An autophagy-inducing and TLR-2 activating BCG vaccine induces a robust protection against tuberculosis in mice

Arshad Khan,Christopher R Singh,Chinnaswamy Jagannath,Kishore Das,N Tony Eissa,Jaymie L Estrella,Yue Ma,Emily Soudani,Subramanian Dhandayuthapani,Jianjun Sun,Jin Wang,Chandrashekhar Pasare,Sankaralingam Saikolappan,Robert L Hunter,Pearl Bakhru,Dekai Zhang

doi:10.1038/s41541-019-0122-8

Abstract

Mycobacterium bovis BCG is widely used as a vaccine against tuberculosis due to M. tuberculosis (Mtb), which kills millions of people each year. BCG variably protects children, but not adults against tuberculosis. BCG evades phagosome maturation, autophagy, and reduces MHC-II expression of antigen-presenting cells (APCs) affecting T-cell activation. To bypass these defects, an autophagy-inducing, TLR-2 activating C5 peptide from Mtb-derived CFP-10 protein was overexpressed in BCG in combination with Ag85B. Recombinant BCG85C5 induced a robust MHC-II-dependent antigen presentation to CD4 T cells in vitro, and elicited stronger TH1 cytokines (IL-12, IL-1β, and TNFα) from APCs of C57Bl/6 mice increasing phosphorylation of p38MAPK and ERK. BCG85C5 also enhanced MHC-II surface expression of MΦs by inhibiting MARCH1 ubiquitin ligase that degrades MHC-II. BCG85C5 infected APCs from MyD88 or TLR-2 knockout mice showed decreased antigen presentation. Furthermore, BCG85C5 induced LC3-dependent autophagy in macrophages increasing antigen presentation. Consistent with in vitro effects, BCG85C5 markedly expanded both effector and central memory T cells in C57Bl/6 mice protecting them against both primary aerosol infection with Mtb and reinfection, but was less effective among TLR-2 knockout mice. Thus, BCG85C5 induces stronger and longer lasting immunity, and is better than BCG against tuberculosis of mice.

Highlights

Mycobacterium tuberculosis (Mtb) causes eight million new cases of tuberculosis and kills about two million people each year
We examined the hypothesis that CFP-10 and ESAT-6 may exert individual effects, while their complexes have a different effect on antigen-presenting cells (APCs).[31,32,33]
An in vitro model of antigen presentation has been described where mouse APCs infected with Mtb or Bacille CalmetteGuérin (BCG) vaccine present the peptide-25 epitope of secreted Ag85B to CD4 T cells (BB7 hybridoma).[13,35,36]

Summary

Introduction

Mycobacterium tuberculosis (Mtb) causes eight million new cases of tuberculosis and kills about two million people each year. Its variable efficacy is multifactorial, including absence of the major immunogenic region of difference-1 (RD1) encoded antigens ESAT-6 and CFP-10 in BCG; variable expression of other antigens like MPT64 among sub-strains of BCG; and exposure of humans to environmental mycobacteria, thought to pre-sensitize and shift vaccine responses from TH1 to TH2 responses.[2] Since BCG vaccine is safe, improving its immunogenicity appears to be a reasonable approach, we and others have generated Mtbderived attenuated candidate vaccines.[3,4,5] Many studies describe recombinant BCG strains with increased immunogenicity.[6] Animal models indicate that both CD4 and CD8 T cells are important for immunity against tuberculosis.[7] In humans, CD4 T cells appear to be critical since HIV-1-induced depletion leads to tuberculosis coinfection and increased death. CD8 T cells seem to contribute to long-term protection against tuberculosis in humans

Methods

Results

Conclusion