Shigellosis is a leading cause of diarrhea worldwide prompting vaccine 
development. The Shigella flexneri Invaplex 50 is a macromolecular complex 
containing IpaB, IpaC, and LPS, formulated from an aqueous extract of virulent 
Shigella delivered via nasal administration. Preclinical vaccine testing 
demonstrated safety, immunogenicity and efficacy. An open-label dose-escalating 
phase 1 study evaluated a 3-dose (2-week intervals) regimen via nasal pipette 
delivery. Thirty-two subjects were enrolled into one of four vaccine dose groups 
(10, 50, 240, or 480 microg). The vaccine was well tolerated with minor 
short-lived nasal symptoms without evidence of dose effect. Antibody-secreting 
cell (ASC) responses were elicited at doses > or =50 microg with the highest IgG 
ASC, Invaplex 50 (100%) and S. flexneri 2a LPS (71%), as well as, serologic 
responses (43%) occurring with the 240 microg dose. Fecal IgA responses, 
Invaplex 50 (38.5%) and LPS (30.8%), were observed at doses > or =240 microg. 
The Invaplex 50 nasal vaccine was safe with encouraging mucosal immune 
responses. Follow-on studies will optimize dose, delivery mechanism and assess 
efficacy in a S. flexneri 2a challenge study.