Entrapment in plasma microparticles: a promising strategy for antigen delivery

We report the preparation of plasma microparticles (PMPs) from autologous blood plasma for sustained in vivo delivery of the entrapped antigens. The PMPs were prepared by high speed-stirring of calcium-enriched plasma, mixed with the antigen to be entrapped, in mineral oil. The preparation of PMPs did not necessitate addition of any external protein/enzyme nor special laboratory setup. Our results suggest that the PMPs release the entrapped invertase in a sustained manner both in vitro and in vivo, especially after crosslinking with glutaraldehyde. The preparations are reasonably stable to proteolysis and constitute strong candidates for eliciting immune response. Induction of humoral immune response by the PMP-entrapped invertase, as evident from the high antibody titers, was remarkable and comparable with that observed in animals receiving the antigen emulsified with Freund's Complete Adjuvant. Isotypic analysis of antibodies showed a Th1-biased immune response in animals administered uncrosslinked or crosslinked PMPs-entrapped invertase, especially after a booster dose. The analysis in animals of the group immunized with adjuvant-emulsified antigen suggested a combined Th1 and Th2 response. PMP-entrapment also caused high expression of surface markers (CD80 and CD86) on antigen presenting cells, as well as effector T-cells surface markers (CD4(+) and CD8(+) ) as revealed by FACS. The study suggests that PMPs offer remarkable promise as adjuvant-free and biocompatible vaccine delivery systems.