Bold takeaway: an injectable silica-based scaffold vaccine can train the immune system to fight bacteria on medical implants, dramatically lowering bacterial load and even eradicating infection in some cases. And this is the part most people miss: the approach not only reduces infection but also broadens protection across different Staphylococcus aureus strains, including MRSA.
A recent study published in the Proceedings of the National Academy of Sciences explored whether scaffold vaccination could prevent or lessen infections linked to orthopedic devices. Staphylococcus aureus remains a leading global cause of bacterial death, and implant-associated infections are especially serious due to prolonged antibiotic courses and the need for revision surgeries. Vaccination seems promising for people needing implants, but past vaccine trials often failed to prevent post-surgical S. aureus infections.
The researchers previously developed a unique vaccine platform built on a biodegradable, injectable scaffold made of mesoporous silica rods. These scaffolds contain aligned nanopores designed to release granulocyte-macrophage colony-stimulating factor (GM-CSF) to recruit dendritic cells (DCs). When loaded with pathogen-associated molecular patterns (PAMPs) from Escherichia coli, scaffold vaccines showed mortality benefits in Enterobacter infections, implying that PAMPs can stimulate broad immunity.
In this study, mice received one of four treatments on day 0: saline injection (naïve); scaffold with chemokine and adjuvant but no antigen (scaffold no-antigen); bolus vaccine containing chemokine, antigen, and adjuvant in saline; or scaffold vaccine containing chemokine, antigen, and adjuvant (scaffold vaccine). The antigen used for vaccination was derived from the S. aureus Xen29 strain.
On day 7, researchers harvested spleens and tissue from the injection site. Spleens from the scaffold vaccine group were markedly heavier—nearly threefold compared to the naïve group and twofold compared to the scaffold no-antigen group. There was also a trend toward more CD11c+ cells, a marker for dendritic cells, at the injection site in the scaffold vaccine group.
Spleens from the scaffold vaccine group contained significantly more CD11c+ cells, and the majority of these cells (>72%) co-expressed MHC II, indicating activated DCs. The scaffold vaccine group also showed higher levels of a range of Th1-associated cytokines in the serum, including IL-2, IL-7, IL-1β, IL-12p70, TNF-α, and IFN-γ, compared with the naïve group. Both bolus and scaffold vaccine groups exhibited elevated Th17-associated cytokines relative to naïve controls.
To assess cell-mediated immunity, vaccinated splenocytes were re-exposed to the bacterial antigen, with IFN-γ expression used as a proxy for antigen-specific Th1 responses. Only mice receiving antigen-containing vaccines showed significantly higher IFN-γ than naïve mice, and the scaffold vaccine group produced notably greater IFN-γ than the bolus vaccine group.
A challenge was performed on day 35 by introducing S. aureus Xen29 to the implants. Two weeks later, the untreated group showed weight loss relative to uninfected controls, while all infected groups had higher anti-S. aureus IgG levels. Importantly, the scaffold vaccine group had substantially higher anti-S. aureus titers than other infected groups. When implants were examined after euthanasia on day 49, no bacteria were recovered from the uninfected controls, while bacteria were found in other groups. The scaffold vaccine group had the lowest bacterial burden overall, and in a subset of animals, no bacteria were detected on the implant, suggesting possible sterilizing immunity in some cases. The reduction in bacterial load with scaffold vaccination equated to roughly a 2.4-log decrease (about 250-fold) compared with untreated controls.
The researchers also tested whether the scaffold vaccine protected against different S. aureus strains. Serum from scaffold-vaccinated mice showed significant IgG binding to several MRSA strains (JE2 and NRS699lux) and methicillin-susceptible strains (UAMS-1 and RN4220). When implants were inoculated with the MRSA strain NRS699lux, scaffold-vaccinated mice had a notably lower bacterial burden at the end of the study. They also evaluated IsdB, the second-most abundant protein in the PAMP pool, as a vaccine antigen. IsdB delivered as a bolus vaccine or via the scaffold elicited better protection when included in the scaffold vaccine than bolus IsdB vaccination alone.
Overall, scaffold vaccination using S. aureus Xen29 PAMPs as the antigen produced strong Th1-type immunity and lowered implant-associated bacterial burden. The protection extended to other S. aureus strains, and using a protein antigen in the scaffold further improved outcomes compared with conventional bolus delivery. The authors conclude that scaffold-based vaccination could generate more robust immunity than traditional bolus vaccines, particularly in scenarios where standard vaccines fail.
Reference:
Tatara AM, Lightbown S, Kang S, et al. Scaffold vaccination for prevention of orthopedic device infection. Proceedings of the National Academy of Sciences, 122(45), e2409562122 (2025). https://www.pnas.org/doi/10.1073/pnas.2409562122
