MIP-3α-antigen fusion DNA vaccine enhances sex differences in tuberculosis model and alters dendritic cell activity...

Tuberculosis disease (TB) caused by Mycobacterium tuberculosis (Mtb) bacteria remains a major cause of global morbidity and mortality. Efforts to control TB are hampered by the lengthy and cumbersome treatment required to eradicate the Mtb infection. Bacterial persistence during exposure to bactericidal antibiotics is at least partially mediated by the bacterial stringent response enzyme, Rel_Mtb. A therapeutic DNA vaccine targeting Rel_Mtb has been shown to increase the efficacy of antitubercular drugs, and fusing macrophage-inflammatory protein 3α (MIP-3α), which interacts with CCR6 on immature dendritic cells (iDCs), to Rel_Mtb further increases the vaccine's therapeutic efficacy. A secondary analysis of these prior studies elucidated prominent sex-based differences in vaccine therapeutic efficacy, with female mice showing improved microbial outcomes compared to males as a result of the Rel and MIP-3α-Rel vaccine constructs, with a more pronounced sex-associated difference in the MIP-3α-Rel group. In the current study, we addressed the hypothesis that these sex-related differences are at least in part due to differential DC activation/function soon after vaccination. An EαGFP reporter vaccine model was used to track vaccine antigen presentation in the draining node with flow cytometry panels by an antibody Y-Ae which binds the Eα peptide tag in complex with I-A^b MHC-II molecules. Additionally, a qRT-PCR panel assessing DC-related genes compared sexes receiving the MIP-3α-Rel vaccine. MIP-3α-EαGFP groups had more DCs presenting vaccine antigen infiltrating from the periphery, with more abundant Langerhans cells in males and greater CD8+ CD103+ cross-presenting dermal DCs in females. This model also shows there is greater DC activation, as measured by CD80 and MHC II MFI, by MIP-3α compared to EαGFP alone, especially in female mice. The genetic panel showed females more enriched for chemokines and genes related to cell movement and cross-presentation. Our findings are consistent with the sex- and MIP-3α-related differences seen in the therapeutic model and supports the hypothesis that in both sexes MIP-3α enhances vaccine uptake and cell activation by peripheral iDCs. Additionally, female mice showed greater levels of antigen presentation, especially in DCs able to cross-present antigen, likely explaining why they had the best outcomes. Further studies are required to understand underlying mechanisms and to link APC results directly to T-cell responses.