Clinical Observation of CD7-Directed CAR-T cell Therapy in Relapsed/Refractory Mixed Phenotype Acute Leukaemia

Technical Summary: Clinical Observation of CD7-Directed CAR-T Cell Therapy in Relapsed/Refractory Mixed Phenotype Acute Leukaemia

Problem Statement
Mixed Phenotype Acute Leukaemia (MPAL) is a rare and heterogeneous malignancy characterized by the expression of lineage-associated antigens from both myeloid and lymphoid cells. Currently, MPAL lacks a specific target for chimeric antigen receptor (CAR) T-cell therapy, leaving patients with relapsed or refractory (R/R) disease with limited effective treatment options. While CD19- and CD22-directed CAR-T therapies have shown success in B-cell ALL, and CD7-directed CAR-T therapy has demonstrated high efficacy in T-cell ALL, there is a significant gap in systematic data regarding CD7-targeted therapy for MPAL. Given that CD7 is expressed on leukaemic blasts in a subset of MPAL patients, this study addresses the urgent clinical need to evaluate the safety and efficacy of humanized CD7-directed CAR-T (hCD7 CAR-T) cells as a salvage therapy for R/R MPAL.

Methodology
This was a single-centre, retrospective study conducted at Beijing GoBroad Boren Hospital involving seven patients with R/R MPAL treated between April 2024 and December 2025.

• Patient Selection: Eligibility required CD7 expression >80% on leukaemic cells as determined by flow cytometry. All patients had failed prior therapies, including chemotherapy, targeted agents, and in some cases, prior CAR-T therapy or allogeneic haematopoietic stem cell transplantation (allo-HSCT).
• Therapeutic Agent: A second-generation humanized CD7 CAR was constructed using a lentiviral vector encoding a CD3ζ signalling domain and a 4-1BB costimulatory domain.
• Treatment Protocol: Patients underwent lymphodepletion with fludarabine and/or cyclophosphamide prior to infusion. hCD7 CAR-T cells were cultured for 5–8 days and infused at doses ranging from 1.0 to 9.0 × 10⁵/kg.
• Post-Infusion Management: No graft-versus-host disease (GVHD) prophylaxis was administered. Patients were monitored for cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), and infections.
• Assessment: Efficacy was evaluated at Day 30 using bone marrow morphology, minimal residual disease (MRD) assessment via flow cytometry and quantitative PCR, and imaging for extramedullary lesions. All patients who achieved remission underwent bridging allo-HSCT 5–8 weeks post-infusion. Follow-up extended to April 30, 2026.

Key Results

• Safety: The therapy demonstrated a favourable safety profile. The primary adverse event was Grade 1 cytokine release syndrome (CRS), which occurred in all patients but was manageable with supportive care, corticosteroids, or anti-IL-6 agents (siltuximab) in severe cases. No treatment-related mortality or ICANS was observed. Infections occurred in four patients but resolved with anti-infective treatment.
• Efficacy: At Day 30, 6 out of 7 patients (85.7%) achieved complete remission (CR). One patient achieved CR with MRD positivity, while the remaining five achieved MRD-negative CR. One patient showed no response (NR).
• Long-term Outcomes: All patients underwent bridging allo-HSCT. With a median follow-up of 8.3 months, five patients (71.4%) maintained continuous complete remission (CCR) with durations ranging from 4.7 to 24.4 months. One patient relapsed 7 months post-transplant. The non-responder patient experienced haematological and extramedullary relapse 6.9 months post-transplant and died of disease progression.
• Biological Observations: CAR-T cell expansion was observed in all patients, with peak absolute counts occurring 12–15 days post-infusion. All patients harbored multiple gene mutations, including those in the IKZF1, NOTCH1, and RAS pathways. Notably, the patient with the RPN1-MECOM fusion gene and IKZF1 mutation relapsed post-transplant.

Significance and Claims
The authors claim that hCD7 CAR-T therapy is a viable and effective salvage strategy for patients with CD7-positive R/R MPAL, achieving a high complete remission rate of 85.7% with a manageable safety profile. The study suggests that achieving remission via hCD7 CAR-T therapy can serve as a successful bridge to allogeneic haematopoietic stem cell transplantation, potentially enabling durable remissions in a disease population with historically poor prognosis.

The paper maintains a modest tone, acknowledging limitations such as the small sample size (n=7), the retrospective nature of the study, and the single-centre design. The authors explicitly state that while the results are encouraging, larger multicentre clinical trials are required to validate these findings and to further clarify the prognostic impact of specific gene mutations (such as IKZF1 and RPN1-MECOM) in the context of MPAL treatment. The study does not propose new applications beyond the observed clinical use but highlights the potential of CD7 as a target for this specific, difficult-to-treat malignancy.