Stabilizing the immunizing antigen of foot-and-mouth disease virus by fixation with formaldehyde

Foot-and-mouth disease and beyond: vaccine design, past, present and future

The first experimental vaccines against foot-and-mouth disease were made in 1925 by Vallee, Carre and Rinjard using formaldehyde inactivation of tongue tissue from cattle infected with the virus. This method was essentially unaltered until the late 1940s when the important experiments by Frenkel in Holland showed that the quantities of virus required for vaccine production could be obtained from fragments of tongue epithelium incubated in vitro following infection with the virus. This major step made possible the comprehensive vaccination programmes which followed in Western Europe and which, in turn, resulted in the elimination of the disease from that part of the world by 1989. This spectacular success has led many to question whether other kinds of vaccine are required to control the disease worldwide. Such reservations ignore the danger to the environment associated with the growth of large amounts of virus. This can never be a zero-risk situation. Consequently, a vaccine which is not based on infectious virus as starting material has many attractions from safety considerations alone. In addition, a vaccine based on more fundamental considerations would not only be more aesthetically satisfying but could possibly provide an understanding at the molecular level of antigenic variation, still a problem in the control of the disease. The advances in our knowledge of the structure of the virus and the fragments which elicit a protective immune response now allow us to envisage a vaccine which does not require infectious virus and which protects against the multiple serotypes of the agent. Since antigenic variation is still a major problem in the control of the disease by vaccination, such a product would have important advantages over the current vaccines.

A multistep procedure for the chemical inactivation of human immunodeficiency virus for use as an experimental vaccine

The kinetics of inactivation of four different strains of HIV-1 (RF, MN, SF2 and IIIB) by beta-propiolactone (BPL) and binary ethylenimine (BEI) were studied under various conditions. The conditions that would be required for the reduction of virus infectivity by at least 10(20) TCID50 ml-1 were estimated on the basis of the experimental rates of inactivation obtained. A multiple step procedure including treatment with 0.2% BPL, 0.05% sodium cholate, 10 mM BEI and 0.02% formaldehyde was designed to inactivate HIV-1 for use as an experimental vaccine. Complete inactivation of virus infectivity was confirmed by prolonged cell culture. The experimental vaccine preparation was analysed for the presence of HIV-1 proviral DNA utilizing the polymerase chain reaction. After treatment with both BPL and BEI proviral DNA was detected in one of four samples using primers encoding a 244 bp segment of the pol region of the viral genome. Proviral DNA could not be detected in any of the four samples using primers encoding segments of > 400 bp in the gag and reverse transcriptase region.

Structure and immunogenicity of experimental foot-and-mouth disease and poliomyelitis vaccines

The physico-chemical properties and immunogenicity of experimental vaccines against foot-and-mouth disease (FMD) and poliomyelitis, prepared by treatment of the viruses with N-acetylethyleneimine (AEI), formaldehyde or neutral red, have been studied. None of these reagents affects the rate of sedimentation of the particles or their reaction with antibody against the major immunogenic sites. FMD vaccines prepared by inactivation with AEI or neutral red, behaved like the untreated virus, in that they were disrupted on lowering the pH below 7. The RNA of the AEI-inactivated virus was degraded into slowly sedimenting molecules. Unlike AEI-inactivated virus, from which all the RNA could be extracted with phenol-SDS, the recovery from the neutral red inactivated virus was variable and was sometimes as low as 40%; this RNA gave a heterogenous profile in sucrose gradients. The capsid proteins in the AEI preparation migrated in SDS-PAGE to the same positions as those of untreated virus, but in the neutral red preparation there was evidence of cross-linking. In contrast, the formaldehyde-inactivated vaccine was stable below pH 7 and the RNA could not be released by extraction with phenol-SDS at pH 5, because the capsid proteins had become cross-linked and/or linked to the RNA. As with foot-and-mouth disease virus (FMDV), poliovirus which had been inactivated with formaldehyde did not release its RNA on extraction with phenol-SDS and the capsid proteins were also cross-linked. Surprisingly, although AEI cleaved the viral RNA slowly in situ, the virus was no longer infectious after 6 h. Neutral red did not reduce the infectivity of the virus. All of the preparations gave similar levels of neutralizing antibody after a single inoculation. The high levels obtained with the formaldehyde-inactivated vaccines have implications for the processing of fixed particles by the antigen-presenting cells.

Prospects for improved foot and mouth disease vaccines

Improved foot and mouth disease (FMD) vaccines which have increased efficiency and stability are highly desirable. Work which aims to increase the stability of FMD virus particles for vaccine use is described and the use of these particles and of antigenic fragments of the virus for controlled release vaccine products is considered.

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.

The effect of acetylethyleneimine upon a strain of inactivated foot-and-mouth disease virus stored at 4 degrees C

The presence of either thiosulphate-neutralized or free AEI was shown to degrade inactivated foot-and-mouth disease virus Type O (Hong Kong) antigen during storage at 4 degrees C. Deterioration was evident after 20 weeks of storage and little antigen remained at 36 weeks. Optimum stability was obtained by removing the residual inactivant immediately after inactivation.

Inactivation of foot-and-mouth disease virus with ethylenimine

Foot-and-mouth disease virus (FMDV) was inactivated by ethylenimine (EI) at three concentrations and two temperatures. Comparison of inactivation kinetics and the antigenic and immunogenic potency of EI and N-acetylethylenimine (AEI)-inactivated FMDV indicates that EI has nearly optimal characteristics as an inactivant for FMDV vaccine preparation. Although AEI-inactivated FMDV has proved to be a potent specific immunogen, an equivalent percentage of EI inactivated FMDV at substantially faster rates and produced an equally potent immunogen. In addition, EI inactivated FMDV at rates that were essentially linear throughout the loss of nearly all measurable infectivity.