Antibody-secreting cells in the evaluation of the immunogenicity of an oral vaccine.

The immune response to different dosage schedules of oral live Salmonella typhi Ty21a vaccines was studied by enumeration of specific antibody-secreting cells (ASC) in the peripheral blood believed to have been stimulated by the vaccine antigen on mucosal surfaces and to be on their way back to those sites for local antibody secretion. Four groups of subjects were vaccinated with either three (3 x S), two (2 x S) or one (1 x S) dose of a suspension-formulated vaccine, or with three doses of vaccine in enteric-coated capsules (3 x E). The ASC-responses were highest in group 3 x S, followed by 3 x E, 2 x S and 1 x S, in this order. These differences parallel differences in protection from disease as observed in field trails with these regimens. This assay might therefore be useful for presumptive assessment of the protective ability of new vaccines or vaccine regimens. It certainly can be used to measure the immunogenicity of an oral vaccine.