Role of SERPINB9 in resistance to CTL-mediated killing exhibited by HIV-infected CD4+ T cells vs macrophages 9391

Description Despite combined anti-retroviral therapy, HIV-infected CD4+ T cells and macrophages persist, creating a barrier to viral clearance. Macrophage killing by CD8+ cytotoxic T cells (CTLs) in vitro has been shown to activate the caspase-3 pathway and require granzyme B. We hypothesize that macrophages use SERPINB9, an inhibitor of granzyme B, to antagonize death by CTLs. Primary CD4+ T cells and macrophages from HIV- PBMCs were used as target cells. Both cell types were infected with HIV89.6 or loaded with cognate peptide for co-culture assays. HIV-specific (B*57-Gag TW10) CTL clones or A*02-restricted CMV-, EBV-, and Flu-specific polyclonal CTLs were used as effector cells. Peptide-loaded CD4+ T cells and macrophages are recognized by CTLs similarly, but high effector-to-target ratios are needed for comparable killing. Surviving macrophages exhibit Caspase-3/7 activity. SERPINB9 expression is similar in infected vs uninfected cells, and SERPINB9 knock out target cells are killed similarly to control-edited targets in both CD4+ T cells and macrophages. While SERPINB9 expression in cancer and HIV-infected cells has been suggested to be protective, our data shows that SERPINB9 does not protect CD4+ T cells or macrophages from CTL attack. Interestingly, caspase-3 and/or -7 are activated in surviving macrophages, which fail to become necrotic following CTL attack. These results emphasize the need to study additional endogenous inhibitors of granzyme-mediated cell death pathways.