Clinical Trial Evaluating DC/AML Fusion Cell Vaccination in AML Patients Who Achieve a Chemotherapy-Induced Remission

We have developed a promising leukemia vaccine in which patient derived AML cells are fused with autologous dendritic cells (DCs), presenting a broad array of antigens.  We are conducting a clinical trial in which AML patients undergo vaccination with DC/AML fusion cells following chemotherapy induced remission.  Twenty-six patients underwent collection of AML cells at disease presentation for vaccine generation and immune monitoring studies.  Median age of the patients is 66 years.  Tumor was collected from either a bone marrow aspirate (N=16), 20 cc of peripheral blood (N=7), or leukapheresis product (N=3) at the time of presentation with newly diagnosed AML (N=25) or first relapsed AML (N=1).  The mean yield of AML cells was 109 x 10⁶ cells with a mean viability of 91%.  Eligible patients achieving CR (N=16) underwent leukapheresis for DC generation.  Adherent peripheral blood mononuclear cells were cultured in the presence of GM-CSF and IL-4 for 5-7 days, and exposed to TNFα for 48-72 hours to generate mature DCs.   Fusion cells were generated by co-culture of DCs with AML cells in the presence of 50% polyethylene glycol and identified as cells co-expressing antigens that were unique to the DC and tumor cells.  Mean fusion efficiency and viability was 38% and 85%, respectively.  Vaccination with DC/leukemia fusion cells was initiated within 12 weeks from count recovery following the final cycle of chemotherapy.  13 patients received at least two monthly vaccinations at a dose of 5x10⁶ fusion cells. 8 patients had intermediate risk cytogenetics, 3 patients had good risk cytogenetics, and 2 patients had a complex karyotype.  Vaccination was well tolerated, and importantly, was not associated with clinically significant auto-immunity.  Biopsy of vaccine site reactions demonstrated a dense infiltrate of CD4 and CD8 T cells consistent with recruitment of reactive T cell populations to the vaccine bed.  To date, 9 patients remain in remission (69%), with a mean follow up of 23 months.  Peripheral blood samples were collected prior to each vaccination and at 1, 3, and 6 months following completion of vaccination.  Vaccination resulted in the potent induction of leukemia specific immunity as measured by an 8 fold increase (mean, n=6) in CD8 T cells expressing IFNγ in response to ex vivo exposure to autologous leukemia cell lysates.  Bone marrow derived T cells were isolated prior to and following vaccination in patients who are HLA2.1+.  Vaccination resulted in the expansion of bone marrow infiltrating T cells recognizing MUC1 (9 fold increase), WT1 (5 fold increase), PRAME (12 fold increase) tumor antigens by tetramer analysis (n=2).  In conclusion, DC/AML fusion cell vaccination results in the potent expansion of leukemia reactive T cells and durable remissions following chemotherapy.  Enrollment to a second cohort in which patients receive DC/AML fusion cell vaccination in combination with antI-PD1 antibody is planned.