A novel quadruple knockout MTb vaccine against tuberculosis (Supplement Resubmission) - Summary
Tuberculosis (TB), caused by the bacterial pathogen Mycobacterium tuberculosis (Mtb), is a global
health issue and is a significant cause of disability and mortality throughout the world. Currently, Bacille
Calmette-Guerin (BCG) remains the only approved vaccine against tuberculosis (TB), but its capability in
preventing the progression of infection to disease is utterly disappointing. We recently discovered that one of
the main reasons for the failure of mycobacterial live-attenuated vaccines, including BCG, is their ability to
evade phagolysosomal fusion (PL fusion) in the antigen presenting cells (APCs) such as macrophages and
dendritic cells. Due to this evasion mechanism, the antigens of these vaccines are not fully processed and
presented to the immune system by APCs, leading to the induction of a limited immune response in the host,
and consequently limited efficacy. To overcome this blockade and also to provide the full repertoire of Mtb
antigens to host immune cells, we developed a novel concept of rationally deleting genes in Mtb whose
products play a critical role in the evasion of PL fusion and other immune suppression mechanisms.
Accordingly, we developed a double knockout (ΔfbpA-ΔsapM; DKO) strain by deleting the genes fbpA
(Rv3804c) and sapM (Rv3310) in Mtb H37Rv. The DKO strain, not only showed increased immunogenicity in
relation to their parental strain and BCG but also displayed enhanced efficacy in the murine model as
compared to BCG. However, subsequent studies demonstrated that the DKO strain still exhibits considerable
virulence in mice, necessitating further attenuation to be a vaccine candidate.
In order to reduce the virulence of the DKO strain and simultaneously further increase its
immunogenicity, we rationally deleted two additional genes in DKO resulting in a quadruple knockout 1 (QKO1)
strain. The deleted genes include zmp1 (Rv0198c) and dosR (Rv3133c) which code for a metalloprotease
enzyme and a dormancy response regulator protein, respectively. Our preliminary results indicate that the
QKO1 vaccine strain is markedly immunogenic both in vitro and in vivo, as compared to DKO and BCG, and
severely attenuated in macrophages. These preliminary results indicate that this strain has a strong potential to
be the ‘new generation TB vaccine’. In this application, we propose studies to evaluate the utility of the QKO1
strain further. The aims are: 1) Assess the efficacy of QKO1 against TB in the murine model of infection and, 2)
Examine the safety of the QKO1 strain in the murine model of infection. We expect that the study will provide a
new Mtb derived highly effective vaccine against TB, possibly a potential replacement to BCG. In addition, we
expect that the research project will help train six graduate students in high quality research in infectious
diseases.
