Nanotechnology in vaccine development to combat bacterial livestock diseases

Prophylaxis is undoubtedly the best strategy for disease management, particularly to combat acute and per acute fatal diseases but effective commercialized vaccines are unavailable for several economically important livestock diseases. And if available, the conventional inactivated vaccines often suffer from the limitations such as high antigenic biomass requirement, denaturation of conformational epitopes, and residual virulence, whereas live attenuated vaccines carry the drawbacks of reversion to virulence and cold-chain maintenance. Although new-generation subunit vaccines have eliminated the concern of safety but often require adjuvantation and multiple doses to elicit satisfactory level of protective immune response. Classical adjuvants such as alum and Freund’s complete and incomplete adjuvants (CFA and IFA) also have some limitations such as toxicity, hyperreactivity, eliciting strong humoral but poor cellular immunity, and others. At this juncture, incorporation of suitable nanoparticles (NPs) in vaccine formulations has extended multi-arrayed benefits. As vaccine delivery system, nano-encapsulation of antigens has extended several advantages in terms of reducing antigenic biomass requirement, stabilization of labile protein or nucleic acid cargo, targeted delivery and sustained release of antigen(s), improved pharmacokinetic properties, biodegradability and biocompatibility, etc. Polymeric NPs, liposomes, and dendrimers have already been employed in nanovaccine formulation as delivery vehicle against various bacterial infections including Salmonella, Brucella, Mycobacterium, E. coli, etc. with promising outcome. Various NPs have also been used as nano-adjuvants to potentiate different multi-subunit/fusion antigens such as aluminum hydroxide NPs with Bacillus anthracis and Mycobacterium tuberculosis antigen EsxV, oil in water adjuvants MF59 and AS03, and liposome-based adjuvants AS01E and CAF01 with Mycobacterial fusion antigens. These nano-adjuvants often elicit strong humoral as well as cell-mediated immune response which is one of the notable advantages of using NPs in vaccine formulations. Incorporation of NPs can also increase the room temperature stability of vaccines to surmount the necessity of cold-chain maintenance. Although nanovaccines have yet to full-bloom but already ushered enough promise toward a bright prospect in near future.