-Author name in bold denotes the presenting author
-Asterisk * with author name denotes a Non-ASH member
Clinically Relevant Abstract denotes an abstract that is clinically relevant.

PhD Trainee denotes that this is a recommended PHD Trainee Session.

Ticketed Session denotes that this is a ticketed session.

460 Complete Responses in Relapsed/Refractory Acute Myeloid Leukemia (AML) Patients on a Weekly Dosing Schedule of Vibecotamab (XmAb14045), a CD123 x CD3 T Cell-Engaging Bispecific Antibody; Initial Results of a Phase 1 Study

Program: Oral and Poster Abstracts
Type: Oral
Session: 613. Acute Myeloid Leukemia: Potpourri of Potential Practice Changing Studies
Hematology Disease Topics & Pathways:
Biological, CRS, Adult, AML, antibodies, Diseases, CML, Therapies, Adverse Events, Biological Processes, Study Population, Myeloid Malignancies, immune mechanism
Sunday, December 6, 2020: 2:30 PM

Farhad Ravandi, MBBS1, Asad Bashey, MD, PhD2, Wendy Stock, MD3, James M. Foran, MD4, Raya Mawad, MD5*, Daniel Egan, MD6*, William Blum, MD7*, Allen Yang, MD, PhD8, Alessandro Pastore, MD9, Chelsea Johnson, BSN, RN8*, Shuo Zheng8*, Musa Yilmaz, MD10 and Alice S. Mims, MD11

1Department of Leukemia, University of Texas- MD Anderson Cancer Center, Houston, TX
2BMT Group of Georgia, Atlanta, GA
3Department of Medicine, Section of Hematology-Oncology, University of Chicago, Chicago, IL
4Division of Hematology and Medical Oncology, Mayo Clinic, Jacksonville, FL
5Swedish Cancer Institute, Seattle, WA
6Center for Blood Disorders and Stem Cell Transplantation, Swedish Cancer Institute, Seattle, WA
7Winship Cancer Institute of Emory University, Atlanta, GA
8Xencor, Inc., San Diego, CA
9Translational Clinical Oncology, Novartis Institutes for BioMedical Research, East Hanover, NJ
10Department of Leukemia, MD Anderson Cancer Center, Houston, TX
11The Ohio State University Comprehensive Cancer Center, Columbus, OH

Background: Blasts and leukemic stem cells of acute myeloid leukemia (AML) as well as several other hematologic malignancies express CD123, potentially providing a target for novel therapies. Vibecotamab (XmAb14045, SQZ622) is a potent bispecific antibody targeting both CD123 and CD3 that stimulates targeted T cell-mediated killing of CD123-expressing cells, regardless of T cell antigen specificity. It is a full-length immunoglobulin molecule designed to be dosed intermittently.

Methods: Patients with relapsed or refractory AML, B-cell acute lymphoblastic leukemia (B-ALL), blast phase chronic myelogenous leukemia, or blastic plasmacytoid dendritic cell neoplasm were eligible to enroll on this first-in-human, multicenter, open-label phase 1 dose-escalation study (XmAb14045-01) with standard 3+3 design. The primary objective was to estimate the maximum tolerated dose (MTD) or recommended dose and schedule of vibecotamab. Secondary objectives included safety, preliminary antileukemic activity, and pharmacokinetics/pharmacodynamics of vibecotamab. Treatment was administered weekly in 28-day cycles, using a weight-based dose with 3 escalating doses in the first week followed by escalating weekly doses. Therapy was continued for as long as tolerated and there was continuing evidence of therapeutic benefit in the opinion of the investigator. Treatment response was assessed by the 2017 European LeukemiaNet (ELN) criteria after Cycle 1 and after each odd-numbered cycle. CRS was graded using the CRS revised grading system (Lee et al., Blood, 2014).

Results: At data cut-off, 104 patients with AML, 1 with B-cell ALL, and 1 with CML as their primary diagnosis have been treated at dosages from 0.003 to 12.0 µg/kg vibecotamab. Patients had a median age of 63 years and were heavily pretreated (median of 3 prior therapies [range 1-8], including 32 (30%) who had undergone prior allogeneic stem cell transplantation). The recommended initial priming dose is 0.75 µg/kg; no MTD has been identified. CRS or its component symptoms was the most common treatment-emergent adverse event (TEAE). CRS occurred in 62 of 106 patients (85% grade 1-2, 15% grade ≥3), the majority on the first dose. Additional events consistent with CRS or infusion related reaction were seen in 24% of subjects (chills, fever, tachycardia, hypotension, etc.), and they were mostly mild or moderate severity. No myelosuppression requiring dose modification or evidence of tumor lysis syndrome was seen. Response of CR (2), CRi (3) or MLFS (2) was observed in 7/51 patients (ORR=14%) treated at higher dose levels ( 0.75 µg/kg). Stable Disease was observed in an additional 36 patients (71%). No CR, CRi, or morphologic leukemia-free state (MLFS) responses were observed at lower doses. Antileukemic activity occurred quickly; 6 out of 7 responders achieved at least a MLFS response after first cycle. A characterization of responders versus non-responders revealed responding patients harbor a lower burden of disease and specific T-cell subtypes. No association was found between response status and CD123 target expression on AML blasts.

Conclusions: Vibecotamab demonstrated evidence of antileukemic activity in heavily pretreated patients with relapsed/refractory AML treated at the ≥0.75 µg/kg doses cohorts, with a 14% response rate. CRS was the most common toxicity but was generally manageable with premedications. The study is ongoing with further optimization of dose and schedule. Biomarker data suggest a population of AML patients that are more likely to respond. Additional information will be provided at the time of the meeting.

Disclosures: Ravandi: Celgene: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Orsenix: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Xencor: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria; Macrogenics: Research Funding. Stock: Adaptive Biotechnologies: Consultancy, Membership on an entity's Board of Directors or advisory committees; Research to Practice: Honoraria; American Society of Hematology: Honoraria; Leukemia and Lymphoma Society: Research Funding; Novartis: Research Funding; Abbvie: Honoraria, Research Funding; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kite: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; UpToDate: Honoraria. Foran: Xencor: Research Funding; H3Biosciences: Research Funding; Agios: Honoraria, Research Funding; Trillium: Research Funding; Takeda: Research Funding; Kura Oncology: Research Funding; Aptose: Research Funding; Aprea: Research Funding; Actinium: Research Funding; Boehringer Ingelheim: Research Funding; Abbvie: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Revolution Medicine: Consultancy. Mawad: Adaptive Biotechnologies: Speakers Bureau; Abbvie: Speakers Bureau. Blum: Leukemia and Lymphoma Society: Research Funding; Amerisource Bergen: Honoraria; Celyad: Research Funding; Syndax: Membership on an entity's Board of Directors or advisory committees; Xencor: Research Funding. Yang: Xencor: Current Employment, Current equity holder in publicly-traded company; Jazz Pharmaceuticals: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Pastore: Novartis NIBR East Hanover New Jersey: Current Employment, Current equity holder in publicly-traded company; Memorial Sloan Kettering Cancer Center: Ended employment in the past 24 months. Johnson: Xencor: Current Employment, Current equity holder in publicly-traded company. Zheng: Xencor: Current Employment, Current equity holder in publicly-traded company; Tocagen: Ended employment in the past 24 months. Yilmaz: Pint Pharma: Honoraria; Pfizer: Research Funding; Daicho Sankyo: Research Funding. Mims: Syndax Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Kura Oncology: Membership on an entity's Board of Directors or advisory committees; Leukemia and Lymphoma Society: Other: Senior Medical Director for Beat AML Study; Jazz Pharmaceuticals: Other: Data Safety Monitoring Board; Agios: Consultancy; Novartis: Speakers Bureau.

*signifies non-member of ASH