Human inborn errors of thymic T cell tolerance underlie the production of autoantibodies (auto-Abs) neutralizing type I IFNs, which predispose to severe viral diseases. We analyze 131 female patients with X-linked dominant incontinentia pigmenti (IP), heterozygous for loss-of-function (LOF) NEMO variants, from 99 kindreds in 10 countries. Forty-seven of these patients (36%) have auto-Abs neutralizing IFN-α and/or IFN-ω, a proportion 23 times higher than that for age-matched female controls. This proportion remains stable from the age of 6 years onward. On imaging, female patients with IP have a small, abnormally structured thymus. Auto-Abs against type I IFNs confer a predisposition to life-threatening viral diseases. By contrast, patients with IP lacking auto-Abs against type I IFNs are at no particular risk of viral disease. These results suggest that IP accelerates thymic involution, thereby underlying the production of auto-Abs neutralizing type I IFNs in at least a third of female patients with IP, predisposing them to life-threatening viral diseases.

Anti-cytokine autoantibodies (ACAAs) are increasingly recognized as modulating disease severity in infection, inflammation and autoimmunity. By reducing or augmenting cytokine signalling pathways or by altering the half-life of cytokines in the circulation, ACAAs can be either pathogenic or disease ameliorating. The origins of ACAAs remain unclear. Here, we focus on the most common ACAAs in the context of disease groups with similar characteristics. We review the emerging genetic and environmental factors that are thought to drive their production. We also describe how the profiling of ACAAs should be considered for the early diagnosis, active monitoring, treatment or sub-phenotyping of diseases. Finally, we discuss how understanding the biology of naturally occurring ACAAs can guide therapeutic strategies.

Inborn errors of IFN-γ immunity underlie Mendelian susceptibility to mycobacterial disease (MSMD). Twenty-two genes with products involved in the production of, or response to, IFN-γ and variants of which underlie MSMD have been identified. However, pathogenic variants of IFNG encoding a defective IFN-γ have been described in only two siblings, who both underwent hematopoietic stem cell transplantation (HCST).

We characterized a new patient with MSMD by genetic, immunological, and clinical means. Therapeutic decisions were taken on the basis of these findings.

The patient was born to consanguineous Turkish parents and developed bacillus Calmette-Guérin (BCG) disease following vaccination at birth. Whole-exome sequencing revealed a homozygous private IFNG variant (c.224 T > C, p.F75S). Upon overexpression in recipient cells or constitutive expression in the patient's cells, the mutant IFN-γ was produced within the cells but was not correctly folded or secreted. The patient was treated for 6 months with two or three antimycobacterial drugs only and then for 30 months with subcutaneous recombinant IFN-γ1b plus two antimycobacterial drugs. Treatment with IFN-γ1b finally normalized all biological parameters. The patient presented no recurrence of mycobacterial disease or other related infectious diseases. The treatment was well tolerated, without the production of detectable autoantibodies against IFN-γ.

We describe a patient with a new form of autosomal recessive IFN-γ deficiency, with intracellular, but not extracellular IFN-γ. IFN-γ1b treatment appears to have been beneficial in this patient, with no recurrence of mycobacterial infection over a period of more than 30 months. This targeted treatment provides an alternative to HCST in patients with complete IFN-γ deficiency or at least an option to better control mycobacterial infection prior to HCST.

Over recent decades, therapeutic proteins have had widespread success in treating a myriad of diseases. Glycosylation, a near universal feature of this class of drugs, is a critical quality attribute that significantly influences the physical properties, safety profile and biological activity of therapeutic proteins. Optimizing protein glycosylation, therefore, offers an important avenue to developing more efficacious therapies. In this review, we discuss specific examples of how variations in glycan structure and glycoengineering impacts the stability, safety, and clinical efficacy of protein-based drugs that are already in the market as well as those that are still in preclinical development. We also highlight the impact of glycosylation on next generation biologics such as T cell-based cancer therapy and gene therapy.

Hepatitis C virus (HCV) infection is a major health concern worldwide. Interferon-α (IFN-α) therapy has been the main antiviral treatment for more than 20 years. Because of its established antitumor effects, IFN-based treatments for chronic HCV infection still have a clinical impact, particularly for patients with high risk conditions of developing hepatocellular carcinoma, such as older age and advanced liver fibrosis. As a result of exhaustive research, several viral factors, including NS5A amino acid mutations such as the IFN sensitivity-determining region and the IFN/ribavirin resistance-determining region, and mutations of amino acids in the core protein region (core 70 and 91) were shown to be associated with the response to IFN-α treatment. In addition, among the host factors related to the response to IFN-α treatment, polymorphisms of the interleukin-28B gene were identified to be the most important factor. In this article, we review the factors associated with the efficacy of IFN-α treatment for chronic HCV infection. In addition, our recent findings regarding the possible involvement of anti-IFN-α neutralizing antibodies in a non-response to pegylated-IFN-α treatment are also described.

Pegylated interferon-α (PEG-IFN-α) plus ribavirin (RBV) treatment fails to achieve a sustained virological response (SVR) in approximately 20-50% of patients with chronic hepatitis C virus (HCV) infection. We assessed the contribution of an anti-IFN-α neutralizing antibody (NAb) on the nonresponse to treatment. NAbs were detected using an antiviral assay that assessed the neutralizing effects of serum samples against IFN. Serum samples were obtained at the end of the treatment and evaluated for the presence of NAbs using recombinant IFN-α as a standard. We studied 129 PEG-IFN-α/RBV-treated patients. In the 82 end-of-treatment responders, no NAbs were detected. Of the 47 patients who did not respond, seven (15%) were positive for NAbs. We also examined an additional 83 patients who had not responded to PEG-IFN-α treatment, and detected 12 with NAbs. Patients with good IFN-responsive characteristics, including HCV genotype 2/3 and major allele homozygotes for interleukin-28B, were included in the 19 patients with NAbs. No NAbs interfered with the antiviral activity of natural human IFN-β (nIFN-β) and re-treatement of patients with NAbs with nIFN-β/RBV achieved SVR. Our analyses revealed that the emergence of anti-IFN-α NAbs was a candidate causal factor of PEG-IFN-α-treatment failure. Therefore, these antibodies should be assayed in patients who do not respond to PEG-IFN-α therapy, and if detected, other effective treatments, i.e., medications that are not neutralized by anti-IFN-α NAbs, should be considered.

This review summarizes and analyzes the clinical outcomes following treatment of a wide range of diseases with recombinant interferons (r-IFNs) and/or natural interferons (n-IFNs). The investigation focuses on the frequency of neutralizing antibodies (NABs) directed against IFN, which are formed during treatment and their clinical impact. r-IFNs (α-2a, α-2b, β-1a, and β-1b) induced seroconversion with generation of NABs in 17.2% of patients studied. The highest incidence of NABs occurred in macular degeneration (61.4%) with the lowest in multiple sclerosis (14.7%). The incidence of antibodies induced against n-IFNs was very low (<0.2%) and was significantly less than that seen for r-IFNs (P<0.0001). Overall, the fraction of relapsed and refractory patients is statistically greater in NAB positive patients compared to NAB negative patients (<0.0001), whereas the percentage of responding patients is higher in the NAB negative cohort (P<0.001). Finally, we also analyzed relapsed and refractory NAB positive patients who switched treatment to n-IFN, such as leukocyte derived Alferon N Injection® (α-n3) or Wellferon® (α-n1). Overall, in 33/40 (82%) of these relapsed or refractory patients, switching to n-IFNs restored the clinical response. This result is consistent with serology studies showing that the NABs directed against r-IFNs do not effectively cross-react with n-IFNs.

Recombinant thrombin (rThrombin) is a potential hemostatic alternative to bovine and human plasma-derived thrombin. This report examines the clinical results for the vascular surgery subgroup of patients enrolled in a larger double-blind, randomized, multicenter trial, which evaluated the comparative safety and efficacy of rThrombin and bovine plasma-derived thrombin (bThrombin) when used as adjuncts to surgical hemostasis.

Data from the 164 vascular patients who underwent either a peripheral arterial bypass (PAB) or arteriovenous graft (AV) procedure are included in this analysis. Time to hemostasis at proximal and distal anastomotic sites at 1.5-, 3-, 6-, and 10-minute intervals was determined by procedure (PAB or AV) and overall (PAB + AV). Baseline and day 29 immunologic sera were analyzed. The incidences of postoperative adverse events were compared between treatment groups. Categorical adverse events were evaluated in relation to thrombin product antibody formation.

Patients were randomized to either bThrombin (n = 82) or rThrombin (n = 82). Procedures included PAB (n = 88) and AV (n = 76). The bThrombin and rThrombin groups were well matched for demographics and baseline characteristics. A comparable incidence of anastomotic hemostasis was observed in both treatment groups at 10 minutes (94% bThrombin, 91% rThrombin). The incidence of hemostasis was lower at all time points for PAB procedures compared with AV procedures. In the PAB group, a significantly greater proportion of patients receiving rThrombin (55%) achieved hemostasis at 3 minutes compared with bThrombin (39%; P < .05). Adverse event profiles and laboratory findings were similar between groups. No patients in the rThrombin group developed anti-rThrombin product antibodies at day 29, whereas 27% of patients in the bThrombin group developed antibodies to bThrombin product (P < .0001).

rThrombin or bThrombin used as a hemostatic ancillary for anastomotic bleeding was equally effective at 10 minutes; however, rThrombin compared with bThrombin may provide a more rapid onset of hemostasis at 3 minutes in PAB procedures. Adverse events were similar between the two thrombins. In patients undergoing vascular surgery, both treatments were similarly well tolerated, although rThrombin demonstrated a superior immunogenicity profile.

This study was conducted to study the influence of protein structure on the immunogenicity in wild-type and immune tolerant mice of well-characterized degradation products of recombinant human interferon alpha2b (rhIFNalpha2b).

RhIFNalpha2b was degraded by metal-catalyzed oxidation (M), cross-linking with glutaraldehyde (G), oxidation with hydrogen peroxide (H), and incubation in a boiling water bath (B). The products were characterized with UV absorption, circular dichroism and fluorescence spectroscopy, gel permeation chromatography, reverse-phase high-pressure liquid chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, Western blotting, and mass spectrometry. The immunogenicity of the products was evaluated in wild-type mice and in transgenic mice immune tolerant for hIFNalpha2. Serum antibodies were detected by enzyme-linked immunosorbent assay or surface plasmon resonance.

M-rhIFNalpha2b contained covalently aggregated rhIFNalpha2b with three methionines partly oxidized to methionine sulfoxides. G-rhIFNalpha2b contained covalent aggregates and did not show changes in secondary structure. H-rhIFNalpha2b was only chemically changed with four partly oxidized methionines. B-rhIFNalpha2b was largely unfolded and heavily aggregated. Nontreated (N) rhIFNalpha2b was immunogenic in the wild-type mice but not in the transgenic mice, showing that the latter were immune tolerant for rhIFNalpha2b. The anti-rhIFNalpha2b antibody levels in the wild-type mice depended on the degradation product: M-rhIFNalpha2b > H-rhIFNalpha2b approximately N-rhIFNalpha2b >> B-rhIFNalpha2b; G-rhIFNalpha2b did not induce anti-rhIFNalpha2b antibodies. In the transgenic mice, only M-rhIFNalpha2b could break the immune tolerance.

RhIFNalpha2b immunogenicity is related to its structural integrity. Moreover, the immunogenicity of aggregated rhIFNalpha2b depends on the structure and orientation of the constituent protein molecules and/or on the aggregate size.

The most relevant randomized controlled trials of interferon-alpha (IFN) for naive patients with chronic hepatitis C (CHC) published in a decade, just before appearance of pegylated IFN trials in 2000, were included in this paper. Its purpose is to review the relationship between sustained biochemical response in active versus control group versus usual clinical variables as IFN regimens, cirrhosis, genotype and versus less frequently addressed variables as funding, methodological quality or location of principal author. Meta-analysis estimates of global treatment effect varied according to trial design: group 1=IFN versus placebo/no treatment, 32 RCTs, 2499 pts, OR 9.5 (6.3-14.2); group 2a=comparison of IFN schedules, 43 RCTs, 7454 pts, OR 1.6 (1.4-1.9); group 2b=IFN+other drugs versus standard IFN, 30 RCTs, 4737 pts, OR 2.0 (1.6-2.6). Fixed effects (arm-level) meta-regression on the complete data set (171 arms, 10,580 pts) revealed that sustained response was most likely in experimental arms of IFN+ribavirin or other drugs (OR 2.4), arms using yearly schedule (OR 2.0), trial principal author from Asia (OR 1.7), trial sample size >200 (OR 1.4) and arms enrolling less than 50% of cirrhotics (OR 1.3). Moreover, focus was on some significant interactions too, as the effect of trial's quality interacting to the recorded funding (more benefit if no-profit, less if for-profit) and the effect of trial funding interacting to the location of first author (more benefit if from Asia). Three main effects (experimental arm, cirrhosis, funding) and one interaction (funding*location of principal author) explained 31% of between study variability in a random-effect meta-regression. In a subgroup analysis on a data set including available information on HCV genotype (93 arms, around 7000 pts), meta-regression revealed that genotype 1 or 4 less than 50% per arm and specialistic journal were significant predictors of either biochemical (transaminases) or virological (HCV-RNA) sustained response, in a model including the same main effects identified in the complete data set analysis. Finally, although mostly captured by different IFN regimens along time, heterogeneity of effect in a large set of (not-pegylated) IFN trials was also explained by HCV genotype and variables of quality and reporting, such as trial's principal author from Asia.

Different mechanisms have been proposed for the failure of interferon (IFN) therapy in patients with chronic hepatitis C and multiple sclerosis, for example, the presence of IFN-neutralizing antibodies. In this study, a novel assay system based on the IFN-inducible Mx-promoter was used to detect IFN-neutralizing antibodies in sera of patients with chronic hepatitis C. To monitor IFN bioactivity in IFN-treated patients, a real-time RT-PCR for MxA gene expression in PBMCs was established. Using these two methods, patients with chronic hepatitis C virus (HCV) infection receiving IFN therapy and patients with treatment induced HCV clearance were monitored. Importantly, neutralizing anti-IFN antibodies were detected in the sera of 3 of 38 chronically HCV-infected patients who failed to respond to therapy but none in sera of patients who cleared HCV after IFN therapy. Interestingly, the presence of these antibodies correlated with the lack of MxA induction in PBMCs after initiation of IFN-alpha therapy. Retrospective analysis of one patient's sera revealed that the anti-IFN-alpha antibodies had already developed after the first of four unsuccessful IFN therapies, suggesting that neutralizing antibodies may have contributed to the failure of previous IFN treatments. In summary, a novel screening assay was established that may be helpful for testing IFN non-responders for the presence of clinically relevant anti-IFN-alpha antibodies and for selecting alternative IFN preparations not neutralized by these antibodies.

Lichen planus (LP) has been reported in association with chronic active hepatitis, primary biliary cirrhosis and other chronic liver diseases. The occurrence of LP in persons with hepatitis C virus (HCV) was reported by Robert et al., and the possible relationship between LP and hepatitis virus has also been supported by cases of LP following hepatitis B vaccination. Exacerbation or appearance of LP during the treatment of chronic hepatitis C, lymphoproliferative diseases and melanoma with alpha-interferon (IFN-alpha) and improvement of these diseases after discontinuation of this drug indicate that IFN-alpha may possibly induce LP. We present a case of cutaneo-mucous LP in a woman with chronic active hepatitis treated with IFN-alpha and in whom local leukocytoclastic vasculitis was induced by the intradermal injection of a very low dose of IFN-alpha.

The efficacy of alpha interferon (IFN-alpha) in the treatment of severe type II essential mixed cryoglobulinemia (EMC) has been reported previously. In some patients, the development of neutralizing antibodies to recombinant IFN-alpha (rIFN-alpha) can affect the clinical response achieved with rIFN-alpha; a second treatment with natural IFN-alpha preparations may reinduce the clinical response. In the present study the ability of leukocyte IFN (LeIFN) to restore the response was investigated from a pharmacodynamic viewpoint. Specifically, the pharmacodynamic profiles of different IFN-alpha preparations were studied by measuring the serum neopterin levels and the levels of expression of protein MxA mRNA in in vivo peripheral blood mononuclear cells in two patients with EMC whose resistance to rIFN-alpha2a treatment increased concomitantly with the development of neutralizing antibodies. These markers were measured before injection and at 24 and 48 h after a single injection of rIFN-alpha2a, consensus IFN [(C)IFN], or LeIFN. No increase or only a slight increase in MxA mRNA levels was detectable after administration of rIFN-alpha2a or (C)IFN, whereas a significant increase (>/=10-fold) in MxA mRNA expression was recorded following administration of LeIFN. The neutralizing antibodies to rIFN-alpha2a cross-react with (C)IFN. Sera from these patients neutralized most but not all of the subtypes present in the natural IFN-alpha (LeIFN) mixture, and no significant increase in neopterin levels was observed after these patients were switched to LeIFN treatment. In summary, the data demonstrate that the problem of neutralizing antibodies still exists and that LeIFN may induce an increase in the level of MxA mRNA expression but not an increase in neopterin levels in patients who are resistant to treatment with rIFN-alpha2a or (C)IFN.

Therapeutic proteins have revolutionized the treatment of many diseases. In the near future, many more therapeutic proteins are likely to become available for an increasingly wide range of indications.

This article reviews the incidence, causes, and consequences of formation of antibodies to therapeutic proteins and suggests ways to address issues surrounding immunogenicity.

Searches of MEDLINE and EMBASE databases were performed, covering the period 1990 to May 2002. Search terms included immunogenicity, antibodies, and the names of specific therapeutic proteins and classes of therapeutic proteins. Bibliographies of retrieved articles were not searched.

All exogenous proteins, including therapeutic ones, have the potential to cause antibody formation. The reported incidence of antibody formation with therapeutic proteins varies widely between proteins and between studies (depending on the assay techniques used). The clinical consequences of antibody formation vary with the type of antibody present; for example, neutralizing antibodies are more likely to cause loss of efficacy than nonneutralizing antibodies. The immunogenicity of therapeutic proteins can be influenced by many factors, including the genetic background of the patient, the type of disease, the type of protein (human or nonhuman), the presence of conjugates or fragments, the route of administration, dose frequency, and duration of treatment. Manufacturing, handling, and storage can introduce contaminants, or alter the 3-dimensional structure of the protein via oxidation or aggregate formation. Various means have been suggested by which therapeutic proteins might be modified to reduce their immunogenicity, including PEGylation, site-specific mutagenesis, exon shuffling, and humanization of monoclonal antibodies. In the future, it may even be possible to predict the immunogenicity of new therapeutic proteins more accurately, using specifically designed animal models, including nonhuman primates and transgenic mice.

Scientists and clinicians are becoming increasingly aware of the importance of assessing the immunogenicity of new molecules as they are introduced, and of existing molecules whenever they are modified or their manufacturing process is changed. Immune responses to therapeutic proteins are usually only of clinical significance if they are associated with the development of treatment resistance. Although various means to reduce the immunogenicity of therapeutic proteins have been suggested, monitoring for antibodies during clinical trials and postmarketing surveillance remains an important issue for all therapeutic proteins.

The frequencies of anti-interferon-beta (IFN-beta) antibody development reported to date in patients treated with different IFN-beta preparations are not readily comparable mainly because of differences in underlying diseases and assay methods. Thus, the frequency of neutralizing antibody (NAb) and binding antibody (BAb) development was analyzed in a sample of sera derived from a homogeneous group of relapsing-remitting multiple sclerosis (RRMS) patients treated with different IFN-beta preparations. The frequency of developing NAb and BAb to IFN-beta varied according to the IFN-beta given. Specifically, the NAb seroconversion frequency was significantly higher in patients treated with Betaferon, Schering AG, Berlin, Germany (31.3%) than in patients treated with both preparations of recombinant IFN-beta 1a (Rebif, Serono, Geneva, Switzerland [7.4%] or Avonex, Biogen, Cambridge, MA [6.3%]). Analysis of BAb seroconversion frequency in the same patients revealed that different IFN-beta preparations may also have different capability to induce BAb development and that BAb are produced during IFN-beta therapy at a significantly higher rate than NAb. Our main conclusion is that different human IFN-beta preparations may possess different immunogenicities, leading to varying frequency of development of antibody to IFN-beta in RRMS.

The influences of dosing time and dosing schedule on the plasma alpha interferon (IFN-alpha) concentration and the production of anti-IFN-alpha neutralizing antibodies were investigated in ICR male mice adapted to cycles of 12 h of light and 12 h of dark. In mice pretreated with IFN-alpha for 21 days, the plasma IFN-alpha concentrations were significantly lower than those in control mice (P < 0.01). The clearance of IFN-alpha and its volume of distribution obtained at steady state were significantly higher in the animals with IFN-alpha pretreatment than in the mice without IFN-alpha pretreatment. The area under the concentration-time curve and the mean residence time of IFN-alpha were significantly smaller in IFN-alpha-pretreated animals than in control animals. The plasma IFN-alpha levels (measured 2 h after dosing) were significantly lower in mice treated daily with IFN-alpha, while the anti-IFN-alpha neutralizing antibody levels (measured 24 h after dosing) were significantly increased on days 15 and 21 of treatment. Plasma IFN-alpha levels were significantly decreased in association with the production of anti-IFN-alpha neutralizing antibodies in mice treated with IFN-alpha daily at either 0900 or 2100 h. By contrast, the plasma IFN-alpha levels (measured 2 h after dosing) remained stable in mice treated with IFN-alpha at 0900 h on alternate days, while they were significantly lower after 21 days of treatment in mice treated with IFN-alpha at 2100 h on alternate days. These changes were associated with a significant increase in the levels of anti-IFN-alpha neutralizing antibodies in the latter group. The present findings suggest that an appropriate dosing schedule and/or dosing time for IFN-alpha may reduce the level of production of anti-IFN-alpha neutralizing antibodies in experimental and clinical situations.

Delivery of pharmacological doses of proteins to people has raised concerns of inducing immune responses, especially when the protein is provided in multiple doses over an extended period of time. Immune responses could impact the therapeutic exposure and efficacy of the protein itself. In addition, there have been fears of anaphylaxis or autoimmunity. This review summarizes the available literature regarding the measurement and evaluation of immune responses observed during clinical assessment of recombinant human proteins. Immune responses have ranged from none at all to inactivation and/or accelerated clearance. Presence of antibodies does not necessarily impact therapeutic viability. While responses are related to frequency and route of delivery, there is no clear relationship that enables one to predict the clinical experience.

The administration of interferon (IFN) could be complicated by the development of neutralizing anti-interferon antibodies (NA). This study evaluates the frequency and associated factors of NA among chronic hepatitis C patients treated with different IFNs.

Ninety-five chronic hepatitis C patients were randomized to be treated with recombinant IFN-alpha2a (n = 28), IFN-alpha2b (n = 39) or lymphoblastoid IFN-alpha1 (n = 28) given intramuscularly, 3-6 million units, thrice weekly for 24 weeks. Serum samples collected before, during and after the cessation of treatment were checked for NA.

Three patients were withdrawn from treatment. All patients were negative for NA before treatment and 13 (14%) patients developed neutralizing antibodies. Of the 26 patients treated with IFN-alpha2a, 6 (23.1%) developed NA. whereas NA were detected in only 6 (15.4%) of 39 and 1 (3.7%) of 27 patients treated with IFN-alpha2b and IFN-alphanl, respectively. Age, gender, HCV genotype, ALT level, IFN total dose and liver histology were not associated with the development of NA. By using multivariate logistic regression it was shown that pretreatment HCV RNA level and IFN preparation were the two major factors related to the production of NA. The response of treatment was related to pretreatment viremia but not to the presence of NA.

The frequency of development of NA among Taiwanese patients with chronic hepatitis C might be related to different IFN preparations and pretreatment HCV RNA level. The response of treatment was related to pretreatment HCV RNA level but not to the presence of NA.

Sixty-eight patients with relapsing-remitting multiple sclerosis (RRMS) were treated with 3 million or 9 million i.u. of recombinant interferon-beta1a (recIFN-beta1a) s.c. three times a week for 2 years. Their sera were tested for antibodies neutralizing the IFN (NAb) in a bioassay. Sera with titers > or = 1:20 were considered positive. We detected NAb in 3.2%, 13.8%, and 15.9% of the patients in sera obtained at 3, 6, and 24 months, respectively. The incidence was not related to the IFN dose. Interestingly, during the 6 month baseline period before the start of the study, relapse rates, baseline disability, and the volume of lesions on T2-weighted images were significantly higher in patients who developed NAb during treatment. Because of interpatient variability, no definitive relationship was observed between NAb formation and loss of clinical or magnetic resonance imaging (MRI) response.

Although several virus- and host-related predictive factors for the response to interferon alfa (IFN-alpha) have been defined in patients with chronic hepatitis C, no pretreatment parameter can definitely predict the response to antiviral treatment. Assessment of the initial response by quantification of serum hepatitis C virus RNA before and 4 weeks after initiation of therapy may be a clinically applicable and reliable parameter to predict long-term response. Therefore, the aims of the present study were to test the predictive value of a decline in HCV RNA of at least 3 log in the first 4 weeks of treatment (deltaHCV RNA) in patients treated with 3 x 10(6) units of recombinant IFN-alpha2a (rIFN-alpha2a) three times per week subcutaneously and to compare deltaHCV RNA with other established predictive factors, such as HCV genotype and pretreatment viremia. Serum HCV RNA was measured by a validated quantitative reverse transcription-polymerase chain reaction (RT-PCR). Geno/subtyping of HCV was performed by direct sequencing of the nonstructural (NS) 5B region of PCR-amplified isolates and subsequent phylogenetic analysis. Stable HCV RNA levels (deltaHCV RNA < or = 1 log) within the first 4 weeks of IFN-alpha treatment were present in 42 of 70 patients. A decline in HCV RNA levels between 1 to 3 log and more than 3 log was observed in 9 (13%) and 19 patients (27%), respectively. In 21 of 70 patients (30%), HCV RNA was not detectable at the end of 12 months' treatment. Three of 26 patients (11%) with a pretreatment viremia of < or = 10(6) copies/mL (all HCV subtype 3a) and 6 of 44 patients (14%) with a pretreatment viremia of > 10(6) copies/mL (HCV subtypes 1b, 2a, 2c, 3a [two patients], and 4) achieved a virological sustained response to interferon-alpha2a treatment. All patients with a virological sustained response had an initial deltaHCV RNA of more than 3 log. In a stepwise discriminant-function analysis, the initial deltaHCV RNA was confirmed as the strongest predictor of virological sustained response (P < .0001). In conclusion, the data of the present study suggest that IFN-alpha treatment can be terminated after 4 weeks in patients with a decrease in HCV RNA levels of less than 3 log, when apparent HCV eradication is considered the therapeutic target. The predictive value of deltaHCV RNA clearly exceeds the significance of HCV genotype and pretreatment viremia as predictors of successful IFN-alpha treatment.

The therapeutic indications for Interferons (IFNs) have dramatically increased in number in recent years to include many different diseases of viral, malignant, angiogenic, allergic, inflammatory and fibrotic origin. In particular, the current pandemic of hepatitis C virus infection has further stimulated the requirement for a comprehensive understanding of both the mechanism of action of IFN and the reasons for therapeutic failure. The role of anti-IFN antibodies as a cause of treatment failure has been a particularly controversial area. In this review we will outline the biology and proposed mechanisms of action of IFN-alpha (IFN-alpha) and discuss the incidence, methods of detection and clinical significance of anti-IFN antibodies.

Alpha interferon induces aminotransferase normalization in about 50% of patients with chronic viral hepatitis C. However, some patients who initially respond experience a relapse during the treatment period (breakthrough phenomenon). The aim of this study was to evaluate the prevalence of breakthrough and its relationship with the emergence of neutralizing anti-interferon antibodies.

We studied 172 patients with histologically proven chronic hepatitis C, treated with interferon alpha 2a or 2b 3 mega units three times a week for 6 months. For each patient, HCV RNA level (polymerase chain reaction and bDNA) and anti-interferon antibodies dosage were determined during therapy.

Among 84 patients with initial response, 13 (15.5%) experienced breakthrough. The kinetics of alanine aminotransferase and HCV RNA levels were strongly correlated, suggesting that breakthrough is not due to a random alanine aminotransferase fluctuation during treatment, but to the reappearance of viral replication. Neutralizing anti-interferon antibodies emergence was observed in 38.5% in patients with breakthrough, as compared to 9.0% and 2.8% of non-responder and complete-responder patients, respectively (p<0.0005). By multivariate analysis, the only factor predictive of breakthrough was the emergence of neutralizing anti-interferon antibodies 3 months after the onset of therapy.

Our results suggest that the emergence of neutralizing anti-interferon antibodies during treatment may explain breakthrough in about one third of cases. Other causes may also be responsible for this phenomenon and they remain to be determined.

Interferons (IFNs) are generally recognized as the most important therapeutic agent in some infectious diseases such as chronic hepatitis B and C. Since the early clinical trials it was documented that the therapeutic use of IFNs could be complicated by the development of antibodies able to neutralize or to bind to the IFN molecule. After several years of research it is now widely accepted that the presence of circulating anti-IFN antibodies may affect the response to IFN. Here we summarize what is currently know on the clinical significance of antibodies to IFN in IFN-treated viral diseases patients.

IFN-alpha has emerged as a promising treatment of chronic viral hepatitis. Although therapeutic response to IFN is far from universal, efficacy has been demonstrated; and studies combining IFN-alpha with other agents, as well as trials with new preparations of IFN-alpha, are under way. Children do not represent a large part of the identified population with chronic viral hepatitis. Yet children, by simple virtue of age, are more recently infected. In addition, longer life expectancies can be expected to be associated with greater morbidity from chronic viral hepatitis. Children seem to tolerate therapy with IFN-alpha well. Treatment of children with chronic viral hepatitis should be strongly considered, with protocols designed to ascertain specific pediatric safety and efficacy.

Two patients with chronic-phase chronic granulocytic leukemia initially responded to recombinant interferon alpha-2a (rIFN-alpha-2a) but relapsed as a result of development of hightiter neutralizing antibodies to rIFN-alpha-2a. Both patients were subsequently treated with natural leukocyte IFN-alpha (IFN-alpha-n3), and one of the two patients achieved a durable second hematologic and cytogenetic remission. IFN-alpha-n3 may be considered for patients in whom antibody-mediated resistance to rIFN-alpha-2a develops.

Interferon-alpha-2a is a recombinant interferon with antiviral, antitumour and immunomodulatory properties. Clinical studies have demonstrated that the drug offers therapeutic benefit in patients with some forms of chronic viral hepatitis. Remission, as measured by clearance of viral DNA and hepatitis B 'e' antigen (HBeAg), and normalisation of serum alanine aminotransferase levels, is observed in approximately 30 to 45% of patients with chronic hepatitis B receiving interferon-alpha-2a (2.5 to 18MU administered 3 times/week); about 5 to 15% of untreated controls remit spontaneously every year. Complete recovery [with loss of hepatitis B surface antigen (HBsAg)] is usually noted in < 20% of treated individuals. Similar response rates have been reported in the relatively small number of children evaluated to date. Although numerous studies have shown that interferon-alpha-2a (at various dosages) induces biochemical amelioration of chronic hepatitis C in approximately 50 to 75% of patients, relapse is common. Thus, long term remission may only be observed in about 15 to 30% of treated patients. On the other hand, this disorder remits spontaneously in only a few patients. The role of interferon-alpha-2a in the treatment of chronic hepatitis D remains unclear. Although preliminary data suggest it may be beneficial, cessation of therapy is generally followed by relapse. As with other types of interferons, most patients receiving interferon-alpha-2a experience an 'influenza-like' syndrome, which tends to diminish with continuing therapy. Other effects such as fatigue, lethargy, anorexia and weight loss are usually dose-limiting. Serum neutralising antibodies develop in approximately 10 to 20% of treated patients. Thus, although response rates are less than optimal, interferon-alpha-2a is a drug of first choice amongst the limited therapeutic options available for the management of well-compensated chronic viral hepatitis B or C.