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868 Engineering Naturally Occurring CD7 Negative Cells for the Immunotherapy of CD7 Positive Leukemia

Program: Oral and Poster Abstracts
Type: Oral
Session: 703. Adoptive Immunotherapy: Mechanisms and New Approaches: New Approaches
Hematology Disease Topics & Pathways:
AML, ALL, Leukemia, Diseases, Lymphoid Malignancies, Myeloid Malignancies
Monday, December 9, 2019: 5:15 PM
W224ABEF, Level 2 (Orange County Convention Center)

Abdullah Freiwan, MSc1*, Abishek Vaidya, MS1*, Caitlin Zebley, MD2*, Yiping Fan, PhD3*, Deanna Langfitt, Ph.D.4*, Benjamin Youngblood, Ph.D.5*, Maksim Mamonkin, PhD6, Stephen Gottschalk, M.D.7 and Mireya Paulina Velasquez, MD1

1Bone Marrow Transplant and Cellular Therapy, St. Jude Children's Research Hospital, Memphis, TN
2Immunology, St. Jude Children’s Research Hospital, Memphis, TN
3Department of Computational Biology, St. Jude Children’s Research Hospital, Memphis, TN
4Department of Bone Marrow Transplantation and Cellular Therapy, St. Jude Children’s Research Hospital, Memphis, TN
5Department of Immunology, St. Jude Children's Research Hospital, Memphis, TN
6Center for Cell and Gene Therapy, Baylor College of Medicine, Texas Children's Hospital, Houston Methodist Hospital, Houston, TX
7Department of Bone Marrow Transplantation and Cellular Therapy, St. Jude Children's Research Hospital, Memphis, TN

Background:

CD7 has emerged as a promising target for the adoptive immunotherapy with T-cells expressing chimeric antigen receptors (CAR T-cells) of CD7+ T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). However, expressing CD7 CARs in T-cells results in fratricide due to high expression of CD7 in most T-cells. While investigators have developed strategies to overcome this limitation by additional genetic modifications of CD7 CAR T-cells, the goal of this project was to explore the feasibility of selecting and genetically modifying naturally occurring CD7 negative (CD7) T cells for the adoptive immunotherapy of CD7+ leukemia.

Methods:

CD7 T-cells were isolated from PBMCs using a 2-step magnetic bead depletion/selection procedure (CD7 depletion followed by selection of CD3+ T cells from the CD7 fraction). Non-selected T-cells (bulk T-cells), CD7+ and CD7 T cells were activated and transduced with a retroviral vector encoding a second-generation CD7 CAR with a CD28 costimulatory endodomain, and expanded with IL7 and IL15. The effector function of CD7 T-cells expressing CD7 CARs (CD7 CARCD7– T cells) was assessed in vitro as well as in xenograft models.

Results:

To assess the feasibility of our approach, we first determined the frequency of CD7 T-cells in PBMCs. On average, 4.7 % of T cells were CD7 (range: 2% - 12.3%; N=22), and we successfully selected these cells from bulk PBMCs with a combined CD7 depletion/CD3 selection procedure. We genetically modified CD7, CD7+ and bulk T cells to express CD7 CARs (CD7 CARCD7–, CD7 CARCD7+, CD7 CARBulk). Transduction efficiencies ranged from 31% to 75% (± 5%) for each T-cell population. Post transduction, CD7 CARCD7– T-cells did not undergo fratricide and had similar expansion kinetics (N=6, p=ns) in comparison to non-transduced (NT) T-cell cultures (NT CD7, NT CD7+, NT bulk). In contrast, CD7 CARCD7+ or CD7 CARBulk T-cells underwent fratricide and did not expand (N=6, p<0.0001). CD7 T-cells (NT and CD7 CARCD7–) had a predominantly CD4+ effector memory phenotype at day 7 and 14 of culture. To assess the effector function of CD7 CARCD7– T-cells, we co-cultured them with CD7+ T-ALL cell lines (CCRF, MOLT3). CD7 CARCD7– T-cells recognized CD7+ targets in contrast to CD7 targets (BV173, Daudi) as evidenced by significant (N=6, p<0.0001) IFN-γ and IL-2 production. Control CAR T-cells (CD19 CARCD7–) did not recognize CD7+ target cells, confirming specificity. CD7 CARCD7– T-cells also had potent cytolytic activity against CD7+ targets in cytotoxicity assays. To assess in vivo the anti-tumor activity of CD7 CARCD7– T-cells, we used a NSG mouse xenograft model with CCRF cells, genetically modified to express firefly luciferase (CCRF.ffluc) to allow for serial bioluminescence imaging. A single infusion of CD7 CARCD7– T-cells had potent anti-leukemia activity as judged by serial imaging resulting in a significant survival (p<0.003) advantage in comparison to control mice.

Conclusion:

We have successfully generated CD7 CARCD7– T-cells from peripheral blood CD7 T-cells. CD7 CARCD7– T-cells had a predominantly CD4+ effector memory phenotype, and potent anti-leukemia activity in vitro and in vivo. Thus, naturally occurring CD7 T cells may present a promising T-cell source for the cellular immunotherapy of CD7+ leukemia.

Disclosures: Freiwan: St. Jude Children's Research Hospital: Patents & Royalties. Langfitt: MBIO: Other: St. Jude Children’s Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy. Youngblood: MBIO: Other: St. Jude Children’s Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy. Gottschalk: NHLBI: Research Funding; America Lebanese Syrian Associated Charities: Research Funding; ASSISI fundation of Memphis: Research Funding; California Institute for Regenerative Medicine: Research Funding; ViraCyte: Consultancy; MBIO: Other: St. Jude Children’s Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; Patents and patent applications in the fields of T-cell & Gene therapy for cancer: Patents & Royalties; TESSA Therapeutics: Other: Research Collaboration; Tidal: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; EMD Serono: Honoraria; Merck: Consultancy; Inmatics: Membership on an entity's Board of Directors or advisory committees. Velasquez: St. Jude: Patents & Royalties: Patent Applications in the Fields of Cell and Gene Therapy ; Rally! Foundation: Membership on an entity's Board of Directors or advisory committees.

*signifies non-member of ASH