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Toward a Single-Dose Vaccination Strategy with Self-Encapsulating PLGA Microspheres.

ABSTRACT: Poly(lactic-co-glycolic acid) (PLGA) microspheres have been widely examined for vaccine applications due to their attractive features of biocompatibility, biodegradability, ability to be internalized by antigen-presenting cells, and long-term antigen release. However, one of the major challenges for PLGA particle vaccines is the potential for antigen instability and loss of antigenicity and immunogenicity. To address this challenge, we have developed a new method of "self-healing" encapsulation in PLGA microspheres, where pre-made PLGA microspheres are loaded with protein antigens under aqueous conditions with minimal impact on their antigenicity and immunogenicity. In this report, we show that mice immunized with self-encapsulating PLGA microspheres in a prime-boost regimen generated significantly enhanced antigen-specific CD8?+ T cell and antibody responses, compared with mice immunized with free, soluble protein admixed with calcium phosphate gel, a widely used adjuvant. Furthermore, a single-dose of microspheres designed for >40 day sustained antigen release elicited robust cellular and humoral immune responses as efficiently as the prime-boost vaccinations with calcium phosphate gel. Overall, these results suggest excellent potential of our self-encapsulating PLGA microspheres as a vaccine platform for multiple-dose as well as single-dose vaccinations.

SUBMITTER: Bailey BA

PROVIDER: S-EPMC5483999 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Toward a Single-Dose Vaccination Strategy with Self-Encapsulating PLGA Microspheres.

Bailey Brittany A BA Ochyl Lukasz J LJ Schwendeman Steven P SP Moon James J JJ

Advanced healthcare materials 20170403 12

Poly(lactic-co-glycolic acid) (PLGA) microspheres have been widely examined for vaccine applications due to their attractive features of biocompatibility, biodegradability, ability to be internalized by antigen-presenting cells, and long-term antigen release. However, one of the major challenges for PLGA particle vaccines is the potential for antigen instability and loss of antigenicity and immunogenicity. To address this challenge, we have developed a new method of "self-healing" encapsulation ...[more]

PMID: 28371568

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Project description: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 a temperature>the hydrated polymer glass transition temperature, respectively. The microsphere formulation parameters and loading conditions to provide optimal active self-healing microencapsulation of vaccine antigens in PLGA was investigated. Active self-healing encapsulation of two antigens, ovalbumin and tetanus toxoid (TT), in PLGA microspheres was adjusted by preparing blank microspheres containing different vaccine adjuvants (aluminum hydroxide (Al(OH)₃) or calcium phosphate). Active loading of vaccine antigen in Al(OH)₃-PLGA microspheres was found to: a) increase 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.

Project description:Microdroplets are an effective platform for segregating individual cells and amplifying DNA. However, a key challenge is to recover the contents of individual droplets for downstream analysis. This paper offers a method for embedding cells in alginate microspheres and performing multiple serial operations on the isolated cells. Rhodobacter sphaeroides cells were diluted in alginate polymer and sprayed into microdroplets using a fingertip aerosol sprayer. The encapsulated cells were lysed and subjected either to conventional PCR, or whole genome amplification using either multiple displacement amplification (MDA) or a two-step PCR protocol. Microscopic examination after PCR showed that the lumen of the occupied microspheres contained fluorescently stained DNA product, but multiple displacement amplification with phi29 produced only a small number of polymerase colonies. The 2-step WGA protocol was successful in generating fluorescent material, and quantitative PCR from DNA extracted from aliquots of microspheres suggested that the copy number inside the microspheres was amplified up to 3 orders of magnitude. Microspheres containing fluorescent material were sorted by a dilution series and screened with a fluorescent plate reader to identify single microspheres. The DNA was extracted from individual isolates, re-amplified with full-length sequencing adapters, and then a single isolate was sequenced using the Illumina MiSeq platform. After filtering the reads, the only sequences that collectively matched a genome in the NCBI nucleotide database belonged to R. sphaeroides. This demonstrated that sequencing-ready DNA could be generated from the contents of a single microsphere without culturing. However, the 2-step WGA strategy showed limitations in terms of low genome coverage and an uneven frequency distribution of reads across the genome. This paper offers a simple method for embedding cells in alginate microspheres and performing PCR on isolated cells in common bulk reactions, although further work must be done to improve the amplification coverage of single genomes.

Dataset Information

Toward a Single-Dose Vaccination Strategy with Self-Encapsulating PLGA Microspheres.

Publications

Toward a Single-Dose Vaccination Strategy with Self-Encapsulating PLGA Microspheres.

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