Method for preparing pertussis toxin toxoid

Abstract: Disclosed is a method for preparing pertussis toxin toxoid by a treatment of pertussis toxin with formaldehyde, which comprises carrying out said treatment in the presence of lysine or glycine in combination with N-acetyltriptophan. The resultant toxoid does not exhibit toxicity reversion, thereby making the toxoid highly suitable for use in pertussis vaccines.

Description: The present invention relates to a method for toxoidizing pertussis toxin, more particularly, to a novel method for preparing pertussis toxin toxoid from pertussis toxin by which the toxoid will not exhibit toxicity reversion, thereby making the toxoid highly suitable for use in pertussis vaccines having no substantial side effects. Furthermore, the invention relates to pertussis toxin toxoids obtainable according to said method and to vaccines containing said pertussis toxin toxoid. Pertussis toxin is a protein produced by Bordetella pertussis and, because of the variety of its physiological and biological activities, is also referred to as leukocytosis promoting factor (LPF), histamine sensitizing factor (HSF), or islets activating protein (IAP). In addition, pertussis toxin is known to exhibit such biological activities as promotion of vascular permeability, CHO-cell clustering activity , and ADP-ribosylase activity. It is also known that pertussis toxin is one of the most important antigens against infection with B. pertussis. Thus, attempts have been made to develop various pertussis vaccines indispensably containing pertussis toxin toxoid by treating pertussis toxin so as to inactivate its toxicity while retaining its immunogenicity. In treating pertussis toxin for obtaining the toxoid thereof, formaldehyde and glutaraldehyde have been most commonly used. However, it has recently been pointed out that treatment with formaldehyde and/or glutaraldehyde does not sufficiently inactivate the pertussis toxin and thus does not provide a toxoid which is totally devoid of all of the toxic physiological and biological activities. For example, Sato et al. have shown that the use of formaldehyde or glutaraldehyde for producing the toxoid from the pertussis toxin only decreases to a limited extent such properties as ADP-ribosylase activity and islets activating property, while substantially decreasing such properties as leukocytosis promoting activity, histamine sensitizing activity and hemagglutionation activity [Journal of Bacteriology in Japan, 42 , 288(1987)]. Furthermore, it has recently been concerned that pertussis toxin toxoid obtained through the detoxification with the conventional agents such as formaldehyde may exhibit toxicity reversion during storage, thereby giving the vaccines containing the toxoid undesirable side effects (Pertussis Vaccine Workshop '87). It is therefore being recommended that the toxoid used be one having no substantial toxicity reversion, which may be determined, for example, by maintaining the toxoid at 37°C for a period of several weeks. The technical problem underlying the present invention therefore is to overcome the above-mentioned problems and to provide a novel method for preparing pertussis toxin toxoid from pertussis toxin by which the resultant toxoid is completely devoid of toxicity and does not exhibit toxicity reversion while retaining the sufficient antigenicity. Furthermore, the technical problem underlying the present invention is to provide new pertussis toxin toxoids and vaccines containing them. The solution of the above technical problem is achieved by providing the embodiments characterized in the claims. The solution of said technical problem is based on the finding that, in the treatment of pertussis toxin with formaldehyde (formalin) for the preparation of the toxoid, the presence of specific amino acids provides sufficient inactivation of the toxin without possibility of the toxicity reversion. Thus, according to the present invention there is provided a method for preparing pertussis toxin toxoid by a treatment of pertussis toxin with formaldehyde, which comprises carrying out said treatment in the presence of lysine or glycine in combination with one or more of amino acids selected from the group consisting of N-acetyl-DL-tryptophan, N-acetyl-D-tryptophan and N-acetyl-L-tryptophan. Furthermore, the present invention provides pertussis toxin toxoids obtainable according to said method and the corresponding vaccines. These vaccines optionally also contain pharmaceutically acceptable carriers, excipients add/or diluents. The present inventors previously suggested that the presence of amino acid(s) may be advantageous in detoxification of antigens which are regarded as having preventive effect against the infection with pertussis (EP-A 0 121 249). However, in the earlier application no mention was made specifically regarding the combination of lysine with N-acetyltryptophan (N-acetyl-DL-tryptophan, Nacetyl-D-tryptophan or N-acetyl-L-tryptophan), or the combination of glycine with N-acetyltryptophan. The present invention is based on the fact that the treatment of pertussis toxin with formaldehyde in the presence of N-acetyltryptophan together with lysine or glycine can produce toxoids which are much superior to those obtained by conventional detoxification methods including the ones described in the above-mentioned earlier application by the present inventors (EP-A 0 121 249) in which there are employed other amino acid(s) than those defined in the present invention. It is particularly notable that the pertussis toxin toxoid prepared by the method of the present invention does not exhibit substantial toxicity reversion even under severe conditions, as evidenced by an assay system recently developed for sensitive analysis. The method of the present invention for the preparation of the toxoid is generally carried out with 0.2 to 1.2% of formalin for 5 to 50µg of pertussis toxin in terms of PN(protein nitrogen)/ml, in which the concentration of N-acetyltryptophan is in the range of 0.1 to 10mM, the concentration of lysine is in the range of 5 to 200mM and the concentration of glycine is in the range of 5 to 200mM, at a temperature of 20 to 45°C for a treatment period of 3 to 30 days. Between lysine and glycine, lysine is preferable. The method of the present invention is practiced preferably with the formalin concentration being 0.3 to 1.0% (most preferably 0.6 to 0.8%), N-acetyltryptophan concentration being 0.2 to 4mM (most preferably 0.5 to 2mM), lysine concentration being 20 to 100mM (most preferably, 10 to 50mM), glycine concentration being 5 to 120mM (most preferably 20 to 40mM), and the temperature being 25 to 45°C (most preferably 37 to 42°C ) for a period of 7 to 21 days (most preferably 7 to 10 days). In the toxoid prepared by the method of the present invention, the various physiological and biological activities possessed by the pertussis toxin are reliably inactivated for detoxification, while the immunogenicity is retained as can be confirmed by the mouse potency test. What is more, the pertussis toxin toxoid obtained by the present invention does not demonstrate substantial change in the degrees of the physiological and biological activities and does not produce toxicity reversion, even when maintained at 37°C for a period of several weeks. Accordingly, the method of the present invention for the preparation of the toxoid is of outstanding utility for providing efficacious and safe pertussis vaccines. The present invention will be more specifically described with reference to the following working example, which does not limit the scope of the present invention. EXAMPLE Amino acid(s) as given in the table below were added to pertussis toxin, 20µg PN/ml (PN:protein nitrogen). Formalin was added to the mixture in an amount of 0.6 to 0.8 % and the resultant was then kept at 40°C for 7 to 21 days. After dialysis against PBS (M/75) to remove the formalin, pertussis toxin toxoids were obtained. 0.2mg/ml aluminium gel were added to each toxoid sample, 2µg PN/ml, in order to prepare vaccine solutions. Each vaccine solution was kept 4°C for 4 weeks, or at 37°C for 4 weeks. The vaccine solutions were then determined for the various physiological and biological activities, with the results as shown in the table. Determinations of the physiological and biological activities were conducted in known ways described in the literature references given below: Mouse Potency[MP]: Minimum Requirements of Biological Products in Japan 1981, edited by Ministry of Health and Welfare of Japan LPF activity (mouse LPF activity)[LPF]: ditto HSF activity (mouse HSF activity) [HSF]: ditto CHO-cell clustering activity (Chinese hamster ovary cell clustering activity)[CHO]: J. Biol. Stand., 13, 61-66(1985). Skin vascular permeability [SVP]: Microbiol. Immunol., 31, 531-539(1987). Blood glucose value [BGV]: Infect. Immun., 41, 137-144 (1983). ADP-ribosylase activity (ADP-ribosyltransferase activity) [ADP]: Infect. Immun., 46, 422-428 (1984). The toxoids (Sample Nos. 1,2,8 and 9) prepared according to the method of the present invention exhibited no toxic activities while possessing high potencies, as can be seen from the data on the physiological and biological activities given in the table. Particularly notable is that the toxoids obtained by the present invention demonstrated no toxic activities and no toxicity reversion even when maintained at 37°C for four weeks. Such effect is particularly notable when N-acetyltryptophan and lysine are added. In contrast, samples subjected to a single addition of N-acetyltryptophan, lysine or glycine (Samples Nos. 3,4 or 5) showed a tendency toward toxicity reversion as such toxoid samples still exhibited some extent of physiological and biological activities when maintained at 37°C. It will also be noted that the treatment with formalin alone (Sample No.6), as commonly practiced, does not provide satisfactory inactivation of the physiological and biological activities. This is particularly the case when the sample was maintained at 37°C, since the results show that the substantial levels of the physiological and biological activities for toxicity are still maintained.

Claims: A method for preparing pertussis toxin toxoid by a treatment of pertussis toxin with formaldehyde, which comprises carrying out said treatment in the presence of lysine or glycine in combination with at least one of the amino acids N-acetyl-DL-tryptophan, N-acetyl-D-tryptophan or N-acetyl-L-tryptophan. The method according to claim 1, wherein 0.2 to 1.2% of formalin is used for 5 to 50µg of pertussis toxin in terms of PN(protein nitrogen)/ml, the concentration of N-acetyltryptophan is in the range of 0.1 to 10mM, the concentration of lysine is in the range of 5 to 200mM, the concentration of glycine is in the range of 5 to 200mM, the temperature is 20 to 45°C, and the treatment period is 3 to 30 days. The method according to claim 2, wherein the formalin concentration is 0.3 to 1.0%, the N-acetyltryptophan concentration is 0.5 to 2mM, the lysine concentration is 10 to 50mM, the glycine concentration is 20 to 40mM, the temperature is 37 to 42°C, and the treatment period is 7 to 10 days. The method according to any of claims 1 to 3, wherein lysine is used. A pertussis toxin toxoid obtainable by a method according to any one of claims 1 to 4. A vaccine containing a pertussis toxin toxoid according to claim 5 and optionally in addition a pharmaceutically acceptable carrier, excipient and/or diluent.

Inventors: AIHARA KATSUTOSHI, GINNAGA AKIHIRO, MOROKUMA KAZUNORI, SAKOH MITSUO, AIHARA, KATSUTOSHI, GINNAGA, AKIHIRO, MOROKUMA, KAZUNORI, SAKOH, MITSUO
Applicants: CHEMO SERO THERAPEUT RES INST, JURIDICAL FOUNDATION THE CHEMO-SERO-THERAPEUTIC RESEARCH INSTITUTE
Application year: 1989
Main classification: A61K39
IPC codes: C12N1, A61P37, A61K38, A61K39