Abstract Rationale Recent vaccine formulations have focused on safety by limiting the antigen components; however, this often results in reduced immunogenicity. Therefore, the development of safe and effective adjuvants is urgently required. We previously reported in murine models that continuous wave near-infrared (NIR) light irradiation of the skin, under specific conditions, enhanced the efficacy of intradermal vaccination. This effect was attributed to the promotion of dendritic cell (DC) migration into draining lymph nodes. Mucosal vaccines have gained attention as a promising strategy for eliciting strong protection against infections; however, additional approaches are required to further enhance their efficacy. In this study, we investigated the potential use of NIR irradiation as a “laser adjuvant” for mucosal vaccination. Methods A 1064-nm diode laser was used to non-invasively irradiate the sublingual mucosa of C57BL/6 mice (X W/cm²) for 1 minute. DCs in the sublingual mucosa were labeled with fluorescein isothiocyanate (FITC), followed by the sublingual administration of ovalbumin (OVA). At designated time points, the submandibular lymph nodes were harvested, and DCs were analyzed using flow cytometry. In the influenza vaccination model, mice received an inactivated A/PR/8 virus vaccine sublingually twice at 2-week intervals. Serum influenza-specific IgG antibody titers were measured using ELISA on days 14 and 28 post-immunization. On day 28, the mice were intranasally challenged with live influenza virus, and their survival was subsequently monitored. Results NIR irradiation prior to OVA administration significantly increased the proportion of FITC+ migratory DCs in submandibular lymph nodes (p 0.05), along with an increase in CD86+ DCs. In the influenza vaccination model, serum IgG antibody titers on day 28 were significantly higher in the NIR-irradiated group than in the control group (p 0.05). Furthermore, survival following influenza virus challenge improved in the NIR group. Conclusions Sublingual NIR irradiation enhanced DC activation and migration, demonstrating an adjuvant effect that improved both the immunogenicity and protective efficacy of vaccination. These findings indicate that 1064-nm NIR light has the potential to serve as a safe and effective physical adjuvant for mucosal influenza vaccination and may facilitate its future clinical application. This abstract is funded by: Japan Agency for Medical Research and Development (AMED), Defense Medicine Basic Research Program (Type A), Defense Medicine Basic Research Program (Type B), and JSPS KAKENHI Grant-in-Aid for Scientific Research (B)
Sano et al. (Fri,) studied this question.