Investigation of antigenic properties of recombinant OmpA protein from Mycobacterium tuberculosis

In this study, it was aimed to investigate the potential of OmpA protein from Mycobacterium tuberculosis to be used for a new vaccine against M. tuberculosis, the causative agent of tuberculosis (TB) disease in human. Development of new recombinant TB vaccines are needed because the BCG vaccine in use worldwide is low in protection among the adults. The ompA gene from M. tuberculosis isolated from a Turkish patient was cloned first in pGEM-T, and then pET28a vector. The his-tagged OmpA protein expressed in E. coli BL21 strain was purified using nickel columns. The vaccine formulation was prepared mixing the recombinant OmpA and an oil-based adjuvant Montanide ISA 720 VG in 7:3 proportion. The vaccine formulation, adjuvant, and BCG vaccine was s.c. injected to 5 BALB/c mice. The sera samples were collected from the tail blood collected pre-immunization, 15th, 30th, 41st, and 66th days post-immunization. Western blot experiment was applied to show the antigenic property of recombinant OmpA qualitatively. The desired molecular weight bands were detected when the sera from recombinant OmpA and BCG injected mice were used; however, no band was seen using the sera specific to adjuvant was used. The capacity of OmpA formulation to induce the humoral and cellular immune response in BALB/c mice was evaluated. It was shown that the OmpA formulation induced the serum IgG level significantly, efficient in induction of serum IFN-γ level as BCG; however, weak in induction of serum IL-12 level. Recombinant OmpA protein might be used in TB vaccine development using double or triple fusions with different proteins, or different adjuvants inducing cellular response, such as CpG oligonucleotides. It is needed to evaluate the the protection capacity of OmpA formulation via assaying the M. tuberculosis adhesion in lungs and spleen.