PD-1 Blockade by CT-011, Anti-PD-1 Antibody, Enhances Ex Vivo T-cell Responses to Autologous Dendritic Cell/Myeloma Fusion Vaccine

We have developed a cancer vaccine in which autologous tumor is fused with dendritic cells (DCs) resulting in the presentation of tumor antigens in the context of DC-mediated costimulation. In clinical trials, immunologic responses have been observed, however responses may be muted by inhibitory pathways. The PD1/PDL1 pathway is an important element contributing to tumor-mediated immune suppression. In this study, we demonstrate that myeloma cells and DC/tumor fusions strongly express PD-L1. Compared with a control population of normal volunteers, increased PD-1 expression was observed on T cells isolated from patients with myeloma. It is interesting to note that after autologous transplantation, T-cell expression of PD-1 returned to levels seen in normal controls. We examined the effect of PD-1 blockade on T-cell response to DC/tumor fusions ex vivo. Presence of CT-011, an anti-PD1 antibody, promoted the vaccine-induced T-cell polarization towards an activated phenotype expressing Th1 compared with Th2 cytokines. A concomitant decrease in regulatory T cells and enhanced killing in a cytotoxicity assay was observed. In summary, we demonstrate that PD-1 expression is increased in T cells of patients with active myeloma, and that CT-011 enhances activated T-cell responses after DC/tumor fusion stimulation.