Interferon Preparations Research Articles

Virus free, cell-based assay for the quantification of murine type I interferons

Interferons (IFNs) are potent biologically active proteins synthesized and secreted by somatic cells of all mammalian species. They have been well characterized, with respect to structure, biological activities and clinical therapeutic effects. Historically, IFN antiviral activity assays were the first type of bioassays developed to measure the relative activity or potency of IFN preparations. Here we report a new virus free, cell-based assay to quantify murine type I IFN. It basically consists of an indicator cell line in which the Cre-recombinase is driven by the IFN-inducible Mx1 promoter and, when activated, deletes a stop cassette upstream of the eGFP coding region, resulting in the expression of eGFP. The percentage of eGFP expressing cells accurately correlates to the amount of type I IFN added to the culture and can easily be monitored.

Is Steroid Therapy Needed in the Treatment of Destructive Thyrotoxicosis Induced by α-Interferon in Chronic Hepatitis C?

Objective: Treatment with interferon (IFN) of patients affected by chronic hepatitis C (CH-C) may produce alterations in thyroid function, such as hypothyroidism, Graves’-like hyperthyroidism and destructive thyrotoxicosis (DT). IFN-induced DT is characterized by suppressed serum TSH levels, normal or elevated FT₄ and FT₃ concentrations, with the presence or absence of thyroid peroxidase antibodies and antithyroglobulin antibodies, the absence of thyroid receptor antibodies and radioactive iodine uptake suppressed or <5%. Design: IFN-induced DT is a mild clinical disease, because thyroid-destructive processes last for a short time and involve a small portion of the gland. At present, the therapeutic approach in DT suggests IFN withdrawal and 1–2 months of methylprednisolone treatment. Methods: In consideration of possible untoward side effects of steroid treatment in patients with CH-C, we studied two groups of patients with CH-C who developed DT after treatments with various preparations of recombinant IFN (with or without ribavirin). Patients sequentially entered the study during a 4-year period, at the time of DT diagnosis, when IFN therapy was discontinued. The first 12 subjects (group A) were treated with 8–16 mg/day methylprednisolone for 30–40 days after IFN withdrawal; in the following 15 patients (group B), IFN withdrawal was not followed by any additional treatment. All patients underwent clinical and laboratory controls of thyroid function at 1, 2, 3 and 6 months after DT diagnosis. Results: The results showed restoration of euthyroidism in both group A and group B patients at 6 months after DT diagnosis, regardless of steroid treatment. Conclusions: The simple withdrawal of IFN therapy in patients with CH-C, who had developed DT, appears to be effective in the treatment of the thyroid disease. This therapeutic approach should be preferred in order to avoid possible undesired side effects of steroid therapy in patients with CH-C.

Neuropsychiatric adverse effects of interferon-alpha: recognition and management.

Recombinant preparations of the cytokine interferon (IFN)-alpha are increasingly used to treat a number of medical conditions, including chronic viral hepatitis and several malignancies. Although frequently effective, IFN alpha induces a variety of neuropsychiatric adverse effects, including an acute confusional state that develops rapidly after initiation of high-dose IFN alpha, a depressive syndrome that develops more slowly over weeks to months of treatment, and manic conditions most often characterised by extreme irritability and agitation, but also occasionally by euphoria. Acute IFN alpha-induced confusional states are typically characterised by disorientation, lethargy, somnolence, psychomotor retardation, difficulties with speaking and writing, parkinsonism and psychotic symptoms. Strategies for managing delirium should be employed, including treatment of contributing medical conditions, use of either typical or atypical antipsychotic agents and avoidance of medications likely to worsen mental status. Significant depressive symptoms occur in 21-58% of patients receiving IFN alpha, with symptoms typically manifesting over the first several months of treatment. The most replicated risk factor for developing depression is the presence of mood and anxiety symptoms prior to treatment. Other potential, but less frequently replicated, risk factors include a past history of major depression, being female and increasing IFN alpha dosage and treatment duration. The available data support two approaches to the pharmacological management of IFN alpha-induced depression: antidepressant pretreatment or symptomatic treatment once IFN alpha has been initiated. Pretreatment might be best reserved for patients already receiving antidepressants or for patients who endorse depression or anxiety symptoms of mild or greater severity prior to therapy. Several recent studies demonstrate that antidepressants effectively treat IFN alpha-induced depression once it has developed, allowing the vast majority of subjects to complete treatment successfully. Recent data suggest that IFN alpha-induced depression may be composed of two overlapping syndromes: a depression-specific syndrome characterised by mood, anxiety and cognitive complaints, and a neurovegetative syndrome characterised by fatigue, anorexia, pain and psychomotor slowing. Depression-specific symptoms are highly responsive to serotonergic antidepressants, whereas neurovegetative symptoms are significantly less responsive to these agents. These symptoms may be more effectively treated by agents that modulate catecholaminergic functioning, such as combined serotonin-noradrenaline (norepinephrine) antidepressants, bupropion, psychostimulants or modafinil. Additional factors to consider in selecting an antidepressant include potential drug-drug interactions and adverse effect profile. Finally, IFN alpha appears capable of inducing manic symptoms. Mania, especially when severe, is a clinical emergency. When this occurs, IFN alpha and antidepressants should be stopped, an emergency psychiatric consultation should be obtained, and treatment with a mood stabilizer should be initiated.

Treatment of chronic hepatitis C infection with peginterferons plus ribavirin.

Interferon monotherapy provided the first hope for patients with chronic hepatitis C that the virus could be permanently eradicated. An important development in treating this disease was the recognition that the effects of interferon could be greatly enhanced by combining it with ribavirin, a nucleoside analogue. This combination regimen essentially doubled the sustained virological response rates seen with interferon alone. Recently, modified forms of interferon have been developed that-when used in combination with ribavirin-demonstrate even better efficacy. Thus, peginterferon alfa-2a (Hoffman La-Roche, Nutley, NJ) and peginterferon alfa-2b (Schering-Plough, Kenilworth, NJ) are the latest innovations for the treatment of chronic hepatitis C. The addition of a polyethylene glycol molecule to the native interferon protein favorably alters the pharmacokinetic profile, allowing for once-weekly administration, and leads to superior efficacy compared to standard interferon preparations. This article reviews the data from clinical trials of peginterferon alfa-2a and peginterferon alfa-2b.

Anti-IFN BAb and NAb antibodies: a minireview.

Interferon (IFN) -α, -β, and -γ have been used for the management of many diseases with varying clinical effects. Like many other proteins, all IFN species are potentially immunogenic, especially those produced by recombinant (r) gene technologies. The reported frequencies and titers of anti-IFN antibodies (Ab) vary considerably depending on diseases, IFN preparations and administration, and the types of assays being used.1–9⇓⇓⇓⇓⇓⇓⇓⇓ However, Ab-mediated decrease in bioactivity of IFN (ADB), a condition in which the clinical effect of continued injection of rIFN is minimized or abrogated, is increasingly being recognized.10 The need for clinically useful, inexpensive, and standardized screening assays is obvious, but attempts in this direction have failed despite the recommendation of the World Health Organization (WHO) to use biologic assays where antiviral neutralization is expressed as a titer defined as the reciprocal of the serum dilution that reduces the IFN potency from 10 LU/mL to 1 LU/mL (1 LU/mL is the level of IFN inducing 50% protection against the challenge virus in a given assay).11,12⇓ A major reason for the lack of standardization is the inconvenience and high cost of carrying out elaborate antiviral neutralization assays in the clinical setting; additionally, some of these assays have not been validated with regard to clinical relevance and therefore may provide little useful information to the clinician. Several years of use of such assays have contributed to the conception of, and distinction between, “non-neutralizing binding antibodies” (BAb) and “neutralizing antibodies” (NAb) occurring in patients receiving IFN therapies,13,14⇓ and this issue has been complicated further by the frequent use of BAb assays that may give false-positive results. Over the years, we have investigated naturally occurring and therapeutically induced antibodies to cytokines, including BAb and NAb to IFN preparations. …

Perspectives on the neutralization of interferons by antibody.

Interferon (IFN) neutralizing antibody (NAb) interferes with the binding of the IFN molecule to its cellular receptor, thereby preventing receptor activation required to trigger the cascade of signal transduction events that lead to the varied actions of IFN. IFN antibody neutralization is measured in an IFN bioassay using cultured human cells. Antibody results need to be represented in a reproducibly quantitative manner to know what proportion of patients treated with an IFN preparation form NAbs and whether the levels of antibody measured are likely to have clinically adverse effects; however, antibody titers have been reported in various ways. Extensive experimental and theoretical analyses of IFN-antibody neutralization reactions have provided the basis for establishing a defined international unit of IFN NAb, described herein, so that the data from different laboratories can be readily compared and interpreted.

High yield expression, refolding, and characterization of recombinant interferon α2/α8 hybrids in Escherichia coli

Interferons (IFNs) are a family of pleiotropic cytokines used for the treatment of various viral infections and cancers. The low-cost production of IFNs with high biological value and the discovery of IFNs with improved properties are important for the treatment of these diseases as well as for understanding the physiological functions of these compounds. We describe a protein expression system for the production of IFNs α2, α8, and their hybrids in insoluble form in Escherichia coli, coupled to an efficient two-step optimized refolding and histidine-tag purification protocol. The expressed IFNs were of high biological value, as shown in antiviral and antiproliferative assays and some had specific activities higher than those of the commercially available interferon preparations and exhibited novel properties. This time-efficient, optimized protein expression method allows for the production of not just a single interferon subtype but several native and hybrid IFNs with relatively high yield and low cost that can be used in functional and potentially clinical assays.

Membrane cartridges for endotoxin removal from interferon preparations

The suitability of membrane cartridges for the removal of endotoxin from both distilled water and interferon preparations was examined. The endotoxin concentrations were reduced to 4.0 and 7.3 EU/ml, respectively, when about 4000 ml of distilled water with 20 and 28 EU/ml were passed through the deoxycholate and chitosan immobilized membrane cartridges. When 200 ml of interferon preparation with endotoxin concentration more than 80 EU/ml and pH 3.9 were applied to a deoxycholate immobilized membrane cartridge at a flow-rate of 9 ml/min, the endotoxin concentration was reduced to less than 10 EU/ml. However, if an interferon preparation of 450 ml, with more than 80 EU/ml of endotoxin and pH 3.9 was applied to the chitosan immobilized membrane cartridge at a flow-rate of 18 ml/min, the endotoxin concentration was reduced to less than 10 EU/ml.

Treatment of canine parvoviral enteritis with interferon-omega in a placebo-controlled challenge trial

Canine parvoviral enteritis continues to cause significant morbidity and mortality in dogs worldwide, and efficacious antiviral therapies are lacking. The present trial was aimed at evaluating the therapeutic efficacy of a recombinant feline interferon (type omega) preparation in the treatment of parvoviral enteritis in dogs. A double-blind, placebo-controlled challenge trial was performed in beagle pups (8–9 weeks); clinical signs, body weight, hematologic parameters, and mortality were monitored for a period of 14 days after challenge. Fourteen animals were inoculated with virulent canine parvovirus; 10 animals that developed clinical signs thereby meeting the inclusion criteria were admitted to the treatment phase in two randomly selected groups (placebo and IFN) of equal size. The IFN group received daily intravenous injections of rFeIFN-ω (2.5 MU/kg) for three consecutive days. The placebo group received daily injections of saline without IFN. Both groups of animals received individual supportive treatment consisting of adjusted diet and electrolyte solution. All five dogs in the placebo group developed fulminating enteritis with typical clinical signs and died within 10 days post-inoculation (or 6 days post-treatment). In the IFN-treated group, one animal died on day 2 after the treatment was started, whereas the other four dogs survived the challenge and gradually recovered. Our data confirm that the rFeIFN-ω can exert a significant therapeutic effect on dogs with parvoviral enteritis by improving clinical signs and reducing mortality.

Temporal relationship between the appearance of thyroid autoantibodies and development of destructive thyroiditis in patients undergoing treatment with two different type-1 interferons for HCV-related chronic hepatitis: a prospective study.

In this prospective study we performed repeated evaluations of thyroid status in patients undergoing treatment with different preparations of recombinant interferons (IFNs), in order to identify early markers of thyroid dysfunction. Moreover, we aimed to investigate whether the development of thyroid dysfunction was related to the appearance of thyroid autoimmunity. Our study included 51 consecutive patients without pre-existing thyroid disease, admitted to our hospital for Hepatitis C virus (HCV)-related chronic hepatitis. Thirty-six patients (Gr. A) were treated with IFN-alpha 2b plus ribavirin (RIBA), whereas 15 patients (Gr. B) underwent treatment with IFN-alphacon-1 (CIFN) plus RIBA. Thyroid autoimmunity and function were prospectively evaluated before, every month during treatment and for 6 months after IFN withdrawal. At study entry, all patients were euthyroid and negative for thyroid autoantibodies. In Gr. A, 10 patients developed thyroid autoimmunity after a median period of 3 months (range: 1-6) treatment with IFN-alpha+RIBA. At the time of appearance of thyroid autoantibodies, 4 patients developed destructive thyrotoxicosis (overt in one case, subclinical in 3 cases), while other 4 patients showed a high reduction of serum TSH levels (median decrease: -75.7%, range: -61.9- -84.2), which reached the low values of normal range. After a median period of 2 months (range: 1-3) from these biochemical abnormalities, 6 patients continuing antiviral treatment developed hypothyroidism (overt in 3 cases and subclinical in the other 3). In Gr. B, 5 patients developed thyroid autoimmunity after a median period of 3 months (range: 2-10) of treatment with CIFN+RIBA. Soon after the appearance of thyroid autoantibodies, all patients developed an overt thyrotoxicosis (with hyperthyroidism in 2 cases). Antiviral treatment was discontinued in all 5 cases. Thereafter, thyroid function recovered spontaneously without significant modifications of serum TGAb and TPOAb levels until the end of the study. In conclusion our prospective study demonstrated that: 1) the appearance of thyroid autoantibodies during treatment with IFN was accompanied in most cases by the occurrence of a destructive process in the thyroid gland; 2) The clinical expression of destructive thyroiditis was more evident in patients treated with CIFN than that in patients treated with IFN; 3) The thyroid clinical outcome of these patients was strictly correlated to the continuation of cytokine treatment.

Presence of Cytokines in Biological Preparations

In vaccines produced in eukaryote cells as well as in commercial medical preparations of leukocyte interferon a number of cytokines such as IL-1β, IL-6 and TNF-α have been detected. Among the vaccines examined in this study the highest level of IL-1β was demonstrated in inactivated hepatitis A vaccine prepared in the green monkey kidney cell line 4647, that of IL-6 in inactivated rabies vaccine produced in Syrian hamster kidney (SHK) cell culture, and that of TNF-α in live poliomyelitis vaccine manufactured in VERO cells. A spontaneous and poliovirus-induced capacity of cell cultures to produce cytokines was detected. The level of cytokines produced depend on the kind of cell culture and the type of virus, a more pronounced effect being generated by types 1 and 2 poliovirus as compared with type 3. The presence of highly active cytokines in virus vaccines and interferon preparations points to the necessity of investigating the influence of the presence of cytokines on the biological activity of these preparations and to the advisability of standardizing and controlling the cytokine content.

Essential Thrombocythemia (ET): Moving from Palliation to Cure

Essential thrombocythemia (ET) is a clonal hematopoietic stem cell myeloproliferative disorder characterized by megakaryocytic hyperplasia and persistent thrombocytosis. The clinical presentation and evolution of ET are heterogeneous. This review highlights the current treatment options in the management of ET, including hydroxyurea, anagrelide and both regular and pegylated interferons. Anagrelide, while very effective at controlling counts and symptoms in most patients, may not consistently reduce the bone marrow megakaryocyte mass. Interferon is very effective and not associated with leukemogenesis, but has not been proven to restore polyclonal hematopoiesis and has significant dose-related adverse events. Pegylated interferon represents a significant improvement over the unmodified interferon preparations. Novel therapeutic options directed towards eradication of the malignant ET clone are required.

Enhanced antiviral effect in cell culture of type 1 interferon and ribozymes targeting HCV RNA.

We have recently shown that the replication of an HCV-poliovirus (PV) chimera that is dependent upon the hepatitis C virus (HCV) 5' untranslated region (UTR) can be inhibited by treatment with ribozymes targeting HCV RNA. To determine the antiviral effects of anti-HCV ribozyme treatment in combination with type 1 interferon (IFN), we analysed the replication of this HCV-PV chimera in HeLa cells treated with anti-HCV ribozyme and/or IFN-alpha2a, IFN-alpha2b, or consensus IFN. The anti-HCV ribozyme, or any of the IFNs alone have significant inhibitory effects on HCV-PV replication compared to control treatment (> or = 85%, P < 0.01). The maximal inhibition due to IFN treatment (94%, P < 0.01) was achieved with > or = 50 U/ml for either IFN-alpha2a or IFN-alpha2b compared to control treatment. A similar level of inhibition in viral replication could be achieved with a 5-fold lower dose of IFN if ribozyme targeting the HCV 5' UTR was given in combination. For consensus IFN, the dose could be reduced by > 12.5-fold if ribozyme targeting the HCV 5' UTR was given in combination. Conversely, the dose of ribozyme could be reduced 3-fold if given in combination with any of the IFN preparations. Moreover, treatment with low doses (1-25 U/mL) of IFN-alpha2a, IFN-alpha2b, or consensus IFN in combination with anti-HCV ribozyme resulted in > 98% inhibition of HCV-PV replication compared to control treatment (P < 0.01). These results demonstrate that IFN and ribozyme each have a beneficial antiviral effect that is augmented when given in combination.

Alternatives to chemotherapy and radiotherapy in the treatment of small cell lung cancer

Despite high initial response rates, most patients with small cell lung cancer (SCLC) relapse shortly after discontinuing therapy, and cure remains an elusive goal, even for patients with limited-stage disease. For this reason, investigators have turned to the evaluation of alternative treatment strategies for patients with this malignancy. Interferon has been evaluated in four trials of adjuvant therapy after response to chemotherapy for SCLC. Different Interferon preparations were used, but none of the trials showed a significant prolongation of survival. Tumor vaccines against gangliosides that are expressed on almost all human SCLC cells have been recently developed. An anti-idiotypic monoclonal antibody against the GD3 ganglioside, BEC-2, is being evaluated after chemotherapy in SCLC patients in a European study. In North America, a bivalent ganglioside vaccine, BMS-248967, is under study at the phase II level. If results are promising, a phase III trial will be undertaken. Trials of anticoagulant therapy using heparin, warfarin, and aspirin were undertaken in the 1980s and early 1990s. Although one study of warfarin and another of heparin showed trends in favor of anticoagulant therapy, there has been little research over the past decade evaluating this form of treatment of SCLC. The matrix metalloproteinase inhibitors marimastat and BMS-275291 are under evaluation in SCLC. In all trials, the matrix metalloproteinase inhibitor is administered after chemotherapy and radiotherapy as adjuvant treatment. These trials are not yet mature and survival results are not available. Miscellaneous treatments, including monoclonal antibody therapy, tamoxifen, and growth factor inhibition have not yet been shown to have a role in the treatment of SCLC.

Human Recombinant Interferon-α2a and Interferon-αA/D Have Different Effects on Bleomycin-Induced Lung Injury

Background: Bleomycin (Bleo)-induced lung injury in mice serves as an animal model of pulmonary fibrosis. The pathogenesis of pulmonary fibrosis remains unclear, but it comprises both inflammatory and fibrotic components. The cytokine interferon (IFN)-α is produced by macrophages and may modulate both fibrogenesis and the determination of T lymphocyte phenotype in pulmonary fibrosis. Objective: To investigate the effect of two preparations of recombinant IFN-α (IFN-αA/D and IFN-α2a) on Bleo-induced lung injury in C57BL/6 mice. Methods: Mice were treated by a single intratracheal (IT) instillation of 0.06 mg of Bleo in 0.1 ml of saline or saline alone. One of two different IFN-α preparations, IFN-αA/D or IFN-α2a in saline, or saline alone were administered by daily intraperitoneal injections starting 1 day prior to IT instillation. The treatment groups were as follows: IT Bleo and intraperitoneal saline; IT Bleo and intraperitoneal IFN-α2a; IT Bleo and intraperitoneal IFN-αA/D; IT saline and intraperitoneal IFN-αA/D or IFN-α2a; IT saline and intraperitoneal saline. The animals were sacrificed 14 days after IT instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage (BAL) fluid, by a semiquantitative morphological index of lung injury and a quantitative image analysis of cellularity and fibrosis fraction and by biochemical analysis of lung hydroxyproline content. Results: In Bleo-treated mice, IFN-α2a treatment caused a significant rise in BAL lymphocytes and in cellularity and fibrosis fractions in lung tissue. In contrast, IFN-αA/D treatment had no effect on Bleo-induced lung injury. Conclusion: IFN-α may enhance Bleo-induced lung injury but this effect varies with different IFN preparations.

Correlations between in vitro effects of preparations of interferon and its inducers on blood cells in patients with multiple sclerosis.

We studied in vitro production of interferon-alpha and interferon-gamma by peripheral blood leukocytes from 15 patients with multiple sclerosis. The priming effects of interferon preparations weakly correlated with interferon-alpha production by leukocytes from patients with multiple sclerosis, but negatively correlated with interferon-gamma production. The effects of interferon inducers in most cases positively correlated with its spontaneous production. We found a weak positive correlation between the priming effect of natural interferon-alpha and the effect of recombinant interferons. There were positive or strong positive correlations between the effects of recombinant interferons on leukocytes from patients with multiple sclerosis. The relationship between the effects of medicinal interferon inducers and interferon preparation varied from negative to strong positive correlations. These data suggest that correlation analysis can be used for dynamic control and elaboration of methods for combined immunotherapy of multiple sclerosis with various interferon preparations or interferon and its inducers.

Hepatitis C in patients with human immunodeficiency virus infection: diagnosis, natural history, meta-analysis of sexual and vertical transmission, and therapeutic issues.

Hepatitis C (HCV) infection occurs in as many as 33% of the patients with human immunodeficiency virus (HIV) infection. In view of their improved survival, liver disease will become more clinically significant in patients coinfected with HIV/HCV. Several studies in patients with hemophilia have shown that coinfected patients develop earlier and more severe liver disease, including hepatocellular carcinoma. In nonhemophilic cohorts, lower CD4 counts are associated with an increased prevalence of cirrhosis. However, HCV infection does not seem to alter the natural history of HIV infection in most cases. Human immunodeficiency virus coinfection in pregnant women increases the risk of perinatal HCV transmission 2-fold, with more than 25% of occurrences involving transmission of both viruses: cesarean delivery significantly decreases this risk. The expanded use of highly active antiretroviral therapy may lead to further improvement in morbidity and mortality from HIV infection. Thus, the management of coexistent HCV liver disease will need to be formulated. We suggest that alcohol be disallowed. Interferon and ribavirin in combination are likely to become the therapy of choice, particularly in coinfected patients with higher CD4 counts, lower HCV viremia, and non-1 genotype. During treatment, complete blood cell counts need to be closely monitored. Future controlled trials will determine the efficacy and safety of long-acting interferon preparations. Administration of highly active antiretroviral therapy, with the intent to prevent decreases in CD4 counts, seems crucial in stemming liver disease progression. However, some drugs have clear-cut hepatotoxic potential and patients with known liver disease should be closely monitored. Arch Intern Med. 2000;160:3365-3373.

Comparison of an antiviral activity of recombinant consensus interferon with recombinant interferon-α-2b

To avoid possible uncertainty in comparing biological activities of interferon samples from different sources where interferon concentrations were determined independently, we prepared chromatographically pure preparations of consensus interferon and interferon-α-2b (one of the two commercially available recombinant alpha interferons). We revealed that consensus interferon has a stronger antiviral activity than interferon-α-2b, although the effects of these two recombinant interferons on the cellular macromolecule synthesis are at similar levels.

The oropharyngeal delivery of interferons: where are we and where do we need to go?

The controversial concept of oral delivery of interferon (IFN) is reviewed in relation to possible mechanisms of action. Although there is a rational basis and some positive clinical results for believing that it may work, problems remain to understand which is the most effective IFN preparation and why. Owing to a minimal cost and lack of toxicity, the oral as well as other unconventional routes of IFN delivery deserve to be evaluated because they may become useful.

A new contained human immunodeficiency virus type 1 host cell system for evaluation of antiviral activities of interferons and other agents in vitro

HIV-host infection systems in vitro are important in the pre-clinical assessment of anti-retroviral drug activity. The present report describes the development of a new HIV-host model comprised of an epithelial cell line of HeLa lineage (HeLa-1), transfected with expression vectors bearing tat and rev (TART) genes of HIV-1 as well as the CD4 receptor gene, and HIV-1 ΔTat/Rev, a biologically contained strain of HIV-1 deleted in tat and rev. Measurement of infectivity, by syncytium formation and reverse transcriptase assay, revealed that HeLa-1 is infected with HIV-1 ΔTat/Rev. This virus failed to productively infect the TART-deficient CD4-positive HeLa cells, confirming its contained, non-infectious nature. The HeLa-1/HIV-1 ΔTat/Rev system was used to measure the anti-retroviral activity of a human leukocyte-derived interferon (IFN-αn3) preparation, several nucleoside analogs, and protease inhibitors. The HeLa-1/HIV-1 ΔTat/Rev model provides a biologically contained system for the study of the HIV pathogenesis and the relative and combined therapeutic effects of anti-retroviral agents in vitro.