Abstract 5644: Generation of clinical grade autologous TLR 7,8-polarized fast dendritic cell vaccines for active immunotherapy of patients with AML

Abstract

Although progress has been made in the treatment of AML in recent years, relapse rates following chemotherapy are still high resulting in only low long-term patient survival rates. Treatment options are often limited following relapse, emphasizing the continued need for new and more effective treatments options.We have developed an active immunotherapy using TLR7/8-polarized fast dendritic cells (DCs), which is currently under evaluation for treatment of patients with AML in morphological remission in a non-randomized phase I/II clinical trial (NCT02405338). The trial subjects receive repeated immunotherapy with autologous vaccine cells, transfected with RNA encoding two leukemia-associated antigens WT1 and PRAME. Patients are vaccinated for two years or until disease progression. Here we present data on the feasibility of clinical grade production of our TLR7/8-polarized fast DC vaccine for long-term vaccination of chemotherapeutically pretreated AML patients. A total of 20 patients with a median age of 59 years (range 24 - 73 years) were recruited to this ongoing trial. For vaccine production, autologous apheresis material was collected from each patient and fast DC generation was performed following isolation of DC precursor cells using a TLR7/8-agonist containing maturation cocktail. Final vaccine cells were cryopreserved in multiple aliquots prepared to deliver 5x106 - 10x106 cells per vaccine dose. Vaccine cells could be generated from all 20 AML patients. A second apheresis was performed during the trial for a second production in order to generate sufficient vaccine doses for the intended treatment period for 4 of 20 patients. The majority of production runs (17 out of 24) yielded 20 or more vaccine doses (8 batches: 20-29 doses, 6 batches: 30-39 doses, 2 batches: 40-49 doses and more than 60 doses from one batch). For seven patients less than 20 vaccine doses were cryopreserved from one production run. To evaluate vaccine cell purity, presence of autologous non-DC cells was determined and revealed a purity of more than 70% for 22 vaccine batches (17 batches 80% - 99%, 5 batches 71% - 77%). Only two productions yielded lower purities (range 64% - 69%). The average post-thawing vaccine cell viability was 83% (range 68%-95%) with the majority of cells showing a viability of >70%. Additionally, DCs generated from all patients showed a mature surface phenotype as demonstrated by high expression of typical DC surface markers such as CD80, CD86, CD83, CD40 and HLA-DR. Furthermore, high expression of the lymphocyte homing receptor CCR7 could be detected for all cell preparations. Taken together, these results clearly demonstrate the feasibility and robustness of our protocol for production of mature clinical grade TLR7/8-polarized fast DCs in high numbers from heavily pretreated post-remission AML patients allowing for long-term vaccination of trial subjects. Citation Format: Iris Bigalke, Lisbeth Johanne Skoge, Kirsti Hønnåshagen, Christiane Geiger, Gunnar Kvalheim, Dolores J. Schendel. Generation of clinical grade autologous TLR 7,8-polarized fast dendritic cell vaccines for active immunotherapy of patients with AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5644.