Journal of Vaccine Research 2024, Vol.14, No.1, 10-16 http://medscipublisher.com/index.php/jvr 13 2.3.5 DNA vaccines DNA vaccines trigger an immune response by introducing the DNA sequence of the pathogen into host cells. DNA vaccines can deliver the pathogen's DNA directly into host cells through methods like injection, electroporation, or gene gun. Once the DNA enters the cells, host cells begin producing antigenic proteins of the pathogen, thereby activating the immune system. DNA vaccines have advantages in terms of ease of synthesis, storage, and the ability to elicit both cellular and humoral immune responses (Shin and Yoo, 2013). 2.3.6 Viral vector vaccines Viral vector vaccines use viruses as carriers to introduce the antigenic genes of the pathogen. Once the virus enters host cells, it releases antigens of the pathogen, activating the immune system. Viral vector vaccines can simulate the actual virus infection process, triggering long-lasting immune protection. Some common viral vectors include adenoviruses, herpes viruses, and recombinant Newcastle disease viruses, among others. 2.3.7 Combination vaccines Combination vaccines combine antigens from multiple pathogens to provide immune protection against several diseases. Combination vaccines can reduce the number of vaccinations needed and simplify management while offering comprehensive immune protection. For example, some canine distemper vaccines also include antigens for canine infectious hepatitis and canine parvovirus. 2.3.8 Others Adjuvanted vaccines have adjuvants added to enhance immune responses. Adjuvants can facilitate antigen absorption and transport, activate immune cells, and increase the vaccine's duration. Commonly used adjuvants include aluminum salts, oil emulsions, and aluminum hydroxide, among others. Glycoprotein vaccines use surface glycoproteins of pathogens as antigens. Glycoproteins play crucial roles in many pathogens, such as the hemagglutinin protein in influenza viruses. Glycoprotein vaccines can activate humoral immune responses and possess broad immunogenicity. Oral vaccines are administered to animals through oral ingestion, activating the immune system via the host's intestinal mucosa. Oral vaccines can mimic the actual pathogen infection route and offer the advantages of convenience, ease of use, and dissemination. 3 Research Status and Challenges of Animal Vaccines 3.1 Current status of animal vaccines The research and development of animal vaccines have a long history, and traditional techniques mainly include inactivated vaccines, live vaccines, and subunit vaccines preparation technologies. The current research status of animal vaccines exhibits characteristics such as technological innovation, application innovation, regulation, and standardization. In the future, with advances in technology and changes in societal demands, research on animal vaccines will also present new trends and opportunities (Wang et al., 2010). Research on animal vaccines has always been an important focus in the fields of animal health and human food safety. Currently, new technologies such as genetic engineering, nanotechnology, and adjuvant technology are widely applied in the development of animal vaccines. For example, genetic engineering technology allows the insertion of foreign antigen genes into pathogens, enabling the pathogens to produce more antigens and thereby enhance the vaccine's efficacy. Simultaneously, nanotechnology can encapsulate pathogen antigens within nanoparticles, improving the stability and immunogenicity of the vaccine. Additionally, adjuvant technology can enhance the immune effectiveness of vaccines and improve their safety (Meeusen et al., 2007; Akkermans et al., 2020) (Figure 2).
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