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4190 A Novel Fc-Optimized Antibody Drug Conjugate Targeting CD7 As a Therapeutic Strategy in T-Cell Acute Lymphoblastic Leukemia

Program: Oral and Poster Abstracts
Session: 605. Molecular Pharmacology and Drug Resistance: Lymphoid Neoplasms: Poster III
Hematology Disease Topics & Pathways:
Biological therapies, Antibody Therapy, Therapies
Monday, December 11, 2023, 6:00 PM-8:00 PM

Carina Lynn Gehlert1*, Denis Martin Schewe2,3*, Katja Klausz1,2*, Steffen Krohn1*, Dorothee Winterberg1*, Fotini Vogiatzi4*, Ammelie Svea Boje1*, Anja Lux5*, Falk Nimmerjahn5*, Regina Scherließ6*, Andreas Humpe7*, Martin Schrappe, MD2,4, Gunnar Cario, MD2,8*, Thomas Valerius2,9*, Lars Fransecky2,10*, Monika Brüggemann2,10*, Claudia D Baldus, MD2,10*, Martin Gramatzki1, Lennart Lenk2,4*, Christian Kellner, PhD7* and Matthias Peipp1,2*

1Division of Antibody-Based Immunotherapy, Department of Hematology and Oncology, Kiel University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany
2Clinical Research Unit CATCH ALL (KFO 5010/1) funded by the Deutsche Forschungsgemeinschaft, Kiel, Germany
3Department of Pediatrics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
4Department of Pediatrics I, University Hospital Schleswig-Holstein, Kiel, Germany
5Division of Genetics, Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
6Department of Pharmaceutics and Biopharmaceutics, Kiel University, Kiel, Germany
7Division of Transfusion Medicine, Cell Therapeutics and Haemostaseology, University Hospital, LMU Munich, Munich, Germany
8Department of Pediatrics I, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany
9Division of Stem Cell Transplantation and Immunotherapy, Department of Hematology and Oncology, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany
10University Hospital Schleswig-Holstein, Department of Hematology and Oncology, Campus Kiel, Kiel, Germany

Despite progress in improving treatment regimens for patients with T-cell acute lymphoblastic leukemia (T-ALL), the therapeutic options are still limited, and especially antibody-based immunotherapy is not established. The CD7 antigen represents a promising target structure in T-ALL since it is strongly expressed in different T-ALL subtypes including early T-cell precursor (ETP)-ALL. Therefore, different approaches are currently pursued for targeting CD7, including CAR-T cell therapy. Due to its high internalization capacity CD7 also represents an ideal target structure for antibody drug conjugates (ADC).

Here, a novel antibody engineering approach for CD7-targeting was evaluated in vitro and in xenograft mouse models of T-ALL. A CD7 antibody was optimized for its ability to trigger antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) by introducing two amino acid substitutions (S239D/I332E; DE-variant) in the Fc-domain. In addition, the Fc-engineered antibody was conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via an enzymatic-cleavable linker (mc-vc-PABC).

The Fc-optimized ADC, CD7-DE-vcMMAE, as well as the unconjugated antibody, CD7-DE, showed improved binding to activating Fcγ receptors (FcγRIIa, FcγRIIIa) compared to a CD7 antibody lacking the DE-modification. This resulted in potent ADCC- and ADCP-activity against different T-ALL cell lines mediated by NK-cells or macrophages as effector cells (EC50 ADCC, 1-7 pM). In contrast to the CD7-DE antibody, CD7-DE-vcMMAE showed strong cytotoxic effects independently of immune effector cell engagement by releasing its cytotoxic compound into T-ALL cells in an antigen-restricted manner, thereby inducing G2/M cell cycle arrest and apoptosis. CD7-DE-vcMMAE was active at subnanomolar concentrations demonstrating dose-dependent cytotoxic effects in six T-ALL cell lines (IC50 0.2 - 1 nM). The extent of maximum growth inhibition ranged between 54-98 % and correlated with CD7 antigen density. Yet, although CD7-DE-vcMMAE did not kill CD7-negative cells directly, the linker design facilitated bystander killing activity. Thus, in co-culture experiments using CEM cells and CEM-CD7-knockout cells mimicking CD7-antigen escape, the ADC demonstrated significant killing of neighbouring CD7-negative cells, thereby extending its mode of action.

The antitumor activity of the CD7-ADC was further investigated in xenograft mouse models of T-ALL. In a first model, CEM cells were injected subcutaneously into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice and CD7-DE-vcMMAE treatment was evaluated in comparison to the unconjugated antibody CD7-DE. Treatment with CD7-DE-vcMMAE led to a significantly reduced tumor growth in comparison to CD7-DE or untreated animals (p<0.05; see panel A). A preclinical phase II-like patient-derived xenograft (PDX) study employing eight randomly selected T-ALL-PDX samples from pediatric and adult patients was conducted. PDX-cells were injected intravenously into NSG mice and treatment was started when the leukemia load reached 1 % human blasts in the peripheral blood, reflecting an overt leukemia situation. Animals receiving therapy with CD7-DE-vcMMAE showed significant prolongation of median survival in comparison to animals treated with a similarly designed control ADC targeting an irrelevant antigen (control-DE-vcMMAE) or which were left untreated (median survival time; CD7-DE-vc-MMAE: 82 days; untreated/control-DE-vcMMAE: 60 days; p<0.05; see panel B). Importantly, no leukemic blasts were found in the peripheral blood, spleen or bone marrow in animals treated with CD7-DE-vcMMAE and surviving the experimental period of 150 days.

Together, the novel ADC CD7-DE-vcMMAE showed a unique set of Fc effector functions, potent direct growth inhibitory effects, bystander killing activity and efficacy in xenograft models of T-ALL. These results exhibit CD7-DE-vcMMAE as a promising therapeutic strategy and form the basis for new approaches in the treatment of T-ALL.

Disclosures: Cario: Servier, Amgen: Research Funding; JazzPharma: Speakers Bureau. Fransecky: Pfizer: Consultancy; Jazz: Consultancy; Amgen: Consultancy; Gilead: Consultancy, Research Funding, Speakers Bureau; Servier: Consultancy. Baldus: Amgen: Consultancy; Jannsen: Consultancy; AstraZeneca: Consultancy; BMS: Consultancy; Astellas: Consultancy; Jazz Pharmaceuticals: Consultancy; Gilead: Consultancy. Peipp: Merck: Research Funding; Evobright: Consultancy, Research Funding; Biomunex: Consultancy, Research Funding; Janssen: Honoraria.

*signifies non-member of ASH