Resistance, drug failure, and disease progression

The clinical significance of the reduced in vitro susceptibility of HIV to antiretroviral agents has been difficult to elucidate for nucleoside analogs such as zidovudine. However, the virological significance of resistance to nevirapine and other HIV-1-specific reverse transcriptase inhibitors has been established. With antiretroviral therapy, disease progression is not equivalent to drug failure, which is not equivalent to drug resistance. Clinical disease progression is only indirectly linked to HIV replication. Drug resistance is complex, and combining drugs does not appear to delay emergence of resistant strains of HIV although it may affect the specific amino acid substitutions. Drug resistance does appear to contribute to drug failure. The clinical trial ACTG 116B/117 found that the duration of prior zidovudine therapy was not related to the relative benefit of switching to didanosine. Preliminary results of analysis of resistant strains of HIV isolated from ACTG 116B/117 patients revealed that the relative hazard of progression was about threefold higher for patients with high-level resistance to zidovudine, syncytium-inducing biological phenotype, and an AIDS diagnosis at baseline. This study showed clearly that acquisition of an HIV strain with high-level resistance to zidovudine was a poor prognostic factor. Although nevirapine resistance emerges rapidly, preliminary data suggest that high dosages may be active against HIV even in the presence of resistant HIV strains. At the present time, viral resistance and biological phenotype are not useful in the management of individual patients.

Biological importance and cooperativity of HIV-1 regulatory gene splice acceptors

The replication of HIV-1 mutants containing altered splice acceptor sequences was studied. The splice acceptor sites 5' of the essential tat and rev AUG codons were altered to eliminate specifically spliced species from the viral repertoire of mRNAs. All splice site mutants were attenuated or fully defective. Mutation of the tat splice acceptor (exon 4) caused loss of the mRNA species containing exon 4 and resulted in an attenuated but replication-competent phenotype. Mutation of the rev splice acceptor sites resulted in viral genomes that failed to propagate in vitro. Mutation of the more 5' of the two major rev acceptors (exon 4A) caused loss of the mRNA species containing exon 4A together with a compensatory increase in use of the more 3' of the rev acceptors (exon 4B). Mutation of the splice acceptor for exon 4B caused the unexpected loss of both exon 4A- and 4B-containing mRNAs. In addition to these effects on the rev splice acceptors, mutations at the 4A and 4B sites also resulted in decreased use of the tat splice site (exon 4) located 175 nucleotides upstream. These effects on utilization of the tat splice acceptor site may explain the requirement for tat to efficiently complement these mutants. The 4A mutant was complemented by tat but not by rev. The 4B mutant was complemented by rev but required both tat and rev for maximum complementation. These data suggested a cooperativity among these splice sites necessary for efficient viral replication. They also indicated that while viral replication persisted at low levels in the absence of splicing to the known site 5' of the tat AUG, failure to splice to at least one of the two major sites 5' of the rev AUG resulted in insufficient rev activity for replication competence.

Stimulation of HIV replication in mononuclear phagocytes by leukemia inhibitory factor

This study examined the effects of leukemia inhibitory factor (LIF) on human immunodeficiency virus (HIV) replication in mononuclear phagocytes (MNP). LIF induced a dose-dependent increase in p24 antigen production in the chronically infected promonocytic cell line U1. The magnitude and time kinetics of the LIF effects were similar to interleukin 1 (IL-1), IL-6, and tumor necrosis factor (TNF), other cytokines known to induce HIV replication in this cell line. To characterize mechanisms responsible for these LIF effects, levels of HIV mRNA, activation of the DNA binding protein nuclear factor (NF)-kB, signal transduction pathways, and potential interactions with other cytokines were analyzed. LIF increased steady-state levels of HIV mRNA at 2.0, 4.3, and 9.2 kB. This was detectable by 24 h and persisted until 72 h. The DNA binding protein NF-kB is a central mediator in cytokine activation of HIV transcription. NF-kB levels were higher in unstimulated U1 cells as compared to the parent cell line U937. In both cell lines LIF increased NF-kB activity. Induction of NF-kB and HIV replication by cytokines are at least in part dependent on reactive oxygen intermediates. The oxygen radical scavenger N-acetyl-L-cysteine, but not an inhibitor of nitric oxide synthase, inhibited LIF-induced HIV replication. LIF induces the production of other cytokines in monocytes but its effects on HIV replication were not inhibited by antibodies to IL-1, TNF, or IL-6. These results identify LIF as a stimulus of HIV replication.(ABSTRACT TRUNCATED AT 250 WORDS)

The impact of the syncytium-inducing phenotype of human immunodeficiency virus on disease progression

Many patients infected with human immunodeficiency virus (HIV) yield syncytium-inducing (SI) virus isolates that are cytopathic in cell culture. The presence of SI virus was assessed in 325 persons entering 11 antiretroviral therapy trials and correlated with both CD4 cell declines and clinical end points. Adjusted mean rates of CD4 cell count decline were 40 and 102 cells/year in the non-SI (NSI) and SI groups, respectively (P < .0001). Rates of decline in 16 persons converting from NSI to SI virus averaged 31 cells/year before conversion and 142 cells/year afterward (P = .04). In a nested case-control analysis, persons who experienced surrogate marker end points or opportunistic infections were 2.3-3.5 times more likely to have SI virus than were controls (P = .01-.04) but who died were similar to controls with respect to virus phenotype (P = .70). Presence of the SI phenotype of HIV is a strong predictor of decline in CD4 cell count and progression of disease; however, controlling for the CD4 cell count, the SI phenotype did not increase the immediate risk of death.

Antiproliferative effect of retinoid compounds on Kaposi's sarcoma cells

A panel of retinoid compounds (tretinoin, isotretinoin, acitretin, and RO13-1470) were tested for inhibitory activity against Kaposi's sarcoma cell (KSC) cultures in vitro. Tretinoin was found to be the most effective retinoid tested, inhibiting the growth of KSC in vitro while having no effect on the expression of interleukin-6 and basic fibroblast growth factor, two important cytokines involved in KSC growth. Tretinoin also did not appear to downregulate the expression of receptors for these two cytokines. At low concentrations (10(-9) M), acitretin and tretinoin selectively inhibited growth of early passage KSC. At higher concentrations (10(-6)-10(-5) M), retinoid treatment induced a pattern of DNA degradation and morphological changes in KSC characteristic of apoptosis (programmed cell death). The inhibitory activity of tretinoin on KSC growth was decreased if human serum (but not fetal calf serum) was present in the growth medium, and partially restored by removal of serum lipids. These data suggest that retinoids possess potential as therapeutic agents in Kaposi's sarcoma.

Optimal infectivity in vitro of human immunodeficiency virus type 1 requires an intact nef gene

The replication competence of human immunodeficiency virus type 1 genomes containing mutations in the nef open reading frame was evaluated in continuous cell lines. Mutants that contained a deletion in the nef open reading frame, premature termination codons, or missense mutations in the N-terminal myristoylation signal were constructed. The replication of these mutants was tested in three ways. First, plasmid genomes were used to transfect T-lymphoblastoid cells. Second, low-passage posttransfection supernatants were used to infect cells with a relatively low virus input. Third, high-titer virus stocks were used to infect cells with a relatively high virus input. These experiments demonstrated a 100- to 10,000-fold decrement in p24 production by the nef mutants compared with that by the wild-type virus. The greatest difference was obtained after infection with the lowest virus input. The myristoylation signal was critical for this positive effect of nef. To investigate the mechanism of the positive influence of nef, nef-positive and nef-minus viruses were compared during a single cycle of replication. These single-cycle experiments were initiated both by infection with high-titer virus stocks and by transfection with viral DNA. Single-cycle infection yielded a three- to fivefold decrement in p24 production by nef-minus virus. Single-cycle transfection yielded equal amounts of p24 production. These results implied that nef does not affect replication after the provirus is established. In support of these results, viral production from cells chronically infected with nef-positive or nef-minus viruses was similar over time. To determine whether the effect of nef was due to infectivity, end point titrations of nef-positive and nef-minus viruses were performed. nef-positive virus had a greater infectivity per picogram of HIV p24 antigen than nef-minus virus. These data indicated that the positive influence of nef on viral growth rate is due to an infectivity advantage of virus produced with an intact nef gene.

Synthesis and antiviral activity of 3'-azido-3'-deoxythymidine triphosphate distearoylglycerol: a novel phospholipid conjugate of the anti-HIV agent AZT

Phospholipid conjugates of 3'-azido-3'-deoxythymidine (AZT) show activity against the human immunodeficiency virus (HIV) in vitro. In a previous report (K.Y. Hostetler, L.M. Stuhmiller, B.H.M. Lenting, H. van den Bosch and D.D. Richman (1991), J. Biol. Chem. 265, 6112-6117) the syntheses and anti-HIV activities of AZT mono- and diphosphate diglyceride have been described. We now report on the synthesis, characterization and biological activity of 3'-azido-3'-deoxythymidine triphosphate distearoylglycerol (AZTTP-DSG). The compound was prepared by the condensation of AZT diphosphate with distearoylphosphatidic acid morpholidate in anhydrous pyridine at room temperature and purified by means of high-performance liquid chromatography using a silica column. Characterization was performed with 31P-NMR and IR analyses and determination of the fatty acid, phosphorus and nucleoside content of the product. AZTTP-DSG inhibited HIV-1 replication in both CEM and HT4-6C cells at a level intermediate in potency between its mono- and diphosphate analogs. The IC50 values of AZTTP-DSG were 0.33 and 0.79 microM in these two cell lines, respectively. In addition, AZTTP-DSG was less toxic to CEM cells in vitro than the other AZT liponucleotides and reduced viable cell numbers in this cell type by 50% at 1000 microM. Initial studies on the metabolism of AZTTP-DSG revealed that both AZT and AZT monophosphate were liberated from the lipid pro-drug by a rat liver mitochondrial enzyme preparation. These phospholipid derivatives of AZT nucleotides represent pro-drugs for the intracellular delivery of phosphorylated antiviral nucleoside analogs.

Risk factors for Kaposi's sarcoma in patients with advanced human immunodeficiency virus disease treated with zidovudine. Zidovudine Epidemiology Study Group

BACKGROUND

Although the cause of Kaposi's sarcoma (KS) is unknown, its unique epidemiology suggests that an infectious, sexually transmitted agent or agents may contribute to its pathogenesis.

METHODS

To assess the natural history of KS associated with the acquired immunodeficiency syndrome and to identify factors associated with its development, data were analyzed from a multicenter, observational cohort study of 1044 persons with the acquired immunodeficiency syndrome or the acquired immunodeficiency syndrome-related complex and a total CD4 cell count of less than 0.25 x 10(9)/L who were treated with zidovudine between April 1987 and April 1988. Records were reviewed bi-monthly. Follow-up continued for 2 years or until death.

RESULTS

One hundred thirty-one patients (13%) had KS a study enrollment, and 143 developed KS (14%) during follow-up, with a 2-year actuarial risk of 21%. The probability of KS at 2 years for patients with initial CD4 cell counts of less than 0.1 x 10(9)/L was 25%, compared with 15% for those with counts of 0.1 x 10(9)/L or more. By logistic regression, a baseline CD4 cell count of less than 0.1 x 10(9)/L (relative odds, 1.43; 95% confidence interval, 1.04 to 1.95), homosexuality (relative odds, 3.71; 95% confidence interval, 1.82 to 7.56), cytomegalovirus disease (relative odds, 1.56; 95% confidence interval, 1.01 to 2.41), and white race (relative odds, 1.64; 95% confidence interval, 1.11 to 2.43) were independently associated with KS. Median survival after KS was 408 days, and KS was an independent predictor of death (relative hazard, 1.78; 95% confidence interval, 1.26 to 2.52).

CONCLUSIONS

Kaposi's sarcoma contributes to human immunodeficiency virus-related morbidity and mortality, especially among male homosexuals. This large cohort study provides further evidence for an association between risk for cytomegalovirus infection and KS.

Synthesis and hypnotic and anti-human immunodeficiency virus-1 activities of N3-substituted 2'-deoxy-2'-fluorouridines

Reaction of 9-[3,5-di-O-(tetrahydropyran-2-yl)-beta-D-arabinofuranosyl]uracil (2) with diethylaminosulfur trifluoride in the presence of pyridine afforded 2'-deoxy-2'-fluororiboside 3a, from which 2'-deoxy-2'-fluorocytidine (4b) has been synthesized in good yield. Compound 3a was deprotected and subsequently treated with various benzyl halides or 2-chloro-4-fluoroacetophenone to give corresponding N3-substituted 2'-deoxy-2'-fluorouridines 5a-c and 6. Compounds 5a-c, as well as 6, showed weak hypnotic activity in mice. Compound 4b showed moderate antiviral activity against human immunodeficiency virus-1 but 3b, 5a-c, and 6 were virtually inactive.

Nevirapine resistance mutations of human immunodeficiency virus type 1 selected during therapy

Drug susceptibility and mutations in the reverse transcriptase (RT) gene were analyzed with 167 virus isolates from 38 patients treated with nevirapine, a potent nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) RT. Resistant isolates emerged quickly and uniformly in all patients administered nevirapine either as monotherapy or in combination with zidovudine (AZT). Resistance developed as early as 1 week, indicating rapid turnover of the virus population. The development of resistance was associated with the loss of antiviral drug activity as measured by CD4 lymphocyte counts and levels of HIV p24 antigen and RNA in serum. In addition to mutations at amino acid residues 103, 106, and 181 that had been identified by selection in cell culture, mutations at residues 108, 188, and 190 were also found in the patient isolates. Sequences from patient clones documented cocirculating mixtures of populations of different mutants. The most common mutation with monotherapy, tyrosine to cysteine at residue 181, was prevented from emerging by coadministration of AZT, which resulted in the selection of alternative mutations. The observations documented that, under selective drug pressure, the circulating virus population can change rapidly, and many alternative mutants can emerge, often in complex mixtures. The addition of a second RT inhibitor, AZT, significantly altered the pattern of mutations in the circulating population of HIV.

Resistance to AZT and ddC during long-term combination therapy in patients with advanced infection with human immunodeficiency virus

To ascertain whether combination therapy with zidovudine (AZT) and zalcitabine (ddC) delayed the emergence of AZT resistance, isolates of human immunodeficiency virus (HIV) were evaluated from 15 previously untreated patients with advanced HIV disease who received combination therapy. Eighteen sequential viral isolates were available from 15 patients who received > or = 6 months of combination therapy. Isolates from eight (73%) of 11 patients obtained between 24 and 48 weeks of therapy were AZT resistant [50% inhibitory concentration (IC50) > or = 0.45 microM; range, 0.45-2.0 microM]. Four of these eight patients yielded virus isolates that were highly AZT resistant (IC50 > 1.0 microM). No changes in ddC susceptibility were discerned. The median IC50 for ddC was 0.2 microM and ranged from 0.07 to 0.5 microM. The CD4 cell counts of patients with AZT-sensitive virus tended to have higher median areas under the curve (AUC) and greater increases compared with patients who had AZT-resistant virus. They also had higher means and ranges of the average CD4 cell counts at week 36 (p = 0.01) and week 48 (p = 0.04). These data would indicate that the previously described more sustained CD4 cell responses conferred by the addition of ddC to AZT therapy cannot be ascribed to delayed emergence of AZT resistance with combination therapy.

Combinative interactions of a human immunodeficiency virus (HIV) Tat antagonist with HIV reverse transcriptase inhibitors and an HIV protease inhibitor

Combinations of the human immunodeficiency virus (HIV) Tat protein antagonist Ro 24-7429 with either the HIV protease inhibitor Ro 31-8959 or the HIV reverse transcriptase inhibitors AZT (3'-azido-3'-deoxythymidine), ddC (2',3'-dideoxycytidine), ddI (2',3'-dideoxyinosine), and nevirapine were synergistic or additive in reducing HIV type 1 p24 antigen production in CEM cells or inhibiting HIV type 1-induced syncytium formation in HT4-6C cells.

The importance of nef in the induction of human immunodeficiency virus type 1 replication from primary quiescent CD4 lymphocytes

The viral regulatory gene, nef, is unique to the human immunodeficiency viruses (HIV) and their related primate lentiviruses. Expression of the nef gene has been shown to be essential to the maintenance of high levels of virus replication and the development of pathogenesis in the animal model of simian immunodeficiency virus (SIV) infection. In contrast to this in vivo model, the use of standard T cell culture systems to study nef function in vitro has produced a spectrum of contradictory results, and has failed to demonstrate a significant positive influence of nef on viral life cycle. We have developed a cell model to study regulation of HIV-1 replication that we believe reflects more accurately virus-cell interactions as they occur in vivo. Our experimental system used acute virus infection of purified, quiescent CD4 lymphocytes and subsequent induction of viral replication through T cell activation. With this cell model, NL4-3 virus clones with open and mutated nef reading frames were compared for replication competence. The clones with nef mutations showed reproducible and significant reductions in both rates of growth and maximal titers achieved. The degree of reduced replication was dependent on initial virus inoculum and the timing of T cell activation. The influence of nef was highly significant for induction of virus replication from a latent state within resting CD4 cells. Its effect was less apparent for virus infection of fully proliferating CD4 cells. This study demonstrates that nef confers a positive growth advantage to HIV-1 that becomes readily discernable in the primary cell setting of virus induction through T cell activation. The experimental cell model, which we describe here, provides not only a means to study nef function in vitro, but also provides important clues to the function of nef in HIV infection in vivo.

A cross-sectional comparison of persons with syncytium- and non-syncytium-inducing human immunodeficiency virus

The association between isolation of the syncytium-inducing (SI) phenotype of human immunodeficiency virus (HIV) and unfavorable clinical and immune status was evaluated in a cross-sectional study. Data on HIV phenotype were available for 341 of 878 persons entering clinical trials of antiretroviral therapies. Patients with SI virus were demographically similar to those with non-SI (NSI) virus but were more likely to have a diagnosis of AIDS and detectable circulating HIV p24 antigen. Patients with SI virus also had a lower CD4+ cell count and a higher serum level of beta 2-microglobulin. The association between phenotype and present status was explained statistically by CD4+ cell count. Phenotype, serum level of beta 2-microglobulin, and the presence of detectable p24 antigen were all independent predictors of present CD4+ cell count. The likelihood of finding SI virus increased with unfavorable virologic and immunologic parameters and varied with the amount of prior antiretroviral therapy.

Microtiter format gene quantification by covalent capture of competitive PCR products: application to HIV-1 detection

We have developed a simple gene quantification system using the competitive polymerase chain reaction (CPCR) followed by microtiter format analysis. CPCR is carried out using a mutant competitor with the same size as the target DNA product, and a minimal base exchange to insure the same amplification kinetics. One primer is aminated at the 5' end to produce PCR products that are captured onto carboxylated wells of microtiter plates through peptide bond formation. The non-aminated DNA strands are stripped off from the wells by alkali washing, and the remaining aminated strands are hybridized with either a digoxigenin-labeled wild type-specific oligonucleotide probe or a competitor-specific probe. To standardize the hybridization conditions of the probes, a DNA construct containing wild type and mutant competitor sequences in tandem is captured at different concentrations, hybridized with the probes, and used to generate a standard curve. Bound probes are detected by anti-digoxigenin antibody conjugated with peroxidase and chromogen. Optical densities are recorded with a conventional microtiter plate reader and converted to concentrations according to the standard curves. The ratios of wild type DNA to mutant competitor are used to determine the initial amounts of wild type DNA in the samples. This method was used successfully to quantify human immunodeficiency virus type 1 (HIV-1) env gene in human lymphocytes. It only requires a thermal cycler and a conventional microtiter plate reader, and can be readily done on a large scale. Potential applications include detection of other pathogens, diagnosis of genetic disorders and studies of gene expression.

Designing phase II studies of chemotherapy for HIV infection using CD4 as an end-point

OBJECTIVE

To provide information that will be helpful in designing AIDS clinical trials that use CD4 as an end-point.

DESIGN

Meta-analysis of randomized AIDS clinical trials comparing zidovudine and placebo.

SETTING

Tertiary care.

PATIENTS

Eight hundred and twenty-seven patients with HIV infection.

INTERVENTIONS

Treatment with zidovudine at various dosages compared with placebo.

MAIN OUTCOME MEASURE

Differences in the log-ratio CD4 count.

RESULTS

The mean difference in the log-ratio CD4 count divided by its standard deviation varied from 0.31 to 0.76 depending on the study. Of the variation in CD4 count 63% is short-term variation.

CONCLUSION

Trials of 12 weeks duration can be used to test for the effect of a new drug on CD4 counts. Testing combination therapies may require somewhat longer trial periods. The sample size for clinical trials can be reduced by replicating baseline and follow-up measurements. Trials of new agents should test for an increase in CD4 over baseline. Such trials will require between 25 and 190 patients per arm depending on the patient population. Trials that compare combinations to standard therapies will require between 32 and 235 patients per arm depending on disease stage and prior therapy of study participants.

Correlation between CD4+ counts and prevalence of cytomegalovirus retinitis and human immunodeficiency virus-related noninfectious retinal vasculopathy in patients with acquired immunodeficiency syndrome

We prospectively studied 132 patients with acquired immunodeficiency syndrome (AIDS) to determine the cross-sectional prevalence of cytomegalovirus retinitis. All patients had serum CD4+ lymphocyte counts to determine the degree of immune dysfunction. Correlations between CD4+ counts, the presence of cytomegalovirus retinitis or human immunodeficiency virus (HIV)-related noninfectious retinal vasculopathy, and ocular symptoms were made. The study disclosed that 26 of 132 patients with AIDS (20%) had cytomegalovirus retinitis. However, subset analysis according to CD4+ count disclosed that in patients with CD4+ counts of 50 cells/mm3 or less, 26 of 87 (30%) had cytomegalovirus retinitis, whereas in patients with CD4+ counts of 50 cells/mm3 or more, none of 45 was noted to have cytomegalovirus retinitis. Similarly, 46 of 132 patients (35%) were noted to have HIV-related noninfectious retinal vasculopathy, with a trend toward increasing prevalence associated with declining CD4+ count. In patients with CD4+ counts of 50 cells/mm3 or less, 39 of 87 (45%) had HIV-related noninfectious retinal vasculopathy, whereas seven of 45 patients (16%) with CD4+ counts of 50 cells/mm3 or more were noted to have these changes. We confirmed the clinical impression that cytomegalovirus retinitis and HIV-related noninfectious retinal vasculopathy are late manifestations of AIDS, demonstrated an increased risk for patients with low CD4+ counts, and suggested a basis for coherent chemoprophylaxis and screening strategies for cytomegalovirus retinitis.

Zidovudine treatment of the AIDS dementia complex: results of a placebo-controlled trial. AIDS Clinical Trials Group

The efficacy of two doses of zidovudine was examined for the treatment of the acquired immunodeficiency syndrome (AIDS) dementia complex in a randomized, double-blinded, placebo-controlled trial conducted at nine study centers. For the initial 16 weeks, 40 subjects with mild to moderate AIDS dementia complex were randomized to one of three treatment arms: 400 mg of zidovudine five times daily, 200 mg of zidovudine five times daily, or placebo five times daily. After week 16, patients initially randomized to the placebo group were rerandomized to one of the two zidovudine treatment arms. The primary efficacy end point was improvement in performance on a battery of seven neuropsychological tests; the secondary end point was improvement on a protocol neurological evaluation directed at the cardinal features of the AIDS dementia complex. For the initial 16-week period, average z scores based on the neuropsychological test battery revealed a significant improvement in the combined treatment groups compared to the placebo group; however, when the two treatment groups were compared separately to the placebo group, only the group receiving the higher zidovudine dose exhibited significant improvement. After rerandomization of the placebo patients to one of the two treatment arms at week 16, this group also showed significant improvement in the average neuropsychological z score by week 32. These results extend previous observations that indicate a therapeutic benefit of zidovudine for the treatment of AIDS dementia complex.

In vitro differentiation of monocytoid THP-1 cells affects their permissiveness for HIV strains: a model system for studying the cellular basis of HIV differential tropism

The prototypic macrophage-tropic HIV-1 isolate, HIV-1BaL, cannot replicate in the monocytoid cell line THP-1. After induction of differentiation by a phorbol diester, a fraction of THP-1 cells became permissive to HIV-1BaL. In contrast, this treatment decreased permissiveness for the lymphotropic isolate HIV-1LAI. Viral DNA was not synthesized in unstimulated THP-1 cells, as determined with PCR, suggesting that the block to HIV-1BaL replication in these cells occurred at an early step of the virus replicative cycle prior to or at the level of reverse transcription. Virus binding studies showed that differences in cell permissiveness for HIV-1BaL were not due to altered virus binding. Substantial amounts of HIV-1BaL bound to both undifferentiated and differentiated THP-1 cells, and this binding could not be prevented by blocking with the anti-CD4 antibody Leu3a, which did prevent the binding of HIV-1LAI to CEM T lymphoid cells. While Leu3a was very effective at preventing the infection by HIV-1LAI in CEM cells, it was less effective in preventing HIV-1BaL infection of differentiated THP-1 cells or primary macrophages. Although it is likely that molecules other than CD4 on monocytic cells can mediate binding of macrophage-tropic HIV, the binding of HIV-1BaL to THP-1 cells was not sufficient for infection, because binding was the same in nonpermissive undifferentiated cells as in permissive differentiated cells. Thus, the restriction of viral replication in this model cell system occurs at some step after virion binding. Comparison of differentiated THP-1 cells with their undifferentiated counterparts may provide an approach to defining cellular determinants of HIV host range other than CD4 expression and to characterizing the incompletely defined steps of viral entry.

Mechanisms for the inhibition of HIV replication by interferons-alpha, -beta, and -gamma in primary human macrophages

Interferons (IFNs) inhibit the replication of a wide range of animal viruses by acting at various steps of the life cycle. Interferons display a particularly potent antiviral effect on HIV-1 replication in primary human macrophages. A high virus-to-cell multiplicity of infection was used to investigate which steps in a single replicative cycle in these primary human cells were affected by IFNs. Monocyte-derived macrophages from healthy seronegative donors were infected with HIV-1BaL. Virus production was assessed by immunoassay for p24 antigen. Viral DNA was detected by PCR while mRNA was detected specifically by RT-PCR with primers bracketing the 5' introns of HIV-1 to detect only spliced transcripts such as tat, rev, nef, and env mRNAs. Macrophages pretreated with IFN-alpha, -beta or -gamma had a reduced viral DNA signal while the spliced mRNA signal was essentially abolished. No virus was produced. To test whether IFNs could reduce HIV transcripts in cells with established productive infection, macrophages were infected and reinfection was then prevented by azidothymidine before starting interferon treatment. Under such conditions, the addition of interferons did not affect significantly the levels of HIV spliced transcripts. No intracellular accumulation of p24 antigen was observed. Therefore, the major effect of IFNs was at an early step of the virus life cycle and resulted in a reduced viral DNA synthesis.

Alternating and intermittent regimens of zidovudine and dideoxycytidine in patients with AIDS or AIDS-related complex

OBJECTIVE

To determine whether alternating regimens consisting of zidovudine and 2',3'-dideoxycytidine (ddC) reduce the toxicity and maintain or increase the antiretroviral effect associated with each drug alone.

DESIGN

An unblinded, randomized (phase II) clinical trial in which seven treatment regimens were compared.

SETTING

Outpatient clinics of 12 AIDS Clinical Trials Units.

PATIENTS

One hundred thirty-one patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex and serum p24 antigenemia (> or = 70 pg/mL).

INTERVENTION

Treatments included weekly or monthly alternating zidovudine (200 mg every 4 hours) and ddC (0.01 or 0.03 mg/kg body weight every 4 hours); weekly intermittent zidovudine, 200 mg every 4 hours, or ddC, 0.03 mg/kg every 4 hours; and continuous zidovudine.

MEASUREMENTS

Toxicity, CD4 cell counts, serum p24 antigen levels, and clinical end points. Data were analyzed for the first 48 weeks of therapy (median follow-up, 40 weeks).

RESULTS

Hematologic toxicity was significantly less frequent in patients who received zidovudine therapy every other week (11% to 15%) or every other month (11% to 14%) than in those who received continuous zidovudine therapy (33%) (P < 0.02). Weekly alternating therapy with zidovudine and ddC, 0.03 mg/kg, or intermittent therapy with ddC, 0.03 mg/kg, produced high rates of peripheral neuropathy (41% and 50%, respectively). Neuropathy occurred in 10% to 21% of patients in the other three alternating-therapy limbs and in 17% of patients receiving zidovudine alone (intermittently or continuously). Initial increases in CD4 cell counts were sustained in three alternating-therapy limbs, but counts returned to baseline by week 28 in the remaining limbs. The median weight gain at week 48 was significantly greater in patients treated with alternating regimens (0.9 to 3.8 kg) compared with those treated with continuous zidovudine therapy (-0.7 kg) (P = 0.008). Patients treated with alternating regimens and those treated with continuous zidovudine had similarly sustained decreases in p24 antigen levels.

CONCLUSIONS

These findings suggest that alternating therapy with zidovudine and ddC reduces the toxicity associated with each drug alone while maintaining strong antiretroviral activity.