Highlights
- Subcutaneous blinatumomab achieved high remission rates (75-79%) in adults with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL).
- Both evaluated dosing regimens exhibited manageable safety profiles, with primary toxicities consistent with known blinatumomab effects.
- The 250 μg/500 μg subcutaneous regimen was selected as the recommended phase 2 dose due to balanced efficacy and tolerability.
- Subcutaneous administration offers logistical and potentially economic advantages that may drive a future trend in immunotherapy delivery.
Clinical Background and Disease Burden
Relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) remains a significant clinical challenge, with dismal outcomes for many adults following standard therapies. The approval of blinatumomab—a bispecific T-cell engager (BiTE)—marked a major advance, leveraging redirected T-cell cytotoxicity against CD19+ leukemic blasts. However, the conventional intravenous (IV) administration requires continuous infusion, imposing substantial burdens on patients, healthcare systems, and resource allocation. There is a pressing unmet need for therapies that are not only effective but also more adaptable to diverse clinical settings and patient lifestyles.
Research Methodology
This post-hoc analysis is based on a multicentre, single-arm, phase 1/2 trial (NCT04521231) that enrolled adults with relapsed or refractory B-ALL across 44 hospitals in 11 countries. Eligible patients were aged 18 or older, had at least 5% bone marrow blasts, and an ECOG performance status of 2 or less. Two subcutaneous blinatumomab regimens were evaluated: an initial 250 μg dose (week 1, cycle 1) followed by 500 μg thrice weekly (250 μg/500 μg group), and a higher-dose regimen of 500 μg then 1000 μg on the same schedule (500 μg/1000 μg group). Each cycle included 4 weeks of treatment and a 1-week break; patients could receive 2-5 cycles. The primary endpoint was the rate of complete remission (CR) or CR with partial hematological recovery (CRh) within the first two cycles. Safety, response rates, and pharmacokinetics were analyzed and compared descriptively between dose groups.
Key Findings
Among 88 patients (36 in the 250 μg/500 μg group and 52 in the 500 μg/1000 μg group) with a median 5-month follow-up, the CR/CRh rates were notably high: 75% (27/36, 80% CI: 60-87%) in the lower-dose group and 79% (41/52, 80% CI: 67-86%) in the higher-dose group. These findings are particularly impressive given the relapsed/refractory setting, where standard salvage regimens often yield much lower response rates.
The most frequent grade 3-4 adverse events included neutropenia (22%), cytokine release syndrome (CRS, 20%), and immune effector cell-associated neurotoxicity syndrome (ICANS, 17%). Serious adverse events were common (80% overall) but generally manageable; importantly, no treatment-related deaths occurred. Pharmacokinetic data indicated dose-proportional exposure with subcutaneous delivery. Together, these results supported the selection of the 250 μg/500 μg regimen as the recommended phase 2 dose based on its favorable balance of safety and efficacy.
Mechanistic Insights and Biological Plausibility
Blinatumomab is a BiTE molecule that transiently links CD3+ T cells to CD19+ B cells, triggering T-cell activation and targeted cytotoxicity. The subcutaneous route, as opposed to intravenous infusion, may reduce peak systemic concentrations, potentially mitigating the risk of acute cytokine-mediated toxicities while maintaining sufficient exposure for therapeutic efficacy. Pharmacokinetic consistency and dose-proportionality observed in this trial reinforce the plausibility of subcutaneous administration achieving the desired immunomodulatory effects without pharmacodynamic compromise.
Expert Commentary
Expert consensus has long highlighted the limitations of continuous IV blinatumomab—chiefly the logistical complexity and requirement for central venous access, which may preclude outpatient care and limit access in resource-constrained environments. The subcutaneous formulation could be a transformative advance, facilitating outpatient administration with improved patient convenience and potentially broader global access. As noted by major hematology guidelines, optimizing both efficacy and quality of life is an increasingly important pillar of care for relapsed/refractory B-ALL.
Advantages and Future Trends of Subcutaneous Administration
Subcutaneous (SC) administration offers several potential advantages:
- Patient Convenience and Quality of Life: Avoids the need for prolonged hospital stays and continuous IV infusions, reducing disruption to daily activities.
- Resource Utilization: May enable outpatient or even home-based therapy, lowering hospital resource consumption and associated costs.
- Safety Profile: SC delivery can yield more gradual systemic absorption, possibly attenuating the severity or incidence of infusion-related reactions such as CRS and ICANS.
- Broader Access: Simplified administration facilitates use in community or low-resource settings, addressing disparities in access to advanced therapies.
Given these advantages, there is a compelling rationale for subcutaneous delivery to become a wider trend not only for blinatumomab but also for other biologics and cellular immunotherapies, provided that efficacy is maintained and safety is not compromised. The ongoing phase 2 study and future comparative trials with IV blinatumomab will be pivotal in defining the clinical role of this approach.
Controversies or Limitations
This study’s single-arm design, relatively short follow-up, and modest sample size limit the ability to draw definitive conclusions regarding durability of remission and long-term safety. The absence of a direct IV comparator arm prevents head-to-head assessment of efficacy and adverse event profiles. Additionally, the trial population, while diverse, may not fully capture outcomes in real-world settings, particularly in patients with higher comorbidity burdens or in pediatric populations, where T-cell dysfunction during blinatumomab therapy has been reported. Further research is needed to clarify the impact of SC administration on immune effector cell function and resistance mechanisms.
Conclusion
Subcutaneous blinatumomab shows robust preliminary activity and a manageable safety profile in adults with relapsed/refractory B-ALL, with remission rates that compare favorably to historical IV experience. The logistical and potential economic benefits of SC administration position it as an attractive future trend in immunotherapy delivery. However, larger, randomized trials are needed to validate these findings, assess long-term outcomes, and define the optimal place of SC blinatumomab in the B-ALL treatment landscape.
References
Jabbour E, Lussana F, Martínez-Sánchez P, et al. Subcutaneous blinatumomab in adults with relapsed or refractory B-cell acute lymphoblastic leukaemia: post-hoc safety and activity analysis from a multicentre, single-arm, phase 1/2 trial. Lancet Haematol. 2025 Jul;12(7):e529-e541. doi: 10.1016/S2352-3026(25)00144-9.
Analysis of Subcutaneous Administration: Advantages and Future Trends (English & Chinese)
English: Subcutaneous injection of blinatumomab offers significant advantages over intravenous administration, including enhanced patient convenience, potential for outpatient care, and a safety profile that may reduce the incidence of severe infusion-related reactions. As healthcare systems increasingly value patient-centered, resource-efficient therapies, subcutaneous delivery is likely to become a key trend in future immunotherapy protocols, particularly for agents requiring prolonged exposure.
Chinese (中文): 皮下注射blinatumomab相较于静脉输注具有显著优势，包括提升患者便利性、促进门诊治疗及可能降低严重输注相关反应的发生率。在医疗体系日益重视以患者为中心和资源高效的治疗方式背景下，皮下注射有望成为未来免疫治疗药物给药的重要趋势，尤其适用于需长时间维持药物暴露的生物制剂。
