Development of rocket electrophoresis technique as an analytical tool in preformulation study of tetanus vaccine formulation.

Rocket Electrophoresis (RE) technique relies on the difference in charges of the antigen and antibodies at the selected pH. The present study involves optimization of RE run conditions for Tetanus Toxoid (TT). Agarose gel (1% w/v, 20 ml, pH 8.6), anti-TT IgG - 1 IU/ml, temperature 4-8 degrees C and run duration of 18 h was found to be optimum. Height of the rocket-shaped precipitate was proportional to TT concentration. The RE method was found to be linear in the concentration range of 2.5 to 30 Lf/mL. The method was validated and found to be accurate, precise, and reproducible when analyzed statistically using student's t-test. RE was used as an analytical method for analyzing TT content in plain and marketed formulations as well as for the preformulation study of vaccine formulation where formulation additives were tested for compatibility with TT. The optimized RE method has several advantages: it uses safe materials, is inexpensive, and easy to perform. RE results are less prone to operator's bias as compared to flocculation test and can be documented by taking photographs and scanned by densitometer; RE can be easily standardized for the required antigen concentration by changing antitoxin concentration. It can be used as a very effective tool for qualitative and quantitative analysis and in preformulation studies of antigens.

Validation of in vitro potency assays for tetanus immunoglobulin.

The European Pharmacopoeia (Ph. Eur.) monograph Human tetanus immunoglobulin (0398) gives a clear outline of the in vivo assay to be performed to determine the potency of human tetanus immunoglobulins during their development. Furthermore, it states that an in vitro method shall be validated for the potency estimation. Since no further guidance is given on the in vitro assay, every control laboratory concerned is free to design and validate an in-house method. At the moment there is no agreed method available. The aim of this study was to validate and compare 2 alternative in vitro assays, i.e. an enzyme-linked immunoassay (EIA) and a toxoid inhibition assay (TIA). The potency of 2 tetanus immunoglobulin preparations (Product 1, Product 2) was estimated against the WHO International Standard for tetanus immunoglobulin, using the tetanus EIA and TIA. The coefficient of variation (CV) to characterise the assay precision was 3.2% (EIA) and 3.6% (TIA), and the corresponding CV for intra-assay variation was 4.7% (EIA) and 5.5% (TIA). Using a spiking procedure, the 2nd part of the experiment investigated recovery of a known anti-tetanus potency. The recovery of samples spiked with defined amounts of reference preparation ranged from 104 112% (EIA) and 114 125% (TIA) respectively, resulting in a mean bias of 2.2 IU/ml (95% confidence interval (CI): -1.1-5.4 IU/ml, EIA) and 5.8 IU/ml (95% CI: 1.4 10.2 IU/ml, TIA). Good agreement was observed between the in vivo and in vitro assay results: the relative potency results of the EIA and TIA as compared to those of the in vivo assay performed by the manufacturers of the 2 tetanus immunoglobulins were for the EIA in the range of 104+/-10% for Product 1 and 100+/-6% for Product 2, and for the TIA in the range of 107+/-6% for Product 1 and 100+/-7% for Product 2. Tetanus EIA and TIA are suitable quality control methods for polyclonal tetanus immunoglobulin, which can be standardised in a quality control laboratory using a quality assurance system. In a collaborative study it will now be evaluated whether the validated methods can be proposed as common in vitro batch potency assays for replacement of the in vivo mouse assay.

Production and purification of ovine anti-tetanus antibody.

We used the ovine as bioreactor for the production and optimization of anti-tetanus toxin antibody. Four female sheep were immunized with human tetanus vaccine (TT-alum) every two weeks for 16 weeks, after which serum was collected and its titer was estimated by ELISA. The highest titer obtained was 39,000 IU ml-1. To optimize a purification protocol for ovine anti-tetanus toxin, we used four procedures; weak anion (DEAE-Sephadex), weak cation (CM-Sephadex), ammonium sulfate precipitation alone or in combination with caprylic acid. Fifty percent saturation with ammonium sulfate combined with caprylic acid gave us the highest yield of protein with specific activity and the purest Fab product.