of external surface proteins or by the removal of the viral membrane and submembrane p17Gag matrix protein. Instead, Vif colocalized with viral core structures which sedimented at a density of 1.25 g/ml on linear sucrose gradients (enveloped HIV-1 particles sediment at a density of 1.17 g/ml). Finally, the amount of Vif protein packaged into virions was estimated to be on the order of 1 molecule of Vif for every 20 to 30 molecules of p24Gag, or between 60 and 100 molecules of Vif per particle. These results indicate that Vif represents an integral component of HIV and SIV particles and raise the possibility that it plays a direct role in early replication events.

Identification and mapping of inhibitory sequences in the human immunodeficiency virus type 2 vif gene

Human immunodeficiency virus (HIV) regulates the expression of its genes temporally at the mRNA processing step. A subset of the mRNA species which encode the structural and some accessory genes contains inhibitory sequences (INS or CRS elements) which prevent nuclear export of the RNA or its utilization in the cytoplasm. Such inhibition is overridden by the interaction of a viral protein, Rev, with its RNA target sequence, RRE. The vif gene product, which is essential for virus replication in vivo, is encoded by a singly spliced mRNA, and its expression is dependent on rev in infected cells. However, INS elements have not been found in the HIV-1 vif gene itself, although such elements have been observed in Gag, Pol, and Env coding sequences. We have now identified an INS within the 5' half of HIV-2 vif which does not show any homology with cellular mRNAs or other previously identified INS and CRS elements of HIV. These results suggest that retroviral mRNAs have novel labile sequences different from those of cellular mRNAs.

Efficiency of reinitiation of translation on human immunodeficiency virus type 1 mRNAs is determined by the length of the upstream open reading frame and by intercistronic distance

In this study, we examined the mechanism of translation of the human immunodeficiency virus type 1 tat mRNA in eucaryotic cells. This mRNA contains the tat open reading frame (ORF), followed by rev and nef ORFs, but only the first ORF, encoding tat, is efficiently translated. Introduction of premature stop codons in the tat ORF resulted in efficient translation of the downstream rev ORF. We show that the degree of inhibition of translation of rev is proportional to the length of the upstream tat ORF. An upstream ORF spanning 84 nucleotides was predicted to inhibit 50% of the ribosomes from initiating translation at downstream AUGs. Interestingly, the distance between the upstream ORF and the start codon of the second ORF also played a role in efficiency of downstream translation initiation. It remains to be investigated if these conclusions relate to translation of mRNAs other than human immunodeficiency virus type 1 mRNAs. The strong inhibition of rev translation exerted by the presence of the tat ORF may reflect the different roles of Tat and Rev in the viral life cycle. Tat acts early to induce high production of all viral mRNAs. Rev induces a switch from the early to the late phase of the viral life cycle, resulting in production of viral structural proteins and virions. Premature Rev production may result in entrance into the late phase in the presence of suboptimal levels of viral mRNAs coding for structural proteins, resulting in inefficient virus production.

Comparative analyses of human immunodeficiency virus type 1 (HIV-1) and HIV-2 Vif mutants

Virion infectivity factor (vif), a gene found in all lentiviruses, plays an essential role in virus replication in certain target cells. We examined the replication competence of the human immunodeficiency virus type 2 (HIV-2) vif mutant in different T-cell lines and primary cells in comparison with that of the HIV-1 vif mutant. Both mutant viruses were unable to replicate in peripheral blood-derived mononuclear cells but replicated with wild-type efficiency in certain T-cell lines, such as SupT1 and MOLT-4/8. These results confirm the importance of vif in the infection of relevant target cells and imply that some cellular factor(s) could compensate for vif function. However, HIV-1 and HIV-2 vif mutant viruses also show differential replications in other cell lines, suggesting either different threshold requirements for the same cellular factor(s) or the involvement of different factors to compensate for vif-1 and vif-2 functions. By cross complementation experiments, we showed that vif-1 and vif-2 have similar functions. Our studies further indicate the existence of two kinds of nonpermissive cells: H9 is unable to complement HIV-1 delta vif but is susceptible to a one-round infection with HIV-1 delta vif produced from permissive cells. In contrast, U937 is nonpermissive for HIV-2 delta vif produced from permissive cells but, once infected, is able to complement the delta vif function. In both types of nonpermissive cells, a step prior to proviral DNA synthesis is affected.

Gene-targeted inhibition of transactivation of human immunodeficiency virus type-1 (HIV-1)-LTR by antisense oligonucleotides

We have used an in vitro approach to study the efficiency of antisense oligonucleotides in inhibiting LTR-(HIV-1)-directed CAT expression catalyzed by tat protein, the functional protein of the transactivator gene. We selected the target sequence localized near the 5' end of the tat mRNA. The following conclusions can be drawn from the data presented here: a) Antisense oligonucleotides modified by conjugation of cholesterol at the 3' end have a severalfold higher inhibitory response, b) inhibitory response is dependent on the mode of introducing oligonucleotides, and c) the inhibition by antisense oligonucleotides is sequence specific and directed towards the targeted region. This approach could be useful for targeting functional regions of regulatory gene products and designing gene-targeted inhibitors of virus replication.

Human immunodeficiency virus type 1 Tat upregulates interleukin-2 secretion in activated T cells

Dysregulation of cytokines secreted by T cells may play an important role in the pathogenesis of AIDS. To investigate the effects of human immunodeficiency virus type 1 (HIV-1) Tat on interleukin-2 (IL-2) expression, we used IL-2 promoter-chloramphenicol acetyltransferase constructs and IL-2-secreting Jurkat T cells as a model system. Transient expression of HIV-1 Tat induced a five- to eightfold increase in IL-2 promoter activity in Jurkat T cells stimulated with phytohemagglutinin and phorbol myristate acetate. IL-2 secretion was increased more than twofold in both Jurkat T cells and primary T cells stimulated by extracellular HIV-1 Tat protein. Analysis of mRNA suggested that Tat exerts its effect on IL-2 primarily at the transcriptional level. The NF-kappa B site at positions -206 to -195 of the IL-2 promoter was required but not sufficient for the Tat effect. The Tat-mediated increase in IL-2 promoter activity could selectively be blocked by antisense tat or-unlike the analogous effect of human T-cell lymphotropic virus type 1 Tax-by cyclosporin A. The observed increase in IL-2 levels might facilitate virus spread from or to T cells. Furthermore, it might contribute to the hypergammaglobulinemia or, together with other cytokines found to be dysregulated, the T-helper cell dysfunctions observed in AIDS patients.

Viral gene products and replication of the human immunodeficiency type 1 virus

The acquired immunodeficiency syndrome (AIDS) epidemic represents a modern-day plague that has not only resulted in a tragic loss of people from a wide spectrum of society but has reshaped our viewpoints regarding health care, the treatment of infectious diseases, and social issues regarding sexual behavior. There is little doubt now that the cause of the disease AIDS is a virus known as the human immunodeficiency virus (HIV). The HIV virus is a member of a large family of viruses termed retroviruses, which have as a hallmark the capacity to convert their RNA genome into a DNA form that then undergoes a process of integration into the host cell chromosome, followed by the expression of the viral genome and translation of viral proteins in the infected cell. This review describes the organization of the HIV-1 viral genome, the expression of viral proteins, as well as the functions of the accessory viral proteins in HIV replication. The replication of the viral genome is divided into two phases, the early phase and the late phase. The early phase consists of the interaction of the virus with the cell surface receptor (CD4 molecule in most cases), the uncoating and conversion of the viral RNA genome into a DNA form, and the integration into the host cell chromosome. The late phase consists of the expression of the viral proteins from the integrated viral genome, the translation of viral proteins, and the assembly and release of the virus. Points in the HIV-1 life cycle that are targets for therapeutic intervention are also discussed.

Subcellular localization of the Vif protein of human immunodeficiency virus type 1

The Vif (viral infectivity factor) protein of human immunodeficiency virus type 1 (HIV-1) has been shown to dramatically enhance the infectivity of HIV-1 virus particles during virus production. The subcellular localization of Vif was examined to elucidate cellular pathways which may be important for Vif function. Indirect immunofluorescence staining of Vif demonstrated a diffuse cytoplasmic distribution and showed that most Vif was not associated with the Golgi complex, a proposed site of localization (B. Guy, M. Geist, K. Dott, D. Spehner, M.-P. Kieny, and J.-P. Lecocq, J. Virol. 65:1325-1331, 1991). Subcellular fractionation of transfected COS cells and HIV-1-infected Jurkat and CEM cells demonstrated that Vif is a cytoplasmic protein which exists in both a soluble cytosolic form and membrane-associated form. The membrane-associated form of Vif is a peripheral membrane protein which is tightly associated with the cytoplasmic side of cellular membranes. The C terminus of Vif was required for the stable association of Vif with membranes. The C terminus was also essential for Vif function, suggesting that the association of Vif with membranes is likely to be important for its biological activity. The highly conserved regions at residues 103 to 115 and 142 to 150 were important for Vif function but did not affect membrane association, indicating that these regions are likely to be important for other, as-yet-unknown functions.

Human immunodeficiency virus type 2 multiply spliced transcripts

Viral transcripts, particularly those of the regulatory genes (e.g., rev) in lymphocytic cells chronically infected with human immunodeficiency virus type 2, consist of two types, differing in the structure of the leader sequence derived from the 5' long terminal repeat (LTR). Some transcripts undergo a specific splicing event within the 5' LTR, removing an intron consisting of a part of the R region whereas others do not. Because this spliced-out R region is a part of the trans-activation response element (TAR), it could influence trans-activator (Tat)-mediated trans-activation of viral gene expression. Moreover, this part of the R region is predicted to contain a stable secondary structure that could affect the efficiency of translation of the transcripts without this splicing. Thus, the 5' LTR splicing could have important consequences for virus replication, latency, and pathogenicity.

Role of vif in replication of human immunodeficiency virus type 1 in CD4+ T lymphocytes

The viral infectivity factor gene vif of human immunodeficiency virus type 1 has been shown to affect the infectivity but not the production of virus particles. In this study, the effect of vif in the context of the HXB2 virus on virus replication in several CD4+ T-cell lines was investigated. vif was found to be required for replication in the CD4+ T-cell lines CEM and H9 as well as in peripheral blood T lymphocytes. vif was not required for replication in the SupT1, C8166, and Jurkat T-cell lines. The infectivity of vif-defective viruses depended on the cell type in which the virus was produced. In CEM cells, vif was required for production of virus capable of initiating infection in all cell lines studied. vif-defective virus produced by SupT1, C8166, and Jurkat cells and the monkey cell line COS-1 could initiate infection in multiple cell lines, including CEM and H9. These results suggest that vif can compensate for cellular factors required for production of infectious virus particles that are present in some cell lines such as SupT1, C8166, and Jurkat but are absent in others such as CEM and H9 as well as peripheral blood T lymphocytes. The effect of vif was not altered by deletion of the carboxyl terminus of gp41, a proposed target for vif (B. Guy, M. Geist, K. Dott, D. Spehner, M.-P. Kieny, and J.-P. Lecocq, J. Virol. 65:1325-1331, 1991). These studies demonstrate that vif enhances viral infectivity during virus production and also suggest that vif is likely to be important for natural infections.

Complex splicing in the human T-cell leukemia virus (HTLV) family of retroviruses: novel mRNAs and proteins produced by HTLV type I

Novel cytoplasmic mRNA species produced by human T-cell leukemia virus type I (HTLV-I) were cloned by using the polymerase chain reaction technique. Five novel 3' splice sites located in the X region and upstream of the env gene were identified. Splicing to the 3' splice sites in the X region generates mRNAs that express two previously unidentified viral proteins, named Rof and Tof. Tof accumulates in the nucleoli of transfected cells. The other viruses of the HTLV family, such as HTLV-II and bovine leukemia virus, also have a complex splicing pattern and are capable of producing additional proteins encoded in the X region. These results suggest that HTLV-I and other members of the HTLV family produce novel proteins, which may contribute to the biological properties of these viruses.

Mechanism of translation of monocistronic and multicistronic human immunodeficiency virus type 1 mRNAs

We have used a panel of cDNA clones expressing wild-type and mutant human immunodeficiency virus type 1 (HIV-1) mRNAs to study translation of these mRNAs in eucaryotic cells. The tat open reading frame (ORF) has a strong signal for translation initiation, while rev and vpu ORFs have weaker signals. The expression of downstream ORFs is inhibited in mRNAs that contain the tat ORF as the first ORF. In contrast, downstream ORFs are expressed efficiently from mRNAs that have rev or vpu as the first ORF. All env mRNAs contain the upstream vpu ORF. Expression of HIV-1 Env protein requires a weak vpu AUG, which allows leaky scanning to occur, thereby allowing ribosomes access to the downstream env ORF. We concluded that HIV-1 mRNAs are translated by the scanning mechanism and that expression of more than one protein from each mRNA was caused by leaky scanning at the first AUG of the mRNA.

Prevalence of antibodies to recombinant virion infectivity factor in the sera of prospectively studied patients with HIV-1 infection

Two hundred twenty-four sera were collected from 34 HIV-1 infected patients during an observation period of up to 4.5 years (109 patient years of observation). The sera were tested for the presence of antibodies against the HIV-1 virion infectivity factor (vif) protein. Thirty sera from 6 HIV-1 seronegative individuals served as negative controls. The sera were immunoblotted against a recombinant, prokaryotically expressed vif protein. The prevalence of anti-vif antibodies increased significantly with progression of the disease from 18% to 81% (P less than 0.0001) which suggests a possible role of vif in HIV-1 replication and pathogenicity.

Mechanism of translation of monocistronic and multicistronic human immunodeficiency virus type 1 mRNAs

We have used a panel of cDNA clones expressing wild-type and mutant human immunodeficiency virus type 1 (HIV-1) mRNAs to study translation of these mRNAs in eucaryotic cells. The tat open reading frame (ORF) has a strong signal for translation initiation, while rev and vpu ORFs have weaker signals. The expression of downstream ORFs is inhibited in mRNAs that contain the tat ORF as the first ORF. In contrast, downstream ORFs are expressed efficiently from mRNAs that have rev or vpu as the first ORF. All env mRNAs contain the upstream vpu ORF. Expression of HIV-1 Env protein requires a weak vpu AUG, which allows leaky scanning to occur, thereby allowing ribosomes access to the downstream env ORF. We concluded that HIV-1 mRNAs are translated by the scanning mechanism and that expression of more than one protein from each mRNA was caused by leaky scanning at the first AUG of the mRNA.

Distinct RNA sequences in the gag region of human immunodeficiency virus type 1 decrease RNA stability and inhibit expression in the absence of Rev protein

The expression of Gag, Pol, Vif, Vpr, Vpu, and Env proteins from unspliced and partially spliced human immunodeficiency virus type 1 (HIV-1) mRNAs depends on the viral protein Rev, while the production of Tat, Rev, and Nef from multiply spliced mRNAs does not require Rev. To investigate the difference between gag and tat mRNAs, we generated plasmids expressing tat-gag hybrid mRNAs. Insertion of the gag gene downstream of the tat open reading frame in the tat cDNA resulted in the inhibition of Tat production. This inhibition was caused, at least in part, by a decrease in the stability of the produced mRNA. Deletions in gag defined a 218-nucleotide inhibitory sequence named INS-1 and located at the 5' end of the gag gene. Further experiments indicated the presence of more than one inhibitory sequence in the gag-protease gene region of the viral genome. The inhibitory effect of INS-1 was counteracted by the positive effect mediated by the Rev-Rev-responsive element interaction, indicating that this sequence is important for Rev-regulated gag expression. The INS-1 sequence did not contain any known HIV-1 splice sites and acted independently of splicing. It was found to have an unusually high AU content (61.5% AU), a common feature among cellular mRNAs with short half-lives. These results suggest that HIV-1 and possibly other lentiviruses have evolved to express unstable mRNAs which require additional regulatory factors for their expression. This strategy may offer the virus several advantages, including the ability to enter a state of low or latent expression in the host.

Antigenic domains of the HIV-1 vif protein as recognized by human sera and murine monoclonal antibodies

To analyze the vif antibody response in individuals infected with the human immunodeficiency virus type 1 (HIV-1) and to determine antigenic epitopes on the vif protein, 104 HIV-1+ sera were screened for reactivity with a recombinant vif protein; 30 (28.8%) of these sera recognized the recombinant vif protein in immunoblot and were employed, together with 17 HIV-1/vif-negative control sera, in an enzyme immunoassay (EIA)-based epitope scanning assay with 183 overlapping decapeptides that covered the complete amino acid sequence of the HIV-1 vif protein (strain BH10). Of the 30 HIV-1/vif+ sera, 87% reacted with decapeptides comprising the two following epitopes: IEWRKKRY (vif amino acids 87-94) or DRWNKPQ (vif amino acids 172-178). The two epitopes were 89% and 100% conserved among different HIV-1 strains and their antigenicity could be confirmed by computer-assisted predictions of vif antigenic determinants. All the sera reactive with recombinant vif protein and with vif peptides originated from patients in CDC stages III or IV. Two murine anti-vif monoclonal antibodies reacted only with the seven C-terminal amino acids of the vif protein (SHTMNGH), which were not recognized by any of the human sera. Our results may be useful for further studies of vif seroreactivity and for the production of anti-vif mono- or polyclonal antibodies using vif peptides.

Immunological study of the nef protein from HIV-1 by polyclonal and monoclonal antibodies

We constructed and expressed different overlapping fusion proteins with the nef gene of HIV-1 and generated specific polyclonal rabbit and monoclonal mouse antibodies against these recombinant proteins. The rabbit antisera, one of the monoclonal antibodies as well as a serum from a HIV-1 infected patient recognized the nef protein with Mr 27 kDa in latently HIV-1 infected glioma cells in the immunoblot. In contrast, these antibodies could not detect nef in productively HIV-1 infected Molt-3 cells neither in immunoblot nor in indirect immunofluorescence assays. These results indicate the possible participation of nef in viral latency. The recombinant nef proteins were used as probes for anti-nef antibodies in human sera. We observed in 17 of 57 sera tested specific anti-nef antibodies. All of these anti-nef positive sera also contained antibodies directed against viral structural proteins. The NH2-terminal region of the recombinant nef was shown to be the major immunodominant antigenic site in the immunoblot assay.

The open reading frame ORF S3 of equine infectious anemia virus is expressed during the viral life cycle

The genome of equine infectious anemia virus (EIAV) contains several small open reading frames (ORFs), the importance of which in the development of the virus is not clear. We investigated the possibility that the largest of these ORFs (ORF S3) is expressed during the course of the viral infection. The ORF S3 information was expressed in Escherichia coli, and the antigen was used to raise monospecific antiserum. A 20-kDa protein expressed in cells producing EIAV was identified as the gene product of ORF S3. Furthermore, sera from EIAV-infected animals specifically recognized this protein, indicating that the ORF S3 antigen is expressed in vivo as well. A model for the expression of this new viral antigen is presented. The proposed splicing pattern is similar to that of the VEP-1 protein of maedi-visna-virus, which tempts us to speculate that ORF S3 defines the second exon of the EIAV Rev protein.

Repressive effect of the nef cDNA of human immunodeficiency virus type 1 on the promoter activity of the viral long terminal repeat

The nef gene product of human immunodeficiency virus type 1 (HIV-1) has been implicated as a negative factor for viral replication and is suspected to play an important role in the maintenance of viral latency. However, there seems to be evidence both for and against the negative effect of nef gene product. In the present report, we reevaluated the function of the nef gene by means of transient CAT assays with two human T cell lines. In most of the experiments, carefully controlled triplicate studies were carried out. We observed that not only the nef-expression plasmid, but also an effector plasmid containing the nef cDNA sequence in a reverse orientation, not expressing the Nef protein, showed a similar extent of repression of the HIV-1 promoter activity. We also examined the repressive effect of the nef cDNA with deletion mutants of HIV-1 long terminal repeat and heterologous promoters. The results led us to conclude that the apparent "repressor"-like action of the nef cDNA itself could be explained by competition for certain transcription factors required for HIV-1 gene expression by identical sequences also present in the nef cDNA.

Env and Vpu proteins of human immunodeficiency virus type 1 are produced from multiple bicistronic mRNAs

Three size classes of human immunodeficiency virus type 1 (HIV-1) mRNAs are produced in infected cells: full-length, intermediate, and small. Here we report that the intermediate-size class of viral mRNAs is heterogeneous, consisting of at least 12 differentially spliced species. This group contains nine bicistronic mRNAs producing Env and Vpu and three mRNAs expressing only the first exon of tat. In the latter mRNAs, Env and Vpu expression is blocked by the presence of the upstream tat open reading frame. We conclude that internal initiation of translation is not the mechanism for generation of the bicistronic env mRNAs. Translation of HIV-1 mRNAs is consistent with the scanning mechanism in which Env is produced by leaky scanning from mRNAs that contain env as the second or third reading frame. Env and Vpu proteins are expressed from the same mRNAs and are coordinately regulated by Rev. This arrangement may reflect a requirement for coordinate expression of Vpu and Env.

A synthetic protein corresponding to the entire vpr gene product from the human immunodeficiency virus HIV-1 is recognized by antibodies from HIV-infected patients

The 95 amino acid-protein encoded by the non-structural vpr gene of the human immunodeficiency virus type 1 (LAV-1BRU isolate) was chemically synthesized by solid phase methodology. The synthetic vpr protein was characterized by amino acid analysis, sequence analysis, RP-HPLC, and urea-SDS PAGE. Using a radioimmunoassay, antibodies to the synthetic protein were detected in sera of 25% of HIV 1-seropositive patients tested. Western blot analysis suggested that the antibodies preferentially recognize the dimeric form of vpr.

Open reading frames on plus strand genome of duck hepatitis B virus

Hepadnaviruses have open reading frames of surface, core, polymerase and X protein on the minus strand of the genome. We analyzed a plus strand of duck hepatitis B virus (DHBV) for the presence of open reading frame with a computer program. We found one frame on the area that is complement to 3' end of polymerase gene and 5' end of precore gene. That open reading frame is conserved in three strains of DHBV, and the predicted protein is about 80 amino acids.

Cloning and functional analysis of multiply spliced mRNA species of human immunodeficiency virus type 1

We have used the polymerase chain reaction technique to clone the small multiply spliced mRNA species produced after infection of human cells by a molecular clone of human immunodeficiency virus type 1 (HIV-1). We identified six Rev-expressing mRNAs, which were generated by the use of two splice acceptors located immediately upstream of the rev AUG. The class of small mRNAs included 12 mRNAs expressing Tat, Rev, and Nef. In addition, HIV-1 produced other multiply spliced mRNAs that used alternative splice sites identified by cloning and sequencing. All of these mRNAs were found in the cytoplasm and should be able to produce additional proteins. The coding capacity of the tat, rev, and nef mRNAs was analyzed by transfection of the cloned cDNAs into human cells. The tat mRNAs produced high levels of Tat, but very low levels of Rev and Nef. All the rev mRNAs expressed high levels of both Rev and Nef and were essential for the production of sufficient amounts of Rev. Therefore, HIV-1 uses both alternatively spliced and bicistronic mRNAs for the production of Tat, Rev, and Nef proteins.

Evolutionary origin of human and simian immunodeficiency viruses

From what viruses the human immunodeficiency viruses (HIVs) originated is an extremely controversial question. To address this question, we have analyzed nucleotide sequences of simian immunodeficiency viruses (SIVs) and HIVs by using the techniques for understanding molecular evolution. In particular, we compared the nucleotide sequences of whole genomes, gene region by gene region, between a given pair of viruses, including four types of SIVs--isolated from mandrills (Papio sphinx), African green monkeys (Cercopithecus aethiops), sooty mangabeys (Cercocebus atys), and rhesus macaques (Macaca mulatta)--as well as HIVs. Phylogenetic trees for all gene regions examined showed that the present HIVs may have emerged as different variants of SIVs of Old World monkeys, possibly from recombination between viruses related to SIVs.

Identification of a cis-acting element in human immunodeficiency virus type 2 (HIV-2) that is responsive to the HIV-1 rev and human T-cell leukemia virus types I and II rex proteins

A simian virus 40 late replacement vector encoding human immunodeficiency virus type 1 (HIV-1) gp120 (pGP120) was used to define a region within the HIV-2 genome that could work as a rev-responsive element (RRE). Our previous work showed that gp120 expression in this system required a functional RRE in cis and required the rev protein in trans (M.-L. Hammarskjöld, J. Heimer, B. Hammarskjöld, I. Sangwan, L. Albert, and D. Rekosh, J. Virol. 63:1959-1966, 1989). Using pGP120, we first mapped an RRE to a 1,042-base-pair (bp) Sau3a fragment in the env region of HIV-2. Both HIV-1 rev (rev1) and HIV-2 rev (rev2) could work in conjunction with this fragment. Further mapping showed that a 272-bp subfragment within the 1,042-bp region was sufficient as an RRE. Surprisingly, the smaller fragment worked only with the rev1 protein and not with its homologous rev2 protein. In addition, the rev2 protein failed to function together with the RRE from HIV-1. We also utilized this system to examine the ability of the rex genes of human T-cell leukemia virus types I and II to functionally substitute for rev. These experiments showed that complementation by both the rexI and rexII proteins required the presence of an RRE. The rex proteins worked well in conjunction with either the HIV-1 or the HIV-2 RRE (the 1,042-bp as well as the 272-bp fragment).

Speed of progression to AIDS and degree of antibody response to accessory gene products of HIV-1

Antibodies to E. coli-produced HIV-1 nef, rev, tat, vpu, and vpr proteins were measured by enzyme immunoassay in serial sets of sera from 72 men seroconverting for antibodies to HIV-1 structural proteins, and from 190 initially symptom-free men who were seropositive for these antibodies at entry into the study. In the men seroconverting for antibodies to structural proteins the levels of nef-, rev-, and tat-specific antibodies, but not of vpu-, and vpr-specific antibodies, within 3 months of seroconversion, appeared to be lower in the five men progressing to AIDS, compared with the men remaining symptom-free during follow-up. Analysis of the prevalence of previously described antibody profiles to these accessory gene products was carried out. In all HIV-1 antibody seroconverters and in those HIV-1 antibody seropositive men with 15 or more months of follow-up who progressed to AIDS, there was a shift from predominantly nef- and vpu-specific antibody negative profiles in the men developing AIDS in the early years of the study to predominantly nef- and vpu-specific antibody positive profiles in men who developed AIDS later. Rev- and tat-specific antibody negative profiles were dominant in men progressing to AIDS throughout follow-up. No vpr-specific antibody profile occurred preferentially in the men progressing to AIDS throughout follow-up. Low antibody reactivity to accessory gene products nef, rev, and tat appears, like low anti-core antibody reactivity, to be associated with progression to AIDS relatively rapidly after infection with HIV-1.

Antibodies to recombinant HIV-1 vif, tat, and nef proteins in human sera

The prevalence of antibodies against HIV-1 regulatory proteins in sera of HIV-infected patients from different stages of disease was investigated. HIV-1 vif, tat, and nef genes were cloned in procaryotic vectors and were expressed as MS-2 fusion proteins (vif and nef) or as a non-fusion protein (tat). These recombinant proteins were employed in immunoblot experiments. The specificity of the recognition was confirmed by competition experiments and with control sera from HIV-negative patients. Analysis of 136 serum samples revealed a high percentage of antibodies against nef, irrespective of the stage of disease. Antibodies against tat were found less frequently and increased from 16% to 40% with disease progression. Vif antibodies were detected only in a low percentage in early stages of disease, but their prevalence increased to 36% and 72% with progression of disease to AIDS-related complex and AIDS. Our data suggest that the detection of antibodies against nef may represent an additional and useful marker for the diagnosis of HIV infection, whereas the detection of vif antibodies may indicate disease progression.

Large fragments of nef-protein and gp110 envelope glycoprotein from HIV-1. Synthesis, CD analysis and immunoreactivity

Chemical synthesis of large peptide fragments (from 18 to 66 amino acid residues long) of the gp110 envelope glycoprotein and of nef-protein from HIV-1 was achieved by the solid phase method. Stepwise assembling of the peptide chains was carried out automatically on 4-(oxymethyl)-phenylacetamidomethyl resin using the N-alpha-butyloxycarbonyl amino acids with benzyl-based side chain protecting groups. Two elongation protocols were used depending on the peptide chain length: a standard cycle, mainly characterized by a single coupling step (Boc-amino acid symmetrical anhydride in dimethylformamide), and an optimized one for large peptides, based on a double coupling strategy (Boc-amino acid symmetrical anhydride first in dimethylformamide, then in dichloromethane). Final cleavage of the peptide from the solid support was carried out by anhydrous hydrogen fluoride and crude peptides were purified by C18 reverse phase medium pressure liquid chromatography after molecular filtration. Characterization of the purified peptides was done by analytical HPLC, amino acid content determination, and circular dichroism analysis both in polar (H2O) and in non-polar (TFE) environments. Immunoreactivity of anti-nef positive sera from HIV-1 infected patients by ELISA with the synthetic peptides was investigated. The results showed four major antigenic regions of nef-protein and mainly the immunodominance of the N- and C-termini of the molecule. Several of these peptides should prove to be useful for both diagnosis and vaccination purposes.

Proviral DNA integration and transcriptional patterns of equine infectious anemia virus during persistent and cytopathic infections

The structure and integration patterns of equine infectious anemia virus (EIAV) proviral DNA and the patterns of viral transcription were examined in persistent and cytopathic infections of cultured cells. The results of Southern blot analyses indicated that, in persistently infected cells, about 30% of the EIAV provirus exists as randomly integrated DNA, while the remaining 70% is equally divided between unintegrated linear and closed circular forms. The cytopathic infection, in contrast, is characterized by levels of integrated provirus ranging from 65 to more than 90% of the total proviral DNA, depending on the extent of cytopathology exhibited by the virus strain employed. In both persistent and cytopathic infections, extensive Northern (RNA) blot analyses have revealed the presence of two major virus-specific transcripts, an 8.2-kilobase (kb) full-length genomic mRNA and a 3.5-kb single-spliced mRNA. A low-abundance 1.5-kb mRNA, presumably formed by a double-splicing event of the full-length RNA, was also detected in the cytopathic EIAV infection. The two major viral transcripts are present in approximately equal quantities in persistently infected cells, while the cytopathic infection reveals nearly a 30-fold higher level of viral transcripts in which the 3.5-kb species constitutes over 75% of the total viral mRNA. The relatively high proportion of proviral DNA integration and the simple pattern of viral transcription observed during EIAV infections appeared to be different from the generally observed patterns of predominantly unintegrated proviral DNA and multi-spliced viral mRNAs in cells infected with other lentiviruses such as visna virus or human immunodeficiency virus type 1. Moreover, the data suggested that the cytopathology of EIAV may be correlated in part with the degree of proviral DNA integration and levels of viral mRNA in infected cells, particularly that of the spliced 3.5-kb mRNA.

Low antigenicity of HIV-1 rev: rev-specific antibody response of limited value as correlate of rev gene expression and disease progression

An enzyme immunoassay based on an E. coli-produced HIV-1 rev gene product was used to detect rev-specific antibodies in longitudinally collected serum samples from 196 initially symptom-free men who were seropositive for antibodies to HIV-1 structural proteins and 72 men who seroconverted for such antibodies. In 61% of men no rev-specific antibodies were detected at all, 30% had persistently detectable rev-specific antibodies, and in 9% rev-specific antibodies were only transiently or intermittently detected. When a persistent rev-specific antibody response occurred in subjects who seroconverted to structural proteins, it was always, with one exception, found within 12 months of seroconversion. The rev-specific antibodies were also studied in a transectional sample of sera from the men who remained symptom-free and from those who developed AIDS-related conditions or AIDS, as well as in sera from 31 other men with AIDS-related conditions and in sera from 6 of these men at the time they developed AIDS. The rev-specific antibodies were found in 34% of symptom-free men, in 28% of patients with AIDS-related conditions, and in 16% of patients with AIDS. The low incidence of rev-specific antibodies early after infection may be due to low antigenicity of rev. The lower prevalence of rev-specific antibodies in sera from patients with AIDS, compared with patients with AIDS-related conditions and symptom-free HIV-1-infected individuals, may be explained by a progressive HIV-1-induced immunodeficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody response to human immunodeficiency virus type 1 protease according to risk group and disease stage

Three groups with different routes of human immunodeficiency virus type 1 (HIV-1) transmission (homosexual men, hemophiliacs, and children) were studied for serum antibodies to a recombinant form of the HIV-1 protease using an enzyme-linked immunoassay. At 1 year after seroconversion, defined as the moment antibodies to HIV-1 proteins were first detected, 56% (34/61) of the homosexual men had antibodies to protease, and 2 years after seroconversion this percentage was 63% (24/38). Within this 2-year period these antibodies were no longer detected in 16% (9/56). A similar pattern was observed in 20 hemophiliacs who seroconverted after exposure to HIV-1-contaminated blood products. We found that 63% (160/255) of homosexual men in Centers for Disease Control stage II or III, 60% (9/15) of patients with acquired immunodeficiency syndrome (AIDS)-related complex, and 36% (14/39) of patients with AIDS had antibodies to protease. In 255 homosexual men in Centers for Disease Control stage II or III, antibodies to protease were significantly more frequently found in samples lacking HIV-1 antigen (P less than 0.001) and possessing antibodies to HIV-1 core proteins (P less than 0.001). Twenty-four persons who developed AIDS were studied longitudinally: 58% (14/24) had antibodies to protease 1 year before developing symptoms; 29% (7/24) showed a decline and 29% (7/24) showed a loss of antibodies to protease at the onset of symptoms. Within a group of 47 HIV-1-infected children, 90% (18/20) with a stable disease course were persistently protease antibody positive, versus 4 of 27 children (15%) with an unstable disease course (P = 0.0001). These data indicate that HIV-1 protease is expressed and antigenic in most HIV-1-infected individuals and that a decline or absence of antibodies to protease is strongly associated with unstable disease in children and AIDS in adults.