A study of the physical properties of the immunizing antigen of foot-and-mouth disease virus and the effect of various inactivating agents on its structure

Validation of a high performance liquid chromatography method for quantitation of foot-and-mouth disease virus antigen in vaccines and vaccine manufacturing

Foot-and-mouth disease (FMD) is an infectious viral disease that affects the main meat and dairy production animals, including cattle, sheep, goats and swine. It is readily transmissible and countries where the disease is present suffer harsh international trade restrictions on livestock products and serious economic losses. Vaccines are important tools to contain outbreaks and maintain the status of free with or without vaccination, as defined by the World Organization for Animal Health (OIE). The efficacy of vaccines is reliant on the content and integrity of inactivated virus particles. The long-established method to quantify the viral content of vaccines along the manufacturing process and in the final product is the 140S sucrose density gradient analysis. This method has been a valuable tool for many decades. However, it requires gradient preparation for each sample, a lengthy ultracentrifugation and a manual UV reading of the gradient, rendering it highly operator dependent and almost impossible to automate. We present a method to quantify FMDV particles in vaccines and intermediate process samples that is based on separation of components by size exclusion high performance liquid chromatography (SE-HPLC) and measurement of virus by absorption at 254 nm. The method has been extensively validated; it is accurate, precise and linear. It is applicable to all FMDV strains and sample materials and has a good concordance with the 140S test. The proposed method uses off the shelf HPLC equipment and columns. It is easily automated for high throughput operation, affording a useful process analytical technology and a novel tool for control of final product by manufacturers and regulatory agencies.

Correlation of 140S antigen dose with the serum neutralizing antibody response and the level of protection induced in cattle by foot-and-mouth disease vaccines

An analysis was made of data from potency tests on fifteen batches of monovalent foot-and-mouth disease vaccine, comprising five batches each of type O, type A and type C. Regressions were calculated for the relation of percentage protection (probit) versus log 140S antigen dose and for the serum neutralizing antibody titre (log SN50) versus log 140S antigen dose. Type O vaccines required a far higher level (220 ng) of 140S antigen to achieve a 50% protection level (PA50) in cattle than did type A (2.4 ng) and type C (4.36 ng) vaccines. Type O antigen, dose for dose, was as effective at provoking neutralizing antibody as the types A and C antigens. Thus, it would appear that a far higher log SN50 value (2.14) was required for type O vaccines to equate with 50% protection of cattle than was required for type A (1.17) and type C (1.41) vaccines. Prior to 1977, however, the PA50 value for type O vaccine strain was only 1.34 and it was concluded that an antigenic shift was the most likely cause for the large difference between that value and the current PA50 value.

The stability and potency of vaccines prepared from inactivated foot-and-mouth disease virus concentrates

The stability of 146S particles in concentrates of foot-and-mouth disease virus stored at 4 degrees C was similar to that of 146S particles in a conventional virus preparation. Proteolytic degradation of VPl was not observed in the stored conventional virus preparation or inhibitor-supplemented concentrate but was observed in a supplement-free concentrate. The potencies of vaccines made from the conventional and concentrated preparations and stored in parallel at 4 degrees C appeared to decrease after 16 weeks. The vaccines made from the supplement-free concentrate and the Trasylol supplemented concentrate appeared to be at least as potent as the conventional vaccine and were clearly superior to vaccine made from ox serum supplemented concentrate.

The effect of antiserum quality on strain specificity assessment of foot and mouth disease virus by the neutralization reaction

The factors affecting the virus strain specificity of antibody to foot an mouth disease virus prepared by a variety of protocols in several species were evaluated by neutralization tests. The time at which the serum was taken, the antigen dose given, whether or not revaccination had occurred and the animal species in which the sera were prepared, did not appear to affect the strain specificity of serum prepared to inactivated antigens when measured in neutralization tests, probably because of the restricted nature of the antigenic site involved. However, variation was observed with convalescent animal sera or sera from animals which had received trypsin cleaved virus were used. For these reasons banks of reference antisera are prepared as pooled sera using one or two inoculations of inactivated antigen.

Antigenic variation in foot-and-mouth disease: studies based on the virus neutralization reaction

The neutralization reaction is the most appropriate in vitro reference test system for assessing intratypic antigenic variation as it involves the antigenic determinants responsible for virus strain specificity and evoking protective antibody. Antigenic relationships determined in different neutralization test systems were independent of the system used and were assumed to truly reflect antigenic variation. The two-dimensional microneutralization test was found to be appropriate for foot and mouth disease (FMD) virus strain differentiation. To minimize test to test variation, comparisons are performed as matched pairs. The pooled variance of the test system is used to assess the significance of the relationships obtained. Antisera from convalescent animals were less specific than those from vaccinates. Serum quality seemed less critical for the virus neutralization than the complement fixation reaction. A system for FMD virus strain differentiation based on the use of the virus neutralization reaction taking into account the statistical and biological significance of observed r values is recommended.

The evaluation of a physical method for the quantification of inactivated poliovirus particles and its relationship to D-antigenicity and potency testing in rats

The use of a density gradient procedure for the quantification of intact, inactivated poliovirus particles in vaccine preparations is described. The procedure is both sensitive and highly reproducible and the results correlate with those of potency tests in rats and with D-antigen content as measured by ELISA. Because of the occasional ambiguity observed with D-antigen assays, it is suggested that the density gradient procedure will provide valuable additional information for the in vitro assessment of inactivated poliovirus preparations.

Thermal stability of foot-and-mouth disease virus

The thermal stabilities of 146S component of seven strains of foot-and-mouth disease virus were found to differ considerably. Inactivation of infectivity with acetylethyleneimine (AEI) reduced the thermal stabilities of all but one of the viruses. Treatment of AEI inactivated and control virus preparations with glutaraldehyde stabilized 146S particles to a considerable extent, whereas treatment with dimethyl suberimidate was less effective. In similar experiments with 75S, natural empty particles, the thermal stabilities were lower than those of the corresponding 146 S particles. Treatment of 75S particles with AEI appeared to have no direct effect on the protein-protein interactions involved in 75S capsid integrity. As with 146S particles, glutaraldehyde stabilized 75S particles.

Stability and immunogenicity of empty particles of foot-and-mouth disease virus

Three strains of foot-and-mouth disease virus were shown to contain significant amounts of naturally occurring 75S, empty particles as well as the infectious, 140S full particles. One of these strains--A Pando (1970)--was studied in detail. The empty particles from this virus strain were shown to have an observed sedimentation coefficient of 67S in 0.04 M phosphate buffer; they were labile in SDS, non-infectious and probably RNA-free and, on heating, they broke down to 12S subunits as did the 140S particles. The empty particles differed from the full particles in their polypeptide composition since they contained VP0, but there was no evidence for a diminished content of VP4. The 75S particles were shown to be present in significant amounts and to be stable to AEI inactivation. At 4 degrees C they were stable for at least two years. In guinea pigs they were as immunogenic as the 140S particles. The antisera raised against the 75S particles had the same serological specificity in neutralization tests as sera prepared against the 140S particle. It was concluded that the 75S particles from the A Pando (1970) strain of FMD virus may provide as important a contribution as 140S particles to the immunogenicity of inactivated vaccines prepared from this virus strain.