Active self-healing encapsulation of vaccine antigens in PLGA microspheres

Abstract

Herein, we describe the detailed development of a simple and effective method to microencapsulate vaccine antigens in poly(lactic-co-glycolic acid) (PLGA) by simple mixing of preformed active self-microencapsulating (SM) PLGA microspheres in a low concentration aqueous antigen solution at modest temperature (10-38 °C). Co-encapsulating protein-sorbing vaccine adjuvants and polymer plasticizers were used to “actively” load the protein in the polymer pores and facilitate polymer self-healing at temperature > hydrated polymer glass transition temperature, respectively. The microsphere formulation parameters and loading conditions to provide optimal active self-healing microencapsulation of vaccine antigen in PLGA was investigated. Active self-healing encapsulation of two vaccine antigens, ovalbumin and tetanus toxoid (TT), in PLGA microspheres was adjusted by preparing blank microspheres containing different vaccine adjuvant (aluminum hydroxide (Al(OH)3) or calcium phosphate). Active loading of vaccine antigen in Al(OH)3-PLGA microspheres was found to: a) increase proportionally with an increasing loading of Al(OH)3 (0.88-3 wt%) and addition of porosigen, b) decrease when the inner Al(OH)3/trehalose phase to 1 mL outer oil phase and size of microspheres was respectively > 0.2 mL and 63 μm, and c) change negligibly by PLGA concentration and initial incubation (loading) temperature. Encapsulation of protein sorbing Al(OH)3 in PLGA microspheres resulted in suppression of self-healing of PLGA pores, which was then overcome by improving polymer chain mobility, which in turn was accomplished by coincorporating hydrophobic plasticizers in PLGA. Active self-healing microencapsulation of manufacturing process-labile TT in PLGA was found to: a) obviate micronization- and organic solvent-induced TT degradation, b) improve antigen loading (1.4-1.8 wt% TT) and encapsulation efficiency (~ 97%), c) provide nearly homogeneous distribution and stabilization of antigen in polymer, and d) provide improved in vitro controlled release of antigenic TT.

Biomaterials for Nanoparticle Vaccine Delivery Systems

“…Yet, one of the major drawbacks for the PLGA particle system has been the potential exposure of antigens to harsh organic solvents since conventional technique for loading antigens into PLGA particles involves formation of single or double emulsion (O/W or W/O/W) and solvent evaporation. However, with the recent advances in micro-encapsulation of biomolecules into pre-formed, self-healing PLGA particles, antigens can be loaded into PLGA vaccine particles in aqueous condition with minimal loss of their integrity and antigenicity (99,100). …”

Injectable controlled release depots for large molecules

“…The alternative to anhydrous encapsulation, which does not require micronization and organic solvents, is to remotely load the protein in preformed microspheres in water. This process has shown improvement in stability of lysozyme and tetanus toxoid [46,97,98] and is described below in Section 3.3.…”

Vaccine Nanoparticles for Protection Against HIV Infection

“…This is due to the loss of 3D structure and aggregation of immunogens during the synthesis of polymeric particles, which typically introduces organic solvents and high mechanical and/or chemical stresses to cargo materials [51]. New approaches to formulation of biologics into PLGA particles include a 'self-healing encapsulation' procedure that exploits the polymer's transition temperature to load antigens into preformed PLGA particles in an aqueous condition, thus avoiding the loss of their antigenicity and immunogenicity [52,53] On the other hand, recent studies have reported successful surface modification of recombinant Env trimers on synthetic lipid vesicles in an orientationspecific manner [54,55]. Using Ni-NTA-functionalized lipids, Env gp140 trimers with terminal polyhistidine tags (Histag) were anchored to the surfaces of interbilayer-crosslinked multilamellar vesicles (ICMVs).…”