Contribution of noncanonical antigens to virulence and adaptive immunity in human infection with enterotoxigenic E. coli

Enterotoxigenic E. coli (ETEC) contribute significantly to the substantial burden of infectious diarrhea among children living in low and middle income countries. In the absence of a vaccine for ETEC, children succumb to acute dehydration as well as non-diarrheal sequelae related to these infections including malnutrition. The considerable diversity of ETEC genomes has complicated canonical vaccine development approaches focused on a subset of antigens known as colonization factors (CFs). To identify additional conserved immunogens, we mined genomic sequences of 89 ETEC isolates, bioinformatically selected potential surface-exposed pathovar-specific antigens conserved in more than 40% of the genomes (n=118), and assembled the representative proteins onto microarrays, complemented with known or putative colonization factor subunit molecules (n=52), and toxin subunits to interrogate samples from individuals with acute symptomatic ETEC infections. Surprisingly, in this open-aperture approach, we found that immune responses were largely constrained to a small number of antigens including individual colonization factor antigens and EtpA, an extracellular adhesin. In a Bangladeshi cohort of naturally infected children < 2 years of age, both EtpA and a second noncanonical antigen, EatA, elicited significant serologic responses that were associated with protection from symptomatic illness. In addition, children infected with ETEC isolates bearing either etpA or eatA genes were significantly more likely to develop symptomatic disease. These studies support a role for more recently discovered noncanonical antigens in virulence and the development of adaptive immune responses during ETEC infections, findings that may inform vaccine design efforts to complement existing approaches.