Deletion of BCG Hip1 protease enhances dendritic cell and CD4 T cell responses

Abstract

Dendritic cells (DCs) play a key role in the generation of CD4 T cell responses to pathogens. Mycobacterium tuberculosis (Mtb) harbors immune evasion mechanisms that impair DC responses and prevent optimal CD4 T cell immunity. The vaccine strain Mycobacterium bovis Bacille Calmette-Guérin (BCG) shares many of the immune evasion proteins utilized by Mtb, but the role of these proteins in DC and T cell responses elicited by BCG is poorly understood. We previously reported that the Mtb serine protease, Hip1, promotes sub-optimal DC responses during infection. Here, we tested the hypothesis that BCG Hip1 modulates DC functions and prevents optimal antigen-specific CD4 T cell responses that limit the immunogenicity of BCG. We generated a strain of BCG lacking hip1 (BCGΔhip1) and show that it has superior capacity to induce DC maturation and cytokine production compared with the parental BCG. Furthermore, BCGΔhip1-infected DCs were more effective at driving the production of IFN-γ and IL-17 from antigen-specific CD4 T cells in vitro. Mucosal transfer of BCGΔhip1-infected DCs into mouse lungs induced robust CD4 T cell activation in vivo and generated antigen-specific polyfunctional CD4 T cell responses in the lungs. Importantly, BCGΔhip1-infected DCs enhanced control of pulmonary bacterial burden following Mtb aerosol challenge compared with the transfer of BCG-infected DCs. These results reveal that BCG employs Hip1 to impair DC activation, leading to attenuated lung CD4 T cell responses with limited capacity to control Mtb burden after challenge.

Immunology ofMycobacterium tuberculosisInfections

“…Additionally, M. tuberculosis promotes suboptimal antigen presentation in vitro and in vivo without detectable differences in the expression levels of costimulatory molecules when compared to BCG infected DCs(266). Interestingly, studies using a mutant M. tuberculosis strain lacking hip1 (discussed above) indicate that M. tuberculosis readily impairs DC costimulation and cytokine production to evade antigen-specific CD4 T-cell responses(107, 109) and a recent study demonstrated that BCG hip1 retains similar immune evasion functions(267). Taken together, the initiation of the adaptive immune response requires the participation of DCs, which themselves are readily infected and subverted by M. tuberculosis infection.…”

Glucose metabolism and its role in the maturation and migration of human CD1c+ dendritic cells following exposure to BCG

“…This may enable bystander cells to bypass pathogen-mediated inhibition of innate immune signaling in the directly infected cell ( Holmgren et al., 2017 ). Indeed, BCG retains immunomodulatory factors like Hip1 that negatively impact DC responses, including CD40 expression, leading to impaired control of Mtb after challenge ( Bizzell et al., 2018 ). Bystander effects have been observed previously in murine DCs infected with BCG: secretion of IL-12p40 was impaired in directly infected splenic CD11c + DCs from mice expressing a YFP-tagged IL-12p40 gene and bystander DCs were responsible for IL-12p40 secretion ( Rothfuchs et al., 2009 ).…”

Mycobacterium tuberculosis impedes CD40-dependent notch signaling to restrict Th17 polarization during infection

“…BCG has previously been shown to affect DC expression of Notch ligands ( Ito et al., 2009 ; Schaller et al., 2016 ) and TLR9 was reported to regulate granulomas induced by BCG via DLL4 ( Ito et al., 2009 ). Our lab has developed a knockout of hip1 in BCG (BCGΔ hip1 ) and found it to induce higher levels of IL-17 than wild type BCG ( Bizzell et al., 2018 ). Thus, it would be interesting to test whether DLL4 signaling is operant in the context of BCGΔ hip1 vaccination and whether engaging the CD40-DLL4 axis has an adjuvant effect on BCGΔ hip1 vaccination.…”