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In vivo uptake of an experimental microencapsulated diphtheria vaccine following sub-cutaneous immunisation
Marisa Peyre1, Roland Fleck, David Hockley
1Division of Bacteriology, National Institute for Biological Standards and Control, South Mimms, Potters Bar, Hertfordshire EN6 3QG, UK. mpeyre@nibsc.ac.uk
Abstract:
Previous studies demonstrated in vitro phagocytosis of poly(lactide-co-glycolide) (PLGA) microspheres (MS) by macrophages and dendritic cells and the biodistribution of fluorescent PLGA particles following oral or intranasal administration. In this study, we report the uptake and biodistribution of sub-cutaneously administered fluorescent labelled PLGA MS loaded with diphtheria toxoid (DT). The cell type and percentage of fluorescent positive cells were determined by flow cytometry and confirmed by fluorescent microscopy. Fluorescent particles were detected inside cells of the peritoneal flush as early as 10 min post-inoculation, predominantly in cells of macrophage morphology. In vivo trafficking of PLGA particles following a sub-cutaneous immunisation of mice appeared to be governed by macrophages. However, in the first week after inoculation, dendritic cells played a significant role in the uptake and digestion of the microspheres, thereby triggering the immune response against the antigen. Fluorescent PLGA MS were also observed in cells of lymphoid tissues such as mesenteric lymph nodes (MLN) and spleen (S). However, microsphere fluorescence in lymphoid tissues decreased rapidly, as they were degraded inside the cells, thereby enabling the presentation of the antigen to specific cells of the immune system. To our knowledge, this is the first time the fate of immunogenic PLGA microspheres was studied in vivo following a sub-cutaneous injection route.
Insights
Subcutaneously injected poly(lactide-co-glycolide) (PLGA) microspheres are rapidly taken up by macrophages and dendritic cells. These cells process the microspheres, enabling antigen presentation and immune response initiation.
Area of Science:
- Biomaterials Science
- Immunology
- Nanomedicine
Background:
- Poly(lactide-co-glycolide) (PLGA) microspheres are widely used drug delivery vehicles.
- Previous research showed in vitro phagocytosis and biodistribution of PLGA particles via oral/intranasal routes.
Purpose of the Study:
- To investigate the in vivo uptake and biodistribution of subcutaneously administered, fluorescently labeled PLGA microspheres loaded with diphtheria toxoid (DT).
- To elucidate the cellular mechanisms and immune response triggered by PLGA microspheres following subcutaneous injection.
Main Methods:
- Subcutaneous administration of fluorescently labeled PLGA microspheres loaded with DT in mice.
- Analysis of cell types and fluorescence using flow cytometry and fluorescent microscopy.
- Tracking of microsphere distribution in peritoneal lavage, spleen, and mesenteric lymph nodes.
Main Results:
- Fluorescent PLGA microspheres were detected intracellularly in peritoneal cells, primarily macrophages, within 10 minutes of inoculation.
- Macrophages governed in vivo trafficking, while dendritic cells played a key role in microsphere uptake and antigen processing during the first week.
- Microspheres were observed in lymphoid tissues (spleen, mesenteric lymph nodes), with fluorescence diminishing as degradation facilitated antigen presentation.
Conclusions:
- Subcutaneous administration of PLGA microspheres leads to rapid uptake by macrophages and dendritic cells.
- Dendritic cell involvement is crucial for initiating the immune response through antigen presentation.
- This study provides the first in vivo characterization of immunogenic PLGA microspheres following subcutaneous injection.
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