DC/Aml Fusion Cell Vaccination Administered to AML Patients Who Achieve a Complete Remission Potently Expands Leukemia Reactive T Cells and Is Associated with Durable Remissions

We have developed an autologous whole cell leukemia vaccine, whereby patient derived leukemic blasts are fused to ex-vivo generated dendritic cells. In this way, a broad array of leukemia-associated antigens are presented in the context of DC mediated co-stimulation, resulting in the expansion of a polyclonal anti-leukemia immune response. We are conducting a clinical trial in which AML patients who are not candidates for allogeneic transplantation undergo vaccination with DC/AML fusion cells after achieving a complete remission. 56 patients underwent collection of AML cells for vaccine generation from either a bone marrow aspirate (N=38), 20cc of peripheral blood (N=15) or a leukapheresis product (N=3) at presentation with newly diagnosed (N=55) or first relapsed (N=1) AML. The mean yield of AML cells was 692 x 10⁶ cells with a mean viability of 99%. Patients who did not achieve remission or who underwent allogeneic transplant in first remission came off study and did not complete vaccine generation. Eligible patients achieving CR who did not proceed to allogeneic transplant (N=21) underwent leukapheresis for DC generation and vaccine preparation.  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 population. Mean fusion efficiency and viability was 42% and 87%, respectively. Vaccination with DC/leukemia fusion cells was initiated within 12 weeks from count recovery following the final cycle of post-remission therapy. 16 patients (median age 60) have received at least two monthly vaccinations at a dose of 5x10⁶ fusion cells. Remission induction therapy consisted of 7+3 in 13 patients, 7+3 followed by 5+2 re-induction in 1 patient, MEC in one patient, and decitabine in 1 patient. 9 patients had intermediate risk cytogenetics, 2 patients had good risk cytogenetics, and 5 patients had poor cytogenetic risk disease. Vaccination was well tolerated, and importantly, was not associated with clinically significant auto-immunity. Possibly related adverse events were transient and of grade 1-2 intensity, including vaccine site reactions, pruritis, arthalgias, myalgias, eosinophilia, leukopenia, thrombocytopenia. 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, 12 of 16 evaluable patients remain in remission (75%), with a median follow up of 45 months. Notably, no patient has relapsed later than 1 year from completing chemotherapy and the patient who was treated in CR2 remains in remission with 51 months of follow up, after having relapsed within a year of CR1. Vaccination resulted in the potent induction of leukemia specific immunity as measured by a mean fold increase of 4.9 CD8 T cells expressing IFNγ in response to ex vivo exposure to autologous leukemia cell lysates (n=14).  In a subset of patients who are HLA2.1+, vaccination resulted in the expansion of T cells recognizing MUC1 (4.4 fold increase), WT1 (2.7 fold increase), NY-ESO (3.8 fold increase) tumor antigens by pentamer analysis. In conclusion, DC/AML fusion cell vaccination administered to patients who achieve complete remission results in the potent expansion of leukemia reactive T cells, and durable remissions. A second cohort is planned in which patients will be treated with DC/AML fusion cell vaccination in conjunction with immune checkpoint blockade.