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2724 IL15 Expressing CD123-Targeted Engager T-Cell Therapy for Adult Acute Myeloid Leukemia

Program: Oral and Poster Abstracts
Session: 616. Acute Myeloid Leukemia: Novel Therapy, excluding Transplantation: Poster II
Hematology Disease Topics & Pathways:
Biological, Therapies, immunotherapy
Sunday, December 2, 2018, 6:00 PM-8:00 PM
Hall GH (San Diego Convention Center)

Hong Mu, MD, PhD1*, Huaxian Ma, MS1*, Abishek Vaidya, MS2*, Challice L. Bonifant, MD, PhD3, Stephen Gottschalk, MD4, Mireya P. Velasquez, MD2 and Michael Andreeff, MD, PhD1

1Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX
2St. Jude Children's Research Hospital, Memphis, TN
3University of Michigan Medical School/C.S. Mott Children's Hospital, Ann Arbor, MI
4Bone Marrow Transplantation and Cellular Therapy, St. Jude Children's Research Hospital, Memphis, TN

Background: CD123 is a potential immunotherapeutic target in AML due to its overexpression on leukemic stem cells that play an essential role in disease progression and relapse. Our previous study using T cells secreting CD123/CD3 bispecific engager molecules (CD123-ENG T cells) showed promising results in pediatric AML. Interleukin-15 (IL15) has emerged as a candidate immunomodulator as it enhances the cytolytic activity of CD8+ T-cells and induces long-lasting memory T cells. To improve the efficacy and persistence of CD123-ENG T-cells we developed IL-15 expressing CD123-ENG T cells. Here, we report characterization and efficacy of IL15 secreting CD123-ENG T cells in adult AML.

Methods/Results: A cDNA encoding IL15 was cloned into retroviral vectors encoding CD123-ENG or CD19-ENG and the CD20 suicide gene separated by 2A sequences (CD20.2A.CD123-ENG.2A.IL15; CD20.2A.CD19-ENG.2A.IL15). ENG T cells were generated from human peripheral blood mononuclear cells (PBMCs) from normal donors by retroviral transduction and expanded in vitro. Non-transduced (NT) T cells and T cells expressing CD20 and CD123 (CD20.CD123-ENG T cells) served as controls. The transduction efficiency was between 62.81-95% (average 72%, n=3) and phenotypic analysis by flow cytometry showed reproducible CD4+, CD8+, central memory (CCR7+CD45RA-), effector memory (CCR7-CD45RA-), and naïve (CCR7+CD45RA+) T cells populations compared to NT cells. IL15 production of CD20.CD19-ENG.IL15 and CD20.CD123-ENG.IL15 T cells was confirmed by ELISA (84-154 pg/ml vs 32 and 44 pg/ml of NT and CD20.CD123-ENG T cells, p<0.01, n=3). Both, CD20.CD123-ENG and CD20.CD123-ENG.IL15 T cells recognized CD123+ AML cell lines as determined by IL2 and interferon γ (IFNγ) production (p<0.01, n=3). In contrast, NT and CD20.CD19-ENG.IL15 T cells did not, confirming specificity. In addition, CD20.CD123-ENG and CD20.CD123-ENG.IL15 T cells induced killing of only CD123-positive target cells in luciferase-and 7AAD-based cytotoxicity assay. CD20.CD123-ENG.IL15 T cells showed greater cytolytic activity than CD20.CD123-ENG T cells (p=0.0002, n=3). Finally, we evaluated the cytolytic activity of ENG T cells against two CD123+ adult AML PDX samples with clinically high-risk features (PDX#440778 [Flt3-ITD and D835 double mutations], and PDX#LFS [p53 mutant Li Fraumeni syndrome]). Both, CD20.CD123-ENG and CD20.CD123-ENG.IL15 T cells significantly killed AML PDX cells compared to NT and CD20.CD19-ENG.IL15 T cells (p<0.001, n=3). Adoptive transfer of CD20.CD123-ENG or CD20.CD123-ENG.IL15 T cells into the AML PDX#440778 mouse model revealed a significant reduction of leukemia burden in mice that received CD20.CD123-ENG.IL15 T cells 5 days post infusion (p=0.004, n=7). We are currently monitoring AML burden, frequency of infused ENG T cells, body weight and survival of treated mice, and conducting experiments in the 2nd AML PDX model. These results will be presented at the meeting.

Conclusion: We demonstrate here that genetically engineering CD123-ENG T cells that express IL15 enhances their effector function resulting in improved anti-AML activity in in vitro and in vivo. The results warrant further exploration of IL15 secreting CD123-specific ENG T-cell therapy in AML.

Disclosures: Bonifant: N/A: Patents & Royalties: Pending patents in cellular immunotherapy. Andreeff: Celgene: Consultancy; Aptose: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy, Patents & Royalties: MDM2 inhibitor activity patent, Research Funding; Oncoceutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Consultancy; Astra Zeneca: Research Funding; Oncolyze: Equity Ownership; United Therapeutics: Patents & Royalties: GD2 inhibition in breast cancer ; Reata: Equity Ownership; SentiBio: Equity Ownership; Eutropics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Research Funding.

*signifies non-member of ASH