Effective transcutaneous immunization by antigen-loaded flexible liposome in vivo.
BACKGROUND
Transcutaneous vaccines have received wide attention due to their easy-to-use, needle-free, noninvasive delivery. However, the novel barrier function of stratum corneum hinders the transport of antigen and adjuvant in transcutaneous immunization. Novel nanoscale delivery systems employing, for example, liposomes and nanoparticles, have been widely investigated to overcome the penetration barrier of stratum corneum for effective transcutaneous immunization.


OBJECTIVE
The objective of this study was to prepare two types of flexible liposomes and determine their efficacies for the transcutaneous delivery of antigen and the subsequent immune response induced in vivo.


METHODS
Ovalbumin (OVA) liposome-based transcutaneous vaccines were prepared using reverse-phase evaporation and film-dispersion methods. Particle sizes and antigen encapsulating efficiency were then evaluated. After application to bare mouse skin, topical sites were examined for the presence of fluorescence-labeled liposome. The efficacy of the transcutaneously delivered OVA-loaded flexible liposome in activating the immune responses was investigated by detecting serum immunoglobulin G levels. The influence of an adjuvant, imiquimod, in the transcutaneous immunization was also tested.


RESULTS
Two flexible liposomes with well-encapsulated OVA were successfully prepared by film-dispersion or reverse-phase evaporation methods. The sizes of the prepared flexible liposomes ranged from 200 to 400 nm. In vivo, the fluorescence-labeled liposome was detected in hair-follicle ducts, indicating that the flexible liposome can penetrate the skin barrier through the hair follicles. Upon transcutaneous administration, the OVA-encapsulated flexible liposome elicited a strong immune response similar to that of positive control (ie, OVA solution administrated by subcutaneous injection with Al(OH)(3) as an adjuvant). Co-administration of imiquimod with the OVA-loaded liposome expressed a significant enhancement on the transcutaneous immune responses.


CONCLUSIONS
Results of this study highlight the nanoscale formulation, flexible liposome, as a promising carrier for the transcutaneous delivery of antigen proteins. Imiquimod was shown to be an effective adjuvant as a transcutaneous immunization enhancer with the potential for transcutaneous vaccine development.
Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China.
Ni
N
Li
Li-Hua
LH
Peng
Xi
X
Chen
Shinsaku
S
Nakagawa
Jian-Qing
JQ
Gao
D000279:Administration, Cutaneous; D000818:Animals; D000941:Antigens / Q000008:administration & dosage*; D005260:Female; D007114:Immunization / Q000379:methods*; D008081:Liposomes / Q000008:administration & dosage* / Q000737:chemistry*; D008422:Materials Testing; D051379:Mice; D008807:Mice, Inbred BALB C; D012869:Skin Absorption / Q000187:drug effects / Q000276:immunology*; D013552:Swine
D000941:Antigens; D008081:Liposomes