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Workshop on Standardisation of Aluminium Adsorbed Vaccines
Biologicals (1997) 25, 351–353
MEETING REPORT
Workshop on Standardisation of Aluminium Adsorbed Vaccines 21 June 1996—Bergen, Norway
1
M. J. Corbel1*, E. Griffiths2† and R. Winsnes3† National Institute for Biological Standards and Control, Potters Bar, Herts, U.K.; 2Biologicals, WHO, Geneva, Switzerland; and 3Statens, Legemiddelkontroll, Oslo, Norway
Recent developments in the field of combination vaccines, particularly those based on acellular pertussis components, have raised a number of questions relating to regulatory issues. One of the main concerns is the interaction of the various individual components with the adjuvant material. This meeting was convened to consider the regulatory requirements relating to the adsorption of vaccine components to aluminium adjuvants and to suggest an approach to determining the requirements for new combination vaccines. The Chairman opened the meeting by indicating a number of key questions that needed to be addressed. (1) The relevance of the WHO/UNDP recommendation of a minimum of 80% adsorption of diphtheria (D) and tetanus (T) toxoids to the adjuvant in the light of the interactions seen with diphtheria–tetanus–acellular pertussis (DTAcP) formulations. (2) The current European Pharmacopoeia (EP) and European regulatory positions on the adsorption of D and T component to adjuvant in DTAcP and other combinations. (3) The specific criteria required to demonstrate satisfactory adsorption of antigenic components to adjuvant in combination vaccines: for example, level of adsorption, consistency of adsorption during storage, demonstration of clinical effectiveness at the beginning and/or end of shelf life. (4) Level of adsorption as a shelf life criterion for combination vaccines or demonstration of *Chairman. †Co-Chairman. 1045–1056/97/030351 + 3 $25.00/0/bg970106
long-term stability in manufacturing lots as an alternative. (5) Recommendation of a standardized procedure for assessing degree of adsorption; for example ELISA or rocket immunoelectrophoresis. Dr E. Griffiths (Chief, Biologicals, WHO) reviewed the position on adsorbed vaccines. In Requirements adopted by the WHO Expert Committee on Biological Standardisation and published in the WHO Technical Report Series, there was no general requirement for a minimum degree of adsorption of vaccine components to adjuvant. However, there were specific recommendations for individual vaccines which had to be considered on a case-by-case basis. The general recommendations indicated that the purity and concentration of adjuvants has to be approved by the National Control Authority. Currently aluminium hydroxide, aluminium phosphate, calcium phosphate and liposomes (virosomes) are the only approved adjuvants. The concentration of Al must not exceed 1⋅25 mg per single human dose (SHD) and that of calcium must not exceed 1⋅3 mg per SHD. The formulation must be such that the vaccine remains suspended for a reasonable time after mixing. The stability of the product must be demonstrated to the satisfaction of the National Control Authority. There is no stipulation for degree of adsorption to the adjuvant for bacterial vaccines including diphtheria–tetanus–pertussis. However, hepatitis A and B vaccines have to undergo an assay for determination of completeness of adsorption to the adjuvant, with the test to be used and the acceptable limits approved by the National Control Authority. 7 1997 The International Association of Biological Standardization
352
M. J. Corbel et al .
The issue of a minimum of 80% adsorption of D and T components to adjuvant originated in a WHO/UNDP document indicating a suggested contractual recommendation for DTP vaccines. Hence, it was clear that there was no requirement for a minimum level of adsorption in pertussis based vaccines in Requirements published by WHO. There was little evidence that antigens needed to be adsorbed, as opposed to closely associated with the adjuvant. The need for complete adsorption and the requirement for a depot effect and slow release had been dismissed by studies conducted half a century previously.1 The basis of adjuvant action is now known to be complex, involving cellular interactions and cytokine release. Even so, the precise mode of action and the basis of the differences in activity of aluminium hydroxide and aluminium phosphate were still unknown. In the preparation of aluminium-adjuvanted vaccines the formulation was critical. The consistency of production and stability of the preparation were more important than the actual proportion of antigen adsorbed. Draft recommendations had been prepared by WHO for acellular pertussis (DTAcP) vaccines. In these, the consistency of adsorption was emphasized and should be within the specifications of lots shown to be clinically effective. Dr I. Heron (Amvax) observed that the aluminium adjuvant was essential for animal potency assays if a single dose was used. Some adsorption of toxoid was necessary as pre-saturation with an irrelevant protein, such as albumin, blocked the response to the vaccine. In guinea-pigs or mice, a single dose of unadsorbed vaccine gave very low responses. There were significant differences between aluminium hydroxide and calcium phosphate. The latter had about one third the binding capacity of the former. In mouse assays the Al preparations gave 2–3-fold higher responses against D and T toxoids than calcium phosphate. However, in man, calcium adsorbed vaccines used as boosters gave 2-fold higher titres than aluminium adsorbed preparations. Similarly, plain toxoid was very effective as a booster in man but poor in rodents. It was clear that there was no correlation between the quantitative responses observed in animal assays and performance of the vaccines in man. Possibly, the present requirements could be modified. However, it should be noted that they had provided an assurance of the potency of these vaccines and their efficacy in man, for many years.
Dr J. Pex tre (Chiron Biocine) noted that diphtheria toxoids were often sub-potent but that this could be corrected by increasing the Al content of the vaccine. For DTAcP preparations it was important to ensure adequate adsorption to increase stability and to enhance the immunogenicity of the P69 component. Dr R. Winsnes (Chairman, Group 15, European Pharmacopoeia Commission) reviewed the Ph.Eur. position on adjuvants in vaccines. The recommendations outlined in the general monograph on vaccines for human use and the individual vaccine monographs were broadly consistent with the recommendations published by WHO. However, the potency requirement for an adsorbed vaccine such as diphtheria could be interpreted as different. The Ph.Eur. requires a lower limit of 30 IU/dose, whereas Requirements published by WHO specify a potency of 30 IU/dose. The potency requirements for diphtheria and tetanus vaccine are currently under review by Group 15. For adsorbed vaccines the draft recommendation was that each product should have a specified limit for the proportion of adsorbed material which should be not less than that used in clinical trial lots and should be demonstrated to be maintained to the end of shelf life. Group 15 was reviewing the requirements for individual and combination vaccines and would pronounce on this in the near future. It was likely that the emphasis would remain on the monographs for individual vaccines with new monographs for some combinations. A key requirement was that the formulations must be shown to have acceptable immunogenicity in man in the intended immunisation schedule. Based on recent information, the precise definition of ‘‘adsorbed’’ in the Ph.Eur. monograph titles on vaccines containing calcium and aluminium will be reviewed. Al components provide an immunological adjuvant effect, not only by sustained release of immunogens, but also by producing a local inflammatory response and by triggering cytokine release. Dr M. Schwanig (Paul Ehrlich Institute, Germany) summarized the European regulatory view point. He emphasized that there was no clear definition of adsorbed as opposed to nonadsorbed vaccines. In adjuvanted formulations it was unclear if the Al gels were vehicles or adjuvants. In the case of whole cell DTP vaccines, the pertussis component does not compete for the adsorption sites. This eases the manufacture
Meeting report
of combined vaccines with a high degree of adsorption of diphtheria and tetanus toxoids. To achieve the same degree of adsorption in DTAcP vaccines a more carefully controlled manufacturing process is necessary as the isolated pertussis proteins, most of them larger than diphtheria or tetanus toxoid, compete for the adsorption sites. As several products show, it is possible with DTAcP vaccines to produce a stable almost 100% adsorbed vaccine by, for example, separate adsorption of each component and/or modification of pH to ensure optimal interaction between gel and antigen. When using the term ‘‘adsorbed’’ it is necessary to have a definition for this. There was little information available on the content of toxoids necessary for adequate responses in man and this issue needs to be addressed in respect of new combination vaccines. The degree of adsorption needed to be consistent with clinical efficacy. It should be at the highest level achievable. It was also necessary to consider whether it should be a self life criterion. Dr R. Mignolet (Wyeth Lederle) suggested that it was desirable to aim for the highest possible degree of adsorption. If the initial level was high, this should be maintained throughout shelf life. For Wyeth Lederle DTAcP–Hib the degree of adsorption was 0100% which was maintained throughout shelf life (excluding the Hib component). The level of adsorption could be assayed by ELIFA (ELISA combined with filtration). The degree of adsorption to be specified in lots for release needed to be justifiable. Dr R. Gupta (Massachusetts Public Health Biologic Laboratories) emphasized that aluminium hydroxide and aluminium phosphate were very different in properties. They had opposite charges and behaved differently in adsorption properties. Phosphate ions affected the behaviour of aluminium phosphate. Thus D toxoid adsorption to aluminium phosphate ranged from 0% in phosphate buffer pH 7⋅2 to 57% at pH 6–6⋅3. In physiological saline it was 93–100%. There were also differences between pre-formed and aluminium gels produced in situ. Ideally, the highest adsorptive capacity should be aimed for as the evidence indicated that adsorbed vaccines were more immunogenic than unadsorbed.
353
Dr D. Lamb (Connaught Laboratories Inc.) reported on the determination of the degree of adsorption of a Biken DTAcP aluminium hydroxyphosphate vaccine. Assay by rocket immunoelectrophoresis of supernatant or whole vaccine dissolved in sodium citrate did not indicate interference by T or AcP components with adsorption of D toxoid. Examination of four consistency lots showed that the proportion adsorbed (040%) remained constant throughout the shelf life. Dr C. Meschevitz (Connaught Laboratories Inc.) reported observations on the correlation between clinical responses and the degree of adsorption of the D and T components of a DTP vaccine. A vaccine which was 050% adsorbed produced D and T antitoxin responses of 0.1 IU per ml in q90% of recipients. There was clearly no correlation between Al content, Lf content, % adsorption and antibody titres achieved. Dr J. Holst (NIPH, Norway) reported that the Group B meningococcal outer membrane vesicle vaccine due to be introduced into routine use in Norway in 1998 contained aluminium hydroxide. This was essential to stabilise the vaccine. Conclusions (1) There is no current WHO requirement for a minimum level of adsorption for DTP vaccines. (2) The use of the term ‘‘adsorbed vaccine’’ should be avoided unless the degree of adsorption is specified. Otherwise vaccines containing aluminium hydroxide, aluminium phosphate or calcium phosphate gels should be referred to as ‘‘adjuvant vaccines’’. (3) It is not feasible to specify a minimum level of adsorption for any particular type of vaccine as this would depend upon the formulation. However, the degree of adsorption must be within the specifications of lots shown to be efficacious in clinical trials. (4) The degree of adsorption should remain constant throughout the shelf life of the product. (5) No specific recommendation is made on the method to be adopted for determination of degree of adsorption—procedures based on filtration followed by ELISA, rocket electrophoresis or other immunoassays may be accepted subject to validation.
MEETING REPORT
Workshop on Standardisation of Aluminium Adsorbed Vaccines 21 June 1996—Bergen, Norway
1
M. J. Corbel1*, E. Griffiths2† and R. Winsnes3† National Institute for Biological Standards and Control, Potters Bar, Herts, U.K.; 2Biologicals, WHO, Geneva, Switzerland; and 3Statens, Legemiddelkontroll, Oslo, Norway
Recent developments in the field of combination vaccines, particularly those based on acellular pertussis components, have raised a number of questions relating to regulatory issues. One of the main concerns is the interaction of the various individual components with the adjuvant material. This meeting was convened to consider the regulatory requirements relating to the adsorption of vaccine components to aluminium adjuvants and to suggest an approach to determining the requirements for new combination vaccines. The Chairman opened the meeting by indicating a number of key questions that needed to be addressed. (1) The relevance of the WHO/UNDP recommendation of a minimum of 80% adsorption of diphtheria (D) and tetanus (T) toxoids to the adjuvant in the light of the interactions seen with diphtheria–tetanus–acellular pertussis (DTAcP) formulations. (2) The current European Pharmacopoeia (EP) and European regulatory positions on the adsorption of D and T component to adjuvant in DTAcP and other combinations. (3) The specific criteria required to demonstrate satisfactory adsorption of antigenic components to adjuvant in combination vaccines: for example, level of adsorption, consistency of adsorption during storage, demonstration of clinical effectiveness at the beginning and/or end of shelf life. (4) Level of adsorption as a shelf life criterion for combination vaccines or demonstration of *Chairman. †Co-Chairman. 1045–1056/97/030351 + 3 $25.00/0/bg970106
long-term stability in manufacturing lots as an alternative. (5) Recommendation of a standardized procedure for assessing degree of adsorption; for example ELISA or rocket immunoelectrophoresis. Dr E. Griffiths (Chief, Biologicals, WHO) reviewed the position on adsorbed vaccines. In Requirements adopted by the WHO Expert Committee on Biological Standardisation and published in the WHO Technical Report Series, there was no general requirement for a minimum degree of adsorption of vaccine components to adjuvant. However, there were specific recommendations for individual vaccines which had to be considered on a case-by-case basis. The general recommendations indicated that the purity and concentration of adjuvants has to be approved by the National Control Authority. Currently aluminium hydroxide, aluminium phosphate, calcium phosphate and liposomes (virosomes) are the only approved adjuvants. The concentration of Al must not exceed 1⋅25 mg per single human dose (SHD) and that of calcium must not exceed 1⋅3 mg per SHD. The formulation must be such that the vaccine remains suspended for a reasonable time after mixing. The stability of the product must be demonstrated to the satisfaction of the National Control Authority. There is no stipulation for degree of adsorption to the adjuvant for bacterial vaccines including diphtheria–tetanus–pertussis. However, hepatitis A and B vaccines have to undergo an assay for determination of completeness of adsorption to the adjuvant, with the test to be used and the acceptable limits approved by the National Control Authority. 7 1997 The International Association of Biological Standardization
352
M. J. Corbel et al .
The issue of a minimum of 80% adsorption of D and T components to adjuvant originated in a WHO/UNDP document indicating a suggested contractual recommendation for DTP vaccines. Hence, it was clear that there was no requirement for a minimum level of adsorption in pertussis based vaccines in Requirements published by WHO. There was little evidence that antigens needed to be adsorbed, as opposed to closely associated with the adjuvant. The need for complete adsorption and the requirement for a depot effect and slow release had been dismissed by studies conducted half a century previously.1 The basis of adjuvant action is now known to be complex, involving cellular interactions and cytokine release. Even so, the precise mode of action and the basis of the differences in activity of aluminium hydroxide and aluminium phosphate were still unknown. In the preparation of aluminium-adjuvanted vaccines the formulation was critical. The consistency of production and stability of the preparation were more important than the actual proportion of antigen adsorbed. Draft recommendations had been prepared by WHO for acellular pertussis (DTAcP) vaccines. In these, the consistency of adsorption was emphasized and should be within the specifications of lots shown to be clinically effective. Dr I. Heron (Amvax) observed that the aluminium adjuvant was essential for animal potency assays if a single dose was used. Some adsorption of toxoid was necessary as pre-saturation with an irrelevant protein, such as albumin, blocked the response to the vaccine. In guinea-pigs or mice, a single dose of unadsorbed vaccine gave very low responses. There were significant differences between aluminium hydroxide and calcium phosphate. The latter had about one third the binding capacity of the former. In mouse assays the Al preparations gave 2–3-fold higher responses against D and T toxoids than calcium phosphate. However, in man, calcium adsorbed vaccines used as boosters gave 2-fold higher titres than aluminium adsorbed preparations. Similarly, plain toxoid was very effective as a booster in man but poor in rodents. It was clear that there was no correlation between the quantitative responses observed in animal assays and performance of the vaccines in man. Possibly, the present requirements could be modified. However, it should be noted that they had provided an assurance of the potency of these vaccines and their efficacy in man, for many years.
Dr J. Pex tre (Chiron Biocine) noted that diphtheria toxoids were often sub-potent but that this could be corrected by increasing the Al content of the vaccine. For DTAcP preparations it was important to ensure adequate adsorption to increase stability and to enhance the immunogenicity of the P69 component. Dr R. Winsnes (Chairman, Group 15, European Pharmacopoeia Commission) reviewed the Ph.Eur. position on adjuvants in vaccines. The recommendations outlined in the general monograph on vaccines for human use and the individual vaccine monographs were broadly consistent with the recommendations published by WHO. However, the potency requirement for an adsorbed vaccine such as diphtheria could be interpreted as different. The Ph.Eur. requires a lower limit of 30 IU/dose, whereas Requirements published by WHO specify a potency of 30 IU/dose. The potency requirements for diphtheria and tetanus vaccine are currently under review by Group 15. For adsorbed vaccines the draft recommendation was that each product should have a specified limit for the proportion of adsorbed material which should be not less than that used in clinical trial lots and should be demonstrated to be maintained to the end of shelf life. Group 15 was reviewing the requirements for individual and combination vaccines and would pronounce on this in the near future. It was likely that the emphasis would remain on the monographs for individual vaccines with new monographs for some combinations. A key requirement was that the formulations must be shown to have acceptable immunogenicity in man in the intended immunisation schedule. Based on recent information, the precise definition of ‘‘adsorbed’’ in the Ph.Eur. monograph titles on vaccines containing calcium and aluminium will be reviewed. Al components provide an immunological adjuvant effect, not only by sustained release of immunogens, but also by producing a local inflammatory response and by triggering cytokine release. Dr M. Schwanig (Paul Ehrlich Institute, Germany) summarized the European regulatory view point. He emphasized that there was no clear definition of adsorbed as opposed to nonadsorbed vaccines. In adjuvanted formulations it was unclear if the Al gels were vehicles or adjuvants. In the case of whole cell DTP vaccines, the pertussis component does not compete for the adsorption sites. This eases the manufacture
Meeting report
of combined vaccines with a high degree of adsorption of diphtheria and tetanus toxoids. To achieve the same degree of adsorption in DTAcP vaccines a more carefully controlled manufacturing process is necessary as the isolated pertussis proteins, most of them larger than diphtheria or tetanus toxoid, compete for the adsorption sites. As several products show, it is possible with DTAcP vaccines to produce a stable almost 100% adsorbed vaccine by, for example, separate adsorption of each component and/or modification of pH to ensure optimal interaction between gel and antigen. When using the term ‘‘adsorbed’’ it is necessary to have a definition for this. There was little information available on the content of toxoids necessary for adequate responses in man and this issue needs to be addressed in respect of new combination vaccines. The degree of adsorption needed to be consistent with clinical efficacy. It should be at the highest level achievable. It was also necessary to consider whether it should be a self life criterion. Dr R. Mignolet (Wyeth Lederle) suggested that it was desirable to aim for the highest possible degree of adsorption. If the initial level was high, this should be maintained throughout shelf life. For Wyeth Lederle DTAcP–Hib the degree of adsorption was 0100% which was maintained throughout shelf life (excluding the Hib component). The level of adsorption could be assayed by ELIFA (ELISA combined with filtration). The degree of adsorption to be specified in lots for release needed to be justifiable. Dr R. Gupta (Massachusetts Public Health Biologic Laboratories) emphasized that aluminium hydroxide and aluminium phosphate were very different in properties. They had opposite charges and behaved differently in adsorption properties. Phosphate ions affected the behaviour of aluminium phosphate. Thus D toxoid adsorption to aluminium phosphate ranged from 0% in phosphate buffer pH 7⋅2 to 57% at pH 6–6⋅3. In physiological saline it was 93–100%. There were also differences between pre-formed and aluminium gels produced in situ. Ideally, the highest adsorptive capacity should be aimed for as the evidence indicated that adsorbed vaccines were more immunogenic than unadsorbed.
353
Dr D. Lamb (Connaught Laboratories Inc.) reported on the determination of the degree of adsorption of a Biken DTAcP aluminium hydroxyphosphate vaccine. Assay by rocket immunoelectrophoresis of supernatant or whole vaccine dissolved in sodium citrate did not indicate interference by T or AcP components with adsorption of D toxoid. Examination of four consistency lots showed that the proportion adsorbed (040%) remained constant throughout the shelf life. Dr C. Meschevitz (Connaught Laboratories Inc.) reported observations on the correlation between clinical responses and the degree of adsorption of the D and T components of a DTP vaccine. A vaccine which was 050% adsorbed produced D and T antitoxin responses of 0.1 IU per ml in q90% of recipients. There was clearly no correlation between Al content, Lf content, % adsorption and antibody titres achieved. Dr J. Holst (NIPH, Norway) reported that the Group B meningococcal outer membrane vesicle vaccine due to be introduced into routine use in Norway in 1998 contained aluminium hydroxide. This was essential to stabilise the vaccine. Conclusions (1) There is no current WHO requirement for a minimum level of adsorption for DTP vaccines. (2) The use of the term ‘‘adsorbed vaccine’’ should be avoided unless the degree of adsorption is specified. Otherwise vaccines containing aluminium hydroxide, aluminium phosphate or calcium phosphate gels should be referred to as ‘‘adjuvant vaccines’’. (3) It is not feasible to specify a minimum level of adsorption for any particular type of vaccine as this would depend upon the formulation. However, the degree of adsorption must be within the specifications of lots shown to be efficacious in clinical trials. (4) The degree of adsorption should remain constant throughout the shelf life of the product. (5) No specific recommendation is made on the method to be adopted for determination of degree of adsorption—procedures based on filtration followed by ELISA, rocket electrophoresis or other immunoassays may be accepted subject to validation.