Expansion and Characterization of Iovance Marrow Infiltrating Lymphocytes: A Potential Novel Therapeutic Strategy for the Treatment of Acute Myeloid Leukemia

Background: Acute myeloid leukemia (AML) is a poor-prognosis malignancy arising from hematopoietic stem/progenitor cells. To date, novel immunotherapies such as checkpoint inhibitors, vaccines and adoptive cell therapy (ACT) using CAR T cells have demonstrated only modest success for the treatment of patients who are ineligible for marrow transplantation and have minimal residual disease; additional approaches are warranted (Beyar-Katz O and Gill S, Clin Cancer Res 2018). ACT with tumor infiltrating lymphocytes (TIL) has emerged as an effective treatment for patients with metastatic melanoma (Goff SL et al, J Clin Oncol 2016), likely owing to the heterogeneous population of tumor-reactive T cells that comprises the TIL products. As demonstrated for solid cancers, such tumor-reactive T cells are preferentially found in the tumor microenvironment (Gros A et al JCI 2014; Thommen DS et al Nat Med 2018). By avoiding the highly immunosuppressive tumor microenvironment, ex vivo activation of those cells rescues them from tolerance and anergic status. We hypothesized that, in the case of AML for which the bone marrow represents the tumor microenvironment, tumor antigen-specific T cells could be recovered from the patient bone marrow to produce a highly effective therapeutic product that is cytotoxic to AML tumor cells. We present findings related to the ex vivo expansion of Iovance marrow infiltrating lymphocytes (MIL) for the treatment of AML patients.

Methods: Immune cell and non-immune cell fractions were sorted from bone marrow mononuclear cells. Immune cell fractions loaded with sonicated non-immune cell fractions were expanded for 14 days in the presence of αCD3/αCD28 beads and interleukin-2 (IL-2) to generate MIL products. Phenotypic and functional characteristics of the cells were determined by flow cytometry and enzyme-linked immunospot assay (ELISpot).

Results: MIL were generated from isolated bone marrow mononuclear cells (n=2) with a mean expansion fold of 86 (range 78-93). Equal percentage of CD4+ and CD8+ T cell subsets constituted the MIL products. Phenotypic analysis of the cells showed that the majority of T cell subsets are effector memory and CD28 positive. Low percentages of the T cell subsets were positive for immunosuppressive markers PD-1 and LAG3. ELISpot analysis demonstrated that MIL were readily activatable and produced normal levels of IFNγ in response to CD3/CD28 stimulation. Antigen specificity of MIL is being investigated.

Conclusion: We demonstrated the feasibility of MIL expansion from bone marrow mononuclear cells from AML patients. MIL are functionally active and mostly comprised of effector memory T cells. Confirmation of tumor cell antigen specificity will determine whether MIL may deploy a robust anti-tumor activity in vivo.