Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in activating cellular and humoral immune responses. DC-based
tumor vaccines targeting
tumor-associated
antigens (TAAs) have been extensively tested and demonstrated to be safe and potent in inducing anti-TAA immune responses in
cancer patients.
Sipuleucel-T (
Provenge), a
cancer vaccine of autologous DCs loaded with TAA, was approved by the United States Food and Drug Administration (FDA) for the treatment of
castration-resistant
prostate cancer.
Sipuleucel-T prolongs patient survival, but has little or no effect on clinical
disease progression or
biomarker kinetics. Due to the overall limited clinical efficacy of
tumor vaccines, there is a need to enhance their potency. PD-L1 is a key
immune checkpoint molecule and is frequently overexpressed on
tumor cells to evade antitumor immune destruction. Repeated administrations of PD-L1 or PD-1
antibodies have induced sustained
tumor regression in a fraction of
cancer patients. In this study, we tested whether vaccinations with DCs, loaded with a PD-L1 immunogen (PDL1-Vax), are able to induce anti-PD-L1 immune responses. We found that DCs loaded with PDL1-Vax induced anti-PD-L1 antibody and T cell responses in immunized mice and that PD-L1-specific CTLs had cytolytic activities against PD-L1+
tumor cells. We demonstrated that vaccination with PDL1-Vax DCs potently inhibited the growth of PD-L1+
tumor cells. In summary, this study demonstrates for the first time the principle and feasibility of DC vaccination (PDL1-Vax) to actively induce anti-PD-L1 antibody and T cell responses capable of inhibiting PD-L1+
tumor growth. This novel anti-PD-L1 vaccination strategy could be used for
cancer treatment and prevention.