PF447 IOVANCE PERIPHERAL BLOOD LYMPHOCYTES (PBL): A POTENTIAL CELL THERAPY STRATEGY FOR THE TREATMENT OF CHRONIC LYMPHOCYTIC LEUKEMIA

Background: Adoptive cell therapy (ACT) using tumor infiltrating lymphocytes (TIL) and chimeric antigen receptor (CAR) T cells is at the forefront in the treatment of patients with solid tumors and hematological malignancies. Success of ACT is dependent on effective in vitro expansion of T cells. It is well known that T cells are in an exhausted/dysfunctional state in several hematological malignancies including adult T‐cell leukemia/lymphoma (ATL), chronic myeloid leukemia (CML), acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL). This adds complexity when attempting to generate T cell product for ACT of these patients. Several reports suggest that ibrutinib, an irreversible inhibitor of Burton tyrosine kinase (BTK), improves proliferative and effector functions of T cells in CLL patients by inhibiting IL‐2 inducible T cell kinase (ITK). We hypothesize that T cells from ibrutinib treated CLL patients could be expanded successfully to generate a bulk T cell product that can effectively kill autologous tumor cells. Aims: The goals of this study are a) to develop a short and efficient method for generation of bulk T cell product (PBL) from peripheral blood mononuclear cells (PBMC) of CLL patients and b) to assure that expanded cells have autologous tumor killing capability. Methods: PBMC obtained from 50 mL of blood from CLL patients (treatment naïve (n = 6), pre‐ibrutinib (n = 6) and post‐ibrutinib (n = 6)) were enriched for the T cell fraction. These fractions were expanded for a duration of 9–14 days in the presence of αCD3/αCD28 beads and 3000 IU/ml interleukin‐2 (IL‐2) to obtain a peripheral blood lymphocyte (PBL) product. Phenotypic and functional characteristics of PBLs were determined by flow cytometry, enzyme‐linked immunospot (ELIspot) and autologous tumor (CD19 + cells) killing assays. Results: PBL could be expanded successfully from PBMC of post‐ibrutinib CLL patients within the timeframe of 9–14 days. PBL obtained from post‐ibrutinib PBMC showed higher fold expansion compared to those obtained from pre‐ibrutinib and treatment‐naïve PBMC (mean fold expansions: post‐ibrutinib PBL 248, pre‐ibrutinib PBL 117, treatment‐naive PBL 35). Final PBL products consisted of 97–99% T cells and phenotype analysis indicated that majority (range 78–82%) of these T cells are effector memory (CD45RA − CCR7 − ) subsets. Functional characterization of PBL demonstrated that IFNγ + T cells per million PBL measured in response to non‐specific stimulus (αCD3/αCD28/αCD137 beads) were significantly higher (p = 0.002, p = 0.003) in post‐ibrutinib PBL (13562) compared to pre‐ibrutinib PBL (8793) and treatment‐naive PBL (1864). Data from autologous tumor (CD19 + cells) killing assays showed that post‐ibrutinib PBL have higher cytotoxic potential (range 15%–45%) against autologous CD19 + cells compared to pre‐ibrutinib PBL (range 0–15%). Fold expansion data show that clinically relevant doses (billions of cells) can be produced starting with 50 mL of blood. Summary/Conclusion: From 50 mL of blood in ibrutinib‐treated CLL patients, we demonstrate successful generation of bulk PBL over a 9–14 days manufacturing process. We intend to investigate PBL for the treatment of CLL patients in clinic simultaneous to further investigating this approach in other hematological malignancies.