Flotetuzumab as salvage immunotherapy for refractory acute myeloid leukemia

Abstract

Approximately 50% of acute myeloid leukemia (AML) patients do not respond to induction therapy (primary induction failure [PIF]) or relapse after <6 months (early relapse [ER]). We have recently shown an association between an immune-infiltrated tumor microenvironment (TME) and resistance to cytarabine-based chemotherapy but responsiveness to flotetuzumab, a bispecific DART antibody-based molecule to CD3ε and CD123. This paper reports the results of a multicenter, open-label, phase 1/2 study of flotetuzumab in 88 adults with relapsed/refractory AML: 42 in a dose-finding segment and 46 at the recommended phase 2 dose (RP2D) of 500 ng/kg per day. The most frequent adverse events were infusion-related reactions (IRRs)/cytokine release syndrome (CRS), largely grade 1-2. Stepwise dosing during week 1, pretreatment dexamethasone, prompt use of tocilizumab, and temporary dose reductions/interruptions successfully prevented severe IRR/CRS. Clinical benefit accrued to PIF/ER patients showing an immune-infiltrated TME. Among 30 PIF/ER patients treated at the RP2D, the complete remission (CR)/CR with partial hematological recovery (CRh) rate was 26.7%, with an overall response rate (CR/CRh/CR with incomplete hematological recovery) of 30.0%. In PIF/ER patients who achieved CR/CRh, median overall survival was 10.2 months (range, 1.87-27.27), with 6- and 12-month survival rates of 75% (95% confidence interval [CI], 0.450-1.05) and 50% (95% CI, 0.154-0.846). Bone marrow transcriptomic analysis showed that a parsimonious 10-gene signature predicted CRs to flotetuzumab (area under the receiver operating characteristic curve = 0.904 vs 0.672 for the European LeukemiaNet classifier). Flotetuzumab represents an innovative experimental approach associated with acceptable safety and encouraging evidence of activity in PIF/ER patients. This trial was registered at www.clinicaltrials.gov as #NCT02152956.

Graphical abstract

Figure 1.

LID and use of tocilizumab decrease CRS incidence, severity and duration, and lead to increase in total dose intensity. (A) Summary of dose and dosing schedule for flotetuzumab: MS-LID of 30, 60, 100, 200, 300, 400, 500 ng/kg per day for 24 hours each for days 1 through 7 given via CIV infusion, followed by 500 ng/kg per day CIV from days 8 to 28 during cycle 1, with subsequent additional 28-day cycles dosed at 500 ng/kg per day doses intermittently 4 days on/3 days off per week in 28-day cycles without LID lead-in. (B-D) LID mitigates CRS and consequently leads to improvement in dose intensity. (B) CRS grade (mean plus or minus standard error of the mean [SEM]) during each week of cycle 1. (C-D) Dose intensity (percentage, mean plus or minus 95% CI) was calculated as the amount of drug received during the time on study (actual drug delivered) relative to the intended dose during weeks 2 to 4 following respective LID during week 1 of 2-step (left) multistep (right) LID. (E) Tocilizumab effect on duration of IRR/CRS, irrespective of grade. Only patients for whom the drug was not modified as a method of controlling IRR/CRS are included. Mean duration of CRS without tocilizumab 1.8 days (n = 42) and with tocilizumab 1.2 days (n = 13); P = .0202, Student t test.

Figure 2.

Best change in BM blasts, duration of remission, and OS in patients receiving flotetuzumab immunotherapy. (A) Fifty patients treated at the RP2D differentiated by AML status at study entry: 45 response-evaluable, 40 patients in waterfall plot, 5 progressive disease (PD) on peripheral blood blasts; nonevaluable patients, 5: 2 patients withdrew consent, 3 patients withdrawn due to non-TRAEs. AML status at study entry and percentage of BM blasts at baseline are indicated. (B) Eight PIF/ER AML patients treated at RP2D who achieved a response on flotetuzumab. Median time to best response represented in red (median, 0.8 months; range, 0.8-2.1 months) and duration of response in blue (median, 9.1 months; range, 1.1-26.4 months). Purple depicts OS beyond relapse. *BM aspirate for this patient was hemodiluted but immunohistochemistry on BM formalin-fixed paraffin embedded confirmed the percent blast. ☆, Time at which patients underwent hematopoietic stem cell transplantation (HSCT).

Figure 3.

Relation between CRS and antileukemic activity. (A) Relation between BM blast change and number of days patient experienced CRS during cycle 1. (B) Relation between BM blast change and number of CRS events during cycle 1. (C) Relation between BM blast change and CRS severity (mean grade for all events per patient) during cycle 1. Simple regression is shown as red line; dotted lines depict 95% CI.

Figure 4.

The TME in patients receiving flotetuzumab immunotherapy. (A) Unsupervised hierarchical clustering (Euclidean distance, complete linkage) of immune cell type–specific scores and biological activity scores in baseline BM samples from 38 patients with R/R AML treated with flotetuzumab immunotherapy (color-coded per the legend). ClustVis, an online tool for clustering of multivariate data, was used for data analysis and visualization. The immune landscape from 29 of the 38 patients in this cohort has been presented in a previous publication. (B) OncoPrint plot summarizing the molecular profile of patients receiving flotetuzumab immunotherapy. The plot was generated using cBioPortal for Cancer Genomics (https://www.cbioportal.org/). (C) Inflammatory chemokine score and tumor-inflammation signature (TIS) score in baseline BM samples from patients with R/R AML. PIF, n = 25; LR AML, n = 7; HMAs, n = 6. Data were compared using the Kruskal-Wallis (KW) test for unpaired determinations. (D) Correlation between the TIS score and antigen processing machinery and inflammatory chemokine scores in baseline BM samples from patients with R/R AML. Spearman rank correlation coefficients and P values are shown. NE, not evaluable.

Figure 5.

The TME in patients receiving flotetuzumab immunotherapy. (A) Unsupervised hierarchical clustering (Euclidean distance, complete linkage) of immune gene expression (n = 770 genes in the NanoString’s PanCancer IO360 panel) in baseline BM samples from 38 patients with R/R AML treated with flotetuzumab immunotherapy (color-coded per the legend). Complete responses were defined as either CR, CRh, CRi, or MLFS at the end of cycle 1. PRs were defined as >50% decrease in BM blasts from baseline or decrease to 5% to 25% BM blasts at the end of cycle 1. ClustVis, an online tool for clustering of multivariate data, was used for data analysis and visualization. (B) Expression of the top 10 genes associated with complete response to flotetuzumab (CR, CRh, CRi). A ranked gene list (χ² values) was generated using the Orange3 software package (version 3.25.0). Unsupervised hierarchical clustering (Euclidean distance, complete linkage). The immune cluster was defined as previously detailed. (C) Heatmap summarizing the correlation coefficients (color-coded per the legend) between our 10-gene signature score and immune cell type–specific and biological activity signature scores in baseline BM samples from patients with R/R AML. (D) Analysis of functional protein association networks using STRING (https://string-db.org/). Top 20 molecules interacting with the top 10 genes in our signature are shown together with their predicted mode of action (highest confidence interaction scores > 0.900). Network nodes (query proteins) represent proteins produced by a single protein-coding gene locus. White nodes represent second shells of interactors. Empty and filled nodes indicate proteins of unknown or partially known 3-dimensional structure, respectively. Edges represent protein-protein associations. Line shapes denote predicted modes of action. (E) AUROC curve measuring the predictive ability of the 10-gene signature score for antileukemic activity from flotetuzumab. Standard errors and confidence intervals are provided in supplemental Table 11. AUROC = 1.0, perfect prediction; AUROC = 0.5, no predictive ability.