Background

Acute myeloid leukemia (AML) blasts and leukemic stem and progenitor cells typically express higher levels of CD123 than their normal hematopoietic stem cell counterparts, making CD123 an attractive target. Leukemic CD123 expression is associated with poor prognosis, high-risk disease, and increased risk of induction failure (Vergez et al 2011). Single-agent flotetuzumab, an investigational CD123 x CD3 bispecific DART protein, has shown evidence of clinical activity in a Phase 1 study of relapsed/refractory (R/R) acute myeloid leukemia (AML). In this study, flotetuzumab led to T-cell activation which in turn was associated with PD-1 induction on T lymphocytes, enhanced IFNɣ secretion, and upregulation of PD-L1 expression by AML blasts (ASH 2018 Rutella, ASH 2018 Uy). In vitro studies have shown synergistic T-cell mediated cytotoxicity of an AML cell line (KG1A) with flotetuzumab in the presence of PD-1/PD-L1 axis blockade compared to flotetuzumab alone. MGA012, also known as INCMGA00012, is an investigational anti-PD-1 antibody that has shown clinical activity in a Phase 1 study (SITC 2018 Mehnert). We hypothesize that combined checkpoint inhibition with MGA012 together with redirected T‐cell killing of CD123+ cells with flotetuzumab may show enhanced activity over flotetuzumab alone.

Methods

This is a Phase 1 dose escalation study designed to characterize the safety, tolerability, dose-limiting toxicities, maximum tolerated dose (MTD) or maximum administered dose (if no MTD is defined), pharmacokinetics, and preliminary anti-leukemic activity of flotetuzumab in combination with MGA012, each administered intravenously (IV) in patients with R/R AML. Response evaluation will be determined by modified ELN 2017 criteria. Activity is measured by complete response (CR) (complete remission [CR], or CR with partial hematologic recovery [CRh], or CR with incomplete hematological recovery [CRi], or morphologic leukemia-free state [MLFS]) rate, relapse-free survival, or mortality rate at 1 and 3 months. The impact of flotetuzumab/MGA012 combination on overall survival and event-free survival will be explored. Eligible patients will consist of adults with relapsed or refractory AML (any subtype except acute promyelocytic leukemia) who have exhausted standard of care options. In Induction Cycle 1, patients will be treated with a step-up lead in dose of flotetuzumab, followed by continuous infusion flotetuzumab, starting at week 2 of Cycle 1 and continuing through each 28-day cycle. MGA012 will be administered every two weeks. Depending on response, patients will transition to either consolidation or second induction. Eligible patients who achieve CR/CRh/CRi can receive maintenance MGA012 alone for up to 12 months.

Disclosures

Wei:AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AHW is a former employee of the Walter and Eliza Hall Institute and receives a fraction of its royalty stream related to venetoclax, Research Funding, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Honoraria, Research Funding; Janssen: Honoraria. Fong:Novartis: Speakers Bureau; Amgen: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Astellas: Consultancy. Montesinos:Karyopharm: Membership on an entity's Board of Directors or advisory committees, Other: Research support; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau. Gil:Jazz Pharmaceuticals: Honoraria; Gilead: Honoraria; Daiichi-Sankyo: Honoraria; Novartis: Honoraria, Research Funding; Pfizer: Honoraria; Abbvie: Honoraria. Perez De Oteyza:Celgene: Speakers Bureau. Rowe:BioSight: Consultancy. Wolach:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker. Sun:MacroGenics, Inc.: Employment, Equity Ownership. Baughman:MacroGenics, Inc.: Employment, Equity Ownership. McNulty:MacroGenics, Inc.: Employment, Equity Ownership. Bonvini:MacroGenics, Inc.: Employment, Equity Ownership. Wigginton:Western Oncolytics: Other: clinical advisory board; MacroGenics, Inc.: Employment, Equity Ownership. Davidson-Moncada:MacroGenics, Inc.: Employment, Equity Ownership.

Author notes

*

Asterisk with author names denotes non-ASH members.