Gene-Edited Universal CD7 Chimeric Antigen Receptor T Cells for Pediatric T-Cell Acute Lymphoblastic Leukemia or Lymphoblastic Lymphoma

Background: T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL) are highly aggressive T-lineage malignancies characterized by an infiltration of immature T cells in the bone marrow (BM) and peripheral blood (PB) or extramedullary organ involvements. Effective treatments were elusive, and the long-term survival of patients with refractory/relapsed (R/R) T-ALL/LBL remains poor despite allogeneic hematopoietic stem cell transplantation (allo-HSCT). CAR-T therapies for T-cell malignancies remain underdeveloped due to the shared antigenicity between normal and malignant T cells. CD7 is highly expressed on the surface of T-ALL/LBL T cells and is considered a viable CAR-T therapeutic target. However, CD7-targeting immunotherapies may be compromised by T-cell fratricide and extermination. And one of the biggest challenges with autologous CAR-T cell therapy is to isolate a sufficient number of healthy T cells from malignant T cells. Thus, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR9-associated protein 9 (Cas9)-mediated gene ablation has been used to produce universal CD7-targeted CAR T cells (UCD7-CAR) from suitable healthy donors that no longer express CD7 and TCR. In vitro killing tests, animal tests, and phase 1 clinical trials have preliminarily verified the efficacy and safety of universal CD7 CAR-T cells. Here we investigated the safety and efficacy of the universal CD7 CAR-T therapy in phase 2 clinical trial(NCT05454241) for pediatric R/R T-ALL/LBL patients.

Aims: To investigate the efficacy and safety of the universal CD7 CAR-T therapy for pediatric R/R T-ALL/LBL patients.

Methods: Patients over three years of age whose disease failed ≥ 2 lines of therapies and had ≥ 80% CD7 expression were eligible, including those who relapsed within 12 months after complete response or relapsed more than 12 months after complete response and failed to achieve remission induced by one or more courses of standard treatment; and patients with recurrence after hematopoietic stem cell transplantation. A lymphodepletion regimen was administered to all patients using fludarabine (30 mg/m2 per day) and cyclophosphamide (500 mg/m2 per day) for three consecutive days (day -5 to day -3) before CAR-T infusion. Patients received one single infusion of UCD7-CAR T cells at a median dose of 2.0×10^6/kg. Consolidative allo-HSCT after remission was allowed after day 28 after UCD7-CART infusion at the discretion of the physician and patient preference. All surviving patients were followed until July 15, 2023; the median follow-up was 109 days (54 to 117 days).

Results: Five eligible children, 1 with r/r T-LBL and 4 with r/r T-ALL, were enrolled between December 2022 and April 2023 (Table 1). The median age of the patients was 5 (4-11) years. One girl(Patient 04) had a history of allo-HSCT before enrollment. Patients were heavily pretreated with a median of 3(2-6) lines of therapies. At registration, the median proportion of blasts in 4 T-ALL patients was 47.275% (6.0%-56.0%) in BM by FCM along with CNS(n=2) or testis(n=1) involvement. In contrast, 1 T-LBL patient(patient 02) did not have BM blasts but with bulky mediastinal masses ≥7 cm in diameter. All five patients had no or mild CRS (no CRS, n=1; grade 1, n=3; grade 2, n=1), and most(n=4) did not show symptoms of neurotoxicity. Patient 04, who received a prior allo-HSCT approximately seven months before CAR-T therapy, had a Herpes virus 6 (HHV-6B) encephalitis on day 17 after CAR-T infusion, but no GVHD was observed. On day 28, 4 of 5 (80.0%) patients who had BM involvement achieved MRD-negative complete remission (CR; n=2) or CR with incomplete hematologic recovery (CRi; n=2); but patient 02 with bulky mediastinal masses did not have an obvious response. Until the cutoff date, patient 04 still kept a sustained MRD negative CR; patient 05 relapsed again 49 days after CAR-T infusion, and the other three patients received a subsequent allo-UCBT with a CR state. All the children are still alive.

Conclusion:UCD7-CAR T therapy is a safe and highly effective pediatric T-ALL/LBL treatment. More patients and longer follow-ups are needed for validation.

Disclosures: No relevant conflicts of interest to declare.

See more of: 704. Cellular Immunotherapies: Early Phase and Investigational Therapies: Poster I
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