Optimization of poly (D-L-lactide-co-glycolide) microsphere production for oral delivery to promote adenovirus stability and intestinal gene transfer
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Adenovirus vectors have demonstrated many of the characteristics necessary to be successfully used as a carrier in a vaccine delivery system. Adenovirus is a good choice for a vaccine carrier because it generates vigorous T and B cell responses to its transgene products. Although current vaccination strategies using this vector have had some success, its use has been constrained by the presence of pre-existing immunity to human serotypes in about 50% of the population. Recently, it has been demonstrated that the induction of these adenovirus-specific neutralizing antibodies that reduce efficacy of initial treatment and booster immunizations does not apply to oral delivery. Adenovirus is a good candidate for oral vaccine delivery because it is capable of inducing antibody responses against an encoded transgene product at mucosal surfaces, which may result in complete systemic and mucosal immunity. Nevertheless, there are some limitations associated with the oral delivery of protein, peptide, and virus-based vaccines. Virus-based vaccines are sensitive to the low pH and presence of proteases in the gut limiting their activity and cellular uptake is also hindered by the rapid transit time of compounds through the intestine. In general, there are two primary strategies for enhancing mucosal immunity: mucosal adjuvants and encapsulation in microparticles. Although several groups have successfully encapsulated adenovirus in polymeric formulations, it has been found that the encapsulation process drastically reduces viral function. However, the best performance has been reported with formulations containing poly(lactide-co-glycolide) (PLGA). Thus, the primary objective of this study was to optimize the encapsulation process of a recombinant adenovirus vector in PLGA microspheres to maximize virus stability and promote intestinal gene transfer. Production parameters were systematically adjusted to find the best formulation for virus release and stability. Optimization of the production process increased viral release from 7 to 15 days and resulted in a 200-fold increase in the total number of infectious virus particles released compared to the original formulation.