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Viral safety of blood derivatives: an overview
CLINICAL THERAPEUTICS®/VOL. 18, SUPPL. B, 1996
Viral Safety of Blood Derivatives: An Overview Florian Horaud, MD, P h i ) Institut Pasteur, Paris, France
ABSTRACT The causes of past accidental viral transmissions associated with blood derivatives are reviewed briefly, as are the safety procedures instituted in Europe on the basis of viral validation studies. A comprehensive five-class classification system for delineating viral risk according to source material and comparative viral safety is presented. Newly emerging viruses are briefly discussed in view of the viral safety of blood products. INTRODUCTION In recent years, transmission of human immunodeficiency virus (HIV) to patients with hemophilia by blood-clotting concentrate preparations has been the most dramatic incident of accidental virus transmission. The emergence of this new virus surprised the scientific community, and, although it was a fairly short time 0149-2918/96/$3.50
before the extent of the acquired immunodeficiency syndrome (AIDS) outbreak was realized, it was long enough to generate one of the most tragic iatrogenic episodes in the history of biologicals. However, after considerable efforts, sufficient knowledge about the causative agent of AIDS was obtained to quickly develop a diagnostic test for HIV. This achievement formed the basis of a strategy for AIDS prevention. More recently, it became possible to identify and characterize hepatitis C virus (HCV), another viral agent transmitted by blood and blood derivatives. This was achieved without cultivation in cell culture or visualization by electron microscopy and in the absence of nucleic acid and protein sequence information or a sensitive assay for the gene products) The experience gained from virus transmission in transfusion medicine clearly shows that the safety of blood and blood derivatives is a complex problem requir37
CLINICAL THERAPEUTICS®
ing a multifaceted approach to obtain virus-safe products. Since the field of plasma derivatives is evolving quickly, only some of the factors helpful in assessing the viral safety of blood products are summarized here. TENTATIVE CLASSIFICATION OF BIOLOGICALS Several factors influence virus transmission by biologic products in general and by products derived from human plasma in particular. An analysis of virus transmission accidents induced by biologicals over the last 10 years has allowed us to identify the primary factors influencing the viral safety of these products. 2,3 These factors include: (1) species origin (eg, human or animal) of the starting material (eg, tissues, fluids, or cell cultures), which is crucial because of the potential for common virus contaminants and the presence of corresponding viral-specific receptors in human cells; (2) degree of variability of the starting material (eg, higher variability in the sources of a plasma pool compared with lower variability in cellculture products derived from a unique cell bank) and the possibility of testing the source material for viral contaminants (feasible for blood donations but not for animal-derived products); (3) nature of the process used to obtain the product and its capacity for eliminating viruses (eg, purification procedures); and (4) inclusion of specific steps in the manufacturing process for viral inactivation (the procedure chosen depends on the target molecule and its stability during treatments to eliminate viruses). 4,5 The table shows a classification of biologic products to facilitate an understanding of their risk of viral transmission. 5 38
The species origin of the source material has been correlated with the risk of virus transmission. This classification supports what has been learned over the last few decades from virus transmission accidents attributable to biologic products. For example, both AIDS and Creutzfeldt-Jakob disease were induced by class V products, which are biologicals derived from human sources. This tentative classification of biologicals can be helpful in assessing the risks and benefits of different products as well as determining the regulatory requirements appropriate for various products. For example, the starting material for class III products (animal sources) is not screened for viral markers, but viral testing of human blood donations (the source material for class V products) is required. Thus the safety of class III products is based solely on the capacity of the manufacturing procedure to inactivate viruses. This does not mean that screening blood donors is in itself capable of ensuring safety, but it contributes significantly to reducing the viral load in the plasma pool. VALIDATION STUDIES AND REGULATORY DOCUMENTS As a result of reported virus transmission by blood derivatives, considerable scientific effort has been devoted to eliminating viruses from plasma-derived products and developing experimental models to validate their safety. 3,6 These investigations have resulted in a better understanding of the fate of different viruses during manufacturing processes, particularly the Cohn-Oncley cold ethanol fractionation process, and improved technology for inactivating viruses in plasma. They also have helped clarify the concept and methods of
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CLINICAL THERAPEUTICS*
viral validation studies, a keystone in assessing viral safety. Approximately 6 years ago, the first European recommendations concerning viral safety of biologicals and blood derivatives were drafted in Brussels by the Biotechnology and Pharmacy Working Group of the Committee for Pharmaceutical and Medicinal Products. 7,8 At that time, the plasma fractionation industry was skeptical about viral validation studies. Today, such studies are well established as a primary criterion for product acceptability. However, the design and use of viral validation studies are complex. Their correct use and interpretation according to regulatory guidelines (which are not exhaustive) require experienced scientists. The European guidelines on viral validation, which are currently being revised, describe not only the general conditions in which validation studies should be conducted but also the rationale and essential considerations for viral safety evaluation. The Biotechnology and Pharmacy Working Group drafted these guidelines to produce a document helpful to both manufacturers and regulatory authorities. Viral validation studies in Europe and the United States confirmed the need for steps to specifically inactivate viruses during the manufacturing of plasma products. In Europe, requirements for viral reduction factors have recently been defined for enveloped and nonenveloped viruses in different blood derivatives. One recommendation was to define, whenever possible, at least two specific virus inactivation steps that should be included in the manufacturing process. This approach is justified by the low capacity of Cohn-Oncley cold ethanol fractionation and various chrotnatographic procedures to eliminate viruses. 40
NEW VIRUSES AND THEIR IMPACT ON VALIDATION STUDIES The history of virus transmission by blood products clearly shows that unknown or unidentified viruses are the source of many viral transmission accidents. For example, this was the case when human sera used to stabilize yellow fever vaccine transmitted hepatitis B virus (HBV), 9 when an outbreak of HIV occurred among patients with hemophilia, 2 and more recently, when blood products were contaminated with HCV. 3 Another aspect of viral safety is the emergence of new viruses and diseases and the fluctuation in the epidemiology of known diseases. Viral diseases pose difficult problems for public health authorities because there are limited ways to control them. Moreover, transmissible viral diseases evoke a strong emotional reaction from the public, as observed in the United Kingdom in response to an outbreak of bovine spongiform encephalopathy.l° Questions about the origin of new transmissible viral diseases have been raised for many years, but only recently has systematic examination of this problem been initiated. This approach was crystallized in a valuable book, Emerging Viruses, 11 and was justified by recent reports of newly characterized pathogenic viruses. This is exemplified by the recent outbreak in Africa of Ebola virus, a highly virulent Filoviridae with an unknown natural host,12 and a new Morbillivirus that causes a respiratory disease in horses and may be lethal to humans. 13 Although the origin of many emerging viruses remains unknown, human activity can create favorable conditions for their spread. This was the case for some blood-
E HORAUD
borne viruses (eg, HIV, HBV, HCV, and other hepatic viruses) transmitted mainly by blood transfusion, administration of medicinal products derived from blood, intravenous drug use, and tattooing. In the past, parenteral transmission also was favored by improperly sterilized needles and syringes in professional and unprofessional medical practices. Up-to-date information on newly characterized viruses is particularly important for investigators conducting viral validation studies. Because many new viruses such as HCV cannot be cultivated in cell culture or even observed under electron microscopy, other viruses closely related to the newly identified virus must be identified. For instance, classification of HCV as a Flavivirus 14 led to the use of bovine viral diarrhea virus and yellow fever virus (both of which are Flaviviruses) in validation studies to assess the safety of blood derivatives.
CONCLUSION The emergence of new viruses underscores the importance of remaining vigilant when assessing the viral safety of blood products. A wise approach is to periodically reexamine the various aspects of the viral safety of biologicals, and, whenever necessary, to reevaluate and renew viral validation studies.
REFERENCES
1. Choo QL, Kuo G, Weiner AJ, et al. Isolation of a cDNA derived from a bloodborne non-A, non-B hepatitis genome. Science. 1989;244:359-362.
2. Horaud F, Brown E Virological aspects of the safety of biological products. Dev Biol Stand. 1991;75. 3. Brown E Virological safety aspects of plasma derivatives. Dev Biol Stand. 1993;81. 4. Horaud F. Viral safety of biologicals. Dev Biol Stand. 1991;75:3-7. 5. Horaud E Biologicals: An attempt at classification and its implication for the viral safety of products. Dev Biol Stand. 1993; 81:17-24. 6. Morgenthaler. Virus inactivation in plasma products. Curr Stud Hematol Blood Transfus. 1989;56. 7. EEC Regulatory Document. Validation of virus removal and inactivation procedures. Biologicals. 1991;19:247-251. 8. EEC Regulatory Document. Guidelines for medicinal products derived from human blood and plasma. Biologicals. 1991; 20:159-164.
9. Findlay MG, MacCallum OF, Murgatroyd E Observation bearing on the etiology of infective hepatitis (called epidemic catarrhal jaundice). Trans R Soc Trop Med Hyg. 1939;32:575-580. 10. Transmissible spongiform encephalopathies: Impact on animal and human health. Dev Biol Stand. 1992. 11. Morse SS, ed. Emerging Viruses. Oxford, England: Oxford University Press; 1993. 41
CLINICAL THERAPEUTICS ®
12. Peters CJ, Sanchez A, Feldman H, et al. Filoviruses as emerging pathogens. Semin Virol. 1994;5:147-154. 13. Murray K, Selleck E Hooper P, et al. A morbillivims that caused fatal disease in horses and humans. Science. 1995;268: 94-97.
42
14. Houghton M, Richman K, Han J, et al. Hepatitis C virus (HCV): A relative of the pestiviruses and flaviviruses. In: Hollinger BF, Lemon SM, Margolis HS, eds. Viral Hepatitis and Liver Disease. Baltimore, MD: Williams & Wilkins; 1990:321-323.
Viral Safety of Blood Derivatives: An Overview Florian Horaud, MD, P h i ) Institut Pasteur, Paris, France
ABSTRACT The causes of past accidental viral transmissions associated with blood derivatives are reviewed briefly, as are the safety procedures instituted in Europe on the basis of viral validation studies. A comprehensive five-class classification system for delineating viral risk according to source material and comparative viral safety is presented. Newly emerging viruses are briefly discussed in view of the viral safety of blood products. INTRODUCTION In recent years, transmission of human immunodeficiency virus (HIV) to patients with hemophilia by blood-clotting concentrate preparations has been the most dramatic incident of accidental virus transmission. The emergence of this new virus surprised the scientific community, and, although it was a fairly short time 0149-2918/96/$3.50
before the extent of the acquired immunodeficiency syndrome (AIDS) outbreak was realized, it was long enough to generate one of the most tragic iatrogenic episodes in the history of biologicals. However, after considerable efforts, sufficient knowledge about the causative agent of AIDS was obtained to quickly develop a diagnostic test for HIV. This achievement formed the basis of a strategy for AIDS prevention. More recently, it became possible to identify and characterize hepatitis C virus (HCV), another viral agent transmitted by blood and blood derivatives. This was achieved without cultivation in cell culture or visualization by electron microscopy and in the absence of nucleic acid and protein sequence information or a sensitive assay for the gene products) The experience gained from virus transmission in transfusion medicine clearly shows that the safety of blood and blood derivatives is a complex problem requir37
CLINICAL THERAPEUTICS®
ing a multifaceted approach to obtain virus-safe products. Since the field of plasma derivatives is evolving quickly, only some of the factors helpful in assessing the viral safety of blood products are summarized here. TENTATIVE CLASSIFICATION OF BIOLOGICALS Several factors influence virus transmission by biologic products in general and by products derived from human plasma in particular. An analysis of virus transmission accidents induced by biologicals over the last 10 years has allowed us to identify the primary factors influencing the viral safety of these products. 2,3 These factors include: (1) species origin (eg, human or animal) of the starting material (eg, tissues, fluids, or cell cultures), which is crucial because of the potential for common virus contaminants and the presence of corresponding viral-specific receptors in human cells; (2) degree of variability of the starting material (eg, higher variability in the sources of a plasma pool compared with lower variability in cellculture products derived from a unique cell bank) and the possibility of testing the source material for viral contaminants (feasible for blood donations but not for animal-derived products); (3) nature of the process used to obtain the product and its capacity for eliminating viruses (eg, purification procedures); and (4) inclusion of specific steps in the manufacturing process for viral inactivation (the procedure chosen depends on the target molecule and its stability during treatments to eliminate viruses). 4,5 The table shows a classification of biologic products to facilitate an understanding of their risk of viral transmission. 5 38
The species origin of the source material has been correlated with the risk of virus transmission. This classification supports what has been learned over the last few decades from virus transmission accidents attributable to biologic products. For example, both AIDS and Creutzfeldt-Jakob disease were induced by class V products, which are biologicals derived from human sources. This tentative classification of biologicals can be helpful in assessing the risks and benefits of different products as well as determining the regulatory requirements appropriate for various products. For example, the starting material for class III products (animal sources) is not screened for viral markers, but viral testing of human blood donations (the source material for class V products) is required. Thus the safety of class III products is based solely on the capacity of the manufacturing procedure to inactivate viruses. This does not mean that screening blood donors is in itself capable of ensuring safety, but it contributes significantly to reducing the viral load in the plasma pool. VALIDATION STUDIES AND REGULATORY DOCUMENTS As a result of reported virus transmission by blood derivatives, considerable scientific effort has been devoted to eliminating viruses from plasma-derived products and developing experimental models to validate their safety. 3,6 These investigations have resulted in a better understanding of the fate of different viruses during manufacturing processes, particularly the Cohn-Oncley cold ethanol fractionation process, and improved technology for inactivating viruses in plasma. They also have helped clarify the concept and methods of
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39
CLINICAL THERAPEUTICS*
viral validation studies, a keystone in assessing viral safety. Approximately 6 years ago, the first European recommendations concerning viral safety of biologicals and blood derivatives were drafted in Brussels by the Biotechnology and Pharmacy Working Group of the Committee for Pharmaceutical and Medicinal Products. 7,8 At that time, the plasma fractionation industry was skeptical about viral validation studies. Today, such studies are well established as a primary criterion for product acceptability. However, the design and use of viral validation studies are complex. Their correct use and interpretation according to regulatory guidelines (which are not exhaustive) require experienced scientists. The European guidelines on viral validation, which are currently being revised, describe not only the general conditions in which validation studies should be conducted but also the rationale and essential considerations for viral safety evaluation. The Biotechnology and Pharmacy Working Group drafted these guidelines to produce a document helpful to both manufacturers and regulatory authorities. Viral validation studies in Europe and the United States confirmed the need for steps to specifically inactivate viruses during the manufacturing of plasma products. In Europe, requirements for viral reduction factors have recently been defined for enveloped and nonenveloped viruses in different blood derivatives. One recommendation was to define, whenever possible, at least two specific virus inactivation steps that should be included in the manufacturing process. This approach is justified by the low capacity of Cohn-Oncley cold ethanol fractionation and various chrotnatographic procedures to eliminate viruses. 40
NEW VIRUSES AND THEIR IMPACT ON VALIDATION STUDIES The history of virus transmission by blood products clearly shows that unknown or unidentified viruses are the source of many viral transmission accidents. For example, this was the case when human sera used to stabilize yellow fever vaccine transmitted hepatitis B virus (HBV), 9 when an outbreak of HIV occurred among patients with hemophilia, 2 and more recently, when blood products were contaminated with HCV. 3 Another aspect of viral safety is the emergence of new viruses and diseases and the fluctuation in the epidemiology of known diseases. Viral diseases pose difficult problems for public health authorities because there are limited ways to control them. Moreover, transmissible viral diseases evoke a strong emotional reaction from the public, as observed in the United Kingdom in response to an outbreak of bovine spongiform encephalopathy.l° Questions about the origin of new transmissible viral diseases have been raised for many years, but only recently has systematic examination of this problem been initiated. This approach was crystallized in a valuable book, Emerging Viruses, 11 and was justified by recent reports of newly characterized pathogenic viruses. This is exemplified by the recent outbreak in Africa of Ebola virus, a highly virulent Filoviridae with an unknown natural host,12 and a new Morbillivirus that causes a respiratory disease in horses and may be lethal to humans. 13 Although the origin of many emerging viruses remains unknown, human activity can create favorable conditions for their spread. This was the case for some blood-
E HORAUD
borne viruses (eg, HIV, HBV, HCV, and other hepatic viruses) transmitted mainly by blood transfusion, administration of medicinal products derived from blood, intravenous drug use, and tattooing. In the past, parenteral transmission also was favored by improperly sterilized needles and syringes in professional and unprofessional medical practices. Up-to-date information on newly characterized viruses is particularly important for investigators conducting viral validation studies. Because many new viruses such as HCV cannot be cultivated in cell culture or even observed under electron microscopy, other viruses closely related to the newly identified virus must be identified. For instance, classification of HCV as a Flavivirus 14 led to the use of bovine viral diarrhea virus and yellow fever virus (both of which are Flaviviruses) in validation studies to assess the safety of blood derivatives.
CONCLUSION The emergence of new viruses underscores the importance of remaining vigilant when assessing the viral safety of blood products. A wise approach is to periodically reexamine the various aspects of the viral safety of biologicals, and, whenever necessary, to reevaluate and renew viral validation studies.
REFERENCES
1. Choo QL, Kuo G, Weiner AJ, et al. Isolation of a cDNA derived from a bloodborne non-A, non-B hepatitis genome. Science. 1989;244:359-362.
2. Horaud F, Brown E Virological aspects of the safety of biological products. Dev Biol Stand. 1991;75. 3. Brown E Virological safety aspects of plasma derivatives. Dev Biol Stand. 1993;81. 4. Horaud F. Viral safety of biologicals. Dev Biol Stand. 1991;75:3-7. 5. Horaud E Biologicals: An attempt at classification and its implication for the viral safety of products. Dev Biol Stand. 1993; 81:17-24. 6. Morgenthaler. Virus inactivation in plasma products. Curr Stud Hematol Blood Transfus. 1989;56. 7. EEC Regulatory Document. Validation of virus removal and inactivation procedures. Biologicals. 1991;19:247-251. 8. EEC Regulatory Document. Guidelines for medicinal products derived from human blood and plasma. Biologicals. 1991; 20:159-164.
9. Findlay MG, MacCallum OF, Murgatroyd E Observation bearing on the etiology of infective hepatitis (called epidemic catarrhal jaundice). Trans R Soc Trop Med Hyg. 1939;32:575-580. 10. Transmissible spongiform encephalopathies: Impact on animal and human health. Dev Biol Stand. 1992. 11. Morse SS, ed. Emerging Viruses. Oxford, England: Oxford University Press; 1993. 41
CLINICAL THERAPEUTICS ®
12. Peters CJ, Sanchez A, Feldman H, et al. Filoviruses as emerging pathogens. Semin Virol. 1994;5:147-154. 13. Murray K, Selleck E Hooper P, et al. A morbillivims that caused fatal disease in horses and humans. Science. 1995;268: 94-97.
42
14. Houghton M, Richman K, Han J, et al. Hepatitis C virus (HCV): A relative of the pestiviruses and flaviviruses. In: Hollinger BF, Lemon SM, Margolis HS, eds. Viral Hepatitis and Liver Disease. Baltimore, MD: Williams & Wilkins; 1990:321-323.