The Synthetic Antimicrobial Peptide KLKL 5 KLK Enhances the Protection and Efficacy of the Combined DNA Vaccine against Mycobacterium tuberculosis

In this study, we evaluated the potential of the synthetic antimicrobial peptide KLKL₅KLK to augment the immune response and protective efficacy of the combined DNA vaccine against Mycobacterium tuberculosis. We demonstrated that immunization of mice with a combined DNA vaccine/KLKL₅KLK mixture resulted in significantly higher protection than that induced by the combined DNA vaccine alone or by the Bacillus Calmette-Guérin (BCG) vaccine after challenge with a virulent M. tuberculosis strain (p < 0.01). Detailed analysis of the immune response revealed that the combined DNA vaccine/KLKL₅KLK mixture stimulated higher IL-12 secretion, resulted in significantly more CD4⁺/CD44^high and CD8⁺/CD44^high T-cell production (p < 0.01), elicited 1.5- to 1.8-fold higher interferon-γ (IFN-γ) production, and produced stronger antigen-specific cytotoxic T lymphocyte activity than the combined DNA vaccine alone. Further, 125 days after the final immunization, mice immunized with the combined DNA vaccine/KLKL₅KLK mixture significantly outpaced their combined DNA vaccine–immunized counterparts regarding antigen-specific IFN-γ–producing cell numbers (p < 0.05) and antigen-specific IgG titers, indicating that KLKL₅KLK provides a stronger and longer Th1-associated immune response. Taken together, our results indicate that the synthetic peptide KLKL₅KLK is a potent adjuvant that can enhance and prolong the immune response of the combined DNA vaccine against M. tuberculosis.