siRNA knockdown of PD-L1 and PD-L2 in monocyte-derived dendritic cells only modestly improves proliferative responses to Gag by CD8(+) T cells from HIV-1-infected individuals.

INTRODUCTION: Due to their capacity to elicit and regulate immunity, dendritic cells (DCs) are important targets to improve vaccination. Knowing that programmed death-1 (PD-1) high virus-specific T cells become functionally exhausted during chronic exposure to human immunodeficiency virus-1 (HIV-1), the development of a therapeutic DC-based HIV-1 vaccine might include strategies that downregulate PD-L1 and PD-L2 counter-receptors.
METHODS: After showing that monocyte-derived DCs rapidly upregulated PD-L1 and PD-L2 expression upon maturation with a variety of stimuli, e.g., Toll-like receptor ligands and cytokines, we determined that PD-L1 and PD-L2 expression could be knocked down by electroporation of a single small interfering RNA (siRNA) sequence twice at the monocyte and immature stages of DC development. This knockdown approached completion and was specific and lasting for several days.
RESULTS: We then added the PD-L1 and PD-L2 silenced monocyte-derived DCs to peripheral blood mononuclear cells from HIV-1-infected individuals along with pools of 15-mer HIV-1 Gag p24 peptides. However, in cultures from six patients, there was only a modest enhancing effect of PD-L1 and PD-L2 silencing on CD8(+) T cell proliferative responses to the DCs. DISCUSSION: These findings suggest that, in monocyte-derived DCs, additional strategies than PD-L1 or PD-L2 blockade will be needed to improve the function of PD-1 high T cells.