Needle- and Cold Chain- Free Rice-Based Oral Vaccine, MucoRice-CTB Shows Microbiota-Dependent Immunogenicity in Humans

Background: Diarrheal disease remains a global health issue. It is estimated that there are 1.3 to 4.0 million cases of cholera and 20,000 to 140,000 cholera-related deaths worldwide each year. In addition, pandemic diarrhea and travelers’ diarrhea caused by enterotoxigenic Escherichia coli heat-labile enterotoxin (LT) are estimated to affect approximately 200 million and 27 million people, respectively, worldwide each year. Our previous studies showed that rice-based cholera toxin B subunit (CTB) vaccine, MucoRice-CTB is a cold-chain and needle-syringe free oral vaccine candidate which will be benefited to less infrastructure conditions. Methods: We conducted a double-blind, randomized, placebo-controlled, three-cohort, dose-escalation phase I study to evaluate the safety, tolerability, and efficacy of MucoRice-CTB (clinical study code name: IMSUT-MR1501) administered as four oral doses at 2-week intervals to healthy Japanese adults. In addition to vaccine evaluation, metagenomic analysis of study participants was performed by using bacterial DNA from fecal samples. Interpretation: MucoRice-CTB induces cross-reactive antigen-specific antibodies against CTB and B subunit of LT in a dose-dependent manner, without inducing serious adverse events. Antibodies isolated from responders to the vaccine inhibited the binding of CT and LT to GM1 ganglioside receptor and the elongation of Chinese hamster ovary cells caused by the both enterotoxins. Metagenome analysis of subjects’ feces collected prior to the start of vaccination revealed that responders had a gut microbiota of higher diversity that was characterized by larger populations of E. coli and Shigella spp. compared with those in non-responders. Findings: This phase I clinical trial showed that MucoRice-CTB induces neutralizing antibodies against diarrheal toxins in a gut microbiota-dependent manner without major adverse events. Trial Registration: (clinical trial registration: UMI18001) Funding Statement: The costs related to this study are covered by support of the “Translational Research Network Program” of the Ministry of Education, Culture, Sports, Science and Technology. Declaration of Interests: The authors stated that: None of the items involve any conflicts of interest. Ethics Approval Statement: The clinical research protocols were approved and received ethical clearance (permit #27-41- 0917 and #27-48-0128) from the IRB of the Institute of Medical Science, The University of Tokyo (IMSUT), Japan.