AbstractVaccines have already made a significant impact on global healthcare with the eradication or reduction in disease states; however, further work is required to develop ‘safer’ vaccines by the use of sub-unit antigens. When considering immunisation, whilst the oral route is the most convenient route for drug and vaccine administration, most vaccines are still delivered via an injection. To be able to be given orally, vaccine antigens need to be associated with carrier systems to both protect the antigen from degradation within the harsh gut environment and to improve uptake by appropriate target sites, namely M cells located in the Peyer’s patches, which are responsible for secretory IgA and other mucosal responses. Therefore, niosomes have been considered within this thesis to enhance the protection and delivery of sub-unit vaccines via the oral route and intramuscularly.
Initial work included using Design of Experiments to optimise niosome/ bilosome vesicles prepared from of Monopalmitoyl glycerol (MPG), Synthecol (Chol), Dicetyl Phosphate (DCP) and bile salt in terms of their vesicle size, surface charge, suspension pH and antigen loading. Optimisation studies, demonstrated that the ideal composition was a 5:4:1 ratio of MPG:Chol:DCP respectively. Langmuir balance and differential scanning calorimetry studies also demonstrated that, cholesterol inserts between the lipids within the bilayer hence, preventing crystallisation of the hydrophobic tails of the other surfactants.
Using the optimised niosome formulation, oral biodistribution of these niosomes (3H) and the H3N2 (125I) antigen showed that of the dose administered (t=1h), significantly (p< 0.05) higher antigen (59.8%) was recovered within all organs of the gastrointestinal tract (GIT) when formulated with niosome vesicles compared to the free antigen (38 %). Uptake at the target site of the Peyer’s patches revealed that on average 1.4 % antigen was present within the Peyer’s patches when associated with the niosome vesicles compared to the free antigen dose which demonstrated only 0.4 % antigen was acquired within the Peyer’s patches. Furthermore, uptake within the mesenteric lymph tissues demonstrated 0.7 % antigen recovery when associated with niosomes compared to 0.2 % recovery of the free antigen dose. Hence, uptake studies demonstrated that niosome associated antigen show a 2-fold improved uptake and retention at the target sites compared to administering the free antigen alone. Reduction in vesicle size of the niosomal systems to 2 μm made no significant difference in recovery of either the vesicles or associated antigen in the mesenteric lymph tissue. However, when comparing the Peyer’s patches, whilst there was no significant difference in localisation of antigen, there was a greater recovery of vesicles within the Peyer's patches of the larger 6 μm vesicles (p< 0.05) in comparison to the 2 μm vesicle formulation, which is an indicator of achieving increased mucosal immunity. Within ferrets, the optimised niosomes containing bile salts were shown to lower median temperature differential change and show inflammatory cell counts in nasal washes to be comparable to the commercial vaccine administered intramuscularly after challenge with a clinical H1N1 isolate.
In terms of intramuscular administration, niosomes incorporating H1N1 and H3N2 antigen provided thermostability when stored at elevated temperatures for 3 months at 40 °C confirmed by HAI and ELISA studies when compared to the commercial vaccine. In addition, the association of antigen confirmed the dose sparing ability of niosome preparations to elicit immune responses comparable to the control vaccine doses.
In conclusion, this thesis demonstrates that niosomes can be used as delivery systems for peptides and protein sub-unit antigens by providing antigen protection thereby, enhancing vaccine efficacy when administered orally and intramuscularly.
|Date of Award||12 Jun 2013|
|Supervisor||Yvonne Perrie (Supervisor) & Afzal-Ur-Rahman Mohammed (Supervisor)|
- oral vaccine delivery
- vaccine delivery