Safety and feasibility of 0.6 mg/kg every 4 weeks dosing of axatilimab in patients treated in the AGAVE-201 study

Abstract Introduction: Axatilimab is an anti–colony-stimulating factor 1 receptor (CSF-1R) monoclonal antibody that targets monocytes and macrophages, key mediators of inflammation and fibrosis in chronic graft-versus-host disease (cGVHD). Axatilimab is approved by the US Food and Drug Administration at a dose of 0.3 mg/kg (up to a maximum dose of 35 mg) every 2 weeks (Q2W) for patients with cGVHD after ≥2 prior lines of therapy, based on results from the pivotal phase 2 AGAVE-201 clinical trial (NCT04710576). Patients treated with the 0.3 mg/kg Q2W dose in the AGAVE-201 study were able to transition to 0.6 mg/kg every 4 weeks (Q4W) dosing based on the investigator's discretion and per study protocol criteria. Aims: To describe the safety and feasibility of transition from axatilimab 0.3 mg/kg Q2W to 0.6 mg/kg Q4W dosing using data from AGAVE-201. Methods: Patients treated with axatilimab 0.3 mg/kg Q2W in AGAVE-201 who had their Cycle 7 assessment and achieved a partial or complete response (PR/CR) per National Institutes of Health criteria that was sustained for ≥20 weeks or had not progressed were able to change their dosing schedule to 0.6 mg/kg Q4W (without dose capping) per the study protocol and investigator discretion. Safety and treatment duration were assessed in this post hoc analysis; patients who received additional systemic therapies were excluded. The data cutoff was March 30, 2025. Results: In the first 6 treatment cycles, 59 of the 80 patients (73.8%) randomized to axatilimab 0.3 mg/kg Q2W had a response to treatment (primary endpoint). Of these 59 patients, 19 (32.2%) transitioned to 0.6 mg/kg Q4W dosing. Among these 19 patients, demographics (median [range] age, 50.0 [20–73] y; male, 63.2%) and baseline clinical characteristics (median [range] number of organs involved at baseline, 3.0 [2–8]; severe disease, 73.7%; prior use of ibrutinib, ruxolitinib, or belumosudil, 89.5%) were comparable to the full cohort initially randomized to 0.3 mg/kg Q2W. Overall response rate in the first 6 treatment cycles among the 19 patients who switched to 0.6 mg/kg Q4W was 94.7% (95% CI, 74.0%–99.9%; CR, 5.3%; PR, 89.5%); 1 patient had stable disease and thus was eligible to switch, per investigator discretion. Patients were on treatment for a median (range) of 20.9 (2–32) months after switching doses; 16 of 19 patients (84.2%) maintained the 0.6 mg/kg Q4W dose after dose switching. The safety profile for axatilimab was generally similar before and after the dosing change. After switching to 0.6 mg/kg Q4W, 10 patients (52.6%) had grade ≥3 treatment-emergent adverse events (TEAEs); pneumonia was the only grade ≥3 TEAE reported in >1 patient (n=2). TEAEs led to treatment interruptions in 4 patients (21.1%) and discontinuations in 3 patients (15.8%) after switching. The most common TEAEs after switching to 0.6 mg/kg Q4W were fatigue (n=5 [26.3%]), upper respiratory tract infection (n=5 [26.3%]), and headache (n=4 [21.1%]); 1 patient (5.3%) had an infusion-related reaction (n=1 [rash]). Incidences of on-target TEAEs were generally similar before and after the switch, including elevations in alanine aminotransferase (n=3 before switching and n=1 after) and amylase (n=0 and n=1).Conclusion: Transition to 0.6 mg/kg Q4W (without dose capping) is feasible and well tolerated in patients treated with axatilimab 0.3 mg/kg Q2W on the AGAVE-201 study. The Q4W dosing strategy at the 0.6 mg/kg dose identified no new safety signals. Patients had a prolonged duration of therapy, with a median of 20.9 months (1.7 y), and 84% of patients continued treatment, suggesting ongoing clinical benefit. These data provide evidence of the safety and feasibility of a 0.6 mg/kg Q4W dosing strategy in alignment with the AGAVE-201 protocol.