(819) BCG vaccine induced CD4 T cell activation is dependent on processing by cDC1 and cDC2 subsets of human dendritic cells.

Introduction/Rationale: Tuberculosis due to Mycobacterium tuberculosis (Mtb) kills a million people each year and the widely used BCG vaccine is partially effective. We examined the mechanism of its antigen processing in human PBMC derived DCs since they are critical for T cell activation preceding TH1 immunity.

Methods: Human cDC1 and cDC2 were bead purified from culture enriched PBMCs, infected with BCG Copenhagen vaccine, followed by gene expression analysis using a RT2-PCR array and in vitro assays to measure BCG infected DCs how well they present Antigen85B-derived peptide to CD4 T cells.

Results: The gene expression array showed that BCG infected cDC1 strongly express autophagy related ATG5 gene along with Cathepsins and HDAC1, which drives DC differentiation. These biomarkers were greatly reduced in cDC2. BCG infected cDC1 overlaid using specific CD4-T cells secreted higher levels of IL-2 than BCG Infected cDC2. Blockade of HDAC1 using vorinostat reduced antigen presentation in cDC1 but not cDC2. Likewise, 3-methyladenine blockade of autophagy, reduced antigen presentation only in cDC1. We propose that cDC1 has autophagy-dependent MHC-II antigen presentation to CD4 T cells unlike cDC2, and hypothesize that targeting BCG during vaccination to cDC1 subset may enhance its efficacy.

Conclusion: We propose that cDC1 has autophagy-dependent MHC-II antigen presentation to CD4 T cells unlike cDC2, and hypothesize that targeting BCG during vaccination to cDC1 subset may enhance its efficacy.