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Anno domini 1881: Louis Pasteur (1822–1895) was on track to become the first leading vaccinologist at the time and to win the race against the development of the first artificial attenuated vaccine to his rival, the veterinarian Henry Toussaint. One year ago, he developed a vaccine against avian cholera (fowl cholera). Pasteur isolated the causative agent of this zoonotic disease, Pasteurella multocida (a gram-negative, nonmotile coccobacillus). The economic losses caused by avian cholera were enormously at this time and also today.

It’s a long way for an antigen from the discovery to the final product with application to the patient.

The original scientific strategy behind vaccinology has historically been to “isolate, inactivate, and inject,” first invoked by Louis Pasteur. Subsequently, this empirical approach dominated the vaccine development over 80 years. The recombinant DNA technology arised, and in 1980 the first recombinant vaccine against hepatitis B virus was presented. With MenACWY in 1990, a quadrivalent meningococcal meningitis vaccine, in which the capsular polysaccharides from Neisseria meningitidis serogroups A, C, W, and Y are conjugated to the diphtheria toxin mutant CRM197, the first glycoconjugate vaccine, was approved. Finally, MenB, meningococcal B vaccine, was the first genome-derived vaccine in 2010 developed by reverse vaccinology. Table 6.1 highlights these technological progresses.

The original scientific strategy behind vaccinology has historically been to “isolate, inactivate, and inject,” first invoked by Louis Pasteur.

Equine arteritis virus (EAV) is the causative agent of the equine viral arteritis. It is a small RNA virus with a linear, non-segmented plus RNA genome. EAV is a member of the Arteriviridae family that includes porcine reproductive and respiratory syndrome virus (PRSSV), simian haemorrhagic fever virus (SHFV) and lactate dehydrogenase virus (LDV). The viral transmission is via respiratory and reproductive routes. Clinical signs in horses vary, and severe infection can lead to abortions in pregnant mares or neonatal foal death. The aim of this study was to investigate the development of the immune response in horses after immunization with a DNA vaccine harbouring and expressing EAV Open Reading Frames (ORF) 2, 5, and 7, in combination with equine interleukin 2 (eqIL2). Three boosters followed the basic immunization in two-week intervals. Each immunization was a combination of gene gun and intramuscular injection. All horses developed a high titer of neutralizing antibodies after basic immunization within 2 weeks. Remarkably, this immune response was found to be independent of the age of animals. The youngest horse was six-years old, and the oldest twenty-two years old. A remarkable difference in the immune response between the young and old were not observed. The duration of immunity was investigated during a period of one year. After 12 months, neutralizing antibodies were still detectable in all the vaccinated horses.

Equine arteritis virus (EAV) is a member of the Arteriviridae family, that includes lactate dehydrogenase-elevating virus (LDV), porcine reproductive and respiratory syndrome virus (PRRSV), and simian haemorrhagic fever virus (SHFV). Equine arteritis is a contagious disease of horses and is spread via respiratory or reproductive tract. The objective of the present study is to evaluate the possibility for developing a model system for prevention horses against an EAV infection by DNA vaccination. A cDNA bank from the RNA of EAV was established. This gene library contains the translation unit of the EAV open reading frames (ORF) 1 to 7. The identity of the cDNA was confirmed by nucleotide sequence analysis. Using this defined EAV cDNA gene library the cDNA sequence of the viral ORFs were molecularly cloned into the corresponding sites of well characterized and powerful expression vectors (pCR3.1, pDisplay, and/or pcDNA3.1/HisC).

Experiments that exposed influenza virus (H5N1)–infected cats to susceptible dogs did not result in intraspecies or interspecies transmission. Infected dogs showed increased body temperatures, viral RNA in pharyngeal swabs, and seroconversion but not fatal disease.

Current vaccines can be divided into “live,” “recombinant” and “killed” vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a “cold chain.” Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed “DNA-, genetic- or nucleic acid-immunization,” is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

International audience; Equine Arteritis Virus (EAV) belongs to the Arteriviridae and causes viral arteritis in horses. In an attempt to develop novel and save therapies against the infection it was tested whether EAV is susceptible to RNA interference (RNAi) in an equine in vitro system. Horse cells were transfected with chemically synthesized small interfering RNA oligonucleotides (siRNAs) and challenged with EAV. Application of these siRNAs led to a significant protection of the cells, and virus titers decreased drastically. siRNAs derived from DNA plasmids expressing small hairpin RNAs (shRNAs) were also effective. The protection was most pronounced with two siRNAs targeting the open reading frame 1 (coding for non-structural proteins), whereas siRNAs targeting sequences for several structural proteins had less or no effect. In addition, it was investigated whether RNAi could be used to treat cells with an already established viral infection. Only application of the siRNAs shortly after viral challenge led to significant survival rates of the cells, whereas transfection at later time points caused much less benefit for the cells. These findings are discussed in a perspective of using RNAi as a therapeutic approach to combat EAV.

Highly pathogenic avian influenza virus (HPAIV) H5N1 of Asian origin continues to circulate in poultry and wild birds, causing considerable concern for veterinary and public health in Asia, Europe and Africa. Natural transmission of HPAIV H5N1 from poultry to humans, resulting in infections associated with high mortality, and from poultry or wild birds to large felids and domestic cats has been reported. Experimental infection of cats with HPAIV H5N1 derived from a human patient resulted in lethal disease. The role of cats in the adaptation of HPAIV H5N1 to mammals and vaccination regimens for the eventual protection of cats, however, remain to be elucidated. Here, it was shown that cats can be protected against a lethal high-dose challenge infection by an inactivated, adjuvanted heterologous H5N6 avian influenza virus vaccine. The challenge HPAIV H5N1 was derived from a naturally infected cat. In non-vaccinated cats, low-dose exposure resulted in asymptomatic infections with minimal virus excretion. As diseased cats can transmit the infection to naïve contact animals, the epidemiological role of H5N1-infected cats in endemically infected areas as a link between wild birds, poultry and humans needs close inspection, and vaccination of cats should be considered to reduce possible human exposure.