A Phase I Trial of the Antibody-Cytokine Fusion Protein F16IL2 in Combination with Anti-CD33 Immunotherapy for Posttransplant AML Relapse

Introduction

Natural killer (NK) cells are key effectors in cancer immunosurveillance and posttransplant immunity, but shortage of environmental growth factors and deficient recognition of malignant cells may limit their anticancer efficacy. We hypothesized that the antibody-mediated anchoring of interleukin-2 (IL-2) to the leukemia-modified extracellular matrix (ECM) would increase NK cell abundance and activity to potentiate antibody-dependent cellular cytotoxicity (ADCC) against acute myeloid leukemia (AML) blasts. In this novel-novel combination dose-escalation phase 1 trial, we enrolled patients with AML relapse after allogeneic hematopoietic stem cell transplantation (HSCT) to evaluate the safety, pharmacokinetics, pharmacodynamics, and preliminary activity of F16IL2, an antibody-cytokine fusion protein composed of the human antibody fragment scFv(F16) in diabody format and two molecules of human IL-2, in combination with the Fc-optimized, ADCC-mediating anti-CD33 monoclonal antibody BI 836858. F16 specifically targets the A1 domain of the ECM protein tenascin C (TnC), which is spliced into the TnC molecule during active angiogenesis and tissue remodeling while it is virtually absent in normal tissues.

Methods

F16IL2 (10 - 20 Mio IU IV) was administered on days 1, 8, 15 and 22 of 28-day cycles, followed by administration of BI 836858 (10 - 40 mg IV) two days after each F16IL2 infusion. Dose escalation was performed over 4 dose levels (DL). Cohort 1 (10 Mio IU F16IL2 and 10 mg BI 836858, n = 5), cohort 2 (10 Mio IU F16IL2 and 20 mg BI 836858, n = 3), cohort 3 (20 Mio IU F16IL2 and 20 mg BI 836858, n = 4), cohort 4 (20 Mio IU F16IL2 and 40 mg BI 836858, n = 3). Safety and tolerability, pharmacodynamics and -kinetics, clinical efficacy and immune effector cell dynamics were investigated. This trial was registered at EudraCT as #2015-004763-37.

Results

Between December 2016 and March 2020, 15 patients with a median age of 50 years (range, 20 - 68) were enrolled and treated across 4 dose levels. Six patients (40%) had received two or more prior HSCT. The most frequent drug-related AEs (F16IL2 or BI 836858 or combination) were pyrexia (n = 13, 87%), chills (n = 12, 80%) and infusion-related reactions (n = 9, 60%), consistent with the expected toxicity profile of cytokine-armed or naked mAbs. These events were generally manageable, transient and of grade ≤ 2. One dose-limiting toxicity occurred at each of DL 3 (pulmonary edema) and 4 (acute GVHD). No patient died within the first 30 days of treatment initiation. Whereas no formal maximum tolerated dose (MTD) was reached, the maximum tested dose of 20 Mio IU F16IL2 and 40 mg BI 836858 was considered the recommended dose (RD). Three objective responses (1 CR, 1 CRi, 1 PR in extramedullary AML) were observed among 7 patients treated at the two higher DL, whereas no responses occurred at the two starting DL. Median OS among all 15 patients was 4.8 months (1.5 - 12.9), with a 6- and 12-month OS of 40% and 27%, respectively. Among those 7 patients whose AML was at least temporarily controlled with study treatment (CR/CRi, PR, SD), 12-month OS was 67% vs. 0% in non-responders. Combination therapy stimulated the expansion and activation of NK cells in bone marrow and peripheral blood.

Conclusions

To the best of our knowledge, this is the first study demonstrating that the strategy of potentiating ADCC with tumor-targeted immunocytokines is feasible in humans. In the difficult-to-treat situation of posttransplant AML relapse, responses were observed at higher DL, even in patients with extramedullary disease. The antibody-mediated targeted delivery of IL-2 to the ECM combined with anti-CD33 immunotherapy represents an innovative experimental approach associated with acceptable safety and encouraging biologic and clinical activity in posttransplant AML relapse.