Abstract
Modern strategies to develop vaccines against Mycobacterium tuberculosis (Mtb) aim to improve the current Bacillus Calmette-Guerin (BCG) vaccine or to attenuate the virulence of Mtb vaccine candidates. In the present study, the impact of wild type or mutated region of difference 1 (RD1) variants on the immunogenicity of Mtb and BCG recombinants was investigated in human primary dendritic cells (DC). A comparative analysis of transcriptome, signalling pathway activation, maturation, apoptosis, cytokine production and capacity to promote Th1 responses demonstrated that DC sense quantitative and qualitative differences in the expression of RD1-encoded factors—ESAT6 and CFP10—within BCG or Mtb backgrounds. Expansion of IFN-γ producing T cells was promoted by BCG::RD1-challenged DC, as compared to their BCG-infected counterparts. Although Mtb recombinants acted as a strong Th-1 promoting stimulus, even with RD1 deletion, the attenuated Mtb strain carrying a C-terminus truncated ESAT-6 elicited a robust Th1 promoting phenotype in DC. Collectively, these studies indicate a necessary but not sufficient role for the RD1 locus in promoting DC immune-regulatory functions. Additional mycobacterial factors are likely required to endow DC with a high Th1 polarizing capacity, a desirable attribute for a successful control of Mtb infection.
Highlights
Several TB vaccination strategies are based either on improvements in bacillus Calmette-Guerin (BCG) immunogenicity or on attenuation of Mycobacterium tuberculosis (Mtb) virulence through insertion, mutation or deletion of this locus
Data set analysis revealed that dendritic cells (DC) infection with either wild type Mtb or MtbΔ region of difference 1 (RD1)::RD1 up-regulated the transcription of 215 genes in DC, whereas infection with MtbΔ RD1::B412 up-regulated ~100 genes
Providing that RD1-encoded factors were shown to influence the signaling pathways leading to cytokine gene expression in Mtb infected cells[26], we investigated in DC challenged with Mtb and BCG recombinants the intracellular activation of Mitogen-activated protein kinase (MAPK) and Nuclear Factor (NF)-kB, both involved in the transcriptional regulation of tumor necrosis factor (TNF) and IL-12 family members (Fig. 4)
Summary
Several TB vaccination strategies are based either on improvements in BCG immunogenicity or on attenuation of Mtb virulence through insertion, mutation or deletion of this locus. A more complex link between RD1 and the control of the autophagic flux was recently identified by our group in human dendritic cells (DC)[16] In this setting, we demonstrated that the autophagy block induced by RD1-encoded ESX-1 secretion system was overcome by a treatment with the autophagy inducer, rapamycin, which further induced IL-12 production and, in turn, strengthened the capacity of DC to expand a T helper (Th)1-oriented response. We sought to investigate how infection with BCG and Mtb recombinant strains, complemented with or deleted in the RD1 locus, or expressing mutated variants of the ESAT-6/CFP-10 complex, would impact DC functions These studies revealed the capacity of DC to sense quantitative and qualitative differences among the Mtb and BCG recombinants, and highlight a necessary but not sufficient role for the RD1 locus in promoting DC immune-regulatory functions
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