PF447 IOVANCE PERIPHERAL BLOOD LYMPHOCYTES (PBL): A POTENTIAL CELL THERAPY STRATEGY FOR THE TREATMENT OF CHRONIC LYMPHOCYTIC LEUKEMIA (2019)

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.