Vaccine-specific T cells in human peripheral blood after oral immunization with an inactivated enterotoxigenic Escherichia coli vaccine.

We have examined whether oral immunization of adult Swedish volunteers with a prototype enterotoxigenic Escherichia coli vaccine would induce antigen-specific T-cell responses in blood. Volunteers were given one to three doses of the whole-cell component of the vaccine, which consisted of formalin-inactivated bacteria expressing the fimbrial colonization factor antigens I and II. Following immunization, in vitro stimulation of blood mononuclear cells with the colonization factor antigens resulted in modest proliferative responses which were accounted for mainly by CD4+ T cells and, to a lesser extent, by CD8+ T cells. A main finding of this study was that a majority of the orally immunized volunteers had circulating T cells capable of producing large quantities of gamma interferon following in vitro exposure to either of the colonization factor antigens. No interleukin 2 production could be detected in the cell cultures. These results suggest that oral immunization of humans induces the migration of specific mucosal T immunocytes from the intestine into peripheral blood.