Table 2.

Summary of key findings, main challenges, and future directions in intranasal DPV research.

Key findings in the literature about IN DPVs	Main challenges of IN DPVs	Prediction/future directions of IN DPVs
Mucoadhesives such as chitosan and GelSite® improved the immunogenicity of DPVs by increasing the residence time of the formulation in the mucosal surface. Mild formaldehyde treatment (0.18%) to stabilize antigens can enhance its immunogenicity. The higher stability of DPVs compared to liquid vaccines was confirmed by the determination of its activity in vitro and in vivo. Common mucosal response after IN vaccination can be tested to provide mucosal immunity in distant mucosal surfaces.	Limited time for antigen absorption due to the rapid nasal mucociliary clearance. Lack of guidelines for dry powder nasal products for in vitro performance and characterization. Limited number of devices for dry powder nasal delivery for in vivo evaluation of DPVs. Storage of the formulation protected from humidity to prevent loss of activity.	Improvement of devices or development of new devices to efficiently deliver DPVs to nasal cavity only. Novel formulations using particle carriers as bulking agents to modulate particle size and density to improve the deposition in the nasal cavity.