Large-scale purification of animal viruses in the RK-model zonal ultracentrifuge. I. Rabies virus

Process standardization for optimal virus recovery and removal of substrate DNA and bovine serum proteins in Vero cell-derived rabies vaccine

Purification of a rabies vaccine by a single zonal centrifugation run was replaced by two runs with optimal standardization of the sucrose density gradient. As a result, significant reductions in the levels of substrate DNA and bovine serum protein in the Vero cell-derived human rabies vaccine were achieved. Following many trials, for the first run, loading of the 3.2-l capacity K-3 rotor with 1800 ml of 60% sucrose solution and 1400 ml of vaccine PBS buffer solution gave a satisfactory linear gradient. However, after the first run, the substrate DNA and bovine serum contents exceeded the required levels. After protamine sulphate and Tween-80 treatment of the concentrated inactivated material, a second run using the same procedure as in the first run was tried. However, these purification procedures resulted in low virus recovery. To achieve optimal virus recovery, and removal of substrate DNA and bovine serum protein, the peak fractions from the first run as indicated by the haemagglutination, sucrose concentration, and optical density values were pooled and the sucrose concentration of the pooled fractions was increased to 60%. A second (flotation) run was then carried out. Using this method, the virus recovery rate was more than 95% that of the first run, and the levels of cellular DNA and bovine serum protein were well within the acceptable limits of less than 100 pg/dose and one part per million, respectively. The substrate DNA was quantified by both radioactive labeling and non-radioactive biotin labeling methods. For the quantification of calf serum protein, a counter-immunoelectrophoresis method was developed and effectively applied. A potency assay was performed using the National Institutes of Health (NIH) and well-standardized in vitro single radial immuno diffusion (SRD) methods. Finally, an immunogenicity study was conducted with human volunteers and the results were confirmed by a rapid fluorescent focus inhibition test (RFFIT).

Enzyme-linked immunosorbent assay (ELISA) using staphylococcal protein A for the measurement of rabies antibody in various species

An ELISA was developed using staphylococcal protein A linked with horseradish peroxidase for detecting IgG antibody of rabies virus in human and carnivore sera (80 human, 270 fox, 40 cat, 35 marten, 5 badger and 4 polecat sera were tested in the present work). In comparison with the serum neutralization (SN) test in cell culture, close overall agreement was obtained particularly in human and cat sera (97.5%). Two post-vaccination human sera were found positive with ELISA values of 2.16 and 2.65 IU/0.2 ml, but with SN titers less than 1:10. All prevaccination human sera were found negative by both tests. Regression analysis on 30 post-vaccination human sera revealed better correlation between ELISA and SN test at a serum dilution of 1:100 than at lower serum dilutions of 1:80 or 1:20. The correlation coefficient (r) was 0.73 (p less than or equal to 0.0001).

Absence of myelin basic protein in an improved purified duck embryo rabies vaccine

The encephalitogenic potential of rabies vaccines prepared from nervous tissue is a result of the presence of myelin basic protein. Vaccines prepared from duck embryos are economical and efficient, but, occasionally, cases of allergic encephalomyelitis have been reported. An improved rabies vaccine has been developed that contains the classical Pitman Moore strain of rabies virus grown in embryonated duck eggs. This vaccine has been highly purified and enriched in immunologically effective rabies virus glycoprotein antigen. We have searched for the presence of myelin basic protein using sensitive radioimmunological and immunoblotting techniques. Whereas the classical duck embryo rabies vaccine contained small amounts of myelin basic protein, in the improved purified duck embryo rabies vaccine, none could be detected.

A new inactivated tissue culture rabies vaccine for use in man. Evaluation of PCEC-vaccine by laboratory tests

A new inactivated rabies vaccine (purified chick embryo cell vaccine) has been developed using the Flury LEP-C 25 strain of rabies virus propagated in primary chick embryo cell cultures. The antigen was purified and concentrated by continuous density gradient centrifugation and inactivated by betapropiolactone. This vaccine was tested for innocuity, tolerability and protective capacity in a series of laboratory tests and compared with human diploid cell strain (HDC)-vaccines of similar antigenicity. The results indicated that this new vaccine was excellently tolerated and that its protective activity met the high standard of HDC-vaccine, conditions which were imposed on this vaccine before entering clinical trials in man.

Enzyme-linked immunosorbent assay: a rapid reproducible test for the measurement of rabies antibody

An enzyme-linked immunosorbent assay (ELISA) was developed for detecting IgG antibodies to the Pitman Moore strain of rabies virus in sera from subjects immunised wih HDCS vaccine. End-point titres of antibody were determined using a pocket calculator preprogrammed to analyse absorbence values of test sera and negative controls. The assay was highly reproducible, and very close agreement was achieved when the results were compared with those of the mouse neutralization test. Rabies enzyme-linked immunosorbent assay is easy to perform, the results are obtained within 48 hours, and because it employs inactivated virus, the test can be used safely without special containment facilities.

Purification, concentration and evaluation of rabies virus antigen

A number of concentration and purification procedures for rabies virus antigen have been developed during the last decades but only ultrafiltration and density gradient centrifugation have been found suitable for large scale production. The antibody binding test developed by Arko, Wiktor and Sikes was modified and was found useful for evaluation of inactivated antigen-concentrates. This test was used as an 'in process' control. Three examples of practical experience are reported and discussed.