Approaches to Enhance the Potency of Vaccines in Chickens

Abstract

Outbreaks of avian pathogens such as Newcastle disease virus, avian influenza virus, and salmonella have a major impact on economies and food security worldwide. Some pathogens also pose a significant zoonotic potential, especially avian influenza viruses. Vaccination plays a key role in controlling many poultry diseases, and there are many vaccines licenced in the United Kingdom for diseases of poultry caused by viruses, bacteria, and parasites. However, these vaccines often do not provide complete protection and can cause unwanted side effects. Several factors affect the potency of poultry vaccines, including the type of vaccination used, the mechanism of delivery, and the use of adjuvants. Advancements in technology have led to the study and development of novel vaccines and vaccine adjuvants for use in poultry. These induce stronger immune responses compared with current vaccine technology and have the potential to protect against multiple poultry diseases. This review aims to discuss the existing poultry vaccine technology; the effect of delivery mechanisms on vaccine efficacy; the use of current and novel adjuvants; the ability to target antigens to antigen-presenting cells; and the use of probiotics, multivalent vaccines, and nanotechnology to enhance the potency of poultry vaccines.

Keywords: adjuvants; antigen-targeted vaccine; nanotechnology; poultry; probiotics; vaccine potency.

Figure 1

Methods used in the poultry industry for vaccinating chickens. Created with BioRender.com.

Figure 2

Illustration of different types of oil emulsions. (a) Water-in-oil emulsion (W/O). This method traps the antigen (Ag) inside water droplets. This protects the structure of the Ag, allowing for slow antigen release due to the breakdown of the oil. This prevents rapid clearance of the antigen, which allows for increased immune cell recruitment and antigen processing. (b) Oil-in-water (O/W) emulsion. Here, the oil helps attract monocytes and chemokines to the injection site. This promotes the differentiation of monocytes into dendritic cells (DCs) and stimulates a strong cellular immune response. (c) Water in oil in water (W/O/W). Here, the antigen is in both the oil and water phases, so the antigen is both taken up quickly from the water phase but also slowly released from the internal water phase. The breakdown of the oil also helps with the attraction of monocytes and chemokines to help induce a strong cellular immunity. Created with BioRender.com.

Figure 3

Overview of 10 known chicken TLRs. TLRs are anchored membrane receptor proteins that are expressed on APCs. They recognise conserved components on microbes and, once activated, result in a proinflammatory response and induce the expression of cytokines involved in immune cell differentiation. This helps the induction of cell-mediated and humoral immunity. IFN = interferon, TLR = Toll-like receptor, LPS = lipopolysaccharide. Created with BioRender.com.

Figure 4

Antigen-presenting cell targets that have been validated in poultry vaccines. CD11c is a β-integrin molecule shown to be on mammalian dendritic cells, neutrophils, macrophages, and NK cells. In chickens, CD11c has been found on dendritic cells and macrophages but has not been well studied. DC-pep means peptides that can recognise dendritic cells from a larger leukocyte population. CD40 is a co-stimulatory cell surface receptor from the tumour necrosis factor family. In humans, CD40 is expressed on dendritic cells, monocytes, macrophages, and B cells. In chickens, CD40 has been detected on monocytes, macrophages, DCs, and B cells. CD83 is an immunoglobulin molecule which, in mammals, is used as an activation molecule. In mammals, CD83 has been found on activated NK cells, monocytes, macrophages, neutrophils, dendritic cells, and B cells. In chickens, CD83 has been found on dendritic cells but has not been well studied. DEC-205 is an endocytic receptor which, in mammals, is expressed on DCs, macrophages, and B and T cells. In chickens, DEC-205 has been detected on DCs, B cells, and T cells but has not been well studied. Figure created with BioRender.com.

Figure 5

Illustration of ligand-based targeting of APCs. PRR ligands can be chemically or recombinantly bound to antigens. TLR ligands are the most used for antigen-targeting studies as these both enable the targeting of antigens to the APC and have adjuvant properties. The antigen–TLR conjugate vaccine binds to its receptor on the APC; this induces receptor-mediated endocytosis. This induces APC maturation and allows for T-cell presentation via either the MHC-I or MHC-II pathway. MHC-I presentation of the antigen to CD8 T cells results in the development of a population of antigen-specific cytotoxic T cells, which are capable of lysing infected cells. MHC-II presentation of the antigen to CD4 T cells, which present the antigen to B cells, results in the development of antigen-specific antibody production. Created with BioRender.com.

Figure 6

Illustration of ligand-based targeting of APCs. Full antibody or antibody-based fragments can be chemically or recombinantly bound to antigens. APC specificity is determined via the use of anti-receptor antibodies, which target the desired receptor on an APC. The antigen–antibody complex will bind to its targeted receptor on an APC. This induces receptor-mediated endocytosis. This induces APC maturation and allows for T-cell presentation via either the MHC-I or MHC-II pathway. MHC-I presentation of the antigen to CD8 T cells results in the development of a population of antigen-specific cytotoxic T cells, which are capable of lysing infected cells. MHC-II presentation of the antigen to CD4 T cells can activate B cells and results in the development of antigen-specific antibody production. Created with BioRender.com.