100% Phase 1 Response Meets Allogeneic Reality Check Ahead of Q4 2026 Readouts

Adults with R/R BCP-ALL including primary refractory disease, relapse after chemotherapy, and relapse after allo-HCT: A prospective observational study enrolled 100 patients (25 Ph-positive, 75 Ph-negative) including 7 primary refractory (4 post-blinatumomab), 36 relapsed after chemotherapy (23 post-blinatumomab), and 57 relapsed after allo-HCT (23 post-blinatumomab), with extramedullary relapse in 39% of patients.

Post-allo-HSCT relapsed or persistent MRD-positive B-ALL requiring bridge to second transplant: Relapse of B-ALL after allo-HSCT remains a major clinical challenge, with inotuzumab ozogamicin evaluated as a bridge to second allo-HSCT constrained by concerns regarding sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD).

Blinatumomab failure with CD19-negative and extramedullary relapse driven by genetics and disease burden: In 267 adults treated with blinatumomab, high disease burden and active extramedullary disease (EMD) were associated with inferior CR/CRi rate, and TP53 mutations were associated with increased risk of CD19- relapse (HR=6.84; 95%CI: 2.68-17.45), with 22 (28%) CD19- and 54 (68%) CD19+ relapse among 79 relapses.

Central nervous system involvement with high relapse risk: CNS is the most common site of extramedullary invasion in ALL, and involvement is often associated with relapse, refractory disease, and poor prognosis, with CNS leukemia patients exhibiting higher cumulative relapse rate following CAR-T-induced remission and increased risk of CNS relapse.

High-risk and relapsed/refractory pediatric B-ALL and high-risk genomic subsets: Approximately 10-15% of pediatric B-cell ALL are high risk at diagnosis or relapsed/refractory, while Philadelphia-like ALL is a high-risk subset with poor prognosis with conventional therapies, and diagnostic challenges and lack of standardized treatment protocols contribute to suboptimal outcomes.

Relapse after CD19 CAR-T with antigen escape and immunosuppression: Poor results are obtained when the same CD19-targeted product is reused in patients who relapse after CAR-T, with antigen escape and PD-L1/PD-1 axis-mediated immunosuppression in the tumor microenvironment as predominant drivers of treatment failure in adult R/R B-ALL.

ZUMA-3 basis and real-world brexucabtagene autoleucel (brexu-cel) standard therapy study across 31 US centers: On the basis of the results of the ZUMA-3 trial, brexucabtagene autoleucel (brexu-cel), a CD19-directed chimeric antigen receptor T-cell therapy, gained US Food and Drug Administration approval in October 2021 for adults with relapsed/refractory (R/R) B-cell ALL (B-ALL). In the real-world cohort, 204 patients had undergone apheresis and 189 were infused, with 151 achieved complete remission (CR), of which 79% were measurable residual disease (MRD) negative remissions. Median progression-free survival (PFS) was 9.5 months and median overall survival was not reached, with Grade 3-4 CRS or ICANS occurred in 11% and 31%, respectively.

UK multicentre tisagenlecleucel study in children and young people with r/r ALL: Of 142 eligible patients, 125 received tisagenlecleucel, 115/125 (92%) achieved complete remission (CR/CRi). Severe cytokine release syndrome and neurotoxicity occurred in 16/123 (13%) and 10/123 (8.1%), with procedural mortality was 3/126 (2.4%). The 2-year intent to treat OS and EFS were 65.2% (95%CI 57.2-74.2%) and 46.5% (95%CI 37.6-57.6%).

CIBMTR registry real-world data for tisagenlecleucel with >2.5 years of follow-up: As of May 4, 2022, 768 patients with B-ALL had received tisagenlecleucel. Among patients with ≥12 months post-infusion follow-up (N=578; median follow-up 32.1 months), the best overall response of complete remission/complete remission with incomplete blood count recovery was 86.0%. Twelve-month relapse-free survival (RFS) and overall survival (OS) were 61.8% and 79.4%, while 24-month RFS and OS were 50.3% and 63.8%, respectively.

Single-center retrospective analysis of blinatumomab or inotuzumab ozogamicin as bridge to allogeneic stem cell transplantation in 34 adult patients with r/r B-ALL: Of the 13 patients with r/r B-ALL receiving blinatumomab, 9 (69%; 95% confidence interval [CI], 39%-91%) achieved complete remission (CR), with 78% of CR patients (95% CI, 40%-97%) reaching MRD negativity. In the inotuzumab ozogamicin group, all 16 patients were treated for overt r/r B-ALL, with rate of CR was 94% (95% CI, 70%-100%), with 67% (95% CI, 38%-88%) of CR patients reaching MRD negativity. Of those patients receiving blinatumomab and inotuzumab ozogamicin as a bridge-to-transplant strategy, 79% and 80%, respectively, proceeded to allogeneic stem cell transplantation, with drug-specific adverse events including cytokine release syndrome, capillary leak syndrome, and neurotoxicity for blinatumomab and transplant-associated veno-occlusive disease of the liver for inotuzumab ozogamicin.

Antigen escape and lineage plasticity drive resistant relapse: Leukemia may escape through antigen downregulation, alternative splicing, acquired genetic alteration, or epitope disruption, generally preserving B-lineage identity. A biologically distinct route is lineage plasticity, including lineage switch (LS) to acute myeloid leukemia or mixed phenotype acute leukemia. Of 420 patients treated with CAR, 166 (39.5%) relapsed, including 83 (50%) CD19pos, 68 (41%) CD19neg, and 12 (7.2%) LS relapses. Among relapsed patients following blinatumomab, 11 (61%) presented with CD19-negative disease. Clinical outcomes are poor, with a median overall survival of approximately 4.8 months in the largest reported series of lineage plasticity, and the median overall survival following a post-CAR relapse was 11.9 months (95% CI, 9-17) and was particularly dismal in patients experiencing an LS, with no long-term survivors following this pattern of relapse.

Short durability without allogeneic transplant consolidation: Targeted and immune-based therapies induce high MRD-negative remission rates, but durability of remission is short in the absence of allogeneic HCT consolidation. The 12-month leukaemia-free survival (LFS) for responders to blinatumomab, InO and CAR T cells was 20%, 11% and 0% (p=0.743) respectively in TP53-mutated ALL. Patients who had undergone allogeneic haematopoietic stem cell transplantation (HSCT) post-response had improved 12-month LFS compared to those who did not (35% vs. 9%, p=0.014). Patients with consolidative allo-HSCT after CAR-T therapy had a superior OS and LFS compared to those who did not.

High-risk genomic and disease-burden predictors of failure: TP53 mutation, bone marrow blasts > 20%, prior CAR-T/blinatumomab treatment, and severe cytokine release syndrome (CRS) were associated with a lower complete remission (CR) rate. The presence of a KMT2A rearrangement was the only preinfusion risk factor associated with LS, while KMT2A-rearranged leukemia accounted for the majority of B-ALL-to-acute myeloid leukemia or mixed-phenotype switches in a large international cohort. By contrast, CD19-negative antigen escape is more strongly associated with TP53 mutations. Poor cytogenetics (P = 0.0001), CD19+ B-cell loss (P = 0.046), and BCR-ABL1 positivity (P = 0.002) were predictors of poor response to blinatumomab, and 50% (2/4) of patients with the BCR::ABL1 T315I mutation experienced early relapse.

Substantial acute and long-term toxicities: Key acute toxicities are cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), whereas longer-term issues include prolonged cytopenias, infection risk, B-cell aplasia, and hypogammaglobulinemia requiring immunoglobulin replacement. Inotuzumab ozogamicin carries risk of sinusoidal obstructive syndrome (SOS) and veno-occlusive disease, with three cases (8%) of non-fatal sinusoidal obstructive syndrome (SOS) observed in one study and grade 3/4 treatment-related liver toxicity in 37.5% in another. After allo-HSCT, incidences of non-relapse mortality were higher in the CAR-T group (10.9% vs. 4.3%, p=0.016), with chronic graft-versus-host disease, acute graft-versus-host disease (GVHD), and viral reactivations including cytomegalovirus (CMV) reactivation and Epstein-Barr virus (EBV) reactivation reported.

Extramedullary disease, immune dysfunction and delivery constraints: All three non-responders to CD19.22.BBζ CAR T-cell therapy had persistent non-central nervous system (CNS) extramedullary disease (EMD), highlighting the persistent challenge of effectively targeting EMD, while CNS involvement continues to pose treatment challenges. Resistance mechanisms also include immune checkpoint pathway dysregulation and T cell exhaustion, and a functional immune system is required for maximal benefit of immunotherapy. Use of adoptive cellular immunotherapy requires a strict clinical pathway and is delivered at designated CART-cell centers, with challenges including complex production logistics, limited clinical site access, restrictive patient eligibility criteria, and financial constraints.