A Phase 1 Study Investigating AFM11 in Patients with Relapsed/Refractory B Cell Precursor Acute Lymphoblastic Leukemia: Preliminary Results

Background AFM11 is a bispecific, tetravalent T cell-engaging antibody construct binding to CD19 on B cell origin malignant cells such as B-precursor acute lymphoblastic leukemia (B-ALL) and to CD3 on T cells. By engaging CD3-positive T cells, AFM11 elicits T cell-mediated killing of CD19-positive (CD19+) leukemia and lymphoma cells. In vivo anti-tumor activity of AFM11 was investigated in a Raji tumor xenograft model in non-obese diabetic/severe combined immunodeficiency (NOD/scid) mice reconstituted with human peripheral blood mononuclear cells (PBMC). Tumor growth in all AFM11-treated animal groups was significantly reduced. In the highest dose group, all animals achieved complete tumor remission. (Reusch et al., 2015). An ongoing Phase 1 study assesses safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD) and preliminary efficacy of AFM11 in patients with relapsed/refractory (R/R) CD19+ B-ALL. Methods Patients (pts) with relapsed or refractory CD19+ B-ALL are being enrolled into escalating cohorts of 1-6 pts. The primary objective of the study is to determine the maximum tolerated dose (MTD) of AFM11 administered as a 2-week continuous intravenous (CIV) infusion. AFM11 is administered over the first 2 weeks (wks) of each 4 wk cycle for up to 3 cycles. Pts with rapidly progressing disease receive pre-treatment with 200 mg cyclophosphamide and 10 mg/m2 dexamethasone over 3-5 days before initiating AFM11. A lower starting dose is employed during the first wk of cycle 1 and escalated to a target dose during the second wk of cycle 1 and all subsequent cycles. An accelerated titration design is used until toxicity is observed, followed by a classical 3+3 design. PD activity is assessed by flow cytometry of peripheral blood lymphocytes and serum cytokine measurements. Tumor response is evaluated by local bone marrow and peripheral blood laboratory results between days 15 and 18 of each cycle. Results As of June 29, 2018, fourteen pts (8 female/6 male) have been treated in 5 cohorts. The median age is 41.5 years (range 19-67) and the median number of prior therapies is 5 (range 1-12). AFM11 was well-tolerated with no dose-limiting toxicities (DLTs) observed in the first 5 cohorts. The study switched to 3+3 design in cohort 3 due to the occurrence of grade 2 AFM11-related events in cohort 2. Enrollment into cohort 6 is ongoing and the MTD has not yet been reached. The most frequent (≥2 pts) AFM11-related adverse events were pyrexia (29%), myalgia (