CT-011, Anti-PD-1 Antibody, Enhances Ex-Vivo T Cell Responses to Autologous Dendritic/Myeloma Fusion Vaccine Developed for the Treatment of Multiple Myeloma.

Abstract 781

We have developed a promising cancer vaccine in which autologous tumor cells are fused with dendritic cells (DCs) resulting in the presentation of tumor antigens in the context of DC mediated costimulation. In animal models, vaccination with fusion cells results in eradication of established tumor, and in clinical trials, both immunologic and clinical responses have been observed. However, response to vaccination may be muted by inhibitory pathways that blunt activated T cell responses. The PD-1/PDL-1 pathway is an important element contributing to tumor mediated immune suppression. In infectious disease models, upregulation of T cell expression of PD-1 is associated with an exhausted phenotype facilitating the development of chronic viral infection. In contrast, PD-1 blockade results in the restoration of functionally active T cells and clearance of infection. The PD-1/PDL-1 pathway is also being evaluated a as a central mechanism by which tumors escape host immunity. CT-011, is a humanized anti PD-1 antibody that is currently evaluated in Phase II studies for the treatment of hematological malignancies and solid tumors. In this study, we evaluated expression of PD-1 on T cells derived from patients with advanced hematologic malignancies, and PDL-1 expression on primary myeloma cells, ex-vivo generated dendritic cells, and DC/tumor fusion cells. We evaluated the effect of PD-1 blockade with CT-011 on T cell response to DC/tumor fusion cell stimulation in vitro. Tumor cells were obtained from bone marrow aspirates of patients with multiple myeloma. Nonadherent peripheral blood mononuclear cells obtained from patients with multiple myeloma and normal volunteers were cultured in RPMI supplemented with 10U/ml IL-2, and expression of PD-1 on CD4+ T cells was assessed by flow cytometric analysis . DCs were generated from adherent mononuclear cells cultured with rhIL-4, GM-CSF and TNFα and fused with tumor cells by coculture in 50% solution of polyethylene glycol. T cells were stimulated by DC/tumor fusions in the presence or absence of 5ug/ml CT-011. We demonstrate that PD-1 expression is markedly upregulated on T cells in patients with advanced multiple myeloma. As compared to a control population of normal volunteers in which mean levels of PD-1 expression was 6% (n=7), mean expression in patients with multiple myeloma was 20% (n=9). These findings suggest that upregulation of PD-1 expression may play a central role in tumor mediated immune suppression. Mean expression of PDL-1 was 91% on dendritic cells generated from adherent peripheral blood mononuclear cells obtained from normal volunteers (n=6), and 66% on patient derived myeloma cells (n=3). In addition, PDL-1 expression is found in greater than 90% of DC/tumor fusions (n=2), which potentially provides an inhibitory signal dampening fusion mediated immunologic response. We examined the effect of PD-1 blockade on T cell response to DC/tumor fusions ex vivo with different anti PD-1 antibodies including CT-011. DC/tumor fusions were co-cultured with autologous T cells alone or with antibodies against PD-1 Enhanced fusion mediated stimulation of T cells was noted particularly with CT-011, resulting in a greater than 5 fold increase in T cell proliferation. Interferon gamma secretion by CD4+ T cells in response to stimulation by DC/myeloma fusion cells was increased from 4% to 11% in the presence of CT-011. In addition, IL-10 secretion by CD4+ cells following DC/myeloma fusion stimulation decreased from 6.5% to 3.5% following PD-1 blocakde . In summary, we have demonstrated that PD-1 expression is increased in T cells of patients with hematologic malignancy, and CT-011, a PD-1 blocking antibody, enhances activated T cell responses following stimulation with a DC/tumor fusion vaccine. A clinical trial in which patients with multiple myeloma are treated with DC/myeloma fusions in conjunction with CT-011 following autologous transplantation is planned.