Encapsulation of adenoviral vectors into chitosan?bile salt microparticles for mucosal vaccination

Encapsulation of adenoviral vectors into chitosan?bile salt microparticles for mucosal vaccination
Received 30 December 2005; revised 4 April 2006; accepted 6 April 2006. Available online 6 June 2006.
Maria Helena Lameiroa, Rita Malpiqueb, Ana Carina Silvab, Paula M. Alvesa, b and Eurico Meloa, c,
Journal of Biotechnology
Volume 126, Issue 2 , 1 November 2006
Copyright ? 2006 Elsevier B.V. All rights reserved.
aInstituto de Tecnologia Qu?mica e Biol?gica, Oeiras, Portugal
bInstituto de Biologia Experimental e Tecnol?gica, Oeiras, Portugal
cInstituto Superior T?cnico, Universidade T?cnica de Lisboa, Lisboa, Portugal
The objective of this study is the incorporation of adenoviral vectors into a microparticulate system adequate for mucosal delivery. Microencapsulation of the vectors was accomplished by ionotropic coacervation of chitosan, using bile salts as counter-anion. The process was optimized in order to promote high encapsulation efficiency, with a minimal loss of viral infectivity. The maintenance of sterility during all the encapsulation procedure was also taken into account. The principle relies on the simple addition of a solution containing adenoviral vectors to a solution of neutralized chitosan, under stirring. Some surfactants were added to the chitosan solution, to improve the efficiency of this process, such as Tween? 80, and Pluronic? F68 at 1% (w/v). Encapsulation efficiency higher than 84% was achieved with formulations containing sodium deoxycholate as counter-anion and Pluronic F68 as dispersant agent. The infectivity of the adenoviral vectors incorporated into microparticles was assessed by release assays in PBS and by direct inoculation in 293 and Caco-2 cells. The release in aqueous media was negligible but, when in contact with monolayers of the cells, an effective release of bioactive adenovirus was obtained. Our work shows that encapsulation in microparticles, not only appear to protect the adenovirus from the external medium, namely from low pH, but can also delay their release that is fully dependent on cell contact, an advantage for mucosal vaccination purposes. The formulations developed are able to maintain AdV infectivity and permit a delayed release of the bioactives that is promoted by digestion in situ of the microparticles by the cell monolayers. The onset of delivery is, that way, host-controlled. In view of these results, these formulations showed good properties for mucosal adenovirus delivery.
Keywords: Adenoviral vectors; Microparticles; Mucosal immunization; Chitosan; Bile salts

Corresponding author at: Instituto de Tecnologia Qu?mica e Biol?gica, Apartado 127, P-2780 Oeiras, Portugal.
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