The results of the present investigation indicate a simple approach to the development of a single-
vaccine formula which may ultimately be used to confer protection against both
cholera and certain types of Escherichia coli diarrheal disease in humans and domestic animals. The design of the
vaccine is based on the well-documented ability of
cholera antitoxin to neutralize both
cholera and heat-labile E. coli
enterotoxins (CT and LT, respectively) and on the ability of killed E. coli to enhance the immune response to
cholera toxoid and, possibly, to conventional
cholera vaccine as well. Evidence presented shows that a parenterally administered E. coli
vaccine, prepared from an LT-only enterotoxigenic strain, reproducibly elevated rabbit
antitoxin responses to
cholera toxoid and that such responses correlated with dramatic protection against live
cholera vibrios and the homologous E. coli strain in the rabbit ligated loop model of diarrheal disease. The results show also that
cholera vaccine acted to suppress the rabbits' immune response to the
cholera toxoid and E. coli
vaccine formula, even though all three
antigens combined still provided significant protection against live organism challenge. On the basis of data presently available, the
vaccine formula would be composed simply of
cholera toxoid and E. coli
vaccine, but may also include
cholera vaccine. Since it has already been established that
cholera toxoid and
cholera vaccine are each safe for human use, additional
vaccine development would require investigation of the safety of E. coli
vaccine, alone and in combination with the other components.