Induction of rapid and extensive beta-chemokine synthesis in macrophages by human immunodeficiency virus type 1 and gp120, independently of their coreceptor phenotype

Human immunodeficiency virus type 1 (HIV-1) interacts with its target cells through CD4 and a coreceptor, generally CCR5 or CXCR4. Macrophages display CD4, CCR5, and CXCR4 that are competent for binding and entry of virus. Virus binding also induces several responses by lymphocytes and macrophages that can be dissociated from productive infection. We investigated the responses of macrophages to exposure to a series of HIV-1 species, R5 species that productively infect and X4 species that do not infect macrophages. We chose to monitor production of several physiologically relevant factors within hours of treatment to resolve virally induced effects that may be unlinked to HIV-1 production. Our novel findings indicate that independently of their coreceptor phenotype and independently of virus replication, exposure to certain R5 and X4 HIV-1 species induced secretion of high levels of macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, RANTES, and tumor necrosis factor alpha. However two of the six R5 species tested, despite efficient infection, were unable to induce rapid chemokine production. The acute effects of virus on macrophages could be mimicked by exposure to purified R5 or the X4 HIV-1 envelope glycoprotein gp120. Depletion of intracellular Ca(2+) or inhibition of protein synthesis blocked the chemokine induction, implicating Ca(2+)-mediated signal transduction and new protein synthesis in the response. The group of viruses able to induce this chemokine response was not consistent with coreceptor usage. We conclude that human macrophages respond rapidly to R5 and X4 envelope binding by production of high levels of physiologically active proteins that are implicated in HIV-1 pathogenesis.

Highly productive infection with pseudotyped human immunodeficiency virus type 1 (HIV-1) indicates no intracellular restrictions to HIV-1 replication in primary human astrocytes

Human astrocytes can be infected with human immunodeficiency virus type 1 (HIV-1) in vitro and in vivo, but, in contrast to T lymphocytes and macrophages, virus expression is inefficient. To investigate the HIV-1 life cycle in human fetal astrocytes, we infected cells with HIV-1 pseudotyped with envelope glycoproteins of either amphotropic murine leukemia virus or vesicular stomatitis virus. Infection by both pseudotypes was productive and long lasting and reached a peak of 68% infected cells and 1.7 microg of viral p24 per ml of culture supernatant 7 days after virus inoculation and then continued with gradually declining levels of virus expression through 7 weeks of follow-up. This contrasted with less than 0.1% HIV-1 antigen-positive cells and 400 pg of extracellular p24 per ml at the peak of astrocyte infection with native HIV-1. Cell viability and growth kinetics were similar in infected and control cells. Northern blot analysis revealed the presence of major HIV-1 RNA species of 9, 4, and 2 kb in astrocytes exposed to pseudotyped (but not wild-type) HIV-1 at 2, 14, and 28 days after infection. Consistent with productive infection, the 9- and 4-kb viral transcripts in astrocytes infected by pseudotyped HIV-1 were as abundant as the 2-kb mRNA during 4 weeks of follow-up, and both structural and regulatory viral proteins were detected in infected cells by immunoblotting or cell staining. The progeny virus released by these cells was infectious. These results indicate that the major barrier to HIV-1 infection of primary astrocytes is at virus entry and that astrocytes have no intrinsic intracellular restriction to efficient HIV-1 replication.

Prolonged infection of peripheral blood lymphocytes by Vif-negative HIV type 1 induces resistance to productive HIV type 1 infection through soluble factors

The auxiliary protein Vif is essential for productive HIV-1 infection of primary lymphocytes and macrophages. Vif is required for the synthesis of infectious progeny virus and infection of peripheral blood lymphocytes (PBLs) by Vif-negative HIV-1 was thought to be confined to a single cycle. Here we define conditions for the maintenance of Vif-negative HIV-1 in PBLs during multiple rounds of viral infection. PBLs were infected with Vif-negative HIV-1 and then were serially cocultivated with uninfected PBLs. As determined by measurement of viral DNA, viral burdens declined but then rebounded and reached 1 copy per 30 cells after 7 weeks of culture. Viral core antigen p24 levels dropped and remained below detection limits after three cocultivations with no observed cytotoxicity. Viral RNA was also undetectable in cocultivated cells. The incapacitating deletion in vif was maintained during cocultivation as shown by the size of the vif amplicon. The presence of viral DNA in the absence of viral p24 RNA or protein suggested that the cells were capable of control of HIV-1 expression. This regulatory capacity was confirmed by the demonstration of resistance of PBLs or isolated CD4-positive cells to expression of exogenous wild-type R5 or X4 HIV-1. Resistant PBLs were susceptible to fusion with HIV-1 envelope-expressing cells and to reverse transcription of incoming viral DNA, indicating that the block to replication of exogenous virus was imposed after viral entry and DNA synthesis. Using a dual-chamber apparatus, we demonstrated that resistant Vif-negative HIV-1-infected PBLs secrete soluble factors that confer resistance on naive cells. These findings indicate that Vif-negative HIV-1 infection of primary CD4-positive lymphocytes results in maintenance of unexpressed virus and induces the production of soluble factors conferring resistance to wild-type HIV-1 replication on uninfected cells.

Human immunodeficiency virus type 1 can infect human retinal pigment epithelial cells in culture and alter the ability of the cells to phagocytose rod outer segment membranes

Human immunodeficiency virus type 1 (HIV-1) has been found in the vitreous of persons with AIDS. Here we investigated the susceptibility of human retinal pigment epithelial (RPE) cells to HIV-1 infection in culture and the effects of HIV-1 on the phagocytic function of the RPE. We found that 10 of 11 populations of RPE cells isolated from different fetal or adult eyes were susceptible to low-level replication of HIV-1/NL4-3 as determined by the detection of viral DNA and spliced viral RNA encoding envelope. HIV-1 infection was not inhibited by recombinant soluble CD4, suggesting that CD4 is not required for virus entry into RPE cells. RPE cells fused with target cells constitutively expressing HIV-1 envelope glycoproteins, indicating that HIV-1 enters cells by receptor-mediated fusion. Exposure to HIV-1 or recombinant gp120 caused a two- to four-fold increase in the binding and uptake of isolated rod outer segments by RPE cells. These findings introduce a new cell target of HIV-1 replication in the eye and indicate that RPE cells function aberrantly when exposed to HIV-1 or its envelope glycoprotein.

Peptide inhibitors of HIV-1 protease and viral infection of peripheral blood lymphocytes based on HIV-1 Vif

We recently reported that HIV-1 Vif (virion infectivity factor) inhibits HIV-1 protease in vitro and in bacteria, suggesting that it may serve as the basis for the design of new protease inhibitors and treatment for HIV-1 infection. To evaluate this possibility, we synthesized peptide derivatives from the region of Vif, which inhibits protease, and tested their activity on protease. In an assay of cleavage of virion-like particles composed of HIV-1 Gag precursor polyprotein, full-length recombinant Vif, and a peptide consisting of residues 21-65 of Vif, but not a control peptide or BSA, inhibited protease activity. Vif21-65 blocked protease at a molar ratio of two to one. We then tested this peptide and a smaller peptide, Vif41-65, for their effects on HIV-1 infection of peripheral blood lymphocytes. Both Vif peptides inhibited virus expression below the limit of detection, but control peptides had no effect. To investigate its site of action, Vif21-65 was tested for its effect on Gag cleavage by protease during HIV-1 infection. We found that commensurate with its reduction of virus expression, Vif21-65 inhibited the cleavage of the polyprotein p55 to mature p24. These results are similar to those obtained by using Ro 31-8959, a protease inhibitor in clinical use. We conclude that Vif-derived peptides inhibit protease during HIV-1 infection and may be useful for the development of new protease inhibitors.

Viral interference in HIV-1 infected cells

The study of viral interference in HIV-1 infected cells has revealed several different means whereby infected cells resist superinfection. The most familiar of these, down-modulation of cellular receptors for virus, can be accomplished through the independent action of at least three HIV-1 proteins. Both the principal viral receptor CD4 and the chemokine receptors which serve as co-receptors are subject to down-modulation as a consequence of infection. Elucidation of the specificity of co-receptor utilisation by HIV-1 strains is an exciting, ongoing task which has opened new avenues to the understanding of viral replication and pathogenesis. Novel routes to resistance to superinfection have been discovered during HIV-1 infection and their investigation may reveal new pathways to control HIV-1 and the loss of immunological function with AIDS. Copyright 1998 John Wiley & Sons, Ltd.

Human immunodeficiency virus type 1 (HIV-1) protein Vif inhibits the activity of HIV-1 protease in bacteria and in vitro

Human immunodeficiency virus type 1 (HIV-1) Vif is required for productive infection of T lymphocytes and macrophages. Virions produced in the absence of Vif have abnormal core morphology and those produced in primary T cells carry immature core proteins and low levels of mature capsid (M. Simm, M. Shahabuddin, W. Chao, J. S. Allan, and D. J. Volsky, J. Virol. 69:4582-4586, 1995). To investigate whether Vif influences the activity of HIV-1 protease (PR), the viral enzyme which is responsible for processing Gag and Gag-Pol precursor polyproteins into mature virion components, we transformed bacteria to inducibly express truncated Gag-Pol fusion proteins and Vif. We examined the cleavage of polyproteins consisting of matrix to PR (Gag-PR), capsid to PR (CA-PR), and p6Pol to PR (p6Pol-PR) and evaluated HIV-1 protein processing at specific sites by Western blotting using antibodies against matrix, capsid, and PR proteins. We found that Vif modulates HIV-1 PR activity in bacteria mainly by preventing the release of mature MA and CA from Gag-PR, CA from CA-PR, and p6Pol from p6Pol-PR, with other cleavages being less affected. Using subconstructs of Vif, we mapped this activity to the N-terminal half of the molecule, thus identifying a new functional domain of Vif. Kinetic study of p6Pol-PR autocatalysis in the presence or absence of Vif revealed that Vif and N'Vif reduce the rate of PR-mediated proteolysis of this substrate. In an assay of in vitro proteolysis of a synthetic peptide substrate by purified recombinant PR we found that recombinant Vif and the N-terminal half of the molecule specifically inhibit PR activity at a molar ratio of the N-terminal half of Vif to PR of about 1. These results suggest a mechanism and site of action of Vif in HIV-1 replication and demonstrate novel regulation of a lentivirus PR by an autologous viral protein acting in trans.

Isolation and long-term culture of primary ocular human immunodeficiency virus type 1 isolates in primary astrocytes

Vitreous specimens from 14 HIV-1 infected persons undergoing medically indicated vitrectomy were assayed for the presence of infectious HIV-1 and viral tropism. Human primary fetal astrocytes, adult lymphocytes, or macrophages were exposed to vitreous in culture and and cells were then assayed for HIV-1 DNA by polymerase chain reaction amplification. We found that 11 of 14 patients tested carried ocular HIV-1 which replicated in one or more primary cell types; of the 13 vitreous samples tested in astrocytes, eight contained transmissible HIV-1. The three patients with no culturable ocular virus were in antiviral therapy at the time of vitrectomy. Comparison of envelope V3 sequences from astrocytes infected in culture to that in uncultured blood cells revealed 21% sequence divergence indicating that ocular HIV-1 transmitted to astrocytes was not recently derived from virus present in the blood. Two ocular samples transmissible to astrocytes were tested further and found capable of sustained replication by serial passage to uninfected astrocytes. However, the viral structural proteins produced by infected astrocytes were abnormal, p24 was absent and higher molecular weight Gag proteins were present. We conclude that the eye is a central nervous system compartment which frequently contains HIV-1 capable of replication in human astrocytes.

vif-negative human immunodeficiency virus type 1 persistently replicates in primary macrophages, producing attenuated progeny virus

The vif gene of human immunodeficiency virus type 1 (HIV-1) is required for efficient infection of primary T lymphocytes. In this study, we investigated in detail the role of vif in productive infection of primary monocyte-derived macrophages (MDM). Viruses carrying missense or deletion mutations in vif were constructed on the background of the monocytotropic recombinant NLHXADA-GP. Using MDM from multiple donors, we found that vif mutants produced in complementing or partially complementing cell lines were approximately 10% as infectious as wild-type virus when assayed for incomplete, complete, and circularized viral DNA molecules by quantitative PCR amplification or for viral core antigen p24 production by enzyme-linked immunosorbent assay. We then determined the structure and infectivity of vif mutant HIV-1 by using MDM exclusively both for virus production and as targets for infection. Biosynthetic labeling and immunoprecipitation analysis of sucrose cushion-purified vif-negative HIV-1 made in MDM revealed that the virus had reduced p24 content compared with wild-type HIV-1. Cell-free MDM-derived vif mutant HIV-1 was infectious in macrophages as determined by the synthesis and maintenance of full-length viral DNA and by the produc- tion of particle-associated viral RNA, but its infectivity was approximately 2,500-fold lower than that of wild-type virus whose titer was determined in parallel by measurement of the viral DNA burden. MDM infected with MDM-derived vif-negative HIV-1 were able to transmit the virus to uninfected MDM by cocultivation, confirming the infectiousness of this virus. We conclude that mutations in vif significantly reduce but do not eliminate the capacity of HIV-1 to replicate and produce infectious progeny virus in primary human macrophages.

Interference to human immunodeficiency virus type 1 infection in the absence of downmodulation of the principal virus receptor, CD4

It is thought that interference during human immunodeficiency virus type 1 (HIV-1) infection is established by downmodulation of the principal virus receptor, CD4. Here we present evidence to the contrary. At various times after primary infection, we superinfected T cells in vitro by exposure to a genetically distinct viral clone or to a virus carrying the chloramphenicol acetyltransferase gene. Replication of each virus strain was determined by restriction enzyme analysis of total cellular DNA, by PCR amplification of viral DNA, or by assay of cell extracts for chloramphenicol acetyltransferase activity. We found that efficient viral interference is established within 24 h of infection at a multiplicity of infection of 1. At that time, expression of viral structural proteins was low and infected cells displayed undiminished levels of surface CD4 and were fully susceptible to virus binding and fusion. Superinfection by either cell-free HIV-1 or cocultivation was blocked. Cells resistant to superinfection by HIV-1 remained susceptible to Moloney murine leukemia and vaccinia viruses. No interference was observed 4 h after primary infection or in cells infected with either UV-inactivated HIV-1 or a mutant virus defective in virus-cell fusion activity, indicating that binding of primary virus to CD4 is insufficient to prevent superinfection. The minimum viral requirements for this interference are that HIV-1 must be able to enter cells and synthesize viral DNA; Tat-mediated transcription is dispensable. Our results support the existence of a novel pathway to interference to HIV-1 infection, which we term postentry interference, which blocks superinfection during intracellular phases of the virus life cycle.

Redefinition of tropism of common macrophage-tropic human immunodeficiency virus type 1

Previous studies have suggested that the abilities of human immunodeficiency virus type 1 (HIV-1) to infect primary macrophages and transformed T cell lines are mutually exclusive and define an important biological distinction among HIV-1 strains. In a survey of eight macrophage-tropic HIV-1 strains and nine T cell lines, all frequently used in studies of tropism, we have found that six virus strains replicate in one or more T cell lines and that four T cell lines are highly susceptible to macrophage-tropic HIV-1. Passage through T cell lines did not affect the tropism or the env V3 sequence of monocytotropic HIV-1 strains. We conclude that HIV-1 replication in transformed T cells and primary macrophages are not mutually exclusive, and that as such, these definitions of tropism per se are not generally useful markers for other biological properties of HIV-1.

Modulation of cellular gene expression of HIV type 1 infection as determined by subtractive hybridization cloning: downregulation of thymosin beta 4 in vitro and in vivo

Chronic infection with HIV-1 has profound effects on host cell growth and function. We used subtractive hybridization cloning to identify genes whose expression is modulated by HIV-1 infection in the T leukemia cell line CEM. The gene encoding thymosin beta 4, a ubiquitous polypeptide associated with hematopoietic differentiation, showed two- to threefold reduced transcription in HIV-1-infected CEM cells and other HIV-1-infected T cells and macrophages in vitro. Solid-phase radioimmunoassay revealed about a threefold decrease in the level of thymosin beta 4 protein in lysates of infected cells. Northern blot analysis of RNA samples from lymphocytes of five AIDS patients reveals an up to fivefold reduction in the level of thymosin beta 4 mRNA. These results indicate that HIV-1 infection may directly influence the expression of certain physiologically important proteins.

Infection of macrophages with lymphotropic human immunodeficiency virus type 1 can be arrested after viral DNA synthesis

Lymphotropic strains of human immunodeficiency virus type 1 (HIV-1), including HTLV-IIIB, replicate poorly in macrophages. We have shown previously that lymphotropic HIV-1 fuses equally well with T lymphocytes and macrophages (M. J. Potash, M. Zeira, Z.-B. Huang, T. Pearce, E. Eden, H. Gendelman, and D. J. Volsky, Virology 188:864-868, 1992), suggesting that events in the virus life cycle following virus-cell fusion limit virus replication. We report here that HIV-1 DNA is synthesized efficiently in either ADA or HTLV-IIIB infected alveolar macrophages or monocyte-derived macrophages within 24 h of virus infection, as observed by polymerase chain reaction for amplification of viral DNA sequences from the gag gene. Infection by a cloned lymphotropic HIV-1 strain, N1T-A, also leads to viral DNA synthesis. However, circular viral DNA was detected during strain ADA infection but not during HTLV-IIIB or N1T-A infection of monocyte-derived macrophages. These findings indicate that during replication of lymphotropic HIV-1 in macrophages, all steps of the virus life cycle up to and including reverse transcription take place and that defects in later events, including DNA migration to the nucleus, may account for the limited production of viral proteins.

Human immunodeficiency virus type 1 infection requires reverse transcription of nascent viral RNA

We have previously shown that during human immunodeficiency virus type 1 (HIV-1) infection in vitro continued reverse transcription is required for stable HIV-1 production, but entry by progeny virus is not. To determine the source of the viral RNA reverse-transcribed late in infection, we employed inhibitors of HIV-1 transmission, reverse transcription, and proteolysis of the Gag-Pol polyprotein to interrupt HIV-1 infection in vitro. The kinetics of synthesis of viral DNA, RNA, and proteins was examined. During single-cycle infection, inhibition of reverse transcription 24-72 hr after infection delayed production of viral RNA and protein 10 days. Although viral DNA was detected in Southern blots, inhibition of Gag-Pol processing or transient inhibition of reverse transcription blocked its expression. We propose that after initial reverse transcription of input virion RNA is complete, newly synthesized HIV-1 RNA is reverse-transcribed before its export in virions to yield the viral DNA required for stable HIV-1 production.

Inhibition of type 1 human immunodeficiency virus replication by a tat antagonist to which the virus remains sensitive after prolonged exposure in vitro

The transactivator of transcription, Tat, of human immunodeficiency virus type 1 (HIV-1) is required for viral replication. Inhibition of Tat function could have the potential to keep integrated provirus in dormancy. In the presence of Tat, Ro 24-7429, an analog of Ro 5-3335, inhibited expression of indicator genes controlled by the HIV-1 long terminal repeat promoter in transient transfection assays and in a constitutive cell line at noncytotoxic concentrations. Reduction of steady-state mRNA of the indicator gene by the compound correlated with reduction of the gene product in the constitutive cell line. Ro 24-7429 has broad activity against several strains of HIV-1 in different cell lines, peripheral blood lymphocytes, and macrophages (IC90 = 1-3 microM). Importantly, Ro 24-7429 inhibited viral replication in both acute and chronic infection in vitro, a characteristic expected of a Tat antagonist and not shared by viral reverse transcriptase inhibitors. Consistent with this, the compound reduced cell-associated viral RNA and proteins and partially restored cell-surface CD4 in chronically infected cells. After 2 years of continued weekly passage of the virus in fresh CEM cells grown in the presence of the compound at 1 or 10 microM, the virus did not develop resistance to the drug. These results indicate that the compound's action might involve a cellular factor.

Human immunodeficiency virus type 1 DNA synthesis, integration, and efficient viral replication in growth-arrested T cells

Human immunodeficiency virus type 1 (HIV-1) replicates efficiently in nonproliferating monocytes and macrophages but not in resting primary T lymphocytes. To determine the contribution of cell division to the HIV-1 replicative cycle in T cells, we evaluated HIV-1 expression, integration of proviral DNA, and production of infectious progeny virus in C8166 T-lymphoid cells blocked in cell division by treatment with either mitomycin, a DNA cross-linker, or aphidicolin, a DNA polymerase alpha inhibitor. The arrest of cell division was confirmed by assay of [3H]thymidine uptake; the nondividing cells remained viable for at least 3 days after treatment. HIV-1 was expressed and replicated equally well in nondividing and dividing C8166 cells, as judged by the comparison of the levels of p24 core antigens in culture supernatants, the proportion of cells expressing HIV-1 specific antigens, the pattern and quantity of HIV-1 DNA present in the extrachromosomal and total cellular DNA fractions, and the biological activity of progeny viruses. A polymerase chain reaction-based viral DNA integration assay indicated that HIV-1 provirus was integrated in C8166 cells treated with either of the two inhibitors of cell division. Similar results were obtained by using growth-arrested Jurkat T-lymphoid cells. We conclude that cell division and cellular DNA synthesis are not required for efficient HIV-1 expression in T cells.

Uniform detection of HIV-1 in alveolar macrophages of pediatric but not adult AIDS patients

Manifestations of pulmonary disease in pediatric AIDS patients differ from those in adults. To evaluate whether differences in the frequency of alveolar macrophage (AM) infection with human immunodeficiency virus type 1 (HIV-1) could account for these clinical distinctions, we undertook a comparative analysis of HIV-1 DNA in AMs from pediatric and adult AIDS patients by enzymatic amplification. A higher frequency of viral DNA detection in pediatric cases (100%) compared with adults (67%) was observed. The sensitivity of detection was 1 viral DNA copy per 4000 AMs; matched peripheral blood mononuclear cells from six of seven pediatric and eight of nine adult patients tested HIV-1 DNA positive. Adult but not pediatric patients exhibited a marked alveolar lymphocytosis, 32% mean lymphocyte count compared with 7.0%, respectively. These results suggest that the burden of HIV-1 in the lungs of pediatric AIDS patients is greater than that in adults.

A Tat antagonist inhibits HIV-1 induction in naturally infected and experimentally infected T cells

Ro 5-3335, a novel antagonist of human immunodeficiency virus type 1 (HIV-1) Tat activity, inhibits acute and chronic HIV-1 infection in T lymphocytes. Here we describe the effects of Ro 5-3335 on the accumulation of viral DNA during primary infection, the induction of virus from a latently infected cell line, and the expression of virus upon activation of naturally infected T cells. Ro 5-3335 permitted initial DNA synthesis during primary infection, but inhibited the subsequent increase in viral DNA copy number. The induction of HIV-1, as determined by the synthesis of p24 core antigen, was inhibited by 99% by Ro 5-3335 in both the model cell line and naturally infected T cells.

Virus-cell membrane fusion does not predict efficient infection of alveolar macrophages by human immunodeficiency virus type 1 (HIV-1)

Alveolar macrophages (AM) are the principal target cells for HIV-1 in lung tissue. To investigate the mechanisms of HIV-1 infection and efficient replication in these cells we isolated AM from 14 HIV-1 negative donors and exposed them to two virus isolates, either N1T, which replicates well in T lymphocytic and monocytic cell lines, or ADA, a monocytotropic virus. Membrane fluorescence dequenching assays demonstrated that HIV-1/N1T fuses efficiently with AM plasma membranes at neutral pH and that this interaction requires cellular CD4. Despite efficient fusion, AM from eight of 14 donors were not susceptible to productive infection with N1T. In contrast, ADA replicated in all AM populations tested. Soluble CD4 blocked infection of AM by either N1T or ADA, indicating that, like membrane fusion, entry of infectious virus requires an interaction with cellular CD4. Analysis of HIV-1 DNA accumulation in infected cells by enzymatic amplification revealed that productive infection by ADA correlated with a high HIV-1 DNA copy number and abortive infection by N1T was characterized by little or no stable cDNA. These studies suggest that the differences between the two HIV-1 strains studied in their ability to replicate in AM reside in phases of the virus life cycle that follow virus-cell fusion.

Discovery and characterization of an HIV-1 Tat antagonist

Ro 5-3335, 7-chloro-5-(2-pyrryl)-3H-1,4-benzo-diazepin-2-(H)-one, has been shown to inhibit gene expression controlled by the human immunodeficiency virus-1 (HIV-1) LTR promoter. The inhibition was specific for the viral transcriptional transactivator Tat. The compound did not inhibit the basal activity of the HIV-1 LTR or the activity of promoters not responsive to Tat. Consistent with its mode of action, Ro 5-3335 inhibited HIV-1 replication (IC50 = 0.1-1 microM) by reducing viral RNA synthesis in acutely, as well as chronically, infected cells in vitro. The compound was active against HIV-1 and HIV-2, and AZT-resistant clinical isolates.

Evaluation of multiple parameters of HIV-1 replication cycle in testing of AIDS drugs in vitro

Evaluation of the activities of antiretroviral agents and an immunoregulatory compound has been made using two models of HIV-1 infection and three measurements of virus expression. Acute infection of Jurkat cells or chronic/inducible infection in U1.1 cells was monitored at multiple time points after drug treatment. The 50% effective concentrations (EC50) of the HIV-1 inhibitors suramin, 3'-azido-3'-deoxythymidine (AZT), and 2',3'-dideoxycytidine, as measured by HIV-1 RNA hybridization in Jurkat cells two days after infection, were comparable to EC50 values obtained in parallel measurements of extracellular p24 levels and percent HIV-1 IF-positive cells. However, these measurements diverged: at seven days after infection the EC50 of AZT was greater than 10 microM when intracellular HIV-1 RNA was assayed, 0.2 microM by IF, and 0.03 microM by p24 assay. Human thymic humoral factor displayed no direct inductive activity in chronic HIV-1 infection in U1.1 cells, while phorbol ester and lymphocyte supernatants induced all parameters. These observations warrant care when interpreting results of only a single assay and suggest that definitive assay of HIV-1 infection requires measurements of multiple parameters of virus expression.

Inhibition of HIV replication in acute and chronic infections in vitro by a Tat antagonist

The human immunodeficiency virus-1 (HIV-1) trans-activator Tat is an attractive target for the development of antiviral drugs because inhibition of Tat would arrest the virus at an early stage. The drug Ro 5-3335 [7-chloro-5-(2-pyrryl)-3H-1,4-benzodiazepine-2(H)-one], inhibited gene expression by HIV-1 at the level of transcriptional trans-activation by Tat. The compound did not inhibit the basal activity of the promoter. Both Tat and its target sequence TAR were required for the observed inhibitory activity. Ro 5-3335 reduced the amount of cell-associated viral RNA and antigen in acutely, as well as in chronically infected cells in vitro (median inhibition concentration 0.1 to 1 micromolar). Effective inhibition of viral replication was also observed 24 hours after cells were transfected with infectious recombinant HIV-1 DNA. The compound was active against both HIV-1 and HIV-2 and against 3'-azido-3'-deoxythymidine (AZT)-resistant clinical isolates.

Contribution of multiple rounds of viral entry and reverse transcription to expression of human immunodeficiency virus type 1. A quantitative kinetic study

Human immunodeficiency virus 1 (HIV-1) infection in vitro has been analyzed by the kinetics of expression of HIV-1 RNA and antigens during treatment with antiviral agents. Intracellular HIV-1 RNA rose from input values of 15 molecules per cell to 28 molecules per cell within 3 h after infection and reached a peak of 13,125 in 5 days. The first detectable increase in levels of HIV-1 capsid protein production was 1 day after infection. Virus infection was interrupted at different time points by the introduction of either 2',3'-dideoxycytidine, 3'-azido-3'-deoxythymidine, or suramin to block reverse transcription, or recombinant soluble CD4 to block binding and re-entry of progeny virus. Two results are noteworthy. First, the three inhibitors of reverse transcription blocked viral expression when added up to 48 h after infection. Second, the extent of infection, although postponed, is not greatly altered by culture of infected cells in recombinant soluble CD4. These data imply that reinfection with progeny virus, while necessary for rapid virus expression, is not required for the establishment of productive HIV-1 infection.

Consequences of frameshift mutations at the immunoglobulin heavy chain locus of the mouse

From an IgM secreting hybridoma line we have isolated 16 spontaneous mutants that produce truncated IgM polypeptides. The size of the mu-mRNAs produced by these mutants is normal, but they express 3- to 100-fold less mu-mRNA and mutant mu-protein than the parental cell line. Nucleotide sequence analysis of cloned mu-genes and/or their mRNAs show frameshift mutations that generate in-phase chain termination codons. The extent of the reduction in mu-mRNA levels depends on the position of the nonsense codon within the gene.

Monoclonal antibodies specific for murine IgM I. Characterization of antigenic determinants on the four constant domains of the mu heavy chain

Seventeen monoclonal rat antibodies with specificities for mouse mu heavy chain recognize seven distinguishable determinants that are located on the four constant region domains. All determinants are present on secreted, intracellular and membrane bound IgM, and all but two are expressed on isolated mu heavy chain. One antibody, specific for a site in the first constant region domain, recognizes a determinant that is present on IgM of AKR, C3H/HeJ, C57BL/6J, SJL, DBA/2, BALB/c, NZB and CBA/J mouse strains, but not on IgM of A.TH, A/J and A.CA strains of mice.

Biochemical genetics of the mouse IgM system

Using a mouse hybridoma system, we have developed methods of isolating a variety of mutant cell lines in which immunoglobulin function or synthesis is defective. The analysis of mutants defective in kappa chain synthesis has defined a class of murine transposons. The deletion mutants produce immunoglobulin M (IgM) bearing mu heavy chain fragments and provide information on the requirements of IgM assembly and mu gene expression. We also describe a transfer system for the mu and kappa genes which will be useful in analyzing the structural basis of IgM function.

Different ways to modify monoclonal antibodies

In this paper we summarize experiments which were undertaken to create altered antibody molecules. Three different approaches were used. Established hybridoma lines were re-hybridized to mouse spleen cells to generate arrays of secondary hybridomas which express one particular heavy chain and one specificity together with a multitude of different light chains. In such hybrids the influence of light chains to the antibody combining site and the influence of affinity to antibody effector functions can be studied. Another way to obtain altered antibodies was the selection of cells producing less lytic IgM. With this technique we obtained (among many other variants) a series of mu-deletion products which were used to map the fine specificity of rat anti-mouse mu monoclonal antibodies. Both the anti-mu antibodies and the deletion variants were used to assign the Clq binding to the fourth C mu-domain demonstrating the power of mutant IgM in the structure-function analysis. In a third series of experiments we show the feasibility of generating new antibody combining sites by the methods of molecular genetics. The variable region gene of a heavy chain was placed in front of a kappa-constant region gene. The plasmid construct was transferred into mouse myeloma lines which stably express a variable heavy-constant light chain protein. Upon fusion with a light chain producing line, chimaeric light chain dimers with a functional antibody combining site were secreted. These experiments demonstrate that new series of man-made antibody molecules can be made in the future.

Deletions in immunoglobulin mu chains

Eight mutant hybridoma lines are described, which synthesize short immunoglobulin mu chains. Four internal deletions were mapped by Southern blot analysis. They are shown to remove DNA from either part or all of the first, and first and second, constant mu exons. The sizes of the deletions range between 0.6 and 5 kb, leaving an equal or unequal number of splice signals. Shorter mu RNA of one size was found irrespective of whether an exon was completely or only partially deleted. These results preclude exclusive 3' (constant region) to 5' (variable region) directional splicing of the mu RNA. No important signals seem to reside in the deleted DNA stretches affecting the transcription or the correct RNA splicing of the remaining exons. The internal mu protein deletions revealed unusual covalent light chain attachment demonstrating functional homology between the first (normally used) and fourth mu constant domain. The other mu protein deletions (10, 11, and 12 kd) involved neither gross DNA nor RNA lesions and are considered to be due to premature chain termination. Since secretion is found in most of the mutant IgM-producing lines, no single one of the four mu constant domains (including the C-terminal one which contains the so-called secretory piece) is necessary for secretion.

Roles of protein and carbohydrate in glycoprotein processing and secretion. Studies using mutants expressing altered IgM mu chains

The role of specific structural elements in glycoprotein metabolism and secretion was studied using the IgM mu chains from normal and mutant hybridoma cell lines. Five classes of altered mu chains were studied, all of which lacked various portions of the normal protein sequence, and three of which had one and the others two fewer carbohydrate units than wild type mu. One mutant secreted mu chains more rapidly than wild type cells. Two of the mutant cell lines secreted very little IgM, and both of these degraded intracellular mu chains at an abnormally high rate. Tunicamycin largely blocked IgM secretion in wild type and three mutant cell lines, but caused less inhibition in the two other mutant lines. When glycosylation in the two low secreting mutants was blocked by tunicamycin, degradation of mu chains was substantially reduced in one but unaffected in the other. All of the above properties were retained by the altered mu chains when the mutants were further hybridized with cells producing wild type mu. Overall, the various carbohydrate units and polypeptide sequences seem to play different roles in a single protein's metabolism and expression. The carbohydrate moieties may exert independent effects on protein degradation and on secretion.

Differential sensitivity of memory cell subpopulations to anti-immunoglobulin and complement

Evidence is presented for the unique sensitivity of memory cells bearing surface immunoglobulin G1 (IgG1) to functional elimination with anti-immunoglobulin (anti-Ig) sera and complement (C). Treatment of cells for adoptive transfer with C and anti-gamma1, anti-kappa, or anti-Ig significantly reduces the number of plaque-forming cells (PFC) of only the IgG1 isotype found in adoptive recipients. An increase in PFC of other isotypes accompanies the decrease in IgG1 PFC; there is no net change in the total PFC response. The depletion of IgG1 PFC requires treatment of transferred cells with both specific antisera and C; antisera directed against other isotypes show no significant effects. The maintenance of the magnitude of PFC response, compensation, is discussed.