Marked differences in quantity of infectious human immunodeficiency virus type 1 detected in persons with controlled plasma viremia by a simple enhanced culture method

Culture of autologous CD4 lymphocytes from peripheral blood mononuclear cells compared favorably with two other methods for the measurement of cell-associated human immunodeficiency virus type 1 (HIV-1). For subjects with undetectable HIV-1 RNA levels in plasma, there was a 10,000-fold range of cell-associated virus detected. This method provides a simple and reproducible means for monitoring cell-associated HIV-1.

In vitro inhibition of HIV-1 by Met-SDF-1beta alone or in combination with antiretroviral drugs

Compounds that can block the CXCR4 chemokine receptor are a promising new class of antiretroviral agents. In these experiments we studied the effect of a modified form of the native stromal cell-derived factor-1 (SDF-1), Met-SDF-1beta. The in vitro susceptibility of two different CXCR4-tropic HIV-1 strains was determined. Antiviral effect was assessed by the reduction of p24 antigen production in PHA-stimulated peripheral blood mononuclear cells with exposure to the modified SDF-1 molecule. The 50% inhibitory concentrations (IC50) were derived from six separate experiments. The IC50 against the two HIV-1 isolates was in 1.0-2.8 microg/ml range for Met-SDF-1beta. Met-SDF-1beta showed synergy to additivity with either zidovudine or nelfinavir at IC75 IC90 and IC95. Additivity was seen when Met-SDF-1beta was combined with efavirenz. No cellular toxicity was observed at the highest concentrations when these agents were used either singly or in combination. This compound is a promising new candidate in a receptor-based approach to HIV-1 infection in conjunction with currently available combination antiretroviral drug therapies.

Induction and maintenance treatment regimens for HIV-1 infection in vitro

Can aggressive anti-human immunodeficiency virus (HIV) induction regimens be simplified after sufficient virus suppression is achieved? In vitro studies were conducted to evaluate the hypothesis that aggressive induction regimens could be followed by less aggressive maintenance regimens. A clinical HIV-1 isolate and lymphoblastoid cell line (H9) were employed. Virus multiplicities were varied, as were drug inhibitory concentrations (IC90, IC99) and induction periods (1, 2 and 3 weeks) of a three-drug regimen (zidovudine plus lamivudine and indinavir), following which maintenance regimens (no drug, zidovudine alone, indinavir alone, zidovudine plus lamivudine) were employed. After 1 week inductions at IC99 concentrations, viral rebound occurred on none or one-drug maintenance regimens but not on a two-drug regimen. After 2 week inductions, viral rebound occurred with no-drug maintenance, but not with one- and two-drug regimens. After 3 week inductions, viral rebound did not occur in zero-, one-, or two-drug maintenance regimens, although HIV-1 DNA persisted in cultured cells. These studies suggest that although some induction-maintenance regimens will fail, after a sufficient period of HIV-1 suppression with a three-drug antiretroviral regimen, maintenance on fewer drugs may be feasible.

Interactions among combinations of two and three protease inhibitors against drug-susceptible and drug-resistant HIV-1 isolates

Protease inhibitors used in combination with reverse transcriptase inhibitors have demonstrated potent anti-HIV-1 activity in vitro as well as in vivo. We evaluated interactions among five protease inhibitors: indinavir (IDV), ritonavir (RTV), saquinavir (SQV), amprenavir (APV), and nelfinavir (NFV), when used in combinations of two and three drugs in vitro against several HIV-1 isolates, including those susceptible and resistant to various nucleoside and nonnucleoside reverse transcriptase inhibitors. Interactions ranged from synergy to slight antagonism depending on the viral isolates and the experimental conditions employed. Further clinical evaluation of protease inhibitor combinations is warranted.

Improved CD4 lymphocyte outgrowth in response to effective antiretroviral therapy

CD4 lymphocyte regenerative capacity was evaluated by use of an ex vivo outgrowth assay in human immunodeficiency virus (HIV)-1-infected subjects enrolled in a clinical trial (Merck 039). CD4 lymphocytes were selectively expanded in vitro by T cell receptor triggering, which also induces HIV production from latently infected cells. CD4 cell expansion and lack of virus production in cultures correlated well with clinical responses and were best in those receiving an aggressive antiretroviral three-drug regimen. Twelve clinical responders receiving triple-drug therapy monitored for 60 weeks had both excellent ex vivo CD4 cell expansion and lack of HIV replication, often in the absence of added drug in culture. Breakthrough viruses recovered from drug-containing arms of the cultures showed phenotypic resistance to the drugs used in vivo. This CD4 lymphocyte outgrowth assay correlates well with clinical outcome in subjects receiving potent antiretroviral regimens and may predict the emergence of early drug resistance.

Sequential versus simultaneous combination antiretroviral regimens for the treatment of human immunodeficiency virus type 1 infection in vitro

Two-, three-, and four-drug antiretroviral combinations in either simultaneous or sequential regimens were evaluated for their ability to suppress human immunodeficiency virus (HIV) type 1 replication in vitro. Zidovudine, lamivudine, saquinavir, and nevirapine were used at IC(90)s, IC(99)s, or IC(> or = 99)s in a CD4-positive human lymphoblastoid cell line (H9 cells) acutely infected with HIV-1. In sequential regimens, drugs were added at weekly intervals. In simultaneous regimens, all drugs were added on day 0. Increasing the number of drugs in a combination regimen both increased the degree of viral inhibition and delayed the time of breakthrough viral replication. Simultaneous regimens provided more profound and earlier viral inhibition than did sequential regimens. However, sequential addition provided relatively more durable viral inhibition than did simultaneous regimens when drug concentrations were low. The relative effectiveness of different HIV-1 therapeutic strategies depends on both the numbers and concentrations of the drugs used.

Antagonism between human immunodeficiency virus type 1 protease inhibitors indinavir and saquinavir in vitro

Human immunodeficiency virus type 1 (HIV-1) protease inhibitors are a promising class of antiretroviral agents that compromise enzymatic function through substrate mimicry. The in vitro susceptibility of a panel of HIV-1 clinical isolates demonstrating various drug resistance phenotypes to combinations of the HIV-1 protease inhibitors saquinavir and indinavir was determined. Antiviral effect was assessed by an HIV-1 p24 antigen reduction assay in phytohemagglutinin-stimulated peripheral blood mononuclear cells after harvesting of cell-free supernatant fluids at peak antigen production (days 4-7). Drug interactions were determined by median-dose-effect analysis, with the combination index (CI) calculated at several inhibitory concentrations (IC50, IC75, IC90, IC95, IC99). The interactive effects ranged from synergy at low efficacy doses to antagonism at higher doses against a pan-susceptible clinical isolate of HIV-1. Against a zidovudine-resistant isolate as well as a multidrug-resistant isolate, the combination of saquinavir and indinavir demonstrated antagonism at all doses.

Lamivudine or stavudine in two- and three-drug combinations against human immunodeficiency virus type 1 replication in vitro

Two- and three-drug combinations of lamivudine or stavudine with other antiretroviral drugs were evaluated for activity against human immunodeficiency virus type 1 (HIV-1) activity in peripheral blood mononuclear cells. Other agents included zidovudine, didanosine, nevirapine, and saquinavir. Paired zidovudine-sensitive and -resistant clinical HIV-1 isolates were used. Additive or synergistic interactions were observed against the zidovudine-sensitive isolate with the following combinations: lamivudine-zidovudine, lamivudine-stavudine, lamivudine-saquinavir, lamivudine-nevirapine, stavudine-zidovudine, stavudine-didanosine, stavudine-saquinavir, stavudine-nevirapine, lamivudine-zidovudine-saquinavir, lamivudine-zidovudine-stavudine, stavudine-zidovudine-nevirapine, lamivudine-zidovudine-nevirapine, and stavudine-zidovudine-saquinavir. Against the zidovudine-resistant isolate, additive or synergistic interactions were seen with most two- and three-drug combinations, but the combination of stavudine-zidovudine was antagonistic. The clinical implications of these in vitro observations should be explored.

Naphthalene sulfonate polymers with CD4-blocking and anti-human immunodeficiency virus type 1 activities

PIC 024-4 and PRO 2000 are naphthalene sulfonate polymers that bind to CD4 with nanomolar affinity and block binding of gp120. Both have activity against human immunodeficiency virus type 1 in H9 cells, peripheral blood mononuclear cells, and primary monocyte/macrophages, are synergistic with zidovudine, and do not inhibit tetanus toxoid-stimulated T-cell proliferation at anti-human immunodeficiency virus type 1 concentrations.

Ex vivo expansion of CD4 lymphocytes from human immunodeficiency virus type 1-infected persons in the presence of combination antiretroviral agents

Expansion of CD4 lymphocytes from human immunodeficiency virus type 1 (HIV-1)-infected persons ex vivo has been limited by enhanced virus replication and cell death. The successful expansion of functional CD4 lymphocytes from HIV-1-infected persons has now been accomplished using a bispecific monoclonal antibody to CD3 and CD8 in combination with three antiretroviral agents. CD4 lymphocytes were polyclonally expanded by a factor of 10(3)-10(7) during 4-8 weeks in culture. Supernatants from most cultures were persistently HIV-1 p24 antigen-negative by day 14 and remained negative despite removal of antiretroviral agents at day 28. In such cultures, HIV-1 could not be recovered by cocultivation, and amounts of HIV-1 DNA declined or remained stable at low levels, eventually becoming undetectable in 2 cases. This approach establishes the feasibility of CD4 lymphocyte expansion in persons with HIV disease and may be useful for immune-based or gene therapies.

Inhibition of human immunodeficiency virus type 1 replication in cytokine-stimulated monocytes/macrophages by combination therapy

Combination regimens against human immunodeficiency virus type 1 (HIV-1) were studied in granulocyte-macrophage colony-stimulating factor (GM-CSF)-stimulated monocyte/macrophage cultures. Regimens included those that inhibited the same target (reverse transcriptase) or multiple targets. Treatment conditions assessed efficacy during prophylaxis and ongoing infection. Drugs included zidovudine, didanosine, nevirapine, foscarnet, pyridinone, the protease inhibitor RO31-8959 (also known as saquinavir), interferon-alpha A, the Tat inhibitor RO24-7429, and N-butyl-deoxynojirimycin. Two-, three-, and four-drug combinations were tested. Drugs were tested at individually inhibitory concentrations of IC99, IC95, IC75, and IC50. All prophylactic regimens prevented HIV-1 replication at IC99. As drug concentrations were reduced, differences among the regimens became apparent. Regimens that acted at both single and multiple targets were effective in prophylactic settings and less so in acute infection. In ongoing infections, only modest reductions in viral replication were seen, even at IC99.

Alternating versus continuous drug regimens in combination chemotherapy of human immunodeficiency virus type 1 infection in vitro

We compared the in vitro efficacies of two-, three-, and four-drug combinations given continuously or in alternating regimens against a clinical isolate of human immunodeficiency virus type 1. In H9 cells and peripheral blood mononuclear cells, at the drug concentrations used in this study, there was greater suppression of human immunodeficiency virus type 1 infection as the number of drugs in the regimen was increased from one to four simultaneously administered agents. Although alternating drug regimens were effective, they were not better than continuous administration of either single drugs or combinations of agents and were less effective than giving all drugs of an alternating regimen simultaneously.

Use of evolutionary limitations of HIV-1 multidrug resistance to optimize therapy

Wild-type reverse transcriptase has evolved for the survival of human immunodeficiency virus type 1 (HIV-1) by natural selection. In contrast, therapy relying on inhibitors of reverse transcriptase by nucleosides like zidovudine (AZT) or dideoxyinosine (ddI), and by non-nucleosides like pyridinones or nevirapine, may exert different selection pressures on this enzyme. Therefore the acquisition of resistance to reverse transcriptase inhibitors by selection of mutations in the pol gene may require compromises in enzyme function that affect viral replication. As single mutations are unlikely to confer broad resistance when combinations of reverse transcriptase inhibitors are used, multiple mutations may occur that result in further compromises. Certain drug combinations may prevent the co-existence of adequate reverse transcription function and multi-drug resistance (MDR). Unlike bacterial or eukaryotic drug resistance, retroviral drug resistance is conferred only by mutations in its own genome and is limited by genome size. Combining drugs directed against the same essential viral protein may thus prevent HIV-1 MDR, whereas the conventional approach of targeting different HIV-1 proteins for combination therapy may not, because genomes with resistance mutations in different HIV-1 genes might recombine to develop MDR. Here we show that several mutations in the HIV-1 reverse transcriptase gene that confer resistance to inhibitors of this enzyme can attenuate viral replication. We tested whether combinations of mutations giving rise to single-agent resistance might further compromise or even abolish viral replication, and if multidrug-resistant viruses could be constructed. Certain combinations of mutations conferring resistance to AZT, ddI and pyridinone are incompatible with viral replication. These results indicate that evolutionary limitations exist to restrict development of MDR. Furthermore, a therapeutic strategy exploiting these limitations by using selected multidrug regimens directed against the same target may prevent development of MDR. This approach, which we call convergent combination therapy, eliminated HIV-1 replication and virus breakthrough in vitro, and may be applicable to other viral targets. Moreover, elimination of reverse transcription by convergent combination therapy may also limit MDR.

Human immunodeficiency virus type 1 (HIV-1) inhibitory interactions between protease inhibitor Ro 31-8959 and zidovudine, 2',3'-dideoxycytidine, or recombinant interferon-alpha A against zidovudine-sensitive or -resistant HIV-1 in vitro

Protease inhibitor Ro 31-8959, a compound that interrupts human immunodeficiency virus (HIV)-specific formation of infectious virions, was evaluated in two-drug combined regimens with zidovudine, 2',3'-dideoxycytidine (ddC), or recombinant interferon-alpha A (rIFN-alpha A) against HIV-1 replication in vitro. By using peripheral blood mononuclear cells infected with HIV-1, drug interactions were evaluated by the median-effect principle and the isobologram technique. A zidovudine-sensitive and -resistant HIV-1 isolate pair was studied. Additive to synergistic anti-HIV-1 interactions were seen with 7.5-30 nM Ro 31-8959 and 0.005-0.02 microM zidovudine (for the zidovudine-sensitive HIV-1 isolate), 0.25-1.0 microM zidovudine (for the zidovudine-resistant HIV-1 isolate), 0.025-0.1 microM ddC, and 8-32 units/mL rIFN-alpha A, without additive toxicity. Phase I/II clinical trials of Ro 31-8959 for therapy of HIV-1 infection are in progress. If results are favorable, combined regimens including Ro 31-8959 deserve consideration for future clinical trials.

Synergistic inhibition of replication of human immunodeficiency virus type 1, including that of a zidovudine-resistant isolate, by zidovudine and 2',3'-dideoxycytidine in vitro

The combination of zidovudine (AZT) and 2',3'-dideoxycytidine synergistically inhibits human immunodeficiency virus type 1 (HIV-1) replication in vitro with AZT-sensitive and AZT-resistant clinical isolates and HIV-1IIIB. Synergy was determined by the median-effect principle and isobologram techniques. Cytotoxicity of the agents was not observed. Clinical trials are ongoing to define the combination's role in HIV-1 therapy.

Two-drug combinations of zidovudine, didanosine, and recombinant interferon-alpha A inhibit replication of zidovudine-resistant human immunodeficiency virus type 1 synergistically in vitro

Optimal management of human immunodeficiency virus type 1 (HIV-1) infections may require combinations of anti-HIV-1 agents. Zidovudine (AZT, 3'-azido-3'-deoxythymidine), didanosine (ddI, 2',3'-dideoxyinosine), and recombinant interferon-alpha A (rIFN-alpha A) were evaluated in two-drug regimens against replication of AZT-resistant HIV-1 in vitro. AZT-sensitive and AZT-resistant isolate pairs derived from two individuals before and after extended AZT monotherapy were studied. Drug interactions using peripheral blood mononuclear cells infected with HIV-1 were evaluated mathematically. Synergistic interactions were seen among AZT, ddI, and rIFN-alpha A in two-drug regimens against AZT-resistant HIV-1 in vitro, even when AZT was included in the treatment regimen. Mixtures of wild-type and mutant reverse transcriptase genes were found in one of the late-AZT therapy isolates, suggesting that the mechanism of synergy of AZT-containing regimens may involve inhibition of AZT-sensitive viruses in the viral pool. These studies suggest that AZT may be useful in drug combination regimens, even when AZT-resistant viruses are isolated in vitro.

Three-drug synergistic inhibition of HIV-1 replication in vitro by zidovudine, recombinant soluble CD4, and recombinant interferon-alpha A

Optimal management of human immunodeficiency virus type 1 (HIV-1) infections may require combinations of agents that attack different targets in the viral replicative cycle. Zidovudine (AZT), recombinant soluble CD4 (rsCD4), and recombinant interferon-alpha A (rIFN-alpha A) were evaluated in 2- and 3-drug regimens against HIV-1 replication in vitro. Peripheral blood mononuclear cells and a CD4+ T cell line (H9) were studied using multiple HIV-1 replicative end points. Drug interactions were evaluated by the median-effect principle and the isobologram technique. AZT, rsCD4, and rIFN-alpha A inhibited HIV-1 synergistically in 2- and 3-drug combinations. The 3-drug regimen provided more complete virus suppression than the 2-drug regimens. In H9 cells, single-drug regimens lost effectiveness at 10-14 days and 2-drug regimens lost effectiveness at 14-18 days. In contrast, the 3-drug regimen showed nearly complete suppression over 28 days in culture without toxicity. Clinical trials of these 3 drugs in combination should be considered.

Purification of human myeloperoxidase by Concanavalin A-Sepharose affinity chromatography

Myeloperoxidase (E.C. 1.11.1.7. Donor: H2O2 oxidoreductase), an enzyme of the azurophil granule of polymorphonuclear leukocytes, has been purified from the blood of a single human donor. Leukocytes were harvested by dextran sedimentation and contaminating erythrocytes were removed by hypotonic lysis. Myeloperoxidase was extracted from the leukocytes by dissolution in cetyltrimethyl-ammonium bromide (CETAB). The extract was adsorbed to a Con A-Sepharose gel, eluted with alpha-methyl-D-mannoside and rechromatographed on Sephadex G-200. Approximately 100% of the initial peroxidase activity was recovered in the final preparation, which was homogeneous by polyacrylamide disc gel electrophoresis at pH 4.5 and displayed the typical oxidized and reduced absorption spectra of purified myeloperoxidase. The oxidized enzyme showed a Soret maximum at 430 nm which shifted to 470 nm upon reduction. The molecular weight was estimated by G-200 Sephadex gel filtration chromatography to be 146,000 daltons.