Progress towards the development of new vaccines against whooping cough Rino Rappuoli*$, Audino Poddat, Mariagrazia Pizza, Antonelio Covacci, Antonella Bartoloni, Maria Teresa de Magistris and Luciano Nencioni#
Acellular vaccines against whooping cough are in the final stage of clinical testing and are likely to become available for mass immunization in the near future. Over a dozen vaccines of similar composition have been developed by vaccine companies and research laboratories; all of them contain a detoxified form of pertussis toxin ( PT) that may be present alone or combined with one or more other non-toxic proteins, such as filamentous haemagglutinin (FHA), pertactin ( 6 9 k D a ) , and the agglutinogens
(AGG). Most of the vaccines contain a PT that has been inactivated by chemical treatment, a process that reduces the immunogenicity of the molecule and may not completely eliminate the risk of reversion to toxicity. To avoid these problems, we have constructed by genetic manipulation a mutant of
Bordetella pertussis that
produces a
non-toxic form of PT. This molecule (PT-9K/129G) contains two amino acid substitutions in the SI subunit (Arg9--*Lys and Glu129~Gly) which abolish the enzymatic activity of the S1 subunit and all the toxic properties of PT, without changing the immunological properties of
the wild-type toxin. Following extensive preclinical studies, which have shown that PT-9K/129G is safe and more antigenic than the toxin treated with chemical agents, this molecule was tested for safety and immunogenicity in adult volunteers, 18-month-old children and 2-month-old infants.
The molecule has been tested alone, combined with FHA and pertactin and also combined with diphtheria and tetanus toxoids. In all clinical studies P T-9K/129G proved to be safe and more immunogenic than chemically
detoxified PT molecules. These results indicate that PT9K/129G belongs to a new generation of molecules that ultimately should replace vaccines made by conventional technologies such as chemical detoxification.
Keywords:Bordetella pertussis, acellular vaccine: detoxified pertussis toxin
INTRODUCTION Pertussis, a disease that affects infants and young children, is caused by Bordetella pertussis, a Gramnegative bacterium that infects virtually all children that are not immune 1 3. The bacterium is transmitted by aerosol from contacts with the disease and may be spread in the population by adults with asymptomatic infections or mild disease 4'5. Following infection, B. pertussis Immunobiology Research Institute Siena, and ?BiocineSclavo, Via Fiorentina 1, 53100 Siena, Italy. ~To whom correspondence should be addressed 0264-410X/92/141027-06 © 1992 Butterworth-HeinemannLtd
adheres specifically to the cilia of the upper respiratory tract, colonizes this tissue, multiplies and releases several toxins that cause local and systemic damage. Locally, the action of the tracheal cytotoxin causes the loss of the ciliated cells that are involved in the clearance of external substances. In the absence of a functional ciliated epithelium, cough is the only way to remove the substances that enter the respiratory tract. Systemically the toxins released reach and modify most tissues, causing different effects in each of them. The systemic effects that are easiest to measure are those caused by pertussis toxin such as lymphocytosis and hypoglycaemia. The resulting clinical disease is characterized by longlasting paroxysmal cough, accompanied by whoops, vomiting, cyanosis and apnoea; fever is either modest or absent. The most common complications are pneumonia, seizures, encephalopathy and death. Antibiotic treatment (erythromycin) is very effective in clearing the bacteria, but has little consequence on the disease, mostly because the disease is usually diagnosed when the bacteria have already damaged the respiratory tract and released the toxins that are responsible for the severe symptoms. For this reason, vaccination is the only way to control pertussis. Mass vaccination using killed bacteria (cellular vaccine) was introduced in the 1950s and reduced by 99% the incidence of disease: in the United States of America, the incidence decreased from 150 cases per 100 000 population in the pre-vaccine era to 0.6 cases per 100000 population in 1980. In spite of the efficacy of vaccination, in the United States alone pertussis is still responsible for over 30000 cases, 3300 hospitalizations and 25 deaths per year 6'7. The disease is most severe in the first few months of life. Of infants that get the disease in the first year of life, 50% are hospitalized and 1% die. After the first year of life, only 4% of children with the disease are hospitalized. Worldwide, pertussis is still responsible for over half a million deaths each year s. Most of these occur in developing countries where in the presence of poor hygiene conditions and in the absence of vaccination, the mortality can be as high as 1% of the total cases. In spite of its efficacy, the use of the cellular vaccine is controversial, mostly because of fear of the side-effects that have been associated with it 2. Most of these are mild reactions such as redness, swelling and fever that occur in 2(~70% of the vaccinees, and prolonged, inconsolable crying, that occurs with a frequency of0.1-1%. In addition to these mild reactions, severe side-effects such as anaphylaxis, brain damage and deaths have been associated in rare cases (3-9 per million
Vaccine, Vol. 10, Issue 14, 1992 1027
New vaccines against whooping cougtT. R. Rappuoli et al.
doses) with pertussis vaccination
Acellular vaccines against whooping cough are in the final stage of clinical testing and are likely to become available for mass immunization in the near future. Over a dozen vaccines of similar composition have been developed by vaccine companies and research laboratories; all of them contain a detoxified form of pertussis toxin ( PT) that may be present alone or combined with one or more other non-toxic proteins, such as filamentous haemagglutinin (FHA), pertactin ( 6 9 k D a ) , and the agglutinogens
(AGG). Most of the vaccines contain a PT that has been inactivated by chemical treatment, a process that reduces the immunogenicity of the molecule and may not completely eliminate the risk of reversion to toxicity. To avoid these problems, we have constructed by genetic manipulation a mutant of
Bordetella pertussis that
produces a
non-toxic form of PT. This molecule (PT-9K/129G) contains two amino acid substitutions in the SI subunit (Arg9--*Lys and Glu129~Gly) which abolish the enzymatic activity of the S1 subunit and all the toxic properties of PT, without changing the immunological properties of
the wild-type toxin. Following extensive preclinical studies, which have shown that PT-9K/129G is safe and more antigenic than the toxin treated with chemical agents, this molecule was tested for safety and immunogenicity in adult volunteers, 18-month-old children and 2-month-old infants.
The molecule has been tested alone, combined with FHA and pertactin and also combined with diphtheria and tetanus toxoids. In all clinical studies P T-9K/129G proved to be safe and more immunogenic than chemically
detoxified PT molecules. These results indicate that PT9K/129G belongs to a new generation of molecules that ultimately should replace vaccines made by conventional technologies such as chemical detoxification.
Keywords:Bordetella pertussis, acellular vaccine: detoxified pertussis toxin
INTRODUCTION Pertussis, a disease that affects infants and young children, is caused by Bordetella pertussis, a Gramnegative bacterium that infects virtually all children that are not immune 1 3. The bacterium is transmitted by aerosol from contacts with the disease and may be spread in the population by adults with asymptomatic infections or mild disease 4'5. Following infection, B. pertussis Immunobiology Research Institute Siena, and ?BiocineSclavo, Via Fiorentina 1, 53100 Siena, Italy. ~To whom correspondence should be addressed 0264-410X/92/141027-06 © 1992 Butterworth-HeinemannLtd
adheres specifically to the cilia of the upper respiratory tract, colonizes this tissue, multiplies and releases several toxins that cause local and systemic damage. Locally, the action of the tracheal cytotoxin causes the loss of the ciliated cells that are involved in the clearance of external substances. In the absence of a functional ciliated epithelium, cough is the only way to remove the substances that enter the respiratory tract. Systemically the toxins released reach and modify most tissues, causing different effects in each of them. The systemic effects that are easiest to measure are those caused by pertussis toxin such as lymphocytosis and hypoglycaemia. The resulting clinical disease is characterized by longlasting paroxysmal cough, accompanied by whoops, vomiting, cyanosis and apnoea; fever is either modest or absent. The most common complications are pneumonia, seizures, encephalopathy and death. Antibiotic treatment (erythromycin) is very effective in clearing the bacteria, but has little consequence on the disease, mostly because the disease is usually diagnosed when the bacteria have already damaged the respiratory tract and released the toxins that are responsible for the severe symptoms. For this reason, vaccination is the only way to control pertussis. Mass vaccination using killed bacteria (cellular vaccine) was introduced in the 1950s and reduced by 99% the incidence of disease: in the United States of America, the incidence decreased from 150 cases per 100 000 population in the pre-vaccine era to 0.6 cases per 100000 population in 1980. In spite of the efficacy of vaccination, in the United States alone pertussis is still responsible for over 30000 cases, 3300 hospitalizations and 25 deaths per year 6'7. The disease is most severe in the first few months of life. Of infants that get the disease in the first year of life, 50% are hospitalized and 1% die. After the first year of life, only 4% of children with the disease are hospitalized. Worldwide, pertussis is still responsible for over half a million deaths each year s. Most of these occur in developing countries where in the presence of poor hygiene conditions and in the absence of vaccination, the mortality can be as high as 1% of the total cases. In spite of its efficacy, the use of the cellular vaccine is controversial, mostly because of fear of the side-effects that have been associated with it 2. Most of these are mild reactions such as redness, swelling and fever that occur in 2(~70% of the vaccinees, and prolonged, inconsolable crying, that occurs with a frequency of0.1-1%. In addition to these mild reactions, severe side-effects such as anaphylaxis, brain damage and deaths have been associated in rare cases (3-9 per million
Vaccine, Vol. 10, Issue 14, 1992 1027
New vaccines against whooping cougtT. R. Rappuoli et al.
doses) with pertussis vaccination
