Conjugation Reaction with 8-Arm PEG Markedly Improves the Immunogenicity of Mycobacterium tuberculosis CFP10-TB10.4 Fusion Protein

Mycobacterium tuberculosis (Mtb) is a serious fatal pathogen responsible for tuberculosis (TB). Effective vaccination is highly desired for immunoprotection against Mtb infection. CFP10 and TB10.4 are two important immunodominant Mtb-secreted protein antigens, which suffer from poor immunogenicity. Thus, an antigen delivery system and adjuvants are needed to improve the immunogenicity of the two proteins. A CFP10-TB10.4 fusion protein (CT) was used as the antigen in the present study. Conjugation of 4-6 CT molecules in one entity with 8-arm polyethylene glycol (PEG) acted as an antigen delivery system. Aluminum-loxoribine mixture (A-L) and poly(I:C) functioned as the adjuvants. As compared with CT, the polymerized CT (CT-PEG) elicited significantly higher CT-specific IgG titers, higher Th1- and Th2-type cytokines and higher percentages of CD4⁺ IFN-γ⁺ and CD4⁺ IL-4⁺ cells in BALB/c mice. The presence of A-L and poly(I:C) could both increase the immune response to CT-PEG. Conjugation reaction with 8-arm PEG showed a predominant driving force to improve the immunogenicity of CT. Pharmacokinetic study in SD rats revealed that conjugation reaction with 8-arm PEG prolonged the systemic circulation of CT and exposure to the immune system. CT-PEG with A-L showed no apparent toxicity to organs, whereas CT-PEG with poly(I:C) displayed some toxicity to organs. Thus, an effective and safe vaccine against Mtb infection could be rationally designed by conjugation reaction of Mtb-secreted protein antigen with 8-arm PEG and subsequent addition of A-L.

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