WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2016 31 Polymeric nanoparticles have the capacity to encapsulate, adsorb or conjugate any foreign material within itself or on its surface. Nanoparticles used in vaccine development usually range from 2-1000 nm. There are synthetic and natural polymers that are biocompatible and usually biodegradable, an essential property in safe vaccine development. Poly (d, l-lactide-co-glycolide) (PLG), Poly (d, l-lactide-coglycolic acid) (PLGA), Poly (g-glutamic acid) (g-PGA), Poly (ethylene glycol) (PEG), Polystyrene are some of the synthetic polymeric nanoparticles. Chitosan and inulin are natural polymeric nanoparticles. (Liang et al. 2014, Nirmal et al. 2014). Inorganic nanoparticles are potential oral vaccine carriers due to their attractive physical and chemical properties. Nanoparticles used in vaccine development usually range from 2-1000 nm. These nanoparticles are biocompatible, however not biodegradable. The advantages of inorganic nanoparticles are the rigidity and controlled synthesis (Liang et al. 2014), better colloidal stability, higher antigen encapsulation and better targeted delivery. Gold nanoparticles, Carbon nanotubes (CNT’s), Silica nanoparticles (SiNP’s) and calcium phosphate nanoparticles are examples of inorganic nanoparticles. Nanoliposomes have been well documented for their diverse ability to deliver various hydrophilic and lipophilic antigens. These are formed by nontoxic and biodegradable self-assembled structures of phospholipids consisting of an internal aqueous core entrapped by a lipid bilayer. The size usually ranges from 100-400 nm. Liposome-polycation-DNA nanoparticles (LPD) and Interbilayer-crosslinked multilamellar vesicles (ICMVs) are some of the liposome nanoparticle formulations. Immunostimulating complexes (ISCOMs) are self-assembling spherical cage-like structured particulate complexes, formed by saponin adjuvant Quil A, phospholipids, cholesterol and antigens. Immunostimulating complex used in vaccine development usually are 40 nm. ISCOMATRIX is a common immunostimulating complex lacking antigen. Virus like particles are self-assembling nanoparticles, formed by biocompatible capsid proteins. They are the ideal nanovaccines because they lack the infectious nucleic acid but have the evolved structure of the virus to induce immunity. Nanoparticles used in vaccine development usually range from 20-800 nm. TABLE 1. Merits and demerits of nanoparticles. NANOPARTICLE SYSTEM MERITS DEMERITS Polymeric nanoparticles Inorganic nanoparticles Nanoliposomes ISCOMS Virus-like particles Nanoemulsions • Better immunogenicity can be obtained by easy modification of surface properties • Biodegradable and targeted antigen delivery • Easy to modify, less chances of premature release and better protection of adsorbed antigens • Possess intrinsic adjuvant properties • Accommodates both hydrophilic and lipophilic antigens • Relatively stable in gastrointestinal fluids when modified • Easy to encapsulate • Built-in adjuvant property of Quil A • Possess self-adjuvant properties • Mimics original virus and high gastrointestinal stability • Possess self-adjuvant properties • Encapsulates both hydrophilic and lipophilic antigens • Low aqueous solubility and synthesis require use of organic solvents • Low antigen loading • Premature release of antigens • Insufficient antigen protection • Low aqueous solubility and low biodegradability • Low mucus penetration • Limited antigen loading • Poor gastrointestinal stability of naked liposomes • Do not form depot • Difficult to incorporate hydrophilic antigens • Lack of reproducibility Premature release of antigens and poor gastrointestinal stability The most investigated nanoparticles in fish vaccine research are polymeric chitosan and PLGA nanoparticles. Chitosan nanoparticles have been used for the development of fish vaccines, for example the inactivated virus vaccine against infectious salmon anemia virus (ISAV) that incorporates the DNA coding for ISAV replicase as an adjuvant. (CONTINUED ON PAGE 32)
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