[Viral safety of intravenous immunoglobulins G for therapeutic use]

Assessment of viral inactivation during pH 3.3 pepsin digestion and caprylic acid treatment of antivenoms

Antivenoms are manufactured by the fractionation of animal plasma which may possibly be contaminated by infectious agents pathogenic to humans. This study was carried out to determine whether pre-existing antivenom production steps, as carried out by EgyVac in Egypt, may reduce viral risks. Two typical manufacturing steps were studied by performing down-scaled viral inactivation experiments: (a) a pH 3.3 pepsin digestion of diluted plasma at 30 degrees C for 1h, and (b) a caprylic acid treatment of a purified F(ab')2 fragment fraction at 18 degrees C for 1h. Three lipid-enveloped (LE) viruses [bovine viral diarrhoea virus (BVDV), pseudorabies virus (PRV), and vesicular stomatitis virus (VSV)] and one non-lipid-enveloped (NLE) virus [encephalomyocarditis virus (EMC)] were used as models. Kinetics of inactivation was determined by taking samples at 3 time-points during the treatments. The pH 3.3 pepsin digestion resulted in complete clearance of PRV (>7.0 log(10)) and in almost complete reduction of VSV (>4.5 but < or =6.4 log(10)), and in a limited inactivation of BVDV (1.7 log(10)). EMC inactivation was > or =2.5 but < or =5.7 log(10). The caprylic acid treatment resulted in complete inactivation of the 3 LE viruses tested: BVDV (>6.6 log(10)), PRV (>6.6 log(10)), and VSV (>7.0 log(10)). For EMC no significant reduction was obtained (0.7 log(10)). Cumulative reduction was >13.6, >11.5, >8.3 and > or =2.5 for PRV, VSV, BVDV and EMC, respectively. Therefore the current manufacturing processes of at least some animal antisera already include production steps that can ensure robust viral inactivation of LE viruses and moderate inactivation of a NLE virus.

Pathogen inactivation: the definitive safeguard for the blood supply

CONTEXT

Pathogen inactivation provides a proactive approach to cleansing the blood supply. In the plasma fractionation and manufacturing industry, pathogen inactivation technologies have been successfully implemented resulting in no transmission of human immunodeficiency, hepatitis C, or hepatitis B viruses by US-licensed plasma derivatives since 1985. However, these technologies cannot be used to pathogen inactivate cellular blood components. Although current blood donor screening and disease testing has drastically reduced the incidence of transfusion-transmitted diseases, there still looms the threat to the blood supply of a new or reemerging pathogen. Of particular concern is the silent emergence of a new agent with a prolonged latent period in which asymptomatic infected carriers would donate and spread infection.

OBJECTIVE

To review and summarize the principles, challenges, achievements, prospective technologies, and future goals of pathogen inactivation of the blood supply.

DATA SOURCES

The current published English-language literature from 1968 through 2006 and a historical landmark article from 1943 are integrated into a review of this subject.

CONCLUSIONS

The ultimate goal of pathogen inactivation is to maximally reduce the transmission of potential pathogens without significantly compromising the therapeutic efficacy of the cellular and protein constituents of blood. This must be accomplished without introducing toxicities into the blood supply and without causing neoantigen formation and subsequent antibody production. Several promising pathogen inactivation technologies are being developed and clinically tested, and others are currently in use. Pathogen inactivation offers additional layers of protection from infectious agents that threaten the blood supply and has the potential to impact the safety of blood transfusions worldwide.

[Plasma fractionation in the world: current status]

From 22 to 25 million liters of plasma are fractionated yearly in about 70 fractionation plants, either private or government-owned, mainly located in industrialized countries, and with a capacity ranging from 50000 to three million liters. In an increasingly global environment, the plasma industry has recently gone through a major consolidation phase that has seen mergers and acquisitions, and has led to the closure of a number of small plants in Europe. Currently, some fifteen countries are involved into contract plasma fractionation programs to ensure a supply of plasma-derived medicinal products. The majority of the plasma for fractionation is obtained by automated plasmapheresis, the remaining (recovered plasma) being prepared from whole blood as a by-product of red cell production. Plasma for fractionation should be produced, and controlled following well established procedures to meet the strict quality requirements set by regulatory authorities and fractionators. The plasma fractionation technology still relies heavily on the cold ethanol fractionation process, but has been improved by the introduction of modern chromatographic purification methods, and efficient viral inactivation and removal treatments, ensuring quality and safety to a large portfolio of fractionated plasma products. The safety of these products with regards to the risk of transmission of variant Creutzfeldt-Jakob disease seems to be provided, based on current scientific data, by extensive removal of the infectious agent during certain fractionation steps. The leading plasma product is now the intravenous immunoglobulin G, which has replaced factor VIII and albumin in this role. The supply of plasma products (most specifically coagulation products and immunoglobulin) at an affordable price and in sufficient quantity remains an issue; the problem is particularly acute in developing countries, as the switch to recombinant factor VIII in rich countries has not solved the supply issue and has even led to an increase of the mean price of plasma-derived factor VIII to the developing world. In the last few years, the plasma fractionation industry has improved greatly, and should remain essential in the years to come for the procurement of many essential medicines.

CJD PrPsc removal by nanofiltration process: Application to a therapeutic immunoglobulin solution (Lymphoglobuline®)

The characteristic of transmissible spongiform encephalopathies (TSE) is an accumulation of partially protease resistant (PrP(res)) abnormal prion protein (PrP(sc)). This pathological prion protein is very resistant to conventional inactivation methods. The risk of transmission of TSE, such as Creutzfeldt-Jakob disease (CJD), by biopharmaceutical products prepared from human cells must be taken into account. The nanofiltration process has been proved to be effective in removing viruses and scrapie agent. The major advantages of this technique are flexibility and efficacy in removing infectious particles without altering biopharmaceutical characteristics and properties. This study focused on the removal of human PrP(sc) by means of a nanofiltration method after spiking a Lymphoglobuline solution with a CJD brain homogenate. Lymphoglobuline equine anti-human thymocyte immunoglobulin is a selective immunosuppressive agent acting mainly on human T lymphocytes. The therapeutic indications are: immunosuppression for transplantation: prevention and treatment of graft rejection; treatment of aplastic anemia. In our study, CJD homogenate was spiked at three different dilutions (low, moderate and high) in the Lymphoglobuline product. The nanofiltration process was performed on each sample. Using the western blot technique, the PrP(res) signal detected in nanofiltrates was compared to that obtained with a reference scale (dilution series of CJD brain homogenate in Lymphoglobuline detected by western blot and elaborated on 3.3 log). After nanofiltration, the PrP(res) western blot signal was detected with a significant reduction in the less dilute sample, whereas the signal was undetectable in the two other samples. These are the first data in CJD demonstrating a clearance between 1.6 and 3.3 log with a Lymphoglobuline recovery of over 93%. The nanofiltration process confirms its relative efficacy in removing human CJD PrP(sc).

Viral safety of Nanogam, a new 15 nm-filtered liquid immunoglobulin product

BACKGROUND AND OBJECTIVES

Producers of plasma derivatives continuously improve the viral safety of their products by, for example, introducing additional virus-reducing steps into the manufacturing process. Here we present virus-elimination studies undertaken for a number of steps employed in a new manufacturing process for liquid intravenous immunoglobulin (Nanogam) that comprises two specific virus-reducing steps: a 15-nm filtration step combined with pepsin treatment at pH 4.4 (pH 4.4/15NF); and solvent-detergent (SD) treatment. The manufacturing process also includes precipitation of Cohn fraction III and viral neutralization, which contribute to the total virus-reducing capacity of the manufacturing process. In addition, the mechanism and robustness of the virus-reducing steps were studied.

MATERIALS AND METHODS

Selected process steps were studied with spiking experiments using a range of lipid enveloped (LE) and non-lipid-enveloped (NLE) viruses. The LE viruses used were bovine viral diarrhoea virus (BVDV), human immunodeficiency virus (HIV) and pseudorabies virus (PRV); the NLE viruses used were parvovirus B19 (B19), canine parvovirus (CPV) and encephalomyocarditis virus (EMC). After spiking, samples were collected and tested for residual infectivity, and the reduction factors were calculated. For B19, however, removal of B19 DNA was measured, not residual infectivity. To reveal the contribution of viral neutralization, bovine parvovirus (BPV) and hepatitis A virus (HAV) were used.

RESULTS

For the pH 4.4/15NF step, complete reduction (> 6 log(10)) was demonstrated for all viruses, including B19, but not for CPV (> 3.4 but < or = 4.2 log(10)). Robustness studies of the pH 4.4/15NF step with CPV showed that pH was the dominant process parameter. SD treatment for 10 min resulted in complete inactivation (> 6 log(10)) of all LE viruses tested. Precipitation of Cohn fraction III resulted in the significant removal (3-4 log(10)) of both LE and NLE viruses. Virus-neutralization assays of final product revealed significant reduction (> or = 3 log(10)) of both BPV and HAV.

CONCLUSIONS

The manufacturing process of Nanogam comprises two effective steps for the reduction of LE viruses and one for NLE viruses. In addition, the precipitation of Cohn fraction III and the presence of neutralizing antibodies contribute to the total virus-reducing capacity of Nanogam. The overall virus-reducing capacity was > 15 log(10) for LE viruses. For the NLE viruses B19, CPV and EMC, the overall virus-reducing capacities were > 10, > 7 and > 9 log(10), respectively. Including the contribution of immune neutralization, the overall virus-reducing capacity for B19 and HAV is estimated to be > 10 log(10).

Assessment of the viral safety of antivenoms fractionated from equine plasma

Antivenoms are preparations of intact or fragmented (F(ab′)₂ or Fab) immunoglobulin G (IgG) used in human medicine to treat the severe envenomings resulting from the bites and stings of various animals, such as snakes, spiders, scorpions, or marine animals, or from the contact with poisonous plants. They are obtained by fractionating plasma collected from immunized horses or, less frequently, sheep. Manufacturing processes usually include pepsin digestion at acid pH, papain digestion, ammonium sulphate precipitation, caprylic acid precipitation, heat coagulation and/or chromatography. Most production processes do not have deliberately introduced viral inactivation or removal treatments, but antivenoms have never been found to transmit viruses to humans. Nevertheless, the recent examples of zoonotic diseases highlight the need to perform a careful assessment of the viral safety of antivenoms.

This paper reviews the characteristics of equine viruses of antivenoms and discusses the potential of some manufacturing steps to avoid risks of viral contamination. Analysis of production parameters indicate that acid pH treatments and caprylic acid precipitations, which have been validated for the manufacture of some human IgG products, appear to provide the best potential for viral inactivation of antivenoms. As many manufacturers of antivenoms located in developing countries lack the resources to conduct formal viral validation studies, it is hoped that this review will help in the scientific understanding of the viral safety factors of antivenoms, in the controlled implementation of the manufacturing steps with expected impact on viral safety, and in the overall reinforcement of good manufacturing practices of these essential therapeutic products.

Inactivation of West-Nile virus during peptic cleavage of horse plasma IgG

Peptic cleavage of horse plasma IgG is a common procedure for the preparation of F(ab)(2) products for human use, such as antivenin and antitoxin. The removal of the Fc fragment from the IgG molecule by enzymatic cleavage at low pH, ensures fewer side-effects of the F(ab)(2) product for passive immunotherapy compared with the whole IgG molecule. Since the starting material may be contaminated by zoonotic horse viruses, it is necessary to demonstrate the removal or inactivation of possible viral contaminants. Guidelines for performing such studies were published by the Commission for Plasma-Derived Medical Products (CPMP), and updated by the Committee for Proprietary Medical Products. It is recommended that viral clearance studies be performed on scaled down production processes that have been identified as possibly contributing to virus clearance and spiking of a model virus to the starting material. The model virus should be non-pathogenic but closely related to the potential infective virus. By quantifying the amount of virus in the product before and after the production process, the amount of virus cleared can be determined. Log(10) reductions of the order of 4 logs or more, and a biphasic inactivation curve (fast initial phase followed by a slower phase), are indicative of a clearance effect with a particular test virus under investigation.