Calibration of pertussis toxin BRP batch 1 in a standardised CHO cell-based clustering assay

The European Pharmacopoeia (Ph. Eur.) pertussis toxin (PT) Biological Reference Preparation (BRP) is used as a working standard for safety testing of acellular pertussis vaccines as prescribed in the Ph. Eur. monographs 1356 "Pertussis vaccine (acellular, component, adsorbed)" and 1595 "Pertussis vaccine (acellular, co-purified, adsorbed)". The BRP was calibrated in 2006 in the murine histamine sensitisation test (HIST) against the World Health Organization (WHO) 1^st International Standard (IS) for PT. In recent years, there have been increasing efforts to replace the in vivo test with in vitro methods. The Chinese hamster ovary (CHO) cell clustering assay has been used for many years by manufacturers to monitor residual PT activity in detoxified non-adjuvanted bulks. More recently a standardised protocol has been developed for this assay and a PT reference preparation was needed. Due to low stocks, the WHO 1^st International Standard for Pertussis Toxin (JNIH-5) needed to be replaced and therefore a joint study between the European Directorate for the Quality of Medicines & HealthCare (EDQM) and WHO was initiated to calibrate the PT BRP for the CHO clustering assay and to replace the IS. The collaborative study involved 14 laboratories from Europe, North America and Asia. The outcome of the study confirmed that the BRP is suitable for use as a reference preparation in the CHO clustering assay. The material was assigned a potency of 1360 IU per vial for the CHO clustering assay.

Collaborative study for the standardisation of the histamine sensitizing test in mice and the CHO cell-based assay for the residual toxicity testing of acellular pertussis vaccines

The European Pharmacopoeia (Ph. Eur.) and the World Health Organisation (WHO) require the performance of extensive quality and safety control testing before the release on the market of vaccine products for human use. Safety testing with regard to residual pertussis toxin (PT) in acellular pertussis combination vaccines is performed through assessment of fatal sensitisation of mice to histamine challenge by the vaccine product under test. Currently, use of different in-house procedures and no requirement for the inclusion of a standard reference in each assay render comparisons of results obtained for identical vaccine batches between different control laboratories very difficult. At the initiative of the European Directorate for the Quality of Medicines and HealthCare (EDQM), an international collaborative study was organised for the standardization of the Histamine Sensitizing Test (HIST) in mice and the Chinese Hamster Ovary (CHO)-cell-based assay (performed at the bulk product level) for the residual toxicity testing of acellular pertussis vaccines or acellular pertussis-based combination vaccines. The study was run under the aegis of the Biological Standardisation Programme, jointly supported by the Council of Europe and the European Commission under the project code BSP076. Ten (10) laboratories participated in the study and were requested to perform 3 independent Histamine Sensitizing Tests in mice and to report results of the lethal end-point measurement as prescribed by the Ph. Eur. monographs. Some of them also reported data from an in-house validated CHO-cell-based assay. In addition, some of the laboratories reported concomitantly data obtained by measurement of the drop in temperature induced after the histamine challenge, a method currently under investigation to be added as an alternative end-point for the HIST in the Ph. Eur. monographs for acellular pertussis-based combination vaccines in order to alleviate animal suffering (in application of the 3Rs principle). Based on the results of the collaborative study, a potency of 7500 IU/vial (International Units per vial) was assigned to the current Ph. Eur. Biological Reference Preparation (BRP) for PT. The results of the study also show that 1) intra- and inter-laboratory variations can be improved by the use of a validated standard operating procedure; 2) inclusion in each assay of a standard reference sample, calibrated in IU, can increase comparability of results among laboratories and thus help to reduce repeat testing; 3) a correlation between mortality data and temperature data was observed although, due to the limited number of data sets and the lack of a common method for the temperature end-point, further investigation of this point is required; 4) the CHO-cell-based assay did not yield comparable results and further standardisation of the assay procedure may be investigated in a follow-up project.

An alternative temperature-based histamine-sensitisation test for absence of residual pertussis toxin in acellular pertussis vaccines

As an extension of the BSP076 study (see the article 'Collaborative Study for the Standardisation of the Histamine Sensitizing Test in Mice and the CHO Cell-based Assay for the Residual Toxicity Testing of Acellular Pertussis Vaccines (BSP076)', page 51 of this issue of Pharmeuropa Bio & Scientific Notes), it was decided to publish the following experimental method for the temperature-based histamine-sensitisation test, validated at the SSI (Statens Serum Institut, Denmark), as a working basis for the growth of the method in individual laboratories.

[Experimental, clinical and immunologic assessment of acellular staphylococcal vaccine "Staphylovac"]

Results of experimental, clinical and immunological effects of acellular dry staphylococcal vaccine "Staphylovac" developed in Mechnikov Research Institute of Vaccines and Sera are presented. Original mildly virulent strains of Staphylococcus aureus having high immunogenicity, and intra- and interspecies protective activity against different representatives of opportunistic microflora were used for construction of the preparation. Low-toxicity and weak anapylactogenicity of the vaccine were established. In experiments on mice, guinea pigs and rabbits significant protective, antigenic and immunomodulate activity of the preparation was revealed with low sensitization of animals. Clinical trials performed in different centers showed that inclusion of vaccinotherapy in complex treatment of chronic staphylococcal infections (chronic pyodermia, lung abscess etc.) resulted in prolonged pathologic locus, decrease of number and severity of exacerbations, prolongation of remission, and complete recovery in significant number of patients. Activation of innate and adaptive immunity was revealed in the same patients. It was shown on the large group of athletes that administration of the vaccine by aerosol route prevents disruption of immunologic adaptation occurring due to excess physical activity and stress situations during competitions.

[Acellular pertussis vaccine]

Protective, immunogenic, toxic, and sensitizing properties of acellular pertussis vaccine (aPV) developed according to original technology were studied, aPV had marked protective activity which lasted more than 2 years. Sera of mice immunized by aPV also possess protective properties, and they were more prominent than in sera of mice immunized by pertussis bacteria suspension (PS). Immune sera to aPV neutralized cytopathogenic effect of pertussis toxin (PT) on ovarian Chinese hamster cells in 1:250 dilution, whereas neutralizing activity of sera to PS was very low. Level of antibodies to PT was higher in rabbits immunized, according to schedules and dosage recommended for children, by aPV than by PS. High immunogenicity of aPV was proved also by levels of IgG to PT in sera of mice immunized three times by aPV in human dosage. During experiments on mice and guinea pigs aPV had mild toxicity, did not induce autoimmune process, did not have anaphylactogenic properties compared with bacterial suspension characterized by high anaphylactogenic activity. Histamine-sensitizing abilityof aPVwas 40 times lower than that of PS. Assessment of pyrogenic properties of aPV and PS performed on rabbits showed that aPV was 1,000 times less pyrogenic than PS. Obtained results demonstrate high protective and immunogenic properties of domestic acellular pertussis vaccine and its low toxic and sensitizing characteristics.

Lung pathology and immediate hypersensitivity in a mouse model after vaccination with pertussis vaccines and challenge with Bordetella pertussis

While evaluating vaccine efficacy against clinical Bordetella pertussis isolates in mice, after challenge vaccinated mice showed increased lung pathology with eosinophilia, compared to challenged, non-vaccinated animals. This led us to study bacterial clearance, lung pathology, lung TNF-alpha expression, and parameters of immediate hypersensitivity (IH), being serum IgE levels, eosinophil numbers in the bronchoalveolar lavage fluid, and ex vivo IL-4, IL-5, IL-10, IL-13, and IFN-gamma production by the bronchial lymph node cells. BALB/c mice received a combined Diphtheria (D), Tetanus (T), Poliomyelitis, and whole-cell Pertussis vaccine (WCV), a combined D, T, and three-component acellular Pertussis vaccine (ACV), aluminium hydroxide adjuvant, or PBS, 28 and 14 days before B. pertussis infection. Similarly treated non-infected mice were taken as a control. Infection induced pathology; this induction was stronger after (especially WCV) vaccination. WCV but not ACV vaccination induced TNF-alpha expression after challenge. After challenge, IH parameters were strongly increased by (especially ACV) vaccination. Vaccinated IL-4 KO mice showed similar clearance and pathology, in the absence of IgE and with reduced numbers of eosinophils. Vaccinated (Th1-deficient) T-bet KO mice showed reduced clearance and similar pathology. In summary, after challenge vaccination increased lung pathology, TNF-alpha expression (only WCV), and IH parameters. Th1 cells were critical for clearance.

Pre-clinical safety and efficacy of TA-CIN, a recombinant HPV16 L2E6E7 fusion protein vaccine, in homologous and heterologous prime-boost regimens

Human papillomavirus (HPV) E6 and E7 oncoproteins are attractive targets for T-cell-based immunotherapy of cervical intraepithelial neoplasia (CIN) and cancer. A newly designed vaccine, comprising the HPV16 L2, E6 and E7 as a single fusion protein (TA-CIN), was shown to elicit HPV16-specific CTL, T-helper cells and antibodies in a pre-clinical mouse model. These immune responses effectively prevented outgrowth of HPV16-positive tumour cells in a prophylactic setting as well as in a minimal residual disease setting. CTL immunity was optimally induced when TA-CIN was employed in heterologous prime-boost regimens in combination with TA-HPV, a clinical grade vaccinia-based vaccine. These data provide a scientific basis for the use of TA-CIN, alone or in combination with TA-HPV in future human trials.