Cytoplasmic delivery of a macromolecular fluorescent probe by poly(d, l-lactic-co-glycolic acid) microspheres

Preparation and application of dextran and its derivatives as carriers

As a natural and renewable biological macromolecule, dextran not only has excellent biodegradability, but also has good biocompatibility. Dextran and its derivatives are functional polymers for the construction of targeted drug delivery systems. Herein, the application of dextran as prodrug and nanoparticle/nanogel/microsphere/micelle carrier for targeting drug delivery system was summarized. It is clarified that dextran is an important biomaterial with application value.

Targeting dendritic cells with nano-particulate PLGA cancer vaccine formulations

Development of safe and effective cancer vaccine formulation is a primary focus in the field of cancer immunotherapy. The recognition of the crucial role of dendritic cells (DCs) in initiating anti-tumor immunity has led to the development of several strategies that target vaccine antigens to DCs as an attempt for developing potent, specific and lasting anti-tumor T cell responses. The main objective of this review is to provide an overview on the application of poly (d,l-lactic-co-glycolic acid) nanoparticles (PLGA-NPs) as cancer vaccine delivery system and highlight their potential in the development of future therapeutic cancer vaccines. PLGA-NPs containing antigens along with immunostimulatory molecules (adjuvants) can not only target antigen actively to DCs, but also provide immune activation and rescue impaired DCs from tumor-induced immuosupression.

Activation of antigen-specific T cell-responses by mannan-decorated PLGA nanoparticles

PURPOSE

Mannosylation of vaccines is a promising strategy to selectively target vaccine antigens to the mannose receptor expressed on dendritic cells (DCs). The purpose of this study was to investigate the effect of mannan (MN) chemically conjugated to poly(D, L-lactide-co-glycolic acid) (PLGA) nanoparticles (NPs) on antigen-specific T-cell responses elicited by a model antigen (ovalbumin, OVA) loaded in PLGA-NPs.

METHODS

In vitro T-cell proliferation assay was done to assess the ability of DCs treated with OVA-NPs (±MN decoration) to induce antigen-specific T-cell activation. The efficacy of this vaccination strategy was further evaluated in vivo, where T-cell proliferation was performed to evaluate activation of T-cell responses in lymph nodes and spleens isolated from the vaccinated mice.

RESULTS

Our results demonstrate that MN-decorated antigen-loaded PLGA-NPs simultaneously enhanced antigen-specific CD4+ and CD8+ T-cell responses compared to non-decorated NPs.

CONCLUSIONS

MN decoration of PLGA-NPs is a promising strategy for enhancing antigen-specific T-cell responses.

Intracellular delivery of a protein antigen with an endosomal-releasing polymer enhances CD8 T-cell production and prophylactic vaccine efficacy

Protein-based vaccines have significant potential as infectious disease and anticancer therapeutics, but clinical impact has been limited in some applications by their inability to generate a coordinated cellular immune response. Here, a pH-responsive carrier incorporating poly(propylacrylic acid) (PPAA) was evaluated to test whether improved cytosolic delivery of a protein antigen could enhance CD8+ cytotoxic lymphocyte generation and prophylactic tumor vaccine responses. PPAA was directly conjugated to the model ovalbumin antigen via reducible disulfide linkages and was also tested in a particulate formulation after condensation with cationic poly(dimethylaminoethyl methacrylate) (PDMAEMA). Intracellular trafficking studies revealed that both PPAA-containing formulations were stably internalized and evaded exocytotic pathways, leading to increased intracellular accumulation and potential access to the cytosolic MHC-1 antigen presentation pathway. In an EG.7-OVA mouse tumor protection model, both PPAA-containing carriers robustly inhibited tumor growth and led to an approximately 3.5-fold increase in the longevity of tumor-free survival relative to controls. Mechanistically, this response was attributed to the 8-fold increase in production of ovalbumin-specific CD8+ T-lymphocytes and an 11-fold increase in production of antiovalbumin IgG. Significantly, this is one of the first demonstrated examples of in vivo immunotherapeutic efficacy using soluble protein-polymer conjugates. These results suggest that carriers enhancing cytosolic delivery of protein antigens could lead to more robust CD8+ T-cell response and demonstrate the potential of pH-responsive PPAA-based carriers for therapeutic vaccine applications.

Antigen delivery with poly(propylacrylic acid) conjugation enhances MHC-1 presentation and T-cell activation

While many infectious diseases are controlled by vaccine strategies, important limitations continue to motivate the development of better antigen delivery systems. This study focuses on the use of a pH-sensitive polymeric carrier based on poly(propylacrylic acid) (PPAA) to address the need for more potent CD8 cytotoxic T-cell (CTL) responses. An MHC-1/CD8 CTL cell model system with ovalbumin as the protein antigen was used to test whether PPAA could enhance the delivery of ovalbumin into the MHC-1 display pathway. Ovalbumin was conjugated to poly(propylacrylic acid-co-pyridyldisulfide acrylate) (PPAA-PDSA) by disulfide exchange to make reversible conjugates that could be reduced by the glutathione redox system in the cytosol of antigen presenting cells. The PPAA-PDSA ovalbumin conjugates displayed the pH-sensitive membrane disruptive properties of the parent polymer as determined by their hemolysis activities (sharply active at the endosomal pH values of 6-6.5). The polymer-ovalbumin conjugates exhibited strong 22-fold increases in the MHC-1 presentation and ovalbumin-specific CTL activation compared to free ovalbumin. No CTL activation was observed with control conjugates of ovalbumin and poly(methylacrylic acid) (PMAA) that do not display membrane disruptive activies, suggesting that it is the membrane destabilizing properties of the polymer that result in increased MHC-1 display and CTL activation. Further mechanistic studies quantitated the time course of stable intracellular localization of radiolabeled conjugates. 52% of initially internalized PPAA-conjugated ovalbumin remained in the cells after 4 h, compared to less than 10% of ovalbumin or PMAA-ovalbumin. These results showing enhanced cytosolic delivery and MHC-1 presentation for the PPAA-antigen conjugates suggest that they warrant future characterization as a CD8-enhancing vaccine delivery system.

Enhanced and prolonged cross-presentation following endosomal escape of exogenous antigens encapsulated in biodegradable nanoparticles

CD8(+) T-cell responses are critical in the immunological control of tumours and infectious diseases. To prime CD8(+) T cells against these cell-associated antigens, exogenous antigens must be cross-presented by professional antigen-presenting cells (APCs). While cross-presentation of soluble antigens by dendritic cells is detectable in vivo, the efficiency is low, limiting the clinical utility of protein-based vaccinations. To enhance the efficiency of presentation, we generated nanoparticles from a biodegradable polymer, poly(D,L-lactide-co-glycolide) (PLGA), to deliver antigen into the major histocompatibility complex (MHC) class I antigen presentation pathway. In primary mouse bone marrow-derived dendritic cells (BMDCs), the MHC class I presentation of PLGA-encapsulated ovalbumin (OVA) stimulated T cell interleukin-2 secretion at 1000-fold lower concentration than soluble antigen and 10-fold lower than antigen-coated latex beads. The microparticles also served as an intracellular antigen reservoir, leading to sustained MHC class I presentation of OVA for 72 hr, decreasing by only 20% after 96 hr, a time at which the presentation of soluble and latex bead-associated antigens was undetectable. Cytosol extraction demonstrated that antigen delivery via PLGA particles increased the amount of protein that escaped from endosomes into the cytoplasm, thereby increasing the access of exogenous antigen to the classic MHC class I loading pathway. These data indicate that the unique properties of PLGA particle-mediated antigen delivery dramatically enhance and sustain exogenous antigen presentation by MHC class I, potentially facilitating the clinical use of these particles in vaccination.

Uptake of poly(D,L-lactic-co-glycolic acid) microspheres by antigen-presenting cells in vivo

Dendritic cells are the most potent antigen-presenting cells (APC) and the most effective stimulators of primary T cell responses. Based on the strong influence of the APC on the immune response, we investigated cellular uptake of a biodegradable antigen delivery system, poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres, at two sites of injection: intraperitoneal and intradermal. We hypothesized that a fluorescent probe, tetramethylrhodamine labeled dextran, loaded in PLGA microspheres would be taken up by APCs and thereby provide a means for studying cellular uptake of PLGA microspheres in vivo. Phagocytic load and cell phenotype were determined using flow cytometry and confocal laser scanning microscopy. The results revealed cellular uptake of tetramethylrhodamine dextran loaded PLGA microspheres at both injection sites. After intraperitoneal immunization, the predominant cell phagocytosing PLGA microspheres in the peritoneal cavity was the macrophage whereas the intradermal immunization resulted in uptake of PLGA microspheres by dendritic cells. Hence, these results suggest that the profile for cellular uptake varies with the site of injection. More importantly, this study provides direct and conclusive evidence of uptake of PLGA microspheres by the most potent APC, the dendritic cell.