Encapsulation of an EP67-Conjugated CTL Peptide Vaccine in Nanoscale Biodegradable Particles Increases the Efficacy of Respiratory Immunization and Affects the Magnitude and Memory Subsets of Vaccine-Generated Mucosal and Systemic CD8⁺ T Cells in a Diameter-Dependent Manner

Abstract

The diameter of biodegradable particles used to co-encapsulate immunostimulants and subunit vaccines affects the magnitude of memory CD8+ T cells generated by systemic immunization. Possible effects on the magnitude of CD8+ T cells generated by mucosal immunization or memory subsets that potentially correlate more strongly with protection against certain pathogens, however, are unknown. In this study, we conjugated our novel host-derived mucosal immunostimulant, EP67, to the protective MCMV CTL epitope, pp89, through a lysosomal protease-labile double arginine linker (pp89-RR-EP67) and encapsulated in PLGA 50:50 micro- or nanoparticles. We then compared total magnitude, effector/central memory (CD127/KRLG1/CD62L), and IFN-γ/TNF-α/IL-2 secreting subsets of pp89-specific CD8+ T cells as well as protection of naïve female BALB/c mice against primary respiratory infection with MCMV 21 days after respiratory immunization. We found that decreasing the diameter of encapsulating particle from ~5.4 µm to ~350 nm: (i.) increased the magnitude of pp89-specific CD8+ T cells in the lungs and spleen (ii.) partially changed CD127/KLRG1 effector memory subsets in the lungs but not the spleen (iii.) changed CD127/KRLG1/CD62L effector/central memory subsets in the spleen (iv.) changed pp89-responsive IFN-γ/TNF-α/IL-2 secreting subsets in the lungs and spleen (v.) did not affect the extent to which encapsulation increased efficacy against primary MCMV respiratory infection over unencapsulated pp89-RR-EP67. Thus, although not observed under our current experimental conditions with MCMV, varying the diameter of nanoscale biodegradable particles may increase the efficacy of mucosal immunization with co-encapsulated immunostimulant/subunit vaccines against certain pathogens by selectively increasing memory subset(s) of CD8+ T cells that correlate the strongest with protection.

Development of multi-epitope peptide-based vaccines against SARS-CoV-2

“…For example, Montanide ISA 51 in combination with a cocktail of HIV-derived peptide antigens (containing a mixture of peptide specifying B- and T-cell epitopes) enhanced the immunogenicity of the antigenic peptide [ 50 ]. The epitopes can also be fused with adjuvant proteins [e.g., toll-like receptor (TLR) ligands] which can be encapsulated or displayed on the surface of nanoparticles [e.g., poly lactic- co -glycolic acid (PLGA)] to elicit sustained T-cell responses and increase long term protection [ 8 , 51 , 52 ].…”

Critical micelle concentration and particle size determine adjuvanticity of cyclic lipopeptides

“…In addition, 357‐nm PLGA particles with co‐encapsulated poly(I:C) and OVA induced a stronger OVA‐specific IgG response than did 17‐μm particles with the same composition . Furthermore, the frequency of murine cytomegalovirus‐specific cytotoxic T lymphocytes was significantly higher in both mucosal and systemic tissues of mice immunized intratracheally with 350‐nm PLGA nanoparticles with encapsulated peptide vaccine than after the immunization with 5.4‐μm PLGA microparticles . Although the optimal size of silica nanoparticles for the induction of immune response was smaller than that used in other vaccines, these previous reports suggested that 100‐500‐nm particles can be adapted for vaccine preparations.…”

“…Because particle size influences the competence of immune responses induced by vaccination, it must be considered when vaccine formulations are intended for intranasal immunization . It has been frequently reported that particle size influences immune responses . With regard to vaccine Ags, it has been noted that only particles in the nanometre range, that is of the size of viruses, can reach lymph nodes and directly interact with B cells, inducing potent immune responses .…”

“…53 Furthermore, the frequency of murine cytomegalovirus-specific cytotoxic T lymphocytes was significantly higher in both mucosal and systemic tissues of mice immunized intratracheally with 350-nm PLGA nanoparticles with encapsulated peptide vaccine than after the immunization with 5.4-μm PLGA microparticles. 56 Although the optimal size of silica nanoparticles for the induction of immune response was smaller than that used in other vaccines, these previous reports suggested that 100-500-nm particles can be adapted for vaccine preparations. In the current study, the particle diameter of the SF-OVA complex in the SF-OVAsaline system with 100 mg/mL SF was 122-255 nm, whereas the diameter of particles in the OVA-saline system was only 24-48 nm.…”

“…47,48 It has been frequently reported that particle size influences immune responses. [48][49][50][51][52][53][54][55][56] With regard to vaccine Ags, it has been noted that only particles in the nanometre range, that is of the size of viruses, can reach lymph nodes and directly interact with B cells, inducing potent immune responses. 48,50 Comparisons of silica nanoparticle vaccines that contained particles of different diameters demonstrated that particles of the most effective formulations were 30-50 nm in diameter.…”