siRNA silencing of PD-L1 and PD-L2 on dendritic cells augments expansion and function of minor histocompatibility antigen–specific CD8+ T cells

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BlankBlood, 25 November 2010, Vol. 116, No. 22, pp. 4501-4511.

Prepublished online as a Blood First Edition Paper on August 3, 2010; DOI

10.1182/blood-2010-04-278739.

siRNA silencing of PD-L1 and PD-L2 on dendritic cells augments expansion and

function of minor histocompatibility antigen–specific CD8+ T cells

Willemijn Hobo1, Frans Maas1, Niken Adisty1, Theo de Witte2, Nicolaas Schaap3,

Robbert van der Voort1, and Harry Dolstra1

1 Department of Laboratory Medicine–Laboratory of Hematology, and Departments of

2 Tumor Immunology and 3 Hematology, Radboud University Nijmegen Medical Center,

Nijmegen Center for Molecular Life Sciences, Nijmegen, The Netherlands

Tumor relapse after human leukocyte antigen–matched allogeneic stem cell

transplantation (SCT) remains a serious problem, despite the long-term presence

of minor histocompatibility antigen (MiHA)–specific memory T cells. Dendritic

cell (DC)–based vaccination boosting MiHA-specific T-cell immunity is an

appealing strategy to prevent or counteract tumor recurrence, but improvement is

necessary to increase the clinical benefit. Here, we investigated whether

knockdown of programmed death ligand 1 (PD-L1) and PD-L2 on monocyte-derived DCs

results in improved T-cell activation. Electroporation of single siRNA sequences

into immature DCs resulted in efficient, specific, and long-lasting knockdown of

PD-L1 and PD-L2 expression. PD-L knockdown DCs strongly augmented

interferon-(gamma) and interleukin-2 production by stimulated T cells in an

allogeneic mixed lymphocyte reaction, whereas no effect was observed on T-cell

proliferation. Moreover, we demonstrated that PD-L gene silencing, especially

combined PD-L1 and PD-L2 knockdown, resulted in improved proliferation and

cytokine production of keyhole limpet hemocyanin–specific CD4+ T cells. Most

importantly, PD-L knockdown DCs showed superior potential to expand

MiHA-specific CD8+ effector and memory T cells from leukemia patients early

after donor lymphocyte infusion and later during relapse. These data demonstrate

that PD-L siRNA electroporated DCs are highly effective in enhancing T-cell

proliferation and cytokine production, and are therefore attractive cells for

improving the efficacy of DC vaccines in cancer patients.