Blockade of PD-1 in Combination with Dendritic Cell/Myeloma Fusion Cell Vaccination Following Autologous Stem Cell Transplantation

Abstract 578

Autologous stem cell transplantation (ASCT) for multiple myeloma (MM) offers a unique setting to explore the role of immunotherapeutic strategies in eradicating residual disease. A fundamental challenge to developing an effective anti-tumor immune response is overcoming the immunosuppressive milieu by which tumor cells evade host immunity. Key elements contributing to tumor-mediated immune suppression are the increased presence of regulatory T cells in patients with malignancy, and upregulation of the PD-1/PDL1 pathway. Tumor expression of PD-L1 promotes T cell tolerance by binding PD-1 on activated T cells and suppressing their capacity to secrete stimulatory cytokines. In addition, the PD-1/PDL-1 pathway has been shown to inhibit T cell-mediated lysis of tumor cells, potentially preventing a clinically meaningful immunologic response to tumor vaccines. We are conducting a clinical trial in which patients with MM are treated with an anti-PD1 antibody (CT-011) alone (Cohort 1) and in combination with a dendritic cell/myeloma fusion cell vaccine (Cohort 2) following ASCT. To date, 27 patients have been enrolled into Cohort 1, in which patients receive three infusions of CT-011 at doses of 3mg/kg given at 6 week intervals beginning 1–3 months following ASCT. Mean age of the patients is 57 years; 61% are male. 11 patients have received at least two infusions of CT-011. The remaining patients are undergoing pre-transplant therapy/transplant. CT-011 has been well tolerated, with possibly related adverse events consisting of transient grade 1–2 leukopenia, diarrhea, fatigue, arthralgia, rash, and peri-orbital edema. One patient developed grade 3 neutropenia, which resolved after two days without growth factor. Immunologic response was determined by quantifying circulating tumor reactive T cells prior to each dose of CT-011 and at 1, 3, 6 months following the last infusion, as defined by the percentage of T cells expressing IFNg in response to ex vivo exposure to autologous tumor lysate. 4 patients have completed 6 months of follow up after the third dose of CT-011, and are evaluable for immune response. CT-011 therapy was associated with the dramatic expansion of myeloma specific T cells. Mean percentage of circulating tumor reactive CD4+ and CD8+ T cells increased from 1.5 and 1.96 respectively prior to the first infusion of CT-011, to 4.26 and 8.28 respectively 1 month following the third infusion. As determined by tetramer staining in the subset of patients who are HLA A2.1, infusion of CT-011 resulted in a mean 9 fold expansion of T cells specific to the MUC1 antigen, which is aberrantly expressed by myeloma cells. Notably, immunologic response to CT-011 persists at 6 months following completion of therapy. Clinical response, as determined by time to disease progression, will be determined with longer follow up, as the median time from transplant is presently 8 months. We are initiating enrollment to Cohort 2, in which patients will be vaccinated with an autologous DC/myeloma fusion vaccine 1 week prior to each dose of CT-011. These data demonstrate that CT-011 results in the expansion of tumor reactive lymphocytes in the early post-transplant period, providing an ideal platform for combination with a tumor vaccine.