Highlights
Efficacy Excellence
In the efficacy population of the CART19-BE-02 trial, 84.4% of patients (27 of 32) achieved a complete response with undetected measurable residual disease (MRD) by day 28, utilizing a sensitivity threshold of 10^-5.
Innovative Dosing Strategy
The study employed a fractionated intra-patient dose escalation (0.1, 0.3, 0.6, and 2.0 × 10^6 CAR T cells/kg), which proved instrumental in maintaining high therapeutic activity while mitigating acute toxicities.
Superior Safety Profile
Severe cytokine release syndrome (CRS) occurred in only 12% of patients, and grade 3 or higher immune effector cell-associated neurotoxicity syndrome (ICANS) was remarkably low at 3%.
Hospital-Based Accessibility
The success of this academic-led trial supports a decentralized, hospital-based manufacturing and administration model, potentially expanding access to advanced CAR T-cell therapies in Europe.
The Clinical Challenge of Adult B-ALL
Adult patients with relapsed or refractory (R/R) B-cell precursor acute lymphoblastic leukaemia (B-ALL) face a historically poor prognosis. While pediatric outcomes have improved significantly, adults often encounter higher rates of treatment resistance and limited durability of response to conventional salvage chemotherapies. The advent of CD19-directed chimeric antigen receptor (CAR) T-cell therapies has revolutionized the landscape, yet commercial products are often associated with significant logistical hurdles and profound toxicities, specifically cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS).
Varnimcabtagene autoleucel (var-cel) represents a critical shift in this therapeutic paradigm. As an autologous CD19-directed CAR T-cell therapy developed within an academic framework in Spain, var-cel was designed to address both the efficacy requirements of a high-burden disease and the safety requirements necessary for broader clinical implementation. Following its initial Spanish approval in 2021 for patients over 25, the results of the pivotal CART19-BE-02 trial provide definitive evidence regarding its clinical utility in a broader adult population.
Methodology: The CART19-BE-02 Trial Design
This multicentre, single-arm, phase 2 trial was conducted across nine academic centers in Spain. The study enrolled 38 patients between May 2021 and July 2023, targeting adults (aged 18-70 years) with CD19+ B-cell precursor ALL. Eligible participants included those in their first relapse, those with refractory disease, or those who had relapsed following an allogeneic haematopoietic cell transplantation (HCT).
Intervention and Dosing
The protocol utilized a standard lymphodepletion regimen consisting of fludarabine (30 mg/m2 per day) and cyclophosphamide (300 mg/m2 per day) for three days. The distinguishing feature of this trial was the intravenous fractionated var-cel escalation. Patients received increasing doses—0.1, 0.3, 0.6, and finally 2.0 × 10^6 CAR T cells per kg—separated by at least 24 hours. Each subsequent fraction was contingent upon the patient meeting specific safety criteria, allowing for real-time monitoring of early toxicity signals.
Study Endpoints
The primary endpoint was the rate of complete response (CR) with undetected measurable residual disease (MRD) by day 28 post-infusion. MRD was assessed via flow cytometry with a high sensitivity of ≤10^-5. Secondary endpoints included safety, overall survival, and the feasibility of the fractionated dosing approach.
Key Findings: Unprecedented MRD-Negative Response Rates
The efficacy population comprised 32 patients who received at least one fraction of var-cel. The results at the data cutoff (January 18, 2024) were striking. Of the 32 patients, 27 (84.4% [95% CI 67.2–94.7]) achieved a complete response with undetected MRD by day 28. This level of deep molecular remission is a critical surrogate for long-term survival in B-ALL.
Patient Demographics and Treatment Flow
The median age of the cohort was 40 years, with a balanced gender distribution. Of the 38 patients enrolled, 37 underwent leukapheresis. However, five patients did not proceed to infusion due to rapid disease progression, death from veno-occlusive disease, or persistent infection (COVID-19), highlighting the aggressive nature of R/R B-ALL and the necessity for efficient manufacturing timelines.
Safety Profile: Mitigating CRS and ICANS
One of the most significant barriers to wider CAR T-cell adoption is the risk of life-threatening toxicity. The CART19-BE-02 trial demonstrated that fractionated dosing significantly alters the safety trajectory of CD19 CAR T therapy.
Cytokine Release Syndrome (CRS)
While 94% of patients experienced some form of treatment-emergent adverse event, the incidence of severe CRS was controlled. Grade 3 or higher CRS occurred in only four patients (12%). Most cases were manageable with standard protocols, including tocilizumab and steroids, without compromising the CAR T-cell expansion or efficacy.
Neurotoxicity and HLH-like Syndrome
ICANS, a frequent and often severe complication of CAR T therapy in B-ALL, was notably rare. Only one patient (3%) experienced grade 3 or higher ICANS or cerebral oedema. Additionally, immune effector cell-associated hemophagocytic lymphohistiocytosis (HLH)-like syndrome occurred in two patients (6%). Notably, one death occurred following a protocol violation where the infusion was administered during uncontrolled sepsis, emphasizing the critical importance of adherence to safety criteria during the fractionation process.
Hematologic Toxicities
As expected with lymphodepleting chemotherapy and CAR T-cell therapy, hematologic adverse events were common. Grade 3 or higher neutropenia was observed in 45% of patients, thrombocytopenia in 21%, and anaemia in 15%.
Expert Analysis: The Academic Manufacturing Paradigm
The results of the CART19-BE-02 trial extend beyond the clinical data of var-cel itself; they validate the “point-of-care” or hospital-based manufacturing model. By producing the CAR T-cells within academic centers, the Spanish network demonstrated that high-quality, advanced biologics could be delivered effectively outside of the traditional large-scale pharmaceutical infrastructure.
Biological Rationale for Fractionation
The fractionated dosing strategy acts as a safety valve. In patients with a high tumor burden, a massive initial bolus of CAR T-cells can trigger an explosive cytokine storm. By starting with a low fraction (0.1 × 10^6 cells/kg) and escalating based on tolerability, clinicians can theoretically allow for a more controlled expansion of the effector cells. This study confirms that this approach does not dilute the therapeutic impact, as evidenced by the 84.4% MRD-negative CR rate.
Future Directions and Limitations
While the 8.6-month median follow-up is encouraging, longer-term data are required to assess the durability of these remissions and the potential for late relapses. Furthermore, as a single-arm trial, direct comparisons to commercial CAR T products must be interpreted with caution, although the safety data for var-cel appears highly competitive.
Conclusion
Varnimcabtagene autoleucel represents a significant advancement for adult patients with R/R B-cell precursor ALL. The CART19-BE-02 trial proves that fractionated dose escalation is a robust strategy that preserves high anti-leukemic activity while substantially limiting the acute toxicities that have historically complicated CAR T-cell administration. This study not only offers a new therapeutic option for clinicians but also provides a blueprint for a sustainable, hospital-based approach to cellular immunotherapy that could expand patient access across global healthcare systems.
Funding and Clinical Registry
This trial was funded by the Instituto de Salud Carlos III, the Fondo Europeo de Desarrollo Regional (FEDER), CaixaResearch, and several Spanish regional health services (Catalunya, Madrid, Murcia, Castilla y León, Andalucía, and Navarra). The study is registered with ClinicalTrials.gov under the identifier NCT04778579.
References
1. Ortiz-Maldonado V, et al. Varnimcabtagene autoleucel for adults with relapsed or refractory B-cell precursor acute lymphoblastic leukaemia in Spain (CART19-BE-02): a multicentre, single-arm, phase 2 trial. Lancet Haematol. 2026 Feb 3:S2352-3026(25)00328-X. doi: 10.1016/S2352-3026(25)00328-X.
2. Shah BD, et al. KTE-X19 for relapsed or refractory adult B-cell acute lymphoblastic leukaemia (ZUMA-3): a multicentre, single-arm, phase 2 study. Lancet. 2021;398(10299):491-502.
3. Hay KA, et al. Factors associated with durable EFS in adult B-cell ALL beneficiaries of CD19 CAR T-cell therapy. Blood. 2019;133(15):1652-1663.
