Evaluation Of CpG ODN As Adjuvant For Subunit Vaccine Of Mycobacterium Tuberculosis

Objective: CpG ODN is a novel adjuvant with strong capacity of stimulating immuneresponse. The present study aimed to investigate the ability of CpG1826and CpG7909adjuvant to enhance immunogenicity and protective efficacy of a subunit vaccine composedof ESAT-6and Ag85a fusion protein (Pe685a) of Mycobacterium tuberculosis.Methods: Mixtures of CpG1826plus Pe685a and CpG7909plus Pe685a wererespectively injected intraperitoneal to homologous mice groups, and PBS, CpG1826,CpG7909, and incomplete Freund’s adjuvant plus Pe685a control groups were included.Immunization was repeated thrice with2-week intervals after the primary immunization.Mice were sacrificed for immunoassay at two weeks after the last immunization. ELISAwas used to detect specific antibody and cytokine expression in sera, MTT assay detectsplenocytes proliferation, FACS detect CD4+and CD8+T lymphocytes activation in spleen,and RT-PCR detect cytokine expression in spleen. The remaining mice were used forchallenge with M. tuberculosis H37Rv virulent strain by the way of caudal vena.Histopathological lesions in lungs of mice at four weeks after challenge with M.tuberculosis H37Rv strain were analyzed.Results: Compared to incomplete Freund’s adjuvant, CpG7909but not CpG1826induced more potent production of Pe685a-specific antibody and higher expression ofIFN-γ and IL-2in sera, enhanced lymphocyte proliferation and differentiation of CD4+andCD8+T lymphocytes in spleen, increased transcription of IFN-γ, TNF-α, IL-6, and TLR9inspleen. However, less severe lung pathology was not observed in CpG7909plus Pe685agroup mice, compared with incomplete Freund’s adjuvant plus Pe685a group. Conclusions: CpG7909but not CpG1826is able to enhance immunological effects ofPe685a subunit vaccine. CpG7909cannot confer more significant protective efficacyagainst M. tuberculosis infection. Thus, CpG ODN adjuvant of subunit vaccine against M.tuberculosis still need to be further investigated.