Immunological evaluation of virulence-deficient Listeria monocytogenes strains in C57BL/6 mice

Attenuated Listeria monocytogenes (L. monocytogenes), which has unique advantages in presenting foreign antigens, was widely used in tumor immunotherapy research. As a live vaccine vector, attenuated L. monocytogenes was required to not only have certain invasiveness but also ensure safety, while the lack of different virulence factors may cause L. monocytogenes to show different safety and invasiveness. To evaluate the potential of virulence-deficient L. monocytogenes strains as a vaccine vector, four mutant strains EGD-e Delta actA, EGD-e Delta actA/inlB, EGD-e Delta hly, and EGD-e Delta prfA were used to infect C57BL/6 mice for determining related immune indexes. Compared with EGD-e, mutant strains showed significantly decreased invasion in C57BL/6 mice and caused relatively minor damage to spleen and liver. However, EGD-e Delta actA and EGD-e Delta actA/inlB were superior to EGDe Delta hly and EGD-e Delta prfA in the comprehensive evaluation of inflammatory factor transcription level, immune cell differentiation and antibody level, which proved that they have a stronger adjuvant effect as a vaccine vector.