Figure 1. (A) Schematic designs of C. difficile toxin A (TcdA) DNA vaccines: TcdA-C (C-terminus of TcdA without leader sequence) and tPA-TcdA-C (TcdA-C with a tPA leader sequence). The amino acid positions for corresponding protein segments are indicated. (B) TcdA-C-specific antibody responses in mouse sera collected at one week after the 4th DNA immunization with either TcdA-C DNA vaccine or the empty vector (Mock) against TcdA-C protein expressed in supernatant of tPA-TcdA-C transfected 293T cells.