Thermostability and Immunostimulatory Activity of Cationic Liposome-based Newcastle Disease Virus Vaccine

Abstract

Cold storage is a huge challenge in maintaining vaccine potency especially in low and middle income countries (LMIC). The aim of this research was to investigate the heat and freeze-thaw stability of Newcastle disease virus (NDV) vaccine encapsulated in 1,2-dioleoyl-3-trimethyl ammonium propane (DOTAP) cationic liposomes as well as its immunostimulatory activity. DOTAP cationic liposomes were prepared using the thin-film hydration technique and characterized for morphology, particle size, polydispersity index, zeta potential and encapsulation efficiency. Experimental birds were challenged with Herts 33 velogenic strain of NDV. Haemagglutination inhibition test was used to assess the formation of antibodies in the birds. The cationic liposomes were further stored at 28 oC or subjected to freeze-thaw cycles for 7 weeks and then assessed for stability using the same parameters of particle size, polydispersity index, zeta potential, morphology, antibody titre or differential white blood cell count. Using TEM, the morphology of the liposomes was found to be spherical, and using Malvern Zetasizer, particle size was in the nanosize range. Zetapotential and polydispersity indices were positive and below 0.1. The HI test showed that the DOTAP cationic liposomes stimulated a higher titre of antibodies than the commercial vaccine. Heat and freeze-thaw stability studies after 7 weeks of storage showed slight aggregation and elevated particle sizes and wider distribution. The HI titer was appreciably lower after secondary immunization with the DOTAP cationic liposomes stored at 28 oC but elevated for the product kept at freeze-thaw conditions. The immunized birds were 100 % protected from the virulent strain of NDV. In conclusion, the development of the DOTAP-cationic liposomes encapsulating NDV vaccine administered orally was found to be more stable under freeze-thaw conditions than when it was exposed to heat for 7 weeks. The liposome-based vaccine had more immunostimulatory effects than the commercial sample.