The degree of protection conferred after receiving an oral cholera vaccine (OCV) varies based on age, prior exposure to Vibrio cholerae , and unknown factors. Recent evidence suggests that the microbiota may mediate some of the unexplained differences in oral vaccine responses. Here, we use metagenomic sequencing of the fecal microbiota at the time of vaccination and relate microbial features to immune responses after OCV using a reference-independent gene-level method. We find that the presence of sphingolipid-producing bacteria is associated with the development of protective immune responses after OCV. We test these associations by stimulating human macrophages with Bacteroides xylanisolvens metabolites and find that sphingolipid-containing extracts increase innate immune responses to OCV antigens. Our findings demonstrate a new analytic method for translating metagenomic sequencing data into strain-specific results associated with a biological outcome, and in validating this tool, we identify that microbe-derived sphingolipids impact immune responses to OCV antigens.

Background/Objectives: Cholera remains a significant global health challenge. Shanchol (ShantaBiotech, India), one of the WHO prequalified Oral Cholera Vaccines (OCVs) available until recently, has been used to immunize people as a two-dose regimen (14 days apart, on day 0 and 14). However, growing evidence suggests that a single-dose strategy may mediate short-term protection, especially in those over 5 years of age. Hence, it is crucial to design a suitable and effective administration scheme for Shanchol, particularly in cholera-endemic regions. Methods: In this study, adult volunteers were vaccinated with either a single dose, a two-dose regimen with a 14-day interval, or a two-dose regiment with a 30-day interval. We studied the antigen-specific helper memory (CD4+CD45RO+) and cytotoxic memory (CD8+CD45RO+) T cells responses of vaccinees along with the specific mucosal immune responses to gut-homing ß7 lipopolysaccharides (LPSs). Results: By day 7 post-vaccination, Shanchol induced robust helper and cytotoxic memory T cell responses to V. cholerae membrane protein (AKI-MP) following a single dose of vaccination. In the two-dose groups, we observed a significant elevation of AKI-MP-specific responses after the 2nd dose. We found that circulatory gut homing (β7+) LPS-specific IgA responses of antibody-secreting cells (ASCs) peaked at D7 among all vaccine groups. Moreover, we observed that β7+ LPS-specific ASCs at D7 significantly correlated with the LPS-specific antibody titer in plasma. Conclusions: These findings suggest that a single dose of OCV in adults induces immune responses comparable to a two-dose regimen, suggesting a single-dose vaccination may be adequate to mediate protection against cholera in cholera endemic zones—especially in reactive campaigns.