Cloning and expression of the fusion protein of interleukin-2 and ESAT6 in Mycobacterium bovis Bacillus Calmette Guerin strain

摘要

Tuberculosis (TB) is the most common cause of death in infectious diseases; it is estimated that approximately 2 million people per year die of TB. The present available TB vaccine is a live attenuated strain, Mycobacterium bovis Bacillus Calmette Guerin (BCG). However, it has been shown that BCG has variable protective efficacy, ranging from 0 to 85% in different clinical experiments. Therefore, a new TB vaccine is urgently needed. Many trials have been done to develop the second-generation TB vaccines in recent years; candidates include avirulent, auxotrophic, subunit, DNA, and recombinant vaccines. The outcomes of these vaccines disappointed investigators. Encouragingly, recombinant BCG, which overexpressed the mycobacterial antigen Ag85B, produced an excellent protective response, suggesting that a vaccine based on recombinant BCG technique was a potential approach against TB. Mouse-, rat- and human-origin interleukin-2 (IL-2) has been expressed in rBCG strains in recent years. It has been manifested that BCG expressing IL-2 enhances the production of interferon-γ (IFN-γ), thus augmenting the host' s immune responses against mycobacteria infection. ESAT6, which is a secretory protein from RD1 region of Mycobacterium tuberculosis genome and does not exist in all available BCG strains, is a dominant antigen for cell-mediated immunity. In order to improve the protective efficacy of the vaccine, we constructed a rBCG strain which could secrete the fusion protein of human cytokine IL-2 (huIL2) and ESAT6, and then investigated the growth characteristics of rBCG in vitro and in vivo.