Map of construction of oral somatostatin (SS) DNA vaccines encoding different lengths somatostatin and delivered by attenuated Salmonella choleraesuis C500. A, Map of construction of oral SS-14 DNA vaccine fused tPA signal peptide and CpG adjuvant named C500 (ptCS/2SS-14-asd); B, Map of construction of oral SS-28 DNA vaccine fused tPA signal peptide and CpG adjuvant named C500 (ptCS/2SS-28-asd); C, Map of construction of oral empty vector vaccine fused CpG adjuvant named C500 (pCpG-asd).