Induction of systemic antifimbria and antitoxin antibody responses in Egyptian children and adults by an oral, killed enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine

We assessed serologic responses to an oral, killed whole-cell enterotoxigen ic Escherichia coli plus cholera toxin B-subunit (ETEC-rCTB) vaccine in 73 Egyptian adults, 105 schoolchildren, and 93 preschool children. Each subjec t received two doses of vaccine or placebo 2 weeks apart, giving blood befo re immunization and 7 days after each dose. Plasma antibodies to rCTB and f our vaccine-shared colonization factors (CFs) were measured by enzyme-linke d immunosorbent assay. Immunoglobulin A (IgA) antibodies to rCTB and CFA/I were measured in all subjects, and those against CS1, CS2, and CS4 were mea sured in all children plus a subset of 33 adults. IgG antibodies to these f ive antigens were measured in a subset of 30 to 33 subjects in each cohort. Seroconversion was defined as a >2-fold increase in titer after vaccinatio n. IgA and IgG seroconversion to rCTB was observed in 94 to 95% of adult va ccinees, with titer increases as robust as those previously reported for th ese two pediatric cohorts. The proportion showing IgA seroconversion to eac h CF antigen among vaccinated children (range, 70 to 96%) and adults (31 to 69%), as well as IgG seroconversion in children (44 to 75%) and adults (25 to 81%), was significantly higher than the corresponding proportion in pla cebo recipients, except for IgA responses to CS2 in adults. IgA anti-CF tit ers peaked after one dose in children, whereas in all age groups IgG antibo dies rose incrementally after each dose. Independently, both preimmunizatio n IgA titer and age were inversely related to the magnitude of IgA response s. In conclusion, serologic responses to the ETEC rCTB vaccine mag serve as practical immune outcome measures in future pediatric trials in areas wher e ETEC is endemic.