Dissecting the immunogenicity of RD1-recombinant live tuberculosis vaccine candidates studying host-pathogen interaction in human primary dendritic cells

New tuberculosis vaccines are highly desirable and urgently needed since the attenuated Mycobacterium bovis Bacillus Calmette-Guerin (BCG) provides only variable efficacy against the pulmonary form of the disease. The region of difference 1 (RD1), which is deleted in BCG and strongly impacts on Mycobacterium tuberculosis (Mtb) virulence and immunogenicity, represents a crucial locus to be engineered for either the improvement of the current BCG vaccine, or the attenuation of Mtb. Therefore, mutants secreting or not wild-type or mutated variants of the RD1-encoded 6 kDa early secreted antigenic target (ESAT-6) were generated. Comparative analysis of the transcriptome, phenotype, cytokine production profiles and the capacity to promote T cell responses were conducted in human primary dendritic cells (DCs), as they represent critical regulators of vaccine-induced immunity, unveiling a distinct immunogenic potential for BCG or Mtb mutants. In contrast to Mtb, BCG induced a poor DC maturation, and to our surprise, a BCG strain complemented with the RD1 region only partially restored DC maturation and expansion of interferon (IFN)-γ producing T cells. In contrast, infection with a recombinant attenuated Mtb strain, secreting a truncated version of ESAT-6 lacking 11 amino acids at the C-terminus portion, drove full maturation in infected DC and maintained their capacity to promote polarization of T helper (Th) 1 cells, as observed upon infection with the virulent Mtb. We performed a comparative microarray analysis of dendritic cells (DCs), infected with Mtb and BCG strains, expressing/complemented (MtbΔRD1::RD1 and BCG::RD1) or not (MtbΔRD1::B412 and BCG::B412) the/with the RD1 region. DCs were challenged with different BCG and Mtb recombinant strains for 8h.